CA1166092A - Prosthetic devices having coatings of selected porous bioengineering thermoplastics - Google Patents
Prosthetic devices having coatings of selected porous bioengineering thermoplasticsInfo
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- CA1166092A CA1166092A CA000397863A CA397863A CA1166092A CA 1166092 A CA1166092 A CA 1166092A CA 000397863 A CA000397863 A CA 000397863A CA 397863 A CA397863 A CA 397863A CA 1166092 A CA1166092 A CA 1166092A
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- porous
- bioengineering
- bone
- thermoplastic material
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Abstract
Prosthetic devices, such as orthopedic, dental and maxillofacial prostheses, are provided which are composed of an inner load bearing, functional component and an outer foamed or sintered porous coating of selected bioengineering thermoplastics. The bioengineering thermoplastic coating is provided in regions where long-term bone fixation is desired by tissue ingrowth. The coatings offer substantial biomechanical advantages over any material system previously reported. Also provided, are anatomically shaped devices comprised totally of bioengineering thermoplastics with select porous areas; these devices include bone gap bridges, bone caps, and alveolar ridge augmentation implants.
Description
~6~09~
11,313 Thi6 ~nventlon rel~te5 ~n gener~l to pro~thetic device~
ha~ing coatin~6 of ~elected porou6 thRrm~plastlcs, ~h~c~
provide ~n opt~mum blomech~n$cal environment for fl~atlon of device6 by A bone lngrowth mech~nism. In one a~pe~t, th$6 invention rel~tes to the use of cert~in lntermedl~te dulus thermopla6t~c6 ~nd fiber reln~srced thermopl~tic~ 8~
porou~ co~ting~ for reglon~ of pros~he~ic device~ where long-term ~one fixatlon ~6 desired by ti~ue ~ngrow.h. I~
a further ~spect, th~ lnvention ~6 directed to ~ proc~s6 for costing proEthet~c devlce~ with selected porou6 bio-engineering thermopl36tic material~.
Prior to the pre~ent invention v~rious method~ hav~
been di6clo6ed in the literature for ~he s~tackment of prosthetic devices ~ the musculoskelet~1 eyGtem. The6e methods can be cstegorized ~ $nvolving: 1) impaction;
11,313 Thi6 ~nventlon rel~te5 ~n gener~l to pro~thetic device~
ha~ing coatin~6 of ~elected porou6 thRrm~plastlcs, ~h~c~
provide ~n opt~mum blomech~n$cal environment for fl~atlon of device6 by A bone lngrowth mech~nism. In one a~pe~t, th$6 invention rel~tes to the use of cert~in lntermedl~te dulus thermopla6t~c6 ~nd fiber reln~srced thermopl~tic~ 8~
porou~ co~ting~ for reglon~ of pros~he~ic device~ where long-term ~one fixatlon ~6 desired by ti~ue ~ngrow.h. I~
a further ~spect, th~ lnvention ~6 directed to ~ proc~s6 for costing proEthet~c devlce~ with selected porou6 bio-engineering thermopl36tic material~.
Prior to the pre~ent invention v~rious method~ hav~
been di6clo6ed in the literature for ~he s~tackment of prosthetic devices ~ the musculoskelet~1 eyGtem. The6e methods can be cstegorized ~ $nvolving: 1) impaction;
2) nails ~nd ccrews; 3) cement; and 4) porous ~urf~c~
materials. The use of porous surface impl~nts for fixation has been recognized ~5 potenti~lly providing ~ign$~icant ~dvantages, however, thi~ technique has not been accepted by the ~urglcal community becau6e of problems of early fix~t~on and lon~ eerm ~t~blllty a~oc~ated wi~h pr~or art dev$ce~0 Prior art lnvention~ ~nclude U~ S. P~te~t No.
materials. The use of porous surface impl~nts for fixation has been recognized ~5 potenti~lly providing ~ign$~icant ~dvantages, however, thi~ technique has not been accepted by the ~urglcal community becau6e of problems of early fix~t~on and lon~ eerm ~t~blllty a~oc~ated wi~h pr~or art dev$ce~0 Prior art lnvention~ ~nclude U~ S. P~te~t No.
3,9869212 wh~ch i6~ued October 19, 1976 So B. W. S~uer describing'~mproved"c~mpo6ite pro6thet~c dev~ces cont~in ing 8 porou~ polymeric co~ting for ~one f~x~t~on by t~ue ingrowthO The porou~ polymerie m~terial6 ~hich ~re ~ndic~ted to be u6efu1 are tho6e hAving a ~pec~f~ed den~l~y ~nd in~er~
connected pores ~f ~ ~peciflc ~versge pore d~amet2r. Among the polymeric ~steri~16 di~clo6ed ~re high den~ty poly-ethylene and polypropylene or ~ixture6 thereof havingcertain critical parameter6. It 16 ~l~o indicated th~t ~,.
r ; 116~092 the coatln3~ c~n be ~echanlcallg $neerlocked or chemic~lly bonded to the devlce.
U, 5, ~te~t 3,971,134 whlch ~ued July 27, 1976 to J. C. 3Okro~ relate~ eo ~ dent~l prosthe~$~ for permanent or prolonged lmplant~t~on $~ ~ J~wbone of ~ lIving body.
me lmpl~nt c~n be co~ted wi~h ~uch materl~ls ~ ~lnyl poly-~er~ ~. g., ~crylic polymers, polyethylene and carbon fiber filled Teflon.
J. Galan~e, ~t al, in J. Bone and Joint Surgery3 53A, No. 1,101 (lg71~ de~cribe6 s~ntered fiber ~etal compo6i~es ~s a ~asi~ for ~ttachment of lwpl~nts to bone and U. S.
Pseent 3,808,606 which is5ued on M~y 7, 1974 to Ray nd G.
TSonzo de6cribes stainless ~teel and cobalt-chr6~1um~molybde-num alloy pro6the~is posse~6ing porou~ ~urf~ce6 for fix~tion by ti~ue ingrowth.
~ 160, of general interese ~re U. S. P~te~t~ 3~992,725 "Implantable M~terlal ~nd Appli~nce6 and Method of Stabiliz ing Body Implant6", which ~6~ued on Nove~ber 23, 1976 to C. ~. Nomsy, U. S. 3,909,852 "Implantable Sub6t~tute Structure 20 for at LeA6t Part of the M~ddle Ear Bony Chain" whlch i~ued October 7 9 1975 to C. A~ Homsy, and U. S. 3~971,670 "Im-plantable Struc~ure and ~ethod of M~king Same" whieh i~ued July 27~ 1976 to C. A. ~om6y.
In ~ddition to patent~, variou6 article~ have ~ppeared ~n the liter~ture relating to bone ~ngrowth into porous m~terial~. Typical ar~icles ~nclude~ among others, S. F.
Hulbert a "Att~chment of Pro6the~es ~o the ~h6culoskele~1 Sy6tem ~y Ti~sue Ingrowth ~nd ~eehanioal Ine.rlockIng"~
J. Blomed. M~ter. Re~. Sympo~i~m, 4, 1 (lg73); M. Spector, et al, "Bone Growth into Porou6 High-Den61ty Polyethylene"~
J. ~ioYed. ~ter. Xe6, Sympo~ium~ 7 9 595 (1976); C. A~ ~omsy 31 ~fi609~ 11,313 "Implant Stabilization - Chemical and Biochemical Consid-erations", Orthopedic Clinics of North America, 4, No.
2,295 (1973) and J. N. Kent, et al, "Proplast in Dental Facial Reconstruction", Oral Surgery, Oral Medicine, Oral Patholo~y, 39, No. 3,347 (1975).
However, the porous materials disclosed in the lit-erature as beinp useful for prosthetic devices provide inappropriate biomechanical environments leadin~ to either of two undesirable situations. First, low modulus-high creep porous coatings such as porous Teflon/graphite com-posites, exhibit metastable fibrous tissues in the pores after extended perîods. This tissue is not suited to support load bearing joint prostheses. The fibrous tissue is a metastable precursor to bone and under normal physio-logical conditions (including physiological loading con-ditions) would remodel to bone. The high loads transmitted through low modulus materials and the excess creep result in fibrous tissue ~hich fail -to remodel to bone. Other low modulus-high creep materials employed for prosthetic de-vices include polyethylenes and polypropylene.
Secondly, high modulus materiaLs such as ceramics (16 x 1~6 psi) and metals like titanium (17 x 106 psi) and cobalt-chromium-molybdenum alloy (34 x 106 psi), do not spread sufficient load to the ingrown or surrounding bone to prevent resorption. In porous metal and ceramic coated femoral and humeral stems, load is concentrated at the apex of these prosthetic components causing stress con-centrations in the surrounding bone and subsequent re-sorption. In addition, the bone spicules in the pores of these porous ceramic and metallic implants do not experience 66~2 11,313 load~, ~h~reby re~orbi~g~ The 10118 of bone frao the pores ln ~rcaa of porou~ lant~ ch exper~ence no lo~d has been demon~trstcd hl~tologlcally. ~hl8 qpe of ~one 10~B
12ads to ~ decr~ase ln compo~lte ~trength ~e. g. lnterfscial she~r lltren~th) and ~ ~ub~e~uent decrcs~e ~ u~e"
perfo~unce ln the~e hlgh modulu~ porou~ ~terial~, .
The above-cited p~eents and l$t~rature de~crlbe the u~e of porou~ co~tlngu ~n pros~hese~ And descr~e accept-able pore ~ize r~r~ge requiremene6. However, ie ha~ been 10 found th~t met816, cer~mic~ and poly~Gers ~uch a0 the ~nyl pol~mer6, polyeehylene, polypropylene, c~rbon filled Teflor and other6 dlsclosed as being u~eful for coat~ng pro~the~lc ~ev~ce~ do not est~bli~h the proper biomechanlcal emriron-ment to achieve appropriate early fixation, l~ng-term stability and strength at the bone-prosthesis interface. Previously de~cribed polymeric m~terial~ can al~o l~ck the toughnes6, creep re~lstence, ten6ile ~nd ~m~act strengeh and ~team 6terilizabillty to be ncceptable 8B ~he polymer of choice for coat~ng pro6ehet$c devices. Even selec~ high denslty polyethylene and polypropylene porou~ compofiitlon~, ~ta~ed to po~3e8~ the rlght ~moun~ of fle~ibility a~d ~trength ln U. S. Patent 3~986,212 sre deficient 8S will be discu~ed below~
The bone ~ngroweh in porou~ orthopedic ~mplant6 can be con6idered ~ a two stage phenomenon. E~ch 6t~ge 1~
influenced by the pore c~ar~cteri~tic~ and biomeehan~cal char~cter~a~c~ of the ~mplan~. In ~he fir~t ~tage a~d ~mc~difltely after lmpl~ntat$on the porou~ component fill~
~lth a bl~od clot which ~ubsequently become~ l'organized", F~brobla~t~ appe~r ~n the clot reg~o~ and flbrogene6i~
occur~. The clot ~ rcpl~ced by 1003e connectlve tl6 ue fifiO~2 I
11~313 snd ccp~ rie~. At th~s point preo~t~oblYst~ b~g~n to appe~r ~n th~ per~pheral p~re~ of ~mplant. The~e eell~ can ~ecome o~teoblasts or chondroblAsts depending u~on the environment. ~f the ~rig~nal pore size of the lmplant 1B
too ~m~ll or ~f the pore Dtruc~ure has ~een dl~tosted by the initial applied loads as wlll occur with Teflon, high density polyethylene and polypropylPne porous ~aterials, one or more of the above sequence of events can be ~n-terrupted. For exEmple, it i~ generally bel~eved that a amaller pore ~ize (C90~)leads to the ultim~te form3tlon of fibrous tis~ue, not bone, in the implant. If the dulu~ of the mater~al i8 toD low, ~icro-motion occurs with lo~dlng. '~li5 would lead to nn envlron-ment that 16 eonducive to fibr~u~ or cartil~ge tl~6ue, ~t ~one, formation. For example, e2ces6ive motion c~n lead to di6ruptlon of va6cularity and A decreafie ~n oxygen, a condition whlch ~vor6 cartilage formation.
~ f~er ~one ha~ filled the pore~ Qf ~he implant, in the ~econd ~ ge $t mdergoe6 re~Dodel~ng ~hieh i6 ~nfluenced pr~marily by lt6 biomechanical environsnerltr Spicule6 ~n the lmplant which e~perience urlifor~D ~tres~ will thieken ~hile ~ho~e ~picules whlch experience no ~tres~ or exce~ive ~eres~
(Btre~5 conce~tr~tion) are re~orbed. me m~dulu~ of me~al~
Jnd ceramic~ 16 Bo high thst the Implant~ do not defonm under the appl~ed load~. The bone ~picule~ in the6e por~u~ im-plant6 thu~ do not exper~encc ~ufficient lo~d ~o thicken.
Bone trabeculae ~n the~e higher modulu~ porou~ m~terlal~
tend to resorb, becoming thlnner than the oplcules in the porous l~plant6 wh~ch are the ~ub~ect of thl~ in~enti~n.
The ~bove di~cu~ion ~ndic9te6 t~8t t~e biom2chanical enviro~m~nt e~tRbllshed by the lm~lant ~ateri~l a~d ~he geomet~ of the porous ~ub~trate hs~e ~ profound ~ffec~ o~
the biologlcal f~e ~ ~mplant8, I~ h~8 ~ow ~een found O 5 _ 0 ~ 2 ll, 313 that certaln thermopl~stic~, here~fter de~cr~bed as ~ cl~ss ~s b~oeng~neering ther~oplastics, provide the delicRte balance which must ~e ~chieved between parameters affecting load trans-~ssl~n, micro-motion, dimentional stabilley, snd strength.
Bioenglneering thenmoplaseics~ us~ally prepared by condensation polymerizations, ~lso show low metal contamination levels (i. e., Low transition ~etal catalysts levels) and exhibit e~cellen~ ch~racterlstic~ $n ~iot~xic~ty ~tudle6 ~ch a6 the U. S. Pharm~copia Class Y~ Stand~rd~. Ihey represent an opeimum m~terisl6 caeegory for orth~pedic, dent~l ~nd maxillofecial ~pplicatio~. The tr~nBml~Bion of stre~s to bone in the pores of bioengineer~ng thermo~
pla6tlc6 mimic~ the phy6iological biomechanical env~ron-men~ ~ evidenced by the repllc~tion of the norm~l bone repair proce~e~. Bone 1~ porous bioengineering therm~-; plastic lmplant6 rem~delled after a clinically ~pproprl&teperiod to reflect the m~gnltude ~nd direct~on of the pre-v~iling stres~e6 ~t the anatomic~ e. Thi6 occurrence permit~ the ingrown ~one to ~e ~ structur~lly efflcien~
memb2r for ~he lDad e~vironment to which 5 pso~the6i~ i~
~ub~ected.
It 18, therefore, an ob~ect of the lnvention to pro-v~de efflcaciou6 pro6thetic devices comprised of an inner lo~d be~ring functional cvmponent snd ~n oueer fo~med or ~intered porou~ c03~ing over ~t lea6t a p~rt~on ~hereof, of ~elected bioeng~neer~ng thermopla~tic~, ~nother ob~ec~
of this in~ention i6 to pr~lde co~ted pro6thetic devlce~
wh~ch after ~mplsnt~tion nchic~e ~ long-tenm bone fixa~ion by lngrowth of tl~ue ~nto and ~hrough ~ ~elec~ pG~OU6 b~oenglneering thermopl~tlc co~ting wlth ~ub~equen~
11 ,313 ren~delllng to bone. A fureher og~ct 18 to pro~de ~
pro~the~ic dev~ce having a coat~g ~f a ~pecified poro~lty whlch prGvide~ the optimu~ ubserate for t~ue ~ngrow~h.
Another ob~ect ~8 to provlde proDthet~c devlces wherein the co~ting ~hlbits ~uff~clent ten~lle ~nd l~psct ~tr~ngth durlng ~nd after bone formation eo ~cc~mm4t~te applied lo~d6 during insertion ~nd ~fter ~urge~y, ~ ~urthc~ ob~ect i~ to provide ~oated pro6th2tic device~ whlch can undergo ~team ~teriliz~tlon w~thout ~dver~e effect~ on the co~ting. A
~ill further ob~ect of thi~ in~ention i~ to provide anatom-~c&lly ~haped porou6 ~tructure~ of eelect ~ioengineering the pl~6tics which are uae~ul ~or recon~truotive procedure6, Another ob~ect of thi6 ~nventlon ls to pr~vide porou~ bio-engineerlng thermopla~tic coating~ or 8tructure6 containing additives f~r enhancement of their b~ologicAl and/or m~ch-an~cal properties. A further ob~ect o~ ~h~6 inYent~on iS
to provide porou~ b~oengineer~ng thermoplastlc coating~
or l;tructures contalnin~ eddi~ive~ ~or increa~in~ wear azld ~bra~ion resi6tance. Another ob3ect ~6 to provide one or more processe6 for preparlng c~ated pro~thetic devic~ or anatomlc~lly ~haped ~tructure6 c~mposed of bioengineer~ng ehermopla~t$c~o The importance ~f the~e and othcr ob~eets will readily become ~pparene to Sho~e ~killed ~n the art in the light of the ~eaching6 herein ~et forth.
In it6 bro~d ~pect the pre~ent ~nvention i~ directed to prosthetic de~ce6 compri~ed ~f or co2ted with porous bioenglneerin~ thermopl~stlc materi21s ~h~ch en~ble~ ~uch deviees to beco~e firmly and pe~m~nently ~nehored ~nto the mu~culo~kelatal sy~tem by t~ue ingrowth ln~o the co~ted ~terial., ~n one e~bodiment the pro~thetic de~ice6 are compri~ed sf a lo~d be~rlng funct~n21 com~onent End over ~ 7 ~
O g 2 11,313 ~t leaEt ~ portlo~ ehere~f~ ~ por~u~ ~o~ting of from ~oue 0~5 to ~out 1~ ~lllneter~ ~n thickne~ ~f a ~oenglneer-lng thermDpls~c ~teri~l ~h~ch ~B comp~t~ble wlth~ and conduclve for, the lngrowth of c~nc~llou~ ~nd cortlcal bone ~pieule~, ~he co~t1ng h~vlnæ the fo~lowing propert~e6:
n ~verage pore d~ameter of rom a~ut 90 ~o ~ut 600 ~icron3;
(b) pore ~nterconnections h2v~ng fiverfl e ~i~meter6 ~f grester ehan ~bout 50 mlcro~s;
(c) a modulus of elasticity fro~ ab~ut 250,000 to ~bout 3,000,000 pounds per ~quare inch for ehe neat thermoplastlc material or the reinforced thermoplastic material;
(d) a porosity of greater than about 50 per cent; ~nd~
- (e) a totsl creep strfli~ of less than one percent at ~
constant ~tress of 1,000 pounds per 6quare inch at ~mbient t~mperature, ~11 of the propertie6 being sufflcient to enable ~tre~es ~pplied on the mu~culo~keletal ~y~em to be ~r~n~ferred to bo~e spicule~ within the pore~ snd maintain ~uffic~ent losd Rnd pore ~tsb~l~ty to promote irrever61ble 066ific~tlon, Hence, 1~ has been ob~erved that the m~erial~ u~ed ln eoatlng the load beasing function~l component of pro6thgt-~c device6 ~u~t po~6e~6 ~pec~fic propertie~ lf long-~enm bone flx3tion ~6 to ~e achlevet. Pro~thetic devic~6 pre-p~red in accordance with the te~ching6 of ehi inventlon hffve been found to pro~ide the ~i~mech~nlo~l ~nvironment nece~6ary to u~lfonmly tr~n~lt the proper ~gn~tude of ~pplied load~ promotlng the ~esired r~m~d~ll$n~ of bone trqb2cul~e .
1 :166~9~
~1,313 ~ psevioualy ~nt~cated, the ~ter~al~ employed ~n the preparat~on of the pro~theelc d~Ylce~ of th~ lnventlon 2re cla361fled B ~ oongineerlng thermoplaMtic~". OTIR lmportent fe~ture of these m~teri~ ehat ~heir performance c~n be pred~cted by the use of Detal de~ign eng~neerlng ~quatlon6 for ~oth long ~nd ~hor~-term. These engineering d~s~gn e~uations only ~pply up toehe l~near ~i~coel~tic limit of the msteri~l, High den~iry polyethylene has a l~ne~r V~8^
coelastic llmit of le~s th n 0.1 percent ~nd with th~ limit on the æmount of tr~ n,the ffllo~able stre~ iB ~inimsl. In conerase, the line~r ~iscsela~tic lim$t of bioengineer~ng ~henmople~tic6, within the definition of thi~ disclosure, ~8 at least 1 percent ~tr~ln. For example, one of the preferred engineering thermopla6t~c material~ found to be suitable for the coatings of thifi invent~on i5 a p~lysulfone which ha~ a 2 percent Btrain l~mit. Hence ~ the met~l engineerin~ de61gn equations for both long ~nd 6hort term can ~pply up to this limit.
The un~que char~ceeristics of the bicengineering thermo-pla~tic m~terial6 are more clearly evident when ~cheir per-formance i6 compared to poly~eric ~aeeri~16 prev~ou81y ti6-clo~ed as belng ueeful for porou~ fi~ation dev~ce~. If ~he creep modulus extenslv~ly varie6 with t~me~ deflec~on lncsease~ markedly, c2u~ng mlcro d~splacement of a prosthesis under load and pore dl~tort~on. Creep te~ts have alre~dy been reported in the literature on porou~ h~gh den~ity poly-ethylene and a po~ytetr~fluor~ethylene-graph~te compo~te, both of w~ch have been ~ndic~ted ~n the prev~usly c~ted ~atent~ . It hs~ been ob6erved thst d gnlficant changes ~n pore structure occurred upon compresslve 6~re~es as low &S
80 p~ for the porou~ polytetr~fluoroethyl~ne~graphlee c~-posltes And at 300 p8i for ~ porou~ blgh d~sn~ poly-2~hylcne. T~picnl ~ime to fs~ e ,rer~us l~tre~ ~os~ the ~wo 9 _ 6 ~ 9 2 11,313 s~oported hl~h den~ty polyethylene fabr~c~tion~ were ~mder~lv~ ~i~ute- ~hen ~tre~s leYeS~ ~reater than 300 ps~ ~ere ~pplied. It ~hould bc noted that thl~ repre~ents the ~tres6 level~ ths~c will ~e e;cperienced in ~me orthopedlc ~oint ~nd deYice appllcat~on~. The $mport~nce of mRinea~ning pore ~eometrles under lo~ding envlronpents ~8~ ~ndicated æ~rlier where ~t ~a~ ob6erved th~t f~brou~ tls~ue lt~ ereated ln ~mall pores. Thi~ 1~ partlcularly cr$tical in e~rly post~operstive perlod~ prior to ehe ~ngrowth of bone when the p~roui poly-meric coating Dn ~oint pro~these~ mu~t hsve ~uff~clentstrength and ri~ldlty to Independently ~upport appl~ed load wlthout aB~i~tance from lngrown ~one. The ~trength of prior polymeric m~terials c~me~ from the ingrown bone. 8ioengineer-ing ehermopls6tic porou6 co~ting ha~e ~trength like ~one.
Illu6trative pro~thetic devlce6 which ~re within the ~cope of the teachings of thi~ lnvention are readily apparent from the followlng de~crlption and from the ~ccompanylng drawings where~n:
Flgure 1 i~ 8 plan v~ew of ehe ~tem ~nd ball portion ZO of ~ total hip pro~thesi~ having 4 coating of a porou6 blo-engineering thermopl~t$c m~terial.
F~gure 2 1~ ~ plan YieW of an endo~e~l ~lade ~mplant having a co~tlng of 8 porou~ bioen~ineerin~ ~hermoplas~lc m~terial on ghe bl~de portion thereof.
Figure 3 i~ ~ ~ide plan view of ~nother endo~teal im-plant havlng the ~lade portion co~ted with the porous blo-engineering thenmopla6tic m~teri~l.
F~gure 4 ~ ide pla~ ~iew of a self-bro~ching intr~
~medullary ~8il h~vlng ~ cO~e~ng oves its ant~re length of the porow b$oengineer~ng ther~opl3~t~c ~aterlal.
a~ 10 -11, 313 ~lgure S 1~ ~ pllm v~ew of ~ pros~het~c ~evice c~nprlsed entlrely of ~ porous bl~ngineering thermopl~t~ c materisl .
P'~gure 6 i.B a gr~ph dep~cting the relationship of inter-faci~l 6hear strength ~er~ implsr~tat~on ti~ne c>f ~everal porous m~teri~l6.
Referring now co Figure 1 of the accomp~nying drawi the total hip pro~the~ls 10 1~ comprised of ball ~nd ~tem ~ember 12 and cup member 14. T~e eem port~on of the b~ll and ~tem member 12 i6 cos~ed over ~e8 ~n~ire ~urf~ce wlth a porous bioengineering the2~nopla0tlc coating 16 of th~6 ~s~ventlon. Although thP stem portion i~ depicted in Figure 0 1 E15 a solld fitem wi~h ~ groove 18 along ~t lea~t a por~ion of lt~ len~t~, it can h~ve opening~, ridge6 or other con-flgurat$on~ to provide co~ted ~ite~ for S ue growth to firmly 4nchor it to the ~Iceletsl ~y6tem. Cup member 14 i6 likewi~e co~ted on it6 ~xt~rior ~urface ~ith the porou6 engineerlng the~pla~tlc 16. The n~ck 20, ball 22 and ~nner surface of the cup 24 do ~ot, of caur6e~ sont~in any coating~
Figures 2 ~nd 3 of the trawings deplct c=ercislly available impl~nt~ 26 and 28 which cen ~e fabric~ted ln ~ ~ariety of 3hape~ snd are decigned for ~upportlng group~ of ~rt~fis:ial ~eeth l'he6e tevices are ususlly cc~m~ri~et o~ cob~lt or tltanlum ~lloys snd ~re in6erted into 810t8 cut lnto she ~Iveol~r ridge.
~e po~ts 30 and 32 protrude ~nto the or~l c~viey ~nd are u~ed for ~nchor~rlg the arti Pical teeth ~ ~ ~hown ln the dr~win~,, the ~tem pQrtions 34 Rnd 36 c~n be c~ated wieh the porous biDengineering ~herk~opla~ic mster~al ~ad pr~rlde for bone ingrowth to firmly ~ffix the pro~thesi~ he alveol~
~idge, An ~tra~nedullar~ ~11 3B i8 lllull~r~t~ n ~gure 4 a~d ha~ ~ eoatir~ 40 of ehe parou~ b~oeng~n~eri~g thc~o-~16~092 11~313 plas-tic material over its entire leng~h. These nails are placed in the medullary canal oE long bones~ such as femurs, and are usually limited to the middle one-third section o~ such bones. These nails are wedged lengthwise into the medullary canal and press a~ainst the interior of the cortex. Finally, Figure 5 provides a plan view of a porous implant 42 which can be used for alveolar ridge re-construction, Thus, ridge reconstructions can be made by using a porous or solid interior bioengineering thermoplastic implant, without a load-bearing functional component, carbed or molded to the desired anatomical shape.
Figure 6 is a graph depicting the relationship of inter-facial shear strength in pounds per square inch versus time in weeks for trochanteric implanted intramedullary rods of porous polysulfone, porous titanium and porous polyethylene.
The porous polysulfone was prepared in accordance with the teachin,gs of this invention and exhibited the physical charac-teristics previously described for bioen~ineering thermo-plastics. The data for the porous titanium and polyethylene implants was reported by other investigators. In each case, the rods were implanted in dogs in accordance wit~ accepted surgical techniques.
While each of the tests was performed in a similar fashion in dogs, there is the possibility that the results could vary somewhat because of differences in implantation and mechanical testing procedures used by the different in-vestigators. However, these variations are not great enough to prevent comparison. Of particular interest is the fact that the interfacial sheer strength of porous polysulfone is high enou~,h after only two weeks (~150 psi) ~66092 11,313 to support the static load and most dynamic loads that might be placed upon a hip prosthesis by a patien~ immediately after surgery. This type of data thus evidences the possi-bility of early weight-bearing postoperatively for polysul-fone, whereas the porous high density polyethylene exhibits an interfacial shear strength value only one-third that of polysulfone. Indeed, only after extended implant periods, did the high density polyethylene come up to the two week value for polysulfone, and it fell short of the ultimate shear strength value for polysulfone.
As hereinbefore indicated, the materials which are employed in the present invention are desiv,nated as bio-engineering thermoplastics. These materials are unique in that they combine melt processability with structural strength, rigidity, creep resistance, toughness, and steam sterilizibility. In corporation of glass, carbon or organic based fibers into the bioengineering thermoplastics extends the load-bearing and structural characteristics. Bioen-gineering thermoplastics exhibit bulk tensile or ~lexural modulus values in the range of 250,000-500,000 psi. ~iber reinforced products exhibit modulus values up to 3.0 million depending on the fiber type and loading. These values of modulus provide the intermediate range required for initial post-operative support and long-term stability of implanted prostheses in high load areas anchored by bone ingrowth.
.~
0 ~ 2 11,313 Each of these materials when prepared in accordance with the teachings o~ this invention provides coatings or free standin~ articles havin~ the physical properties herein-before enumerated. Illustrative of these materials are the polysulfones, such as, polyphenylsulfone, polyethersul~one, polyarylsul~ones, and the like; polyphenylenesulfide, poly-acetal, thermoplastic polyesters such as the aromatic poly-esters polycarbonates; aromatic polyamides, aromatic poly-amideimides, thermoplastic polyimides and the polyaryletherke-tones, polyarylethernitriles, aromatic polyhydroxyethers, and the like. The most preferred materials for use in the in-vention are the aromatic polysulfones. These polysulfones contain repeatin~ units having the ~ormula:
TAr-S02]
wherein Ar is a divalent aromatic radical containlng at least one unit having the structure:
~-Y-~
1 :166092 1~9313~e-l in which Y is oxygen, sulfur or the radical residuum of an aromatic diol, such as 4,4' bis(p-hydroxyphenyl~-alkane. Particularly preferred polyarylene polyether polysulfone thermoplastic resins are those composed o~
repeating UnLtS having the structure sho~n below:
r _ ~SO~O ~C_~O l CH3 n wherein n equals 10 to about 500. These are commercially available from Union Carbide Corporation as UDEL*
Polysulfones P-1700 and P-3703. These materials differ in that P-3703 has a lower molecular weight. Also useful are Astrel*360 a polysulfone sold by 3M Corporation and Polysulfone 200 P sold by ICI and Radel polyphenyl-sulfone sold by Union Carbide Corporation. Certain crystalline bioengineering thermoplastics like Stilan from Raychem Corporation, Polyarylene and Phenoxy A
from Union Carbide Corporation, are also useful.
*Trademarks.
1 lB6092 11, 313 In practice, the prosthetic devices of this invention having an inner load-bearing functional component or those existing as free standing anatomically shaped devices are conveniently prepared by one or more methods. In one method the coating or article can be formed by a sintering technique whereby particles of the bioengineering thermoplastic material are heated for a period of time and at a temperature suffi-cient to cause sintering that is, the particles fuse together at one or more contact points to provide a porous continuous composite material of the bioengineerin~ thermoplastic. In a second method, the coatin~ or article can be formed by a process which involves the formation of a low density foam of the normally solid thermoplastic material. This second method which can be described as the dough foam technique is particularly useful for the preparation of the porous materials. However, its use is limited to the aforementioned polysulfones and phenoxy A aromatic polyhydroxyethers.
Porous bioengineering thermoplastic coatings and blocks prepared by these methods exhibit intermediate modulus values, high strength and hi~h creep resistance. They can uniquely be fabricated with high total porosities and pore sizes, while still meeting -the strength and biomechanical criteria observed to be necessary for bone repair and prosthesis fixa-tion/stabilization. For example, slntered polysulfone having an average pore size of 200 and a 53 per cent porosity, had a flexual strength of 2000 psi and flexural modulus of 60,000 psi.
Foamed specimens with a 70 percent porosity had a flexural modulus of about 105 psi. This value increased to 8 x 105 psi with the introduc-tion of 30 weight percent carbon fibers.
~-16-6~92 i 11,313 ~ lth r~p~ct to the fir~ ~eth9d, lt h~s been ~bserved that through e~reful control of temper~ture, ~lme ~nd pres~ure, all bloengineering thermoplastic~ c~n be ~intered.
~or exsmple, I~EL-P-1700 polyRulfone can be ~at~sfactorily 61ntered ~t ~pprox~tnqtely 245~C and Radel poly3~1fone i~
enerally sinter~d at lapproximately 285C~ At ~ppropriate temper~tures, t~mes ~nd pres6ures the other thenmoplastic materials can also be 6intered to provide a porou~ product 6uitable for the intendet use. It h~s been ~b6erved, however, and p~rticularly for use ln preparing the coa~ngs and srticles of this invention, eh~t optimum properties can be obtained in a ~u~$que ~nd facile m~ er by proper choice of ~oth (a)particle s~ze and tb) molecular we~ght dis~ribution.
As ind~caeed previously, the de~ired properties are exhibieed by ~he prosthetic device when the bioengineering thermoplastic ~a~erial has ~ poroslty of ~b~ut 50 per cent and more prefer~bly ~rom about 40 t~ ~bout 70 per cent. Poros~ ty i6 influenced by the p~rticle s~ze employed in the sintering operation. Particle slze also lnfluence~ the strength of ~he porous ~intered m~terials~
Large particles result in large pore slzes, while ~mall particles ~mprove ~trength by increas~ng the fusion area of the particles.
It hss been observed ~hat the modulus ~f 8 porous material can be predicted through the Rerner equ~tion or ~hrough ~od~ f~ ed Halpin-T~ai equ~tlo~. ~ence, ~n order t~ ~chie~e ma~eriel with ~ poro~lty, or ~xample~ of 55 per cent, ~nd an ~lastic ~tulu~ greater than 40,~00 p~l~the ~odulus of ~he ~;~
1 16~ 0~ 313 æt~rtin~ polymer ~uct ~xce~ 200,000 p~ hus, ~t polypropylene~, and all high density polyethy}ene~ are incapable of belng fabr~cseed ~n ~ ~ster$al cf 55 per cent poro~ity with a modul~s o~ 40,000 psi. On the other hand ~ce the modulus ~f solld poly~ulfone exceeds 34~;000 psi,a ~ater~1 of 55 per cent poros$ty whose ~odulus exceeds 70,000 p6i can be obtained.
Even though it was possible to predict the modulus of a thermoplastic h~ving a desired poro~ity there was no s~mple method ~va~lable to fabricate ~ m~teri~l appro~chirlg these predictions which would be u~eful for the devices of thls lnvention. It was unexpectedly found, however, that the desired degree of poro~ity could be obtained without 6acrificing mechanical properties b~ the proper choice of par~icle 6ize, molecular weight distribution and 6intering conditions. All three ~re ~nter-related and neceæ6ary to ~ch~ eve a costing or article h~ving the neces6ary char2cter-~ 6tiC6 . For example, the s~nter~ng time and temperature which results in ~ desired pore ~ize distribution may not produce the desired modulus of ela~ticity and/or tensile ~trength. Starting particle 6ize distribut:ion, 6intering time, and 'ce~perature must be adju~et to achieve the de~ired balance of pore s~ze, porosi~y~ ~d mech~nical properties.
With respec~ ~Q part~cle 6ize di~tribution, ~ blend of two or m~re different ~l~es of the ~loe~gineering ~hermo-pla~tic ~ateri~l was fvund t~ provide ~ ~ntered material ~hich be6t met the por~itg ~nd meehanical requirement~ needed for a ~ucces~ul pro~thetic device. ~ ~
1~66092 11,313 ,In practice, a mi~ture of partic~e sizes wherein the ratio of particle diameters ranges from about 7:1 to about 5:1 has been found to be acceptable. Particle sizes o~ rom about 300 microns to about 50 microns are particularly preferred. For exam~le, a mixture o particles whic~ are retained on a 50 mesh screen (U.S. Standard Sieve) and pass through a 270 mesh screen have provided coatings and articles having the desired porosity and biomechanical features. It has also been observed that optimun result~s are achieved when the particle size distribution ranges from about 40 to about 60 wei,ght per cent.
As indicated, the sintering conditions are also im-portant to achieve ~he desired properties. Sintering has been accomplished by charging a metal mold with powder and heating the mold to a prescribed sintering temperature, Ts, greater than the glass transition temperature, Tg, and less than the melting or melt processing temperature, Tm, (i.e.
Tg cTS cTm)- The sintering temperature is held constant for a given time, t. Essentially, no pressure, other than that induced by differential thermal expansion, is applied.
The application oE pressure at Ts leads to fluxing of the material. This indicates that if pressure is applied, lower temperatures and shorter time cycles must be employed to retain porosity in the sintered parts. Experiments were run and set forth in the examples to delineate the effects of the sintering conditions on the pore size, porosity, and tensile properties of the porous sintered plastic for various powder size and molecular weight distributions.
~6~9~
11,313 In ~ ~ccsnd ~ethot it has beon ~u~d eh~t ~nce s~me bisengln~rlng ~hermopla~t~c6 ~re aol~ble ~n low-goiling org~n~c ~ol~ent5 ~ ~ol~ent ~vamlng technique cen ~e utlllzed for ~olding open cell porcu~ foa~ coa~lng6 snto protheses or for the prepar~tion of fo~med art~cles. Porous fo~ed co~tings ~nd artlcle6 offer advant~ge6 over slntered porous co~tings and ~rticles ~n ~hat hig~er p~ro~itl~fi can be ch~eved nt higher ~rengths, due to the thin contiguous pore wall6 obtained in the foAming processes. ~urther9 low fabricstion temperatures are ~xperienced due to the pla~ti-cizing effects of the ~olvent on the thermoplastic. This tec~.nique is not amenable to Teflon, polyethylene or polypropylene being described as preferred materials i~ prior art patents.
This ~olvent foaming technique for fabricat~ng low density, foamed ar~icles c~mprises the l;teps cf:
(a) blending at lea~t on norm~lly solid bioengineering thermopl~st~c with ~bout 25 to about 80 parts, per 100 parts by weight, of a normally liquid organlc ~o}vent ha~ng a 601ubility par~meter,S , within (1.3 calories per cc) of that of the thermoplsstic, or ~ mixture of ~ormally liquid org~nic 501vent5 having the ~ame ~olubility parEmeter;
(b) blending the mixture obtained ln 6tep (a) with ~t lea~t about 1 part by weight; per hundred parts of thermo-pla~tic, of water whereby ~ non-t~c~y hydrogel dough ls obtalned;
(c) ~hAp$ng the hydrogel dough obta~ned ~n step ~b~;
(d) vapor~zlng ehe ~olvent and ~ter and (e) recover~ng a foEmed re~n ~rtiole, It has been found that foam prep~re~ ~n thi~ manner posse~es ~he desired degree~ of ~oth poro~i~y ~nd b$amechanlc~1 proper-~ie6~ .
It h~ been ob~erYed, howev~r~ ~hat the ~alue~ of the 1 16~;0~ ' 11,31 solubili~y p~r~me~ers of the norfflally liquid organic ~olvent6 used ~re falrly crit~c~l ~6 ~vidence~l by the fACt ehat wlth ~ preferred ehermopla6~ic r~n BUCh A6 the polysulfone depicted above ehere is o d~stinct dlfference between st~ucturally ~milar ~olvent ~80mers.
~hus, ~r example, the a~ove-descr~bed polysulfone, which has a solubility p~rameter calculated to be 10.55, is ~oluble ln 1,1,2-trichloroethane having a ~olubility par~meter of 10.18 but in~oluble in l,l,l-trichloroethane havin~
a ~olubility parameter of 8.57. However, a m~xture of organic ~olvents which indivitually 15 unsaelsf~cto~y can be used as long ~s ehe average 601ubil~ty parameter of ~he ~ix~ure i~
w~thin (1.3 calories per cc) / of the re~in being blown.
In addition, if ehe T~ of the polymer that i5 to be pl~sticized i5 exceptionally high $n value, plastie~ty of the gel can ~e prolonged during the fo~ming ~tep by ~orming ~ ~$xt~re of 601vents, one of which shoult have a much higher ~o~ling point value. Thus for example while e~hanolor l,l,1-trichloroethane cannot ~e used ~ndiv~dually with the polysulfone depicted abo~e B mixture c~mpri~ng equal p~rts by volume of ethanol and l,l,l-trichloroethane c~n ~e u~ed. Oeher combin-ations which function a5 organic 601vent5 for poly6ulfone are:
957. ehloroform ~nd 5% s~ater, 85Z methylene chloride, ethanol 20% ~nd w~ter 5~, 95Z ~etrahydrofuran and ~ster 5%, 75% methylene chloride" 10% ~cet~e, lOZ ~thanol, ~d 5Z water, ~nd 80% cyclohexsnone, ~ nol 15Z~ ~nd b~ ter ~%.
:11 1660~
11, 313 ~ he umount of water ~dded 16 not crltlc~l ~ut generally at lea~t 1 p~rt i6 required per 100 parts by weight of resin. Ihere ~6 no m~ximuYn amount ~ecauce excess water ~ep~rates fr~m the dough-llke ~Q~ as ~
8epar~te phase. ~ecau6e of ~he p~se ~epara~ion, whPre the 601vent employed ~ for ~he ~ost p2rt not m$~clble wlth ehe w~ter phase, the exce6 water ~c~ a~ A prot~gtive blanket which prevents rapid 601vene 10s6 from the plast~
c~zed polymer. This feature ~llows the pla~ticized poly-meric gel to be exposet in an open ve~sel during handl~ng and transfer w~thout sealed contsin~ent. ~n this form the polymer blend can be easily transferred fr~m one vessel or container to another ~nd can be 6haped ~nd ~olded or oth r wise worked w~thout the necessity for using colltaminating release agents. S~mple mixing equipment known to tho~e skilled in the ~rt ~8 all tha~ is required ~o blend the water into the mixture of the~:moplastie resin and li~uid organic 601vent. The result~t hydrogels can be u~ed ~mm~di~tDly or ~f desired ~tored ~ndefini~ely under water and then recovered and u~ed wlthout further tre~tment.
The ~rganic ~olvent once ~t d~ffuses into polymer resin, ~erves two purposes, n~mely, the formation of ~ gel retai~ng finite solvent concentrat$on ~n B pl&6eicizet fonm and 6econdly the ~olvent ~erve5 a~ ~ blowln~ or fo~ing agent ~t 8 much lower tempera~ure ~nd v$~cos~ty th~n ~h~t whlch would be required ~D foam the original non-plastici2ed polymer re~in with ~ convent~onal ~6eous ~ype blowing or o~ing ~gent, At ~lowing temper~ture6 ~ from 165~200C~ ~ece~6~ry for . -22~
, 11~6~9~
,3~3 polysulfone~, ~06t of the commonly used organic ~olvents d$ffuse DUt of the polymer blend too quickly to provlde ~dequate blowing of the resin. Durlng the blowing oper~tlon the water in the hydrogel is also removed wlth the norm~lly l~quit iorganlc 601vent. Thus ~h~le the ~ec~nd orter ~ran61tion temper~ture (Tg) of ehe polymer resin ~eing treated $n t~.$s ~an~er is lowered, enhancing the proce~sing of the polymer ae lower tempesature, the l~qu$t or~anlc 601vent and ehe water being fugitlve in naeure, ~hen removed from the polymer resin leave the foa~ed art~cle with the physical properties of the or~g~nal resin prior to processing. Th~5 i5 extre~ely ~mportant in the case of polymers whiieh ~re d~fficult to proce~ becau e of their vl~coel~stic and rheolog~cal properties or heat ~nst~bility;
The wide lat~tude cf conditions under which the foaming operatii~n can be carried out in ehis proeess was also qulte 6urpri~ng. Thus for example, while one can pr~ceice the fosming ~tep at higher temper~tures, one c~n al60 oper~te ~t the other end of the 6pectrum, ehat i6, ~t room temper~ture or ~y pl~cing the hydrogel in a vacuum tevice, 6uch ~s, ~ vacuum oYen and with organic ~olvents of low vol-atili~y, 6uch 8S, methylen chlorlde, readlly r~move the ~olvent and water in a relatively short ~e~
- 11,313 1~6~0~2 As previously indicated, another embodiment o~ this invention is directed to prosthetic devices which do not contain a separate inner load-bearing functional component but rely on the structural integrity of the bioengineering thermoplastic material itself. For example, a porous block can be carved to an anatomically appropriate shape, and used to au,gment atrophic mandibular alveolar ridges and deficient facial contours in the mental, mandibular border, and zygomatic areas. Other devices, can include bone gap bridges and bone caps (used to control bone overgrowth in amputees) which are either totally porous bioen~ineering thermoplastics, or bioengineering thermoplastic coated metals or bulk polymers (reinforced and unreinforced). The alveolar ridge recon-s~ruction au~menta~ion device shown in Figure 5 is prepared from a porous bioengineerin~ thermoplas~ic composite by molding and/or carving a block of the composite to the de-sired shape.
The porous bioengineering thermoplastics can also be carved to anatomical shapes without destruction or collapse of the surface porosity. Bone gap bridges, bone caps and other pre-sized implants can be machined without destroyin~
the porosity and surface of the porous engineering thermo-plastics. Porous high density polyethylene, polypropylene, and the polytetrafluoroethylene creep and "feather" durin~
carving and machining operations.
The ~i~,h stren~th-lo~ cree~ of the bioen~ineering thermoplastics and reinforced bioengineering thermoplastics also translate to the load-bearing components of prosthetic devices and implants. For this reason, prostheses can be ~ _ 11,313 developed ~ncorpc~r~nng ~ compo~e xyst~m of bloengineering ther~oplast~c load-~e~ring eomponent~ and ~rticul~t~ng 3uraces, w~th porou~ bioenglneerlng thermoplastic coatings in ~reas ~her2 ~ttachmen~ to ehe ~u~culo6kelet21 ~y~tem ~s de~ired, The bio-.
englneering thermoplastics rema~n tough after being illed - wlth ~einforcing filler~, where polyolefins ~uch a~ high density polyethylene become brit~le ~t high fiber loadings.
Bone ~ap bridges and joint prosthesec demonctrate this principle.
Such ~mplantables are rendered more useful ~ecau6e of the ~bility to achieve high ~nterfacisl ~trengths ~etween the bulk lo~d-bearing component and the porous coating when the ident~cal ma~erials are cGm~i~ed in the constructio~.
Ihese o~mblnations are not achievable with polyolefins due to the poor 6tructur21 characteristics of these m~terilas, nor with cerEmics or metal6 because of ehe biomechanicEl unsuit~bil~ty of the respective porous coatings.
In ~olnt prosthe6es ~here the bioeng~neerlng thermo-pl~stic ~ust al~o onm the srtlcul~ting ~urface, i~ i~ often desirable to incorporate additlves whieh increase ~he wear ~nd abrasion res~stanee of ehe composi~e. Car~on fiber, graph$te fiber, teflon, ~olybdenu~ dl~ulflde are useful addit~ve~ which ~fford wear re~i~tance engineering thermoplas~ic~ ~qual vr ~uperior to ~elf-lubricated m~terial~ typical~y u~ed in c~mmerclally svailable ~o~nt pro6theses.
In ~ournal bearlng wesr te~ts*~ the fdlowi~g c~mparat~ve results were obt~ined:
*Ccnditi~n~ ~STM-D1242 - 1400 hour6, 110 ppm, 5 lbs. vn le~el arm ;60~2 11,3:13 ,Sample ei~ht Lo6s (~r~ms Conerol HDPE 0.0806 Control polypropylene ~O 0404 UDEL poly~ulfor~e 0.279h UDEL ~ith 20% c~rbsn i~er 0. ~362 UDEL w~th 2~% graphlte 0.0324 Compo~ltions wlth carbon fiber are preferred for the in~ect~on ~aolding or machinlng o~ articul~ting pro6ehesi6 ouch as acee~bular C:Up8, tlbial, ~md glenoid componen~s o total knee and shoulter replacements.
In another embodiment of this inven~ion 6ilyl reactlYe poly~Ders like ~ilyl rea~t~on poly6ulforse are utilized for bonding porous polymeric coatings to metal ~ubstr~ees.
Silyl reactive polysulfone (PSF-SR) resins possess three ~mportant fe~tures. First, the presence of hydrolyzable silane end groups pro~ites en inherent coupling abili~cy 1:o etallic ~urfaces. Second, the PSF-SR reslns have a low melt (or ~olution) vi6cosi~ bdhich greatly f~cilit~tes '~ett~ng' during ~he forma~cion of adhesive bonds,. ~$rd, ~chey are pol~meric adhe~ives which exhlbit no ~olubility in physlological flu~ds ~nd hence h~ve no ~iological/toxicological ~ffects when ~mpl~nted.
) 9 2 ' 1~,313 The load ~esrlng f~meti~nsl c~mponen~ ~ the pro~tketic device6 o~ th~s is~ven~ior. cAn be comprîsed of a variety ~f etal~ ~nd alloy6 known ~Ln the art. Wh$1e titaniu~ d tantalum ~re3 for the most part, ~he only pure l~eCal6 Cc7n-sidered ~s ~fe for ~ntern~l use, . æ variety of ~lloy~ have ~ound general ~cceptance, Stainle~ Bte 16, cobalt-ba~;e alloys and titanium basJ.qlloy~ all sre tolerated by the ~ody as well as being corrosion re~i~tant and fabricated into desired ~hape.
~27-~ 0g ~ ~ 11,3~3 E~FECT OF SINTERING ~ONDITIONS ON P~RE SIZE
For thls exper~ment aimple ~old~ were f~bricseed from 3/8 ~nch outer dlEmeter ~teel tub~ng. The tub~ng ~as c~t t~
a 6 ~nch length and fitted wi~h thre~ded ~nd plugs. Wall thickness of the tubing was approx~maeely 0 038 lnch. The resulting sin~ered pl~stic part had ~ diameter of 0.300 inch nnd was 6 inches long. This proved to be a con~enient 6ample size for tensile property characteri~ation.
~ SF-3703 powder with She particle ~ize distr~bution ~hown in Table I below was u6ed This ~aterial was sintered according to the following schedule: pack powder in a mold;
immerse mold in an oll bath at 220~C for various t~mes ranging from 10 eo 30 min. The resul~ing rod ~f 0.300 inch diameter was then cut to sample lengths sf 2.5 inches.
Intercon~ecting pore 6ize distribution was then determined through ~ercury ~ntru~ion poro~imetry. Data are reported in Table I . Characteristic pore ~ze is ~hown a~ the percentage of pores larger than or equal to 132~. As the time at temper ature is incre~sed from 10 ~o 30 minutes, the ~umb~r of pores 132~ in diameter increases. However, if the ~aterial is held at 220C for times greater ~han 30 minutes, the resulting s~mple w~uld no longer be por~us. On the oeher hand, if the ~aterial were exposed to tempera~ure for less than 10 ~nut~s~ little or no s~nter~ng would have ~ccurred. Thus~ there $5 an optimum time at temperature ~nd temperature ~or a given p~rticle size ~nd molecul~r we~ght di~trlbution to ~chieve ~ desired pore ~ize.
:~ 16~092 11 ,313 TABLE I
r U . S . SCREEN DISTRIB~JTION
,~, on 35 ~~
on 40 Trace on 50 __ on 60 14 . o on 80 50.0 on 100 18.0 thru 100~~
on 140 10.0 on 2 304 . 0 thr~ 2304.0 Slnterin~ Time% Pore Volume at 220~,L ~13? __ 49.4 12 52.6 14 56. 5 16 58.1 18 61.8 69.5 . 75 . 4 ~ 11,313 EXAMPLE II
EFFECT OF MOLECULAR WEIGHT ON SINTERING
The following experiment was conducted to demon-strate the effect of a low molecular weight tail upon sintering conditions and resultin~ mechanical properties.
PSF-3703 was "plasticized" via the addition of 0.5 and 1.0 weight percent of diphenysulfone. Blendin~ was accomplished in an ~gan 1 inch laboratory extruder. The "plasticized"
PSF was then ground into powder on a laboratory WEDCO
grinder. The resulting powder was sintered into porous rods 0.300 inch diameter and 6 inches long. Tensile properties of the rods were measured.
Table II presents the mechanical properties for the porous materials after sinterin~ for 20 minutes at various temperatures. The material containin~ 1 wt. ~ diphenylsul-fone was weakly sintered at 200C while the other materials did not sinter at this temperature. In all cases, as the sintering temperature is increased, the "plasticized"
material possesses superior mechanical properties in the porous sintered form. It is evident that addition of diphenylsulfone, (or similar low molecular weight species) provide a method to control sintering conditions. Speci-fically, shorter sintering time cycles at a given tempera-ture or lower temperatures at a given time may be possible.
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6~0~2 11,313 EXAMPLE I I I
Pree~ret ~ on of Porous Bioengineerin,~
Thes~DoPlastlc Co~ted Prosthesis ~ he stem ~ection of ~ R~ch~rts ~nufactus:ing c~ninè
femoral component w~s dlp coated in ~ ln percent ~olution of PSF-SR/methyle~le chloride, air dried and b~ked ~t 110C
for 1 hour. The ~tem seceion of the prosthesis w~s then tip cohted wieh ~ 15 percent ~olution of P-3703/te~ra-hydrofuran and while tacky ~ dusted with p~wdered P-3703.
The primed prosthesis was plsced $n 8 t~pered alumlnum mold whose cavity replic~ted the stem section of the femoral ccmponent, with ~ toler~nce o~ 100 mil. The cavi~y was loosely packed with powdered P-3703, ~ealed ~t the bottom and placed in an oil bath st 215C for 24 minutes.
After cooling, the prosthesis was removed. The ~em sec-tion had a tightly ~dherant co2ting of porous polysulfone.
~32-6~92 11~3~3 EXAMPLE IV
PreDaratlon of Porous ~ioen~neerin~
Thermopl~stic Artlcle To 400 gms. of U~EL polysulfone P-1700 re~in ln ~
~ne gallon wlde ~outh ~ar was ~dded 31~.2 gms. of methy-lene chlor~de with gitstion. The ~8r was 6caled and ~llowed to 6tand at room temperature for 16 hours. A
polysulfone/methylene chloride brown gel w~s ~bta~ned to which 55~ ~ms of w~ter were ~dded wlth mixing. The brown gel turned wh~te in col~r. These proportions formed B 6tsndard dough mix (S~M). A 30 g. portion of the S~M was shaped ~t room temper~ture by hand compres-sion into a 1/8" aluminur2 metal plate 8" x 81' having B
circular hole measuring 4 7/8" ~n diameter. The r~sult-ant dough preform was then fnserted ~t 135C. into a heated telescoping type ~luminum mold consisting of an upper 5"
aluminum disc, fastened to the upper platen of a press, whlch slides ~nto a rlng and meets anotber 5" ~lumin~m disc within the ring. The ring ~nd bot~om disc wçre not fastened to the bottom pl~ten of the press.
Upon insertion of ~he dough preform ~he p~ess was closed ~llowing both disc ~old surfaces ~o compress the preformed dough with a pressure of S0 psl. During the followin~ 15~25 secDnds ~ pressur2 bulld up occurs due to the volatiliz~tion of the ~olverl~s. The pres~ure ~ullds up ~co 152 p~i at which point ehe pres~ W85 released 61Owly to D~int~in 8 pres~ure of 125 to lS~ psi. The release of the pressure all~ws movement of ~he mold ~ur-f~6es ~ctiv~t~ng an expansion of ehe ~old wl~h ~ubs~quen~
release of ~olvent ~nd w~ter v~por from the ~old ~nd ~ 33-; 0 ~ 2 ~ 11, 313 polymer exp~nE~orl. During ~he dwell t~me in the moldcontinuou6 ~olvent u~d ~rater v~por lo~ fur~cher reduces the pre~ure to ~bout 50 p6i or le66. After a total of ~our minute~ the ~old was opened ~nd the foamed disc was removed. The dl6c h~d ~oc~h 6urfsce6 ~n both 8'1 des nd hl~d a density of 0.19 g. cs. the ~urfaces when machined revealed ~n open pore network and the disc ~ould be cut to desired ~hapes.
~ 09~ ~ 11,313 EXA~F y Shear Stren~th Me~ure~ents of ~orous BioenglneerinR Thermopla5tics Sta~nle~s ~teel pl~ees 0.0625" x 1" ~ 4" (type 304)~ere dlp costed in a lO wt. percent of PSF-SR solutlon using ~ethylene chloride as a 601vent. The PSF~SR had an R.V. of 0.45. Af~er air drying for 1 hour and oven ~rying for lO minutes at 110C the 6~mples were ~ubsequent-ly dip coated again ln a 15 wt. percent 601ution of P-37039 a lcwer mol. wt. polysulfone, ~n methylene chloride, a~r dried 1 hour, oven drled 110C for 15 m~nutes. The ~amples were then baked in a hot air oven for 5 minutes at 245C
- removed and ~mmediately were powder ~o~ted with 40 mesh powdered P-37û3 polysulfone, u6ing a t~pped ~ieve. The ~mples were then clamped together to form lap-~hear test specimens ~nd placed ln ~ 240 C hot ~ir oven ~or l/2 hour to ~use. The same procedure was ~epe~ted only P-1700 powdered (40 mesh) re~in was 6~fted aver the pr$med, hot ~ample plates. The samples were then tested in lap-~hear follow$ng ~STM D1002-72 elle~chod. In ~able III below the results c~btained are ~et forth:
Table III
Thermopl~stic Shear Stren~th ~ Tvpe of Failure P-3703 1596 Cohesive P-3703 1435 Cohesive P-1700 1407 Coh~ ive P~1700 1340 Coheslve ~35-1 1~6092 11~13 EX~WLE VI
Shear StrenRth Measuremen~c6 of Re~nforced ~orous Bioen~ineerin~ Therm~plas~ics S~nless ~teel strlps ~type 304) .0625" x l" x 4"
were ~ashed in hexane ft~llowed by ~6c~propsnol and dr~ed.
The strips were then d~p coated ~n a 10% ~y wt. polysulfone SR (R.V. 0. 517) methylene chloride ~olut~on us$ng a mechan~ ca1 dipping motor which prov~ ded a uniform rate of withdr~wal from ehe solutlon of ~he 6tainless ~trip of
connected pores ~f ~ ~peciflc ~versge pore d~amet2r. Among the polymeric ~steri~16 di~clo6ed ~re high den~ty poly-ethylene and polypropylene or ~ixture6 thereof havingcertain critical parameter6. It 16 ~l~o indicated th~t ~,.
r ; 116~092 the coatln3~ c~n be ~echanlcallg $neerlocked or chemic~lly bonded to the devlce.
U, 5, ~te~t 3,971,134 whlch ~ued July 27, 1976 to J. C. 3Okro~ relate~ eo ~ dent~l prosthe~$~ for permanent or prolonged lmplant~t~on $~ ~ J~wbone of ~ lIving body.
me lmpl~nt c~n be co~ted wi~h ~uch materl~ls ~ ~lnyl poly-~er~ ~. g., ~crylic polymers, polyethylene and carbon fiber filled Teflon.
J. Galan~e, ~t al, in J. Bone and Joint Surgery3 53A, No. 1,101 (lg71~ de~cribe6 s~ntered fiber ~etal compo6i~es ~s a ~asi~ for ~ttachment of lwpl~nts to bone and U. S.
Pseent 3,808,606 which is5ued on M~y 7, 1974 to Ray nd G.
TSonzo de6cribes stainless ~teel and cobalt-chr6~1um~molybde-num alloy pro6the~is posse~6ing porou~ ~urf~ce6 for fix~tion by ti~ue ingrowth.
~ 160, of general interese ~re U. S. P~te~t~ 3~992,725 "Implantable M~terlal ~nd Appli~nce6 and Method of Stabiliz ing Body Implant6", which ~6~ued on Nove~ber 23, 1976 to C. ~. Nomsy, U. S. 3,909,852 "Implantable Sub6t~tute Structure 20 for at LeA6t Part of the M~ddle Ear Bony Chain" whlch i~ued October 7 9 1975 to C. A~ Homsy, and U. S. 3~971,670 "Im-plantable Struc~ure and ~ethod of M~king Same" whieh i~ued July 27~ 1976 to C. A. ~om6y.
In ~ddition to patent~, variou6 article~ have ~ppeared ~n the liter~ture relating to bone ~ngrowth into porous m~terial~. Typical ar~icles ~nclude~ among others, S. F.
Hulbert a "Att~chment of Pro6the~es ~o the ~h6culoskele~1 Sy6tem ~y Ti~sue Ingrowth ~nd ~eehanioal Ine.rlockIng"~
J. Blomed. M~ter. Re~. Sympo~i~m, 4, 1 (lg73); M. Spector, et al, "Bone Growth into Porou6 High-Den61ty Polyethylene"~
J. ~ioYed. ~ter. Xe6, Sympo~ium~ 7 9 595 (1976); C. A~ ~omsy 31 ~fi609~ 11,313 "Implant Stabilization - Chemical and Biochemical Consid-erations", Orthopedic Clinics of North America, 4, No.
2,295 (1973) and J. N. Kent, et al, "Proplast in Dental Facial Reconstruction", Oral Surgery, Oral Medicine, Oral Patholo~y, 39, No. 3,347 (1975).
However, the porous materials disclosed in the lit-erature as beinp useful for prosthetic devices provide inappropriate biomechanical environments leadin~ to either of two undesirable situations. First, low modulus-high creep porous coatings such as porous Teflon/graphite com-posites, exhibit metastable fibrous tissues in the pores after extended perîods. This tissue is not suited to support load bearing joint prostheses. The fibrous tissue is a metastable precursor to bone and under normal physio-logical conditions (including physiological loading con-ditions) would remodel to bone. The high loads transmitted through low modulus materials and the excess creep result in fibrous tissue ~hich fail -to remodel to bone. Other low modulus-high creep materials employed for prosthetic de-vices include polyethylenes and polypropylene.
Secondly, high modulus materiaLs such as ceramics (16 x 1~6 psi) and metals like titanium (17 x 106 psi) and cobalt-chromium-molybdenum alloy (34 x 106 psi), do not spread sufficient load to the ingrown or surrounding bone to prevent resorption. In porous metal and ceramic coated femoral and humeral stems, load is concentrated at the apex of these prosthetic components causing stress con-centrations in the surrounding bone and subsequent re-sorption. In addition, the bone spicules in the pores of these porous ceramic and metallic implants do not experience 66~2 11,313 load~, ~h~reby re~orbi~g~ The 10118 of bone frao the pores ln ~rcaa of porou~ lant~ ch exper~ence no lo~d has been demon~trstcd hl~tologlcally. ~hl8 qpe of ~one 10~B
12ads to ~ decr~ase ln compo~lte ~trength ~e. g. lnterfscial she~r lltren~th) and ~ ~ub~e~uent decrcs~e ~ u~e"
perfo~unce ln the~e hlgh modulu~ porou~ ~terial~, .
The above-cited p~eents and l$t~rature de~crlbe the u~e of porou~ co~tlngu ~n pros~hese~ And descr~e accept-able pore ~ize r~r~ge requiremene6. However, ie ha~ been 10 found th~t met816, cer~mic~ and poly~Gers ~uch a0 the ~nyl pol~mer6, polyeehylene, polypropylene, c~rbon filled Teflor and other6 dlsclosed as being u~eful for coat~ng pro~the~lc ~ev~ce~ do not est~bli~h the proper biomechanlcal emriron-ment to achieve appropriate early fixation, l~ng-term stability and strength at the bone-prosthesis interface. Previously de~cribed polymeric m~terial~ can al~o l~ck the toughnes6, creep re~lstence, ten6ile ~nd ~m~act strengeh and ~team 6terilizabillty to be ncceptable 8B ~he polymer of choice for coat~ng pro6ehet$c devices. Even selec~ high denslty polyethylene and polypropylene porou~ compofiitlon~, ~ta~ed to po~3e8~ the rlght ~moun~ of fle~ibility a~d ~trength ln U. S. Patent 3~986,212 sre deficient 8S will be discu~ed below~
The bone ~ngroweh in porou~ orthopedic ~mplant6 can be con6idered ~ a two stage phenomenon. E~ch 6t~ge 1~
influenced by the pore c~ar~cteri~tic~ and biomeehan~cal char~cter~a~c~ of the ~mplan~. In ~he fir~t ~tage a~d ~mc~difltely after lmpl~ntat$on the porou~ component fill~
~lth a bl~od clot which ~ubsequently become~ l'organized", F~brobla~t~ appe~r ~n the clot reg~o~ and flbrogene6i~
occur~. The clot ~ rcpl~ced by 1003e connectlve tl6 ue fifiO~2 I
11~313 snd ccp~ rie~. At th~s point preo~t~oblYst~ b~g~n to appe~r ~n th~ per~pheral p~re~ of ~mplant. The~e eell~ can ~ecome o~teoblasts or chondroblAsts depending u~on the environment. ~f the ~rig~nal pore size of the lmplant 1B
too ~m~ll or ~f the pore Dtruc~ure has ~een dl~tosted by the initial applied loads as wlll occur with Teflon, high density polyethylene and polypropylPne porous ~aterials, one or more of the above sequence of events can be ~n-terrupted. For exEmple, it i~ generally bel~eved that a amaller pore ~ize (C90~)leads to the ultim~te form3tlon of fibrous tis~ue, not bone, in the implant. If the dulu~ of the mater~al i8 toD low, ~icro-motion occurs with lo~dlng. '~li5 would lead to nn envlron-ment that 16 eonducive to fibr~u~ or cartil~ge tl~6ue, ~t ~one, formation. For example, e2ces6ive motion c~n lead to di6ruptlon of va6cularity and A decreafie ~n oxygen, a condition whlch ~vor6 cartilage formation.
~ f~er ~one ha~ filled the pore~ Qf ~he implant, in the ~econd ~ ge $t mdergoe6 re~Dodel~ng ~hieh i6 ~nfluenced pr~marily by lt6 biomechanical environsnerltr Spicule6 ~n the lmplant which e~perience urlifor~D ~tres~ will thieken ~hile ~ho~e ~picules whlch experience no ~tres~ or exce~ive ~eres~
(Btre~5 conce~tr~tion) are re~orbed. me m~dulu~ of me~al~
Jnd ceramic~ 16 Bo high thst the Implant~ do not defonm under the appl~ed load~. The bone ~picule~ in the6e por~u~ im-plant6 thu~ do not exper~encc ~ufficient lo~d ~o thicken.
Bone trabeculae ~n the~e higher modulu~ porou~ m~terlal~
tend to resorb, becoming thlnner than the oplcules in the porous l~plant6 wh~ch are the ~ub~ect of thl~ in~enti~n.
The ~bove di~cu~ion ~ndic9te6 t~8t t~e biom2chanical enviro~m~nt e~tRbllshed by the lm~lant ~ateri~l a~d ~he geomet~ of the porous ~ub~trate hs~e ~ profound ~ffec~ o~
the biologlcal f~e ~ ~mplant8, I~ h~8 ~ow ~een found O 5 _ 0 ~ 2 ll, 313 that certaln thermopl~stic~, here~fter de~cr~bed as ~ cl~ss ~s b~oeng~neering ther~oplastics, provide the delicRte balance which must ~e ~chieved between parameters affecting load trans-~ssl~n, micro-motion, dimentional stabilley, snd strength.
Bioenglneering thenmoplaseics~ us~ally prepared by condensation polymerizations, ~lso show low metal contamination levels (i. e., Low transition ~etal catalysts levels) and exhibit e~cellen~ ch~racterlstic~ $n ~iot~xic~ty ~tudle6 ~ch a6 the U. S. Pharm~copia Class Y~ Stand~rd~. Ihey represent an opeimum m~terisl6 caeegory for orth~pedic, dent~l ~nd maxillofecial ~pplicatio~. The tr~nBml~Bion of stre~s to bone in the pores of bioengineer~ng thermo~
pla6tlc6 mimic~ the phy6iological biomechanical env~ron-men~ ~ evidenced by the repllc~tion of the norm~l bone repair proce~e~. Bone 1~ porous bioengineering therm~-; plastic lmplant6 rem~delled after a clinically ~pproprl&teperiod to reflect the m~gnltude ~nd direct~on of the pre-v~iling stres~e6 ~t the anatomic~ e. Thi6 occurrence permit~ the ingrown ~one to ~e ~ structur~lly efflcien~
memb2r for ~he lDad e~vironment to which 5 pso~the6i~ i~
~ub~ected.
It 18, therefore, an ob~ect of the lnvention to pro-v~de efflcaciou6 pro6thetic devices comprised of an inner lo~d be~ring functional cvmponent snd ~n oueer fo~med or ~intered porou~ c03~ing over ~t lea6t a p~rt~on ~hereof, of ~elected bioeng~neer~ng thermopla~tic~, ~nother ob~ec~
of this in~ention i6 to pr~lde co~ted pro6thetic devlce~
wh~ch after ~mplsnt~tion nchic~e ~ long-tenm bone fixa~ion by lngrowth of tl~ue ~nto and ~hrough ~ ~elec~ pG~OU6 b~oenglneering thermopl~tlc co~ting wlth ~ub~equen~
11 ,313 ren~delllng to bone. A fureher og~ct 18 to pro~de ~
pro~the~ic dev~ce having a coat~g ~f a ~pecified poro~lty whlch prGvide~ the optimu~ ubserate for t~ue ~ngrow~h.
Another ob~ect ~8 to provlde proDthet~c devlces wherein the co~ting ~hlbits ~uff~clent ten~lle ~nd l~psct ~tr~ngth durlng ~nd after bone formation eo ~cc~mm4t~te applied lo~d6 during insertion ~nd ~fter ~urge~y, ~ ~urthc~ ob~ect i~ to provide ~oated pro6th2tic device~ whlch can undergo ~team ~teriliz~tlon w~thout ~dver~e effect~ on the co~ting. A
~ill further ob~ect of thi~ in~ention i~ to provide anatom-~c&lly ~haped porou6 ~tructure~ of eelect ~ioengineering the pl~6tics which are uae~ul ~or recon~truotive procedure6, Another ob~ect of thi6 ~nventlon ls to pr~vide porou~ bio-engineerlng thermopla~tic coating~ or 8tructure6 containing additives f~r enhancement of their b~ologicAl and/or m~ch-an~cal properties. A further ob~ect o~ ~h~6 inYent~on iS
to provide porou~ b~oengineer~ng thermoplastlc coating~
or l;tructures contalnin~ eddi~ive~ ~or increa~in~ wear azld ~bra~ion resi6tance. Another ob3ect ~6 to provide one or more processe6 for preparlng c~ated pro~thetic devic~ or anatomlc~lly ~haped ~tructure6 c~mposed of bioengineer~ng ehermopla~t$c~o The importance ~f the~e and othcr ob~eets will readily become ~pparene to Sho~e ~killed ~n the art in the light of the ~eaching6 herein ~et forth.
In it6 bro~d ~pect the pre~ent ~nvention i~ directed to prosthetic de~ce6 compri~ed ~f or co2ted with porous bioenglneerin~ thermopl~stlc materi21s ~h~ch en~ble~ ~uch deviees to beco~e firmly and pe~m~nently ~nehored ~nto the mu~culo~kelatal sy~tem by t~ue ingrowth ln~o the co~ted ~terial., ~n one e~bodiment the pro~thetic de~ice6 are compri~ed sf a lo~d be~rlng funct~n21 com~onent End over ~ 7 ~
O g 2 11,313 ~t leaEt ~ portlo~ ehere~f~ ~ por~u~ ~o~ting of from ~oue 0~5 to ~out 1~ ~lllneter~ ~n thickne~ ~f a ~oenglneer-lng thermDpls~c ~teri~l ~h~ch ~B comp~t~ble wlth~ and conduclve for, the lngrowth of c~nc~llou~ ~nd cortlcal bone ~pieule~, ~he co~t1ng h~vlnæ the fo~lowing propert~e6:
n ~verage pore d~ameter of rom a~ut 90 ~o ~ut 600 ~icron3;
(b) pore ~nterconnections h2v~ng fiverfl e ~i~meter6 ~f grester ehan ~bout 50 mlcro~s;
(c) a modulus of elasticity fro~ ab~ut 250,000 to ~bout 3,000,000 pounds per ~quare inch for ehe neat thermoplastlc material or the reinforced thermoplastic material;
(d) a porosity of greater than about 50 per cent; ~nd~
- (e) a totsl creep strfli~ of less than one percent at ~
constant ~tress of 1,000 pounds per 6quare inch at ~mbient t~mperature, ~11 of the propertie6 being sufflcient to enable ~tre~es ~pplied on the mu~culo~keletal ~y~em to be ~r~n~ferred to bo~e spicule~ within the pore~ snd maintain ~uffic~ent losd Rnd pore ~tsb~l~ty to promote irrever61ble 066ific~tlon, Hence, 1~ has been ob~erved that the m~erial~ u~ed ln eoatlng the load beasing function~l component of pro6thgt-~c device6 ~u~t po~6e~6 ~pec~fic propertie~ lf long-~enm bone flx3tion ~6 to ~e achlevet. Pro~thetic devic~6 pre-p~red in accordance with the te~ching6 of ehi inventlon hffve been found to pro~ide the ~i~mech~nlo~l ~nvironment nece~6ary to u~lfonmly tr~n~lt the proper ~gn~tude of ~pplied load~ promotlng the ~esired r~m~d~ll$n~ of bone trqb2cul~e .
1 :166~9~
~1,313 ~ psevioualy ~nt~cated, the ~ter~al~ employed ~n the preparat~on of the pro~theelc d~Ylce~ of th~ lnventlon 2re cla361fled B ~ oongineerlng thermoplaMtic~". OTIR lmportent fe~ture of these m~teri~ ehat ~heir performance c~n be pred~cted by the use of Detal de~ign eng~neerlng ~quatlon6 for ~oth long ~nd ~hor~-term. These engineering d~s~gn e~uations only ~pply up toehe l~near ~i~coel~tic limit of the msteri~l, High den~iry polyethylene has a l~ne~r V~8^
coelastic llmit of le~s th n 0.1 percent ~nd with th~ limit on the æmount of tr~ n,the ffllo~able stre~ iB ~inimsl. In conerase, the line~r ~iscsela~tic lim$t of bioengineer~ng ~henmople~tic6, within the definition of thi~ disclosure, ~8 at least 1 percent ~tr~ln. For example, one of the preferred engineering thermopla6t~c material~ found to be suitable for the coatings of thifi invent~on i5 a p~lysulfone which ha~ a 2 percent Btrain l~mit. Hence ~ the met~l engineerin~ de61gn equations for both long ~nd 6hort term can ~pply up to this limit.
The un~que char~ceeristics of the bicengineering thermo-pla~tic m~terial6 are more clearly evident when ~cheir per-formance i6 compared to poly~eric ~aeeri~16 prev~ou81y ti6-clo~ed as belng ueeful for porou~ fi~ation dev~ce~. If ~he creep modulus extenslv~ly varie6 with t~me~ deflec~on lncsease~ markedly, c2u~ng mlcro d~splacement of a prosthesis under load and pore dl~tort~on. Creep te~ts have alre~dy been reported in the literature on porou~ h~gh den~ity poly-ethylene and a po~ytetr~fluor~ethylene-graph~te compo~te, both of w~ch have been ~ndic~ted ~n the prev~usly c~ted ~atent~ . It hs~ been ob6erved thst d gnlficant changes ~n pore structure occurred upon compresslve 6~re~es as low &S
80 p~ for the porou~ polytetr~fluoroethyl~ne~graphlee c~-posltes And at 300 p8i for ~ porou~ blgh d~sn~ poly-2~hylcne. T~picnl ~ime to fs~ e ,rer~us l~tre~ ~os~ the ~wo 9 _ 6 ~ 9 2 11,313 s~oported hl~h den~ty polyethylene fabr~c~tion~ were ~mder~lv~ ~i~ute- ~hen ~tre~s leYeS~ ~reater than 300 ps~ ~ere ~pplied. It ~hould bc noted that thl~ repre~ents the ~tres6 level~ ths~c will ~e e;cperienced in ~me orthopedlc ~oint ~nd deYice appllcat~on~. The $mport~nce of mRinea~ning pore ~eometrles under lo~ding envlronpents ~8~ ~ndicated æ~rlier where ~t ~a~ ob6erved th~t f~brou~ tls~ue lt~ ereated ln ~mall pores. Thi~ 1~ partlcularly cr$tical in e~rly post~operstive perlod~ prior to ehe ~ngrowth of bone when the p~roui poly-meric coating Dn ~oint pro~these~ mu~t hsve ~uff~clentstrength and ri~ldlty to Independently ~upport appl~ed load wlthout aB~i~tance from lngrown ~one. The ~trength of prior polymeric m~terials c~me~ from the ingrown bone. 8ioengineer-ing ehermopls6tic porou6 co~ting ha~e ~trength like ~one.
Illu6trative pro~thetic devlce6 which ~re within the ~cope of the teachings of thi~ lnvention are readily apparent from the followlng de~crlption and from the ~ccompanylng drawings where~n:
Flgure 1 i~ 8 plan v~ew of ehe ~tem ~nd ball portion ZO of ~ total hip pro~thesi~ having 4 coating of a porou6 blo-engineering thermopl~t$c m~terial.
F~gure 2 1~ ~ plan YieW of an endo~e~l ~lade ~mplant having a co~tlng of 8 porou~ bioen~ineerin~ ~hermoplas~lc m~terial on ghe bl~de portion thereof.
Figure 3 i~ ~ ~ide plan view of ~nother endo~teal im-plant havlng the ~lade portion co~ted with the porous blo-engineering thenmopla6tic m~teri~l.
F~gure 4 ~ ide pla~ ~iew of a self-bro~ching intr~
~medullary ~8il h~vlng ~ cO~e~ng oves its ant~re length of the porow b$oengineer~ng ther~opl3~t~c ~aterlal.
a~ 10 -11, 313 ~lgure S 1~ ~ pllm v~ew of ~ pros~het~c ~evice c~nprlsed entlrely of ~ porous bl~ngineering thermopl~t~ c materisl .
P'~gure 6 i.B a gr~ph dep~cting the relationship of inter-faci~l 6hear strength ~er~ implsr~tat~on ti~ne c>f ~everal porous m~teri~l6.
Referring now co Figure 1 of the accomp~nying drawi the total hip pro~the~ls 10 1~ comprised of ball ~nd ~tem ~ember 12 and cup member 14. T~e eem port~on of the b~ll and ~tem member 12 i6 cos~ed over ~e8 ~n~ire ~urf~ce wlth a porous bioengineering the2~nopla0tlc coating 16 of th~6 ~s~ventlon. Although thP stem portion i~ depicted in Figure 0 1 E15 a solld fitem wi~h ~ groove 18 along ~t lea~t a por~ion of lt~ len~t~, it can h~ve opening~, ridge6 or other con-flgurat$on~ to provide co~ted ~ite~ for S ue growth to firmly 4nchor it to the ~Iceletsl ~y6tem. Cup member 14 i6 likewi~e co~ted on it6 ~xt~rior ~urface ~ith the porou6 engineerlng the~pla~tlc 16. The n~ck 20, ball 22 and ~nner surface of the cup 24 do ~ot, of caur6e~ sont~in any coating~
Figures 2 ~nd 3 of the trawings deplct c=ercislly available impl~nt~ 26 and 28 which cen ~e fabric~ted ln ~ ~ariety of 3hape~ snd are decigned for ~upportlng group~ of ~rt~fis:ial ~eeth l'he6e tevices are ususlly cc~m~ri~et o~ cob~lt or tltanlum ~lloys snd ~re in6erted into 810t8 cut lnto she ~Iveol~r ridge.
~e po~ts 30 and 32 protrude ~nto the or~l c~viey ~nd are u~ed for ~nchor~rlg the arti Pical teeth ~ ~ ~hown ln the dr~win~,, the ~tem pQrtions 34 Rnd 36 c~n be c~ated wieh the porous biDengineering ~herk~opla~ic mster~al ~ad pr~rlde for bone ingrowth to firmly ~ffix the pro~thesi~ he alveol~
~idge, An ~tra~nedullar~ ~11 3B i8 lllull~r~t~ n ~gure 4 a~d ha~ ~ eoatir~ 40 of ehe parou~ b~oeng~n~eri~g thc~o-~16~092 11~313 plas-tic material over its entire leng~h. These nails are placed in the medullary canal oE long bones~ such as femurs, and are usually limited to the middle one-third section o~ such bones. These nails are wedged lengthwise into the medullary canal and press a~ainst the interior of the cortex. Finally, Figure 5 provides a plan view of a porous implant 42 which can be used for alveolar ridge re-construction, Thus, ridge reconstructions can be made by using a porous or solid interior bioengineering thermoplastic implant, without a load-bearing functional component, carbed or molded to the desired anatomical shape.
Figure 6 is a graph depicting the relationship of inter-facial shear strength in pounds per square inch versus time in weeks for trochanteric implanted intramedullary rods of porous polysulfone, porous titanium and porous polyethylene.
The porous polysulfone was prepared in accordance with the teachin,gs of this invention and exhibited the physical charac-teristics previously described for bioen~ineering thermo-plastics. The data for the porous titanium and polyethylene implants was reported by other investigators. In each case, the rods were implanted in dogs in accordance wit~ accepted surgical techniques.
While each of the tests was performed in a similar fashion in dogs, there is the possibility that the results could vary somewhat because of differences in implantation and mechanical testing procedures used by the different in-vestigators. However, these variations are not great enough to prevent comparison. Of particular interest is the fact that the interfacial sheer strength of porous polysulfone is high enou~,h after only two weeks (~150 psi) ~66092 11,313 to support the static load and most dynamic loads that might be placed upon a hip prosthesis by a patien~ immediately after surgery. This type of data thus evidences the possi-bility of early weight-bearing postoperatively for polysul-fone, whereas the porous high density polyethylene exhibits an interfacial shear strength value only one-third that of polysulfone. Indeed, only after extended implant periods, did the high density polyethylene come up to the two week value for polysulfone, and it fell short of the ultimate shear strength value for polysulfone.
As hereinbefore indicated, the materials which are employed in the present invention are desiv,nated as bio-engineering thermoplastics. These materials are unique in that they combine melt processability with structural strength, rigidity, creep resistance, toughness, and steam sterilizibility. In corporation of glass, carbon or organic based fibers into the bioengineering thermoplastics extends the load-bearing and structural characteristics. Bioen-gineering thermoplastics exhibit bulk tensile or ~lexural modulus values in the range of 250,000-500,000 psi. ~iber reinforced products exhibit modulus values up to 3.0 million depending on the fiber type and loading. These values of modulus provide the intermediate range required for initial post-operative support and long-term stability of implanted prostheses in high load areas anchored by bone ingrowth.
.~
0 ~ 2 11,313 Each of these materials when prepared in accordance with the teachings o~ this invention provides coatings or free standin~ articles havin~ the physical properties herein-before enumerated. Illustrative of these materials are the polysulfones, such as, polyphenylsulfone, polyethersul~one, polyarylsul~ones, and the like; polyphenylenesulfide, poly-acetal, thermoplastic polyesters such as the aromatic poly-esters polycarbonates; aromatic polyamides, aromatic poly-amideimides, thermoplastic polyimides and the polyaryletherke-tones, polyarylethernitriles, aromatic polyhydroxyethers, and the like. The most preferred materials for use in the in-vention are the aromatic polysulfones. These polysulfones contain repeatin~ units having the ~ormula:
TAr-S02]
wherein Ar is a divalent aromatic radical containlng at least one unit having the structure:
~-Y-~
1 :166092 1~9313~e-l in which Y is oxygen, sulfur or the radical residuum of an aromatic diol, such as 4,4' bis(p-hydroxyphenyl~-alkane. Particularly preferred polyarylene polyether polysulfone thermoplastic resins are those composed o~
repeating UnLtS having the structure sho~n below:
r _ ~SO~O ~C_~O l CH3 n wherein n equals 10 to about 500. These are commercially available from Union Carbide Corporation as UDEL*
Polysulfones P-1700 and P-3703. These materials differ in that P-3703 has a lower molecular weight. Also useful are Astrel*360 a polysulfone sold by 3M Corporation and Polysulfone 200 P sold by ICI and Radel polyphenyl-sulfone sold by Union Carbide Corporation. Certain crystalline bioengineering thermoplastics like Stilan from Raychem Corporation, Polyarylene and Phenoxy A
from Union Carbide Corporation, are also useful.
*Trademarks.
1 lB6092 11, 313 In practice, the prosthetic devices of this invention having an inner load-bearing functional component or those existing as free standing anatomically shaped devices are conveniently prepared by one or more methods. In one method the coating or article can be formed by a sintering technique whereby particles of the bioengineering thermoplastic material are heated for a period of time and at a temperature suffi-cient to cause sintering that is, the particles fuse together at one or more contact points to provide a porous continuous composite material of the bioengineerin~ thermoplastic. In a second method, the coatin~ or article can be formed by a process which involves the formation of a low density foam of the normally solid thermoplastic material. This second method which can be described as the dough foam technique is particularly useful for the preparation of the porous materials. However, its use is limited to the aforementioned polysulfones and phenoxy A aromatic polyhydroxyethers.
Porous bioengineering thermoplastic coatings and blocks prepared by these methods exhibit intermediate modulus values, high strength and hi~h creep resistance. They can uniquely be fabricated with high total porosities and pore sizes, while still meeting -the strength and biomechanical criteria observed to be necessary for bone repair and prosthesis fixa-tion/stabilization. For example, slntered polysulfone having an average pore size of 200 and a 53 per cent porosity, had a flexual strength of 2000 psi and flexural modulus of 60,000 psi.
Foamed specimens with a 70 percent porosity had a flexural modulus of about 105 psi. This value increased to 8 x 105 psi with the introduc-tion of 30 weight percent carbon fibers.
~-16-6~92 i 11,313 ~ lth r~p~ct to the fir~ ~eth9d, lt h~s been ~bserved that through e~reful control of temper~ture, ~lme ~nd pres~ure, all bloengineering thermoplastic~ c~n be ~intered.
~or exsmple, I~EL-P-1700 polyRulfone can be ~at~sfactorily 61ntered ~t ~pprox~tnqtely 245~C and Radel poly3~1fone i~
enerally sinter~d at lapproximately 285C~ At ~ppropriate temper~tures, t~mes ~nd pres6ures the other thenmoplastic materials can also be 6intered to provide a porou~ product 6uitable for the intendet use. It h~s been ~b6erved, however, and p~rticularly for use ln preparing the coa~ngs and srticles of this invention, eh~t optimum properties can be obtained in a ~u~$que ~nd facile m~ er by proper choice of ~oth (a)particle s~ze and tb) molecular we~ght dis~ribution.
As ind~caeed previously, the de~ired properties are exhibieed by ~he prosthetic device when the bioengineering thermoplastic ~a~erial has ~ poroslty of ~b~ut 50 per cent and more prefer~bly ~rom about 40 t~ ~bout 70 per cent. Poros~ ty i6 influenced by the p~rticle s~ze employed in the sintering operation. Particle slze also lnfluence~ the strength of ~he porous ~intered m~terials~
Large particles result in large pore slzes, while ~mall particles ~mprove ~trength by increas~ng the fusion area of the particles.
It hss been observed ~hat the modulus ~f 8 porous material can be predicted through the Rerner equ~tion or ~hrough ~od~ f~ ed Halpin-T~ai equ~tlo~. ~ence, ~n order t~ ~chie~e ma~eriel with ~ poro~lty, or ~xample~ of 55 per cent, ~nd an ~lastic ~tulu~ greater than 40,~00 p~l~the ~odulus of ~he ~;~
1 16~ 0~ 313 æt~rtin~ polymer ~uct ~xce~ 200,000 p~ hus, ~t polypropylene~, and all high density polyethy}ene~ are incapable of belng fabr~cseed ~n ~ ~ster$al cf 55 per cent poro~ity with a modul~s o~ 40,000 psi. On the other hand ~ce the modulus ~f solld poly~ulfone exceeds 34~;000 psi,a ~ater~1 of 55 per cent poros$ty whose ~odulus exceeds 70,000 p6i can be obtained.
Even though it was possible to predict the modulus of a thermoplastic h~ving a desired poro~ity there was no s~mple method ~va~lable to fabricate ~ m~teri~l appro~chirlg these predictions which would be u~eful for the devices of thls lnvention. It was unexpectedly found, however, that the desired degree of poro~ity could be obtained without 6acrificing mechanical properties b~ the proper choice of par~icle 6ize, molecular weight distribution and 6intering conditions. All three ~re ~nter-related and neceæ6ary to ~ch~ eve a costing or article h~ving the neces6ary char2cter-~ 6tiC6 . For example, the s~nter~ng time and temperature which results in ~ desired pore ~ize distribution may not produce the desired modulus of ela~ticity and/or tensile ~trength. Starting particle 6ize distribut:ion, 6intering time, and 'ce~perature must be adju~et to achieve the de~ired balance of pore s~ze, porosi~y~ ~d mech~nical properties.
With respec~ ~Q part~cle 6ize di~tribution, ~ blend of two or m~re different ~l~es of the ~loe~gineering ~hermo-pla~tic ~ateri~l was fvund t~ provide ~ ~ntered material ~hich be6t met the por~itg ~nd meehanical requirement~ needed for a ~ucces~ul pro~thetic device. ~ ~
1~66092 11,313 ,In practice, a mi~ture of partic~e sizes wherein the ratio of particle diameters ranges from about 7:1 to about 5:1 has been found to be acceptable. Particle sizes o~ rom about 300 microns to about 50 microns are particularly preferred. For exam~le, a mixture o particles whic~ are retained on a 50 mesh screen (U.S. Standard Sieve) and pass through a 270 mesh screen have provided coatings and articles having the desired porosity and biomechanical features. It has also been observed that optimun result~s are achieved when the particle size distribution ranges from about 40 to about 60 wei,ght per cent.
As indicated, the sintering conditions are also im-portant to achieve ~he desired properties. Sintering has been accomplished by charging a metal mold with powder and heating the mold to a prescribed sintering temperature, Ts, greater than the glass transition temperature, Tg, and less than the melting or melt processing temperature, Tm, (i.e.
Tg cTS cTm)- The sintering temperature is held constant for a given time, t. Essentially, no pressure, other than that induced by differential thermal expansion, is applied.
The application oE pressure at Ts leads to fluxing of the material. This indicates that if pressure is applied, lower temperatures and shorter time cycles must be employed to retain porosity in the sintered parts. Experiments were run and set forth in the examples to delineate the effects of the sintering conditions on the pore size, porosity, and tensile properties of the porous sintered plastic for various powder size and molecular weight distributions.
~6~9~
11,313 In ~ ~ccsnd ~ethot it has beon ~u~d eh~t ~nce s~me bisengln~rlng ~hermopla~t~c6 ~re aol~ble ~n low-goiling org~n~c ~ol~ent5 ~ ~ol~ent ~vamlng technique cen ~e utlllzed for ~olding open cell porcu~ foa~ coa~lng6 snto protheses or for the prepar~tion of fo~med art~cles. Porous fo~ed co~tings ~nd artlcle6 offer advant~ge6 over slntered porous co~tings and ~rticles ~n ~hat hig~er p~ro~itl~fi can be ch~eved nt higher ~rengths, due to the thin contiguous pore wall6 obtained in the foAming processes. ~urther9 low fabricstion temperatures are ~xperienced due to the pla~ti-cizing effects of the ~olvent on the thermoplastic. This tec~.nique is not amenable to Teflon, polyethylene or polypropylene being described as preferred materials i~ prior art patents.
This ~olvent foaming technique for fabricat~ng low density, foamed ar~icles c~mprises the l;teps cf:
(a) blending at lea~t on norm~lly solid bioengineering thermopl~st~c with ~bout 25 to about 80 parts, per 100 parts by weight, of a normally liquid organlc ~o}vent ha~ng a 601ubility par~meter,S , within (1.3 calories per cc) of that of the thermoplsstic, or ~ mixture of ~ormally liquid org~nic 501vent5 having the ~ame ~olubility parEmeter;
(b) blending the mixture obtained ln 6tep (a) with ~t lea~t about 1 part by weight; per hundred parts of thermo-pla~tic, of water whereby ~ non-t~c~y hydrogel dough ls obtalned;
(c) ~hAp$ng the hydrogel dough obta~ned ~n step ~b~;
(d) vapor~zlng ehe ~olvent and ~ter and (e) recover~ng a foEmed re~n ~rtiole, It has been found that foam prep~re~ ~n thi~ manner posse~es ~he desired degree~ of ~oth poro~i~y ~nd b$amechanlc~1 proper-~ie6~ .
It h~ been ob~erYed, howev~r~ ~hat the ~alue~ of the 1 16~;0~ ' 11,31 solubili~y p~r~me~ers of the norfflally liquid organic ~olvent6 used ~re falrly crit~c~l ~6 ~vidence~l by the fACt ehat wlth ~ preferred ehermopla6~ic r~n BUCh A6 the polysulfone depicted above ehere is o d~stinct dlfference between st~ucturally ~milar ~olvent ~80mers.
~hus, ~r example, the a~ove-descr~bed polysulfone, which has a solubility p~rameter calculated to be 10.55, is ~oluble ln 1,1,2-trichloroethane having a ~olubility par~meter of 10.18 but in~oluble in l,l,l-trichloroethane havin~
a ~olubility parameter of 8.57. However, a m~xture of organic ~olvents which indivitually 15 unsaelsf~cto~y can be used as long ~s ehe average 601ubil~ty parameter of ~he ~ix~ure i~
w~thin (1.3 calories per cc) / of the re~in being blown.
In addition, if ehe T~ of the polymer that i5 to be pl~sticized i5 exceptionally high $n value, plastie~ty of the gel can ~e prolonged during the fo~ming ~tep by ~orming ~ ~$xt~re of 601vents, one of which shoult have a much higher ~o~ling point value. Thus for example while e~hanolor l,l,1-trichloroethane cannot ~e used ~ndiv~dually with the polysulfone depicted abo~e B mixture c~mpri~ng equal p~rts by volume of ethanol and l,l,l-trichloroethane c~n ~e u~ed. Oeher combin-ations which function a5 organic 601vent5 for poly6ulfone are:
957. ehloroform ~nd 5% s~ater, 85Z methylene chloride, ethanol 20% ~nd w~ter 5~, 95Z ~etrahydrofuran and ~ster 5%, 75% methylene chloride" 10% ~cet~e, lOZ ~thanol, ~d 5Z water, ~nd 80% cyclohexsnone, ~ nol 15Z~ ~nd b~ ter ~%.
:11 1660~
11, 313 ~ he umount of water ~dded 16 not crltlc~l ~ut generally at lea~t 1 p~rt i6 required per 100 parts by weight of resin. Ihere ~6 no m~ximuYn amount ~ecauce excess water ~ep~rates fr~m the dough-llke ~Q~ as ~
8epar~te phase. ~ecau6e of ~he p~se ~epara~ion, whPre the 601vent employed ~ for ~he ~ost p2rt not m$~clble wlth ehe w~ter phase, the exce6 water ~c~ a~ A prot~gtive blanket which prevents rapid 601vene 10s6 from the plast~
c~zed polymer. This feature ~llows the pla~ticized poly-meric gel to be exposet in an open ve~sel during handl~ng and transfer w~thout sealed contsin~ent. ~n this form the polymer blend can be easily transferred fr~m one vessel or container to another ~nd can be 6haped ~nd ~olded or oth r wise worked w~thout the necessity for using colltaminating release agents. S~mple mixing equipment known to tho~e skilled in the ~rt ~8 all tha~ is required ~o blend the water into the mixture of the~:moplastie resin and li~uid organic 601vent. The result~t hydrogels can be u~ed ~mm~di~tDly or ~f desired ~tored ~ndefini~ely under water and then recovered and u~ed wlthout further tre~tment.
The ~rganic ~olvent once ~t d~ffuses into polymer resin, ~erves two purposes, n~mely, the formation of ~ gel retai~ng finite solvent concentrat$on ~n B pl&6eicizet fonm and 6econdly the ~olvent ~erve5 a~ ~ blowln~ or fo~ing agent ~t 8 much lower tempera~ure ~nd v$~cos~ty th~n ~h~t whlch would be required ~D foam the original non-plastici2ed polymer re~in with ~ convent~onal ~6eous ~ype blowing or o~ing ~gent, At ~lowing temper~ture6 ~ from 165~200C~ ~ece~6~ry for . -22~
, 11~6~9~
,3~3 polysulfone~, ~06t of the commonly used organic ~olvents d$ffuse DUt of the polymer blend too quickly to provlde ~dequate blowing of the resin. Durlng the blowing oper~tlon the water in the hydrogel is also removed wlth the norm~lly l~quit iorganlc 601vent. Thus ~h~le the ~ec~nd orter ~ran61tion temper~ture (Tg) of ehe polymer resin ~eing treated $n t~.$s ~an~er is lowered, enhancing the proce~sing of the polymer ae lower tempesature, the l~qu$t or~anlc 601vent and ehe water being fugitlve in naeure, ~hen removed from the polymer resin leave the foa~ed art~cle with the physical properties of the or~g~nal resin prior to processing. Th~5 i5 extre~ely ~mportant in the case of polymers whiieh ~re d~fficult to proce~ becau e of their vl~coel~stic and rheolog~cal properties or heat ~nst~bility;
The wide lat~tude cf conditions under which the foaming operatii~n can be carried out in ehis proeess was also qulte 6urpri~ng. Thus for example, while one can pr~ceice the fosming ~tep at higher temper~tures, one c~n al60 oper~te ~t the other end of the 6pectrum, ehat i6, ~t room temper~ture or ~y pl~cing the hydrogel in a vacuum tevice, 6uch ~s, ~ vacuum oYen and with organic ~olvents of low vol-atili~y, 6uch 8S, methylen chlorlde, readlly r~move the ~olvent and water in a relatively short ~e~
- 11,313 1~6~0~2 As previously indicated, another embodiment o~ this invention is directed to prosthetic devices which do not contain a separate inner load-bearing functional component but rely on the structural integrity of the bioengineering thermoplastic material itself. For example, a porous block can be carved to an anatomically appropriate shape, and used to au,gment atrophic mandibular alveolar ridges and deficient facial contours in the mental, mandibular border, and zygomatic areas. Other devices, can include bone gap bridges and bone caps (used to control bone overgrowth in amputees) which are either totally porous bioen~ineering thermoplastics, or bioengineering thermoplastic coated metals or bulk polymers (reinforced and unreinforced). The alveolar ridge recon-s~ruction au~menta~ion device shown in Figure 5 is prepared from a porous bioengineerin~ thermoplas~ic composite by molding and/or carving a block of the composite to the de-sired shape.
The porous bioengineering thermoplastics can also be carved to anatomical shapes without destruction or collapse of the surface porosity. Bone gap bridges, bone caps and other pre-sized implants can be machined without destroyin~
the porosity and surface of the porous engineering thermo-plastics. Porous high density polyethylene, polypropylene, and the polytetrafluoroethylene creep and "feather" durin~
carving and machining operations.
The ~i~,h stren~th-lo~ cree~ of the bioen~ineering thermoplastics and reinforced bioengineering thermoplastics also translate to the load-bearing components of prosthetic devices and implants. For this reason, prostheses can be ~ _ 11,313 developed ~ncorpc~r~nng ~ compo~e xyst~m of bloengineering ther~oplast~c load-~e~ring eomponent~ and ~rticul~t~ng 3uraces, w~th porou~ bioenglneerlng thermoplastic coatings in ~reas ~her2 ~ttachmen~ to ehe ~u~culo6kelet21 ~y~tem ~s de~ired, The bio-.
englneering thermoplastics rema~n tough after being illed - wlth ~einforcing filler~, where polyolefins ~uch a~ high density polyethylene become brit~le ~t high fiber loadings.
Bone ~ap bridges and joint prosthesec demonctrate this principle.
Such ~mplantables are rendered more useful ~ecau6e of the ~bility to achieve high ~nterfacisl ~trengths ~etween the bulk lo~d-bearing component and the porous coating when the ident~cal ma~erials are cGm~i~ed in the constructio~.
Ihese o~mblnations are not achievable with polyolefins due to the poor 6tructur21 characteristics of these m~terilas, nor with cerEmics or metal6 because of ehe biomechanicEl unsuit~bil~ty of the respective porous coatings.
In ~olnt prosthe6es ~here the bioeng~neerlng thermo-pl~stic ~ust al~o onm the srtlcul~ting ~urface, i~ i~ often desirable to incorporate additlves whieh increase ~he wear ~nd abrasion res~stanee of ehe composi~e. Car~on fiber, graph$te fiber, teflon, ~olybdenu~ dl~ulflde are useful addit~ve~ which ~fford wear re~i~tance engineering thermoplas~ic~ ~qual vr ~uperior to ~elf-lubricated m~terial~ typical~y u~ed in c~mmerclally svailable ~o~nt pro6theses.
In ~ournal bearlng wesr te~ts*~ the fdlowi~g c~mparat~ve results were obt~ined:
*Ccnditi~n~ ~STM-D1242 - 1400 hour6, 110 ppm, 5 lbs. vn le~el arm ;60~2 11,3:13 ,Sample ei~ht Lo6s (~r~ms Conerol HDPE 0.0806 Control polypropylene ~O 0404 UDEL poly~ulfor~e 0.279h UDEL ~ith 20% c~rbsn i~er 0. ~362 UDEL w~th 2~% graphlte 0.0324 Compo~ltions wlth carbon fiber are preferred for the in~ect~on ~aolding or machinlng o~ articul~ting pro6ehesi6 ouch as acee~bular C:Up8, tlbial, ~md glenoid componen~s o total knee and shoulter replacements.
In another embodiment of this inven~ion 6ilyl reactlYe poly~Ders like ~ilyl rea~t~on poly6ulforse are utilized for bonding porous polymeric coatings to metal ~ubstr~ees.
Silyl reactive polysulfone (PSF-SR) resins possess three ~mportant fe~tures. First, the presence of hydrolyzable silane end groups pro~ites en inherent coupling abili~cy 1:o etallic ~urfaces. Second, the PSF-SR reslns have a low melt (or ~olution) vi6cosi~ bdhich greatly f~cilit~tes '~ett~ng' during ~he forma~cion of adhesive bonds,. ~$rd, ~chey are pol~meric adhe~ives which exhlbit no ~olubility in physlological flu~ds ~nd hence h~ve no ~iological/toxicological ~ffects when ~mpl~nted.
) 9 2 ' 1~,313 The load ~esrlng f~meti~nsl c~mponen~ ~ the pro~tketic device6 o~ th~s is~ven~ior. cAn be comprîsed of a variety ~f etal~ ~nd alloy6 known ~Ln the art. Wh$1e titaniu~ d tantalum ~re3 for the most part, ~he only pure l~eCal6 Cc7n-sidered ~s ~fe for ~ntern~l use, . æ variety of ~lloy~ have ~ound general ~cceptance, Stainle~ Bte 16, cobalt-ba~;e alloys and titanium basJ.qlloy~ all sre tolerated by the ~ody as well as being corrosion re~i~tant and fabricated into desired ~hape.
~27-~ 0g ~ ~ 11,3~3 E~FECT OF SINTERING ~ONDITIONS ON P~RE SIZE
For thls exper~ment aimple ~old~ were f~bricseed from 3/8 ~nch outer dlEmeter ~teel tub~ng. The tub~ng ~as c~t t~
a 6 ~nch length and fitted wi~h thre~ded ~nd plugs. Wall thickness of the tubing was approx~maeely 0 038 lnch. The resulting sin~ered pl~stic part had ~ diameter of 0.300 inch nnd was 6 inches long. This proved to be a con~enient 6ample size for tensile property characteri~ation.
~ SF-3703 powder with She particle ~ize distr~bution ~hown in Table I below was u6ed This ~aterial was sintered according to the following schedule: pack powder in a mold;
immerse mold in an oll bath at 220~C for various t~mes ranging from 10 eo 30 min. The resul~ing rod ~f 0.300 inch diameter was then cut to sample lengths sf 2.5 inches.
Intercon~ecting pore 6ize distribution was then determined through ~ercury ~ntru~ion poro~imetry. Data are reported in Table I . Characteristic pore ~ze is ~hown a~ the percentage of pores larger than or equal to 132~. As the time at temper ature is incre~sed from 10 ~o 30 minutes, the ~umb~r of pores 132~ in diameter increases. However, if the ~aterial is held at 220C for times greater ~han 30 minutes, the resulting s~mple w~uld no longer be por~us. On the oeher hand, if the ~aterial were exposed to tempera~ure for less than 10 ~nut~s~ little or no s~nter~ng would have ~ccurred. Thus~ there $5 an optimum time at temperature ~nd temperature ~or a given p~rticle size ~nd molecul~r we~ght di~trlbution to ~chieve ~ desired pore ~ize.
:~ 16~092 11 ,313 TABLE I
r U . S . SCREEN DISTRIB~JTION
,~, on 35 ~~
on 40 Trace on 50 __ on 60 14 . o on 80 50.0 on 100 18.0 thru 100~~
on 140 10.0 on 2 304 . 0 thr~ 2304.0 Slnterin~ Time% Pore Volume at 220~,L ~13? __ 49.4 12 52.6 14 56. 5 16 58.1 18 61.8 69.5 . 75 . 4 ~ 11,313 EXAMPLE II
EFFECT OF MOLECULAR WEIGHT ON SINTERING
The following experiment was conducted to demon-strate the effect of a low molecular weight tail upon sintering conditions and resultin~ mechanical properties.
PSF-3703 was "plasticized" via the addition of 0.5 and 1.0 weight percent of diphenysulfone. Blendin~ was accomplished in an ~gan 1 inch laboratory extruder. The "plasticized"
PSF was then ground into powder on a laboratory WEDCO
grinder. The resulting powder was sintered into porous rods 0.300 inch diameter and 6 inches long. Tensile properties of the rods were measured.
Table II presents the mechanical properties for the porous materials after sinterin~ for 20 minutes at various temperatures. The material containin~ 1 wt. ~ diphenylsul-fone was weakly sintered at 200C while the other materials did not sinter at this temperature. In all cases, as the sintering temperature is increased, the "plasticized"
material possesses superior mechanical properties in the porous sintered form. It is evident that addition of diphenylsulfone, (or similar low molecular weight species) provide a method to control sintering conditions. Speci-fically, shorter sintering time cycles at a given tempera-ture or lower temperatures at a given time may be possible.
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6~0~2 11,313 EXAMPLE I I I
Pree~ret ~ on of Porous Bioengineerin,~
Thes~DoPlastlc Co~ted Prosthesis ~ he stem ~ection of ~ R~ch~rts ~nufactus:ing c~ninè
femoral component w~s dlp coated in ~ ln percent ~olution of PSF-SR/methyle~le chloride, air dried and b~ked ~t 110C
for 1 hour. The ~tem seceion of the prosthesis w~s then tip cohted wieh ~ 15 percent ~olution of P-3703/te~ra-hydrofuran and while tacky ~ dusted with p~wdered P-3703.
The primed prosthesis was plsced $n 8 t~pered alumlnum mold whose cavity replic~ted the stem section of the femoral ccmponent, with ~ toler~nce o~ 100 mil. The cavi~y was loosely packed with powdered P-3703, ~ealed ~t the bottom and placed in an oil bath st 215C for 24 minutes.
After cooling, the prosthesis was removed. The ~em sec-tion had a tightly ~dherant co2ting of porous polysulfone.
~32-6~92 11~3~3 EXAMPLE IV
PreDaratlon of Porous ~ioen~neerin~
Thermopl~stic Artlcle To 400 gms. of U~EL polysulfone P-1700 re~in ln ~
~ne gallon wlde ~outh ~ar was ~dded 31~.2 gms. of methy-lene chlor~de with gitstion. The ~8r was 6caled and ~llowed to 6tand at room temperature for 16 hours. A
polysulfone/methylene chloride brown gel w~s ~bta~ned to which 55~ ~ms of w~ter were ~dded wlth mixing. The brown gel turned wh~te in col~r. These proportions formed B 6tsndard dough mix (S~M). A 30 g. portion of the S~M was shaped ~t room temper~ture by hand compres-sion into a 1/8" aluminur2 metal plate 8" x 81' having B
circular hole measuring 4 7/8" ~n diameter. The r~sult-ant dough preform was then fnserted ~t 135C. into a heated telescoping type ~luminum mold consisting of an upper 5"
aluminum disc, fastened to the upper platen of a press, whlch slides ~nto a rlng and meets anotber 5" ~lumin~m disc within the ring. The ring ~nd bot~om disc wçre not fastened to the bottom pl~ten of the press.
Upon insertion of ~he dough preform ~he p~ess was closed ~llowing both disc ~old surfaces ~o compress the preformed dough with a pressure of S0 psl. During the followin~ 15~25 secDnds ~ pressur2 bulld up occurs due to the volatiliz~tion of the ~olverl~s. The pres~ure ~ullds up ~co 152 p~i at which point ehe pres~ W85 released 61Owly to D~int~in 8 pres~ure of 125 to lS~ psi. The release of the pressure all~ws movement of ~he mold ~ur-f~6es ~ctiv~t~ng an expansion of ehe ~old wl~h ~ubs~quen~
release of ~olvent ~nd w~ter v~por from the ~old ~nd ~ 33-; 0 ~ 2 ~ 11, 313 polymer exp~nE~orl. During ~he dwell t~me in the moldcontinuou6 ~olvent u~d ~rater v~por lo~ fur~cher reduces the pre~ure to ~bout 50 p6i or le66. After a total of ~our minute~ the ~old was opened ~nd the foamed disc was removed. The dl6c h~d ~oc~h 6urfsce6 ~n both 8'1 des nd hl~d a density of 0.19 g. cs. the ~urfaces when machined revealed ~n open pore network and the disc ~ould be cut to desired ~hapes.
~ 09~ ~ 11,313 EXA~F y Shear Stren~th Me~ure~ents of ~orous BioenglneerinR Thermopla5tics Sta~nle~s ~teel pl~ees 0.0625" x 1" ~ 4" (type 304)~ere dlp costed in a lO wt. percent of PSF-SR solutlon using ~ethylene chloride as a 601vent. The PSF~SR had an R.V. of 0.45. Af~er air drying for 1 hour and oven ~rying for lO minutes at 110C the 6~mples were ~ubsequent-ly dip coated again ln a 15 wt. percent 601ution of P-37039 a lcwer mol. wt. polysulfone, ~n methylene chloride, a~r dried 1 hour, oven drled 110C for 15 m~nutes. The ~amples were then baked in a hot air oven for 5 minutes at 245C
- removed and ~mmediately were powder ~o~ted with 40 mesh powdered P-37û3 polysulfone, u6ing a t~pped ~ieve. The ~mples were then clamped together to form lap-~hear test specimens ~nd placed ln ~ 240 C hot ~ir oven ~or l/2 hour to ~use. The same procedure was ~epe~ted only P-1700 powdered (40 mesh) re~in was 6~fted aver the pr$med, hot ~ample plates. The samples were then tested in lap-~hear follow$ng ~STM D1002-72 elle~chod. In ~able III below the results c~btained are ~et forth:
Table III
Thermopl~stic Shear Stren~th ~ Tvpe of Failure P-3703 1596 Cohesive P-3703 1435 Cohesive P-1700 1407 Coh~ ive P~1700 1340 Coheslve ~35-1 1~6092 11~13 EX~WLE VI
Shear StrenRth Measuremen~c6 of Re~nforced ~orous Bioen~ineerin~ Therm~plas~ics S~nless ~teel strlps ~type 304) .0625" x l" x 4"
were ~ashed in hexane ft~llowed by ~6c~propsnol and dr~ed.
The strips were then d~p coated ~n a 10% ~y wt. polysulfone SR (R.V. 0. 517) methylene chloride ~olut~on us$ng a mechan~ ca1 dipping motor which prov~ ded a uniform rate of withdr~wal from ehe solutlon of ~he 6tainless ~trip of
4"ll-l/2 minueec. The 6trlps were air ~ried ~t room temperature for 2 hours ~nd then hot ~ir oven baked ~t various tempers~cures for l/2 hour. After ~ryirlg, ehe ~pec~mens were sp~ced 3/16" apart with shims, clamped together ~nd a 15% by wt. carbon fiber 2'illed polysulfone/
CH2Cl2/H20 dough was ~nsertet between the ~tAinless plates.
The assembly was pl~cet in a hot air overl ~t 150C for 15 minutes to foa~ the "dou~h" ~nd bond lt to the metal plates. The s~mples were then tested ~n lap ~hear follow-ing . he ASTM D1002-72 method. The results obtained are ~et forth ln T~ble IV below:
T.lble IV
co~ein~ (:ure TC ~ ~y~
R.T. air dry 245.2 Athesive 190C lO ~nin. 428. 5 Adhe~$ve 25%
Cohes~ ve 75Z
24 0 C lO s~i~ . 444 6:ohe s ive 1 ~6~2 2. 11,313 The ~uJe pr~cedure was repe~ted to coat l~entic~l ~t~inles~ ~teel 6t~1p~ u6ing ~ 10 wt. percent aolutlon Of P-1700 polysulfone ~n ~ethylene chlorlde. The results Dbtalned ~re set forth ln Table V below:
T~ble V
Coating Cure TC 5heer Stren~th ~psi~ ~ype of Fallure R.T. air dry (ccatlng peeled off) 190C 10 ~in. 113.1 Adhesive 240C 10 min. 340 Cohesive 320C 10 ~ln. 410 Cohesive 1 I6~0~2 11,313 ~LE VII
..-C ~
D~t~ on She~noPl~6tlc6 ~n order to ~emon~trAte the dlfference6 ln creep InOdUlU~; 8t: 75~C ~or ~he bloengineering ehermoplastic6 ~f thl~ :Lslvent~on ~nd other mat~ri41s, daea wa6 compiled ~t6 ~6 lle~t forth ~ T~ble VI below:
'r-ble VI
~ceri~l ~n~elal Applied Creeg (~pparent) m~dulus ~Stre6s p. ~ t ousa~d p. ~
1 hr. ~00 hr 1000 hr.
ENGINEERING
PLASTICS
trel 360 * 8200 2730 1365 ICI 300 P * 4000 350 320 310 llDEL ~-1700 * 4000 345 340 325 LEXAN 141-111** 3000 ~45 3~0 310 Ol~ER
MATERLUS
D$~ken MG 102***1450 386 269 N.. A.
MARLEX 6D50*~* 1500 30 7 0 5 ~. A.
Seamylan ~309**** 1075 170 80 31 Profax 6423*****1500 104 38 37 Prop~thene GWM
;!01***** ~25 1~ 56 41 *Polysulfone ****~DPE
**Polycarbonaee ~****Polypropylene ~p~A
3~P
~ :~ 6 ~
.
~ lth4ugh the ~nvention ~as been ~llu~tr~tet ~y the p~e-c~ding exa~aples, It ~ not to ~e cons trued as 'Deing li~ited eo the materlals employed sherein, but rather the 1rlven~n rel~tes . ., to the gener~e area as hereln~efore di~closed. ~ari~ Rodifi-cations and emb~d~ments c~n ~e ~ade withDut departing from the ~pirit ~d ~c~pe ~ereof.
CH2Cl2/H20 dough was ~nsertet between the ~tAinless plates.
The assembly was pl~cet in a hot air overl ~t 150C for 15 minutes to foa~ the "dou~h" ~nd bond lt to the metal plates. The s~mples were then tested ~n lap ~hear follow-ing . he ASTM D1002-72 method. The results obtained are ~et forth ln T~ble IV below:
T.lble IV
co~ein~ (:ure TC ~ ~y~
R.T. air dry 245.2 Athesive 190C lO ~nin. 428. 5 Adhe~$ve 25%
Cohes~ ve 75Z
24 0 C lO s~i~ . 444 6:ohe s ive 1 ~6~2 2. 11,313 The ~uJe pr~cedure was repe~ted to coat l~entic~l ~t~inles~ ~teel 6t~1p~ u6ing ~ 10 wt. percent aolutlon Of P-1700 polysulfone ~n ~ethylene chlorlde. The results Dbtalned ~re set forth ln Table V below:
T~ble V
Coating Cure TC 5heer Stren~th ~psi~ ~ype of Fallure R.T. air dry (ccatlng peeled off) 190C 10 ~in. 113.1 Adhesive 240C 10 min. 340 Cohesive 320C 10 ~ln. 410 Cohesive 1 I6~0~2 11,313 ~LE VII
..-C ~
D~t~ on She~noPl~6tlc6 ~n order to ~emon~trAte the dlfference6 ln creep InOdUlU~; 8t: 75~C ~or ~he bloengineering ehermoplastic6 ~f thl~ :Lslvent~on ~nd other mat~ri41s, daea wa6 compiled ~t6 ~6 lle~t forth ~ T~ble VI below:
'r-ble VI
~ceri~l ~n~elal Applied Creeg (~pparent) m~dulus ~Stre6s p. ~ t ousa~d p. ~
1 hr. ~00 hr 1000 hr.
ENGINEERING
PLASTICS
trel 360 * 8200 2730 1365 ICI 300 P * 4000 350 320 310 llDEL ~-1700 * 4000 345 340 325 LEXAN 141-111** 3000 ~45 3~0 310 Ol~ER
MATERLUS
D$~ken MG 102***1450 386 269 N.. A.
MARLEX 6D50*~* 1500 30 7 0 5 ~. A.
Seamylan ~309**** 1075 170 80 31 Profax 6423*****1500 104 38 37 Prop~thene GWM
;!01***** ~25 1~ 56 41 *Polysulfone ****~DPE
**Polycarbonaee ~****Polypropylene ~p~A
3~P
~ :~ 6 ~
.
~ lth4ugh the ~nvention ~as been ~llu~tr~tet ~y the p~e-c~ding exa~aples, It ~ not to ~e cons trued as 'Deing li~ited eo the materlals employed sherein, but rather the 1rlven~n rel~tes . ., to the gener~e area as hereln~efore di~closed. ~ari~ Rodifi-cations and emb~d~ments c~n ~e ~ade withDut departing from the ~pirit ~d ~c~pe ~ereof.
Claims (14)
1. A process for the preparation of a prosthetic device comprised of a load-bearing func-tional component and over at least a portion thereof a porous coating of a bioengineering thermoplastic material which is biocompatible with, and conducive for, the ingrowth of bone spicules, said process com-prising fabricating said porous coating by the steps of:
(a) blending at least one normally solid bio-engineering thermoplastic material with about 25 to about 80 parts, per 100 parts by weight, of a normally liquid organic solvent having a solubility parameter, .delta.
within (1.3 calories per cc)1/2 of that of said thermo-plastic material or a mixture of normally liquid organic solvents having the same solubility parameter;
(b) blending the mixture obtained in step (a) with at least about 1 part by weight, per hundred parts of thermoplastic, of water whereby a non-tacky hydrogel dough is obtained;
(c) shaping said hydrogel dough obtained in step (b) to form a coating over said load-bearing functional component;
(d) vaporizing said solvent and said water and obtaining said porous coating having:
(i) an average pore diameter of from about 90 to about 600 microns;
(ii) pore interconnections having average diameters of greater than about 50 microns; and (iii) a porosity of greater than about 40 percent.
11,313-C-l
(a) blending at least one normally solid bio-engineering thermoplastic material with about 25 to about 80 parts, per 100 parts by weight, of a normally liquid organic solvent having a solubility parameter, .delta.
within (1.3 calories per cc)1/2 of that of said thermo-plastic material or a mixture of normally liquid organic solvents having the same solubility parameter;
(b) blending the mixture obtained in step (a) with at least about 1 part by weight, per hundred parts of thermoplastic, of water whereby a non-tacky hydrogel dough is obtained;
(c) shaping said hydrogel dough obtained in step (b) to form a coating over said load-bearing functional component;
(d) vaporizing said solvent and said water and obtaining said porous coating having:
(i) an average pore diameter of from about 90 to about 600 microns;
(ii) pore interconnections having average diameters of greater than about 50 microns; and (iii) a porosity of greater than about 40 percent.
11,313-C-l
2. The process of claim 1 wherein said solvent is methylene chloride.
3. The process of claim 1 wherein said solvent is 1, 1, 2-trichloroethane.
4. The process of claim 1 wherein said bioengineering thermoplastic material is a polysulfone.
5. The process of claim 1 wherein said bioengineering thermoplastic material is a polyaryl-sulfone.
6. The process of claim 1 wherein said bio-engineering thermoplastic material is a polyethersulfone.
7. The process of claim 1 wherein said bio-engineering thermoplastic material is a polyphenyl-sulfone.
8. The process of claim 1 wherein particulate or fibrous filler is blended into said hydrogel.
9. The process of claim 8 wherein said filler is metal particles.
10. The process of claim 8 wherein said filler is Teflon.
11. The process of claim 8 wherein said filler is graphite.
12. The process of claim 8 wherein said filler is absorbable or resorbable.
13. The process of claim 12 wherein said filler 11,313-C-1 is tricalcium phosphate.
14. A process for the preparation of a prosthetic device comprised of a load-bearing func-tional component and over at least a portion thereof a porous coating of a bioengineering thermoplastic mater-ial which is biocompatible with, and conducive for, the ingrowth of bone spicules, said process comprising fabricating said porous coating by the steps of:
(a) blending at least one normally solid bioengineering thermoplastic material with about 25 to about 80 parts, per 100 parts by weight, of a normally liquid organic solvent having a solubility parameter, within (1.3 calories per cc)1/2 of that of said thermo-plastic material or a mixture of normally liquid organic solvents having the same solubility parameter;
(b) blending the mixture obtained in step (a) with at least about 1 part by weight, per hundred parts of thermoplastic, of water whereby a non-tacky hydrogel dough is obtained;
(c) shaping said hydrogel dough obtained in step (b) to form a coating over said load-bearing functional component;
(d) vaporizing said solvent and said water and obtaining said porous coating having a porosity, pore diameter and pore interconnections which enables such device to become firmly and permanently anchored into a musculoskeletal system in which it is employed by tissue ingrowth into the coating.
(a) blending at least one normally solid bioengineering thermoplastic material with about 25 to about 80 parts, per 100 parts by weight, of a normally liquid organic solvent having a solubility parameter, within (1.3 calories per cc)1/2 of that of said thermo-plastic material or a mixture of normally liquid organic solvents having the same solubility parameter;
(b) blending the mixture obtained in step (a) with at least about 1 part by weight, per hundred parts of thermoplastic, of water whereby a non-tacky hydrogel dough is obtained;
(c) shaping said hydrogel dough obtained in step (b) to form a coating over said load-bearing functional component;
(d) vaporizing said solvent and said water and obtaining said porous coating having a porosity, pore diameter and pore interconnections which enables such device to become firmly and permanently anchored into a musculoskeletal system in which it is employed by tissue ingrowth into the coating.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/787,531 US4164794A (en) | 1977-04-14 | 1977-04-14 | Prosthetic devices having coatings of selected porous bioengineering thermoplastics |
| CA000300700A CA1138153A (en) | 1977-04-14 | 1978-04-07 | Prosthetic devices having coatings of selected porous bioengineering thermoplastics |
| US06/113,317 US4362681A (en) | 1977-04-14 | 1980-01-18 | Prosthetic devices having coatings of selected porous bioengineering thermoplastics |
Related Child Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000431693A Division CA1182961A (en) | 1977-04-14 | 1983-06-30 | Prosthetic devices having coatings of selected porous bioengineering thermoplastics |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1166092A true CA1166092A (en) | 1984-04-24 |
Family
ID=27165607
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000397863A Expired CA1166092A (en) | 1977-04-14 | 1982-03-08 | Prosthetic devices having coatings of selected porous bioengineering thermoplastics |
| CA000431693A Expired CA1182961A (en) | 1977-04-14 | 1983-06-30 | Prosthetic devices having coatings of selected porous bioengineering thermoplastics |
Family Applications After (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000431693A Expired CA1182961A (en) | 1977-04-14 | 1983-06-30 | Prosthetic devices having coatings of selected porous bioengineering thermoplastics |
Country Status (1)
| Country | Link |
|---|---|
| CA (2) | CA1166092A (en) |
-
1982
- 1982-03-08 CA CA000397863A patent/CA1166092A/en not_active Expired
-
1983
- 1983-06-30 CA CA000431693A patent/CA1182961A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| CA1182961A (en) | 1985-02-26 |
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