ACTA oTorhinolAryngologiCA iTAliCA 2016;36:101-106; doi: 10.14639/0392-100X-965
Rhinology
In vivo tissue response and durability of five novel
synthetic polymers in a rabbit model
Biocompatibilità e durata in vivo di cinque nuovi polimeri sintetici testati
su coniglio
E. SAHIN1, C. CINGI2, G. ESKIIZMIR3, N. ALTINTOPRAK4, A. CALLI5, C. CALLI6, I. YILGÖR7, E. YILGÖR7
1
Bayindir Icerenkoy Hospital, ENT Clinic, Istanbul; 2 Eskisehir Osmangazi University, Department of OtolaryngologyHead and Neck Surgery, Eskisehir, Turkey; 3 Celal Bayar University, Department of Otolaryngology-Head and Neck
Surgery, Manisa, Turkey; 4 Tuzla State Hospital, ENT Clinic, Istanbul, Turkey; 5 Izmir Atatürk Training and Research
Hospital, Department of Pathology, Izmir, Turkey; 6 Ekol ENT Hospital, Izmir, Turkey, 7 Koc University, Department of
Chemistry, Istanbul, Turkey
SummAry
Alloplastic materials are frequently used in facial plastic surgeries such as rhinoplasty and nasal reconstruction. unfortunately, the ideal
alloplastic material has not been found. This experimental study evaluates the tissue response and durability of five novel polymers developed as an alloplastic material. in this experimental study involving a tertiary university hospital, six subcuticular pockets were formed
at the back of 10 rabbits for the implantation of each polymer and sham group. Each pocket was excised with its adjacent tissue after
three months, and collected for histopathological examination. Semi-quantitative examination including neovascularisation, inflammation,
fibrosis, abscess formation, multinucleated foreign body giant cells was performed, and integrity of polymer was evaluated. A statistical
comparison was performed. no statically significant difference was detected in neovascularisation, inflammation, fibrosis, abscess formation and multinucleated foreign body giant cells when a paired comparison between sham and polymer ii, iii and iV groups was performed
individually. nevertheless, the degree of fibrosis was less than sham group in polymer i (p = .027) and V (p = .018), although the other
variables were almost similar. The integrity of polymers iii (9 intact, 1 fragmented) and iV (8 intact, 2 absent) was better than the other
polymers. These novel synthetic polymers could be considered as good candidates for clinical applicability. All polymers provided satisfactory results in terms of tissue response; however, fibrovascular integration was higher in polymers ii, iii and iV. in addition, the durability
of polymer iii and iV was better than the others.
Key woRds: Alloplastic material • Polymer • Rhinoplasty • Nasal reconstruction • Bioavailability
riASSunTo
I materiali alloplastici vengono frequentemente utilizzati negli interventi di chirurgia plastica sul volto, quali la rinoplastica e la chirurgia
ricostruttiva del naso. Ad oggi non è stato ancora individuato un materiale alloplastico con caratteristiche ottimali. Il presente studio sperimentale si propone di valutare la risposta tissutale e la resistenza nel tempo di cinque nuovi polimeri proposti come materiali alloplastici.
Il presente studio è stato condotto presso un ospedale universitario di terzo livello. Sono state ricavate sei tasche sottocutanee sul dorso
di 10 conigli che sono state usate per l’impianto di ciascuno dei polimeri testati più una tasca di controllo. Ciascuna delle tasche è stata
escissa congiuntamente al tessuto circostante dopo tre mesi, ed è stata sottoposta ad un esame istopatologico. È stata quindi condotta
una valutazione semi quantitativa con focus su neo angiogenesi, infiammazione, fibrosi, formazione di ascessi, presenza di cellule giganti
multinucleate contenenti corpi estranei e stato dei polimeri testati. E’ stata inoltre effettuata una valutazione statistica, che per quanto
riguarda la comparazione diretta fra la tasca di controllo e i polimeri II, III e IV non ha mostrato differenze significative in merito alla neo
vascolarizzazione, all’infiammazione, alla fibrosi, alla presenza di ascessi ed alla presenza di cellule giganti multinucleate. Il polimero I ha
invece mostrato un grado di fibrosi inferiore rispetto alla tasca di controllo (p = .027) and V (p = .018), benché le altre variabili prese in
considerazione fossero sostanzialmente uguali. L’integrità nel tempo dei polimeri III (9 intatti, uno frammentato) e IV (8 intatti, 2 assenti)
è stata migliore di quella ottenuta con gli altri polimeri testati. Questo gruppo di nuovi polimeri può essere considerato interessante per
future applicazioni cliniche. Tutti i polimeri hanno mostrato risultati accettabili in termini di risposta dei tessuti, tuttavia i fenomeni di
integrazione fibrovascolare sono stati maggiori nel caso dei polimeri II, III e IV. Inoltre la durata nel tempo dei polimeri III e IV è stata la
migliore in assoluto.
PaRole chiave: Materiali alloplastici • Polimeri • Rinoplastica • Ricostruzione nasale • Biocompatibilità
Acta Otorhinolaryngol Ital 2016;36:101-106
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E. Sahin et al.
introduction
Materials and methods
Alloplastic materials play a significant role and are widely
used in the field of facial plastic and reconstructive surgery, although autogenous tissues (e.g. cartilage, bone,
skin/dermis, etc.) are generally preferred for most cases,
if possible. They generally provide a significant decrease
in operative time and prevent donor-site morbidity, especially in revision cases in whom a second surgical site for
harvesting a graft is almost always inevitable 1. A virtual
explosion in the technologies of alloplastic materials has
taken place; indeed, several types of different alloplastic materials such as expanded polytetrafluoroethylene
(gore-Tex; W. l. gore and Associates, Flagstaff,Ariz),
silicone rubber (such as silastic), polyethylene (such as
Medpore; Porex, Fairburn, Ga), plastipore (Richards Manufacturing Company, memphis, Tenn), polyesters and
polyamides (such as Dacron; Ethicon inc., Somerville,
nJ), mersilene (Ethicon inc), Supramid (S. Jackson inc,
Alexandria, Va), Cooley Dacron knitted implant (meadox; Boston Scientific, Quincy, Mass) have been used
in different aspects of surgery in order to reconstruct or
augment facial structures or improve deformities. unfortunately, most of these alloplastic materials have different amounts of potential risk for inflammatory reaction,
extrusion, infection and resorption 2-5. Therefore, an ideal
alloplastic material should be: (i) biocompatible, (ii) noncarcinogenic, (iii) non-mutagenic, (iv) non-antigenic, (v)
resistant to infections, (vi) durable, (vii) easily carved,
(viii) pliable, (ix) easily fixed and removed, (x) inexpensive and (xi) available in sufficient quantities.
Biocompatibility has been recently defined as “the ability
of a material to perform its desired function with respect to a medical therapy, without eliciting any undesirable
local or systemic effects in the recipient or beneficiary of
that therapy, but generating the most appropriate beneficial cellular or tissue response in that specific situation,
and optimizing the clinically relevant performance of that
therapy”6. Therefore, the main component of biocompatibility is tissue response. it is well known that once a tissue
is injured for the implantation of an alloplastic material, a
wound healing response which constitutes a sequence of
complex events such as neovascularisation, inflammatory
reaction, fibrosis and foreign body reaction take place in
the adjacent tissues. Experimental and clinical studies
have demonstrated that physical and chemical properties
of alloplastic materials may influence and affect host response and lead to extrusion, overinflammation, infection
and resorption or fragmentation of implants 2-5. Therefore,
the search for an ideal alloplastic material still remains
a challenge. in this study, five novel synthetic polymers
were introduced as potential candidates for clinical application. moreover, durability of polymers and quality and
intensity of tissue response against polymers were histologically examined in a rabbit model.
The experimental study was approved by the research
Ethics Committee of the Eskişehir osmangazi university
and DETAm (Eskişehir osmangazi university hospital
Experimental Study Center), Eskişehir. All procedures
were supervised by a veterinarian. Animals were placed
in appropriate cages and had free access to water and a
standardised commercial ration.
Ten adult new Zealand Albino rabbits, weighting between
2.5 and 4 kg and aged between 15 to 18 months, were included and followed for three months. The pieces of polymers were prepared in a standardised fashion (0.5x0.5 cm
in size). All pieces were packed separately and sterilised
in a gas autoclave prior to surgery.
102
Polymer production
Five newly synthesised polymers were used in this study.
The properties of these materials were as follows:
1. ElASToSil lr3003/20 (shore hardness 30A, soft);
2. ElASToSil lr3003/30 (shore hardness 37A, medium soft);
3. IY-PO-03-149-B FTPU (fluorinated thermoplastic
polyurethane) (shore hardness 50A, medium soft);
4. PTMO-1K/PDMS/50% EXTR (shore hardness 90A,
hard);
5. PTMO1K/PDMS/40% EXTR (shore hardness 80A,
hard).
Physical and chemical properties of polymers
ELASTOSIL LR3003/20 and ELASTOSIL LR3003/30:
Both polymers were highly elastic, cross-linked silicone
rubbers supplied by Wacker Chemie. They were obtained
by the platinum catalysed reactions of methylhydrogensiloxane oligomers with methylvinylsiloxane oligomers.
Elastosil rubbers were usually filled with small amounts
of fumed silica and display good mechanical integrity.
IY-PU-03-149-B (FTPU (fluorinated thermoplastic
polyurethane): Poly(tetramethylene oxide) glycol (PTmo-2000) with a <mn> value of 2040 g/mol was kindly
provided by DuPont, USA. Fluorolink E10 H, which is
an ethylene glycol terminated perfluoroether oligomer
(E10 h) with a <mn> value of 1400 g/mol, is a product
of Solvay Solexis, Belgium. Bis(4-isocyanatocyclohexyl)
methane (HMDI) (99.5%) was supplied by Bayer. 2-methyl-1,5-diaminopentane (Dytek A) (DuPont) and reagent
grade reaction solvents, isopropyl alcohol (IPA) (Merck)
and tetrahydrofuran (ThF) (merck) were all used as received. Dibutyltindilaurate (DBTDL) catalyst was obtained from Air Products, USA. The polymerisation procedure was conducted in a 3-neck, round-bottom Pyrex
flask equipped with an overhead stirrer, addition funnel
and thermometer. reaction was carried out by using a
two-step procedure. PTMO-2000 2.283 g (1.119 mmol),
E10 h 2.264 g (1.617 mmol) and hmDi 1.203 g (4.585
Bioavailability of novel polymers
mmol) were weighed into the reactor, stirred and heated
to 700C. Next, 150 ppm of DBTDL in THF was added as
the catalyst and the reaction was continued for 60 min
to form the prepolymer. The mixture was then cooled to
room temperature, dissolved in 15 g of ThF and diluted
with 8 g of IPA. Chain extender, 0.215 g (1.849 mmol)
Dytek A, was dissolved in 7 g IPA and added to the reaction mixture drop-wise, under strong agitation. The yield
was quantitative. Polymer films were prepared by solution casting into Teflon molds from THF/IPA. The solvent
was first evaporated in an air oven at 500C overnight and
then in a vacuum oven at 500C until constant weight was
reached. Films obtained were kept in sealed polyethylene
bags in a desiccator.
PTMO-1K/PDMS/40% EXTR and PTMO1K/PDMS/50%
EXTR: These polymers are polyurethaneurea elastomers based on PTMO-1000 and polydimethylsiloxane
(PDMS-2000). They contained 40% and 50% by weight
of PDMS, respectively, for improved biocompatibility.
They were obtained by melt polymerisation in a twinscrew extruder.
Animals and implantation procedure
All experiments were performed under anaesthesia using
intramuscular injection of xylazine (5 mg/kg) and ketamine (50 mg/kg). Six surgical pockets for five polymer
implantations and sham operation were generated to the
dorsal area of rabbits after a skin incision of 1.5 cm in
size, and undermining and elevation of subcutaneous tissue. All surgical pockets were performed approximately
2 cm apart from each other. Afterwards, pieces of preshaped and sterilised polymers were administered into the
surgical pockets and placed just over muscles, under the
subcutaneous tissue. Skin incisions were closed by simple
interrupted sutures of mononylon 3-0 sutures. in the sham
group, all surgical procedures were performed similarly
except for polymer implantation.
The animals were given a single injection of intramuscular ceftriaxone (100 mg/kg) for five days, and followed
for a period of three months. none of the polymers were
extruded during the experimental period. All rabbits were
sacrificed with anaesthetic (combination of xylazine and
ketamine) overdose at the end of 3 months. The surgical
pockets at the sites of polymer implantation and sham
sites were dissected and excised. The integrity of polymer
(absent, fragmented or intact) was evaluated and noted
initially. Finally, all specimens were immediately fixed in
neutralised 10% buffered formaldehyde for histopathological examination.
Histopathological examination
Sections of 5 μm in size were obtained from paraffin
blocks and processed individually. Paraffin sections were
submitted to deparaffinisation in xylene for a short time
and followed by rehydration in decreasing alcohol solu-
tions. All sections were embedded. The paraffin sections
were stained with haematoxylin-eosin and toluidine Blue
for histopathological examination. The areas of tissue adjacent to the implants were first observed under low magnification and later scrutinised under high magnification.
The tissue response was examined and graded with the
following criteria: (i) vascular congestion (mild congestion, significant congestion with dilated vessels, highly
dilated vessels with red blood cell extravasation), (ii) inflammation (absent, mild, moderate, intense), (iii) fibrosis
(absent, present of fibroblasts alone, reparative fibroblastic proliferation with thickness), (iv) abscess formation
(absent, present), (v) foreign body giant cell (absent, present).
All histopathological examinations were performed by a
blinded board-certified pathologist.
Statistical analysis
The statistical analysis was performed using SPSS for
Windows 17.0. A paired comparison between polymers
and sham group was performed for each variable individually using the chi square test. A p value <0.05 was
considered statistically significant.
Results
none of the animals was lost before the planned schedule.
All polymers were tolerated well without causing gross
infection, and no extrusion was observed. The distribution
of tissue responses in polymer and sham groups are presented in Figure 1. The degree of vascularisation is very
similar to sham group in polymers ii and iii, although
none of the polymers demonstrated a statistically significant difference compared with the sham group (Table i).
The inflammatory reaction against all polymers was comparable with sham group (Fig. 2A-C, Table i). no significant difference was observed when comparisons between
polymer ii-sham group, polymer iii-sham group and
polymer iV-sham group were performed according to the
degree of fibrosis (Fig. 2A-C, Table i). on the other hand,
the statistical comparison between polymer i-sham group
and polymer V-sham group showed significant differences in the favour of sham group (p = .027 and p = .018). Finally, when polymer groups were individually compared
with sham group according to the presence of abscess formation and multinucleated foreign body giant cell, none
of the polymers showed a statistically significant difference (Table i).
The durability of polymer iii was considered excellent
(90% intact) as shown in Figure 1. In addition, the durability of polymer IV (80% intact) and I (70% intact) was
acceptable. however, more than half of polymer ii was
fragmented or lost at the end of the experiment. however,
no significant difference was detected when polymer iiiii, polymer ii-iV, polymer ii-i and polymer ii-V were
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E. Sahin et al.
Fig. 1. The distribution of tissue response [neovascularisation (A), inflammation (B), fibrosis (C), abscess formation (D), foreign body
giant cell (E) and integrity of polymers (F)] in polymer and sham groups.
Fig. 2. Photomicrograph showing the intact implant material (haemotoxylin and eosin, x40). (A), Infiltration of the connective tissue
capsule surrounding the implant by the inflammatory infiltrate which is mainly composed of lymphocytes and plasma cells (B),
accompanied by eosinophils in some (C).
compared according to durability (p = 0.057, p = 0.069,
p = 0.403 and p = 0.301).
discussion
Several alloplastic materials have been used in surgery.
in general, they shorten the duration of surgery, reduce
trauma to donor region and are readily available. however, one of the main drawbacks of these alloplastic mate104
rials is tissue response, which may also lead to extrusion
and/or poor resistance to infection. Therefore, the quest
for finding an ideal alloplastic material still remains of
wide interest. in this study, five new synthetic polymers,
differing in physical structure and hardness, were introduced as potential candidates for clinical application. An
in vitro experimental model was preferred for assessment
of tissue response and durability of these polymers, and
histopathological examination, a gold standard technique
Bioavailability of novel polymers
Table I. Statistical comparison between polymer and sham groups according to neovascularisation, inflammation, fibrosis, abscess formation and multinucleated foreign body giant cells.
Neovascularisation
Inflammation
Fibrosis
0.301
0.779
0.027
0.041
0.580
0.327
0.301
0.270
0.148
0.118
0.494
.550
Polymer I-Polymer III
Polymer I-Polymer IV
Polymer I-Polymer V
Polymer II-Sham group
Polymer II-Polymer III
Polymer II-Polymer IV
Polymer II-Polymer V
0.682
0.912
0.450
0.221
0.246
0.680
0.099
0.036
0.364
0.148
0.470
0.329
0.319
0.587
Polymer III-Sham group
Polymer III-Polymer IV
Polymer III-Polymer V
Polymer IV-Sham group
Polymer IV-Polymer V
Polymer V-Sham group
0.801
0.788
0.638
0.881
0.400
0.645
0.392
0.566
0.767
0.514
0.244
0.343
Polymer I-Sham group
Polymer I-Polymer II
0.043
0.264
0.815
0.264
0.418
0.144
0.018
Abscess formation Multinucleated foreign body
giant cell
0.305
0.136
1.000
1.000
0.531
0.305
0.305
0.305
0.531
0.305
0.305
0.136
1.000
0.606
0.136
0.136
1.000
0.606
0.136
0.136
0.136
NS
NS
NS
NS
0.136
0.060
0.136
0.606
0.060
NS: Not computed because parameter was a constant. Statistically significant (p<0.05).
for determining the degree of tissue response, was performed 3 5 7. The assessment of tissue response includes
neovascularisation, inflammation, fibrosis, abscess formation and multinucleated foreign body giant cells.
Previous histopathological examination of explanted porous polyethylene implants demonstrated a significant
decrease in fibrovascular invasion, increase in inflammatory reaction and presence of multinucleated foreign body
cells8. in this study, none of the polymers was extruded,
which considered a high tissue ingrowth and low inflammatory response. in fact, implants that have a high capacity of fibrovascular integration are prone to behave more
like natural tissue; thus, they can become more stable and
more resistant to infections. in addition, naik et al. emphasised the positive effect of vascularisation for reduction of extrusion, migration and infection after polymer
implantation9. in this experimental study, assessment of
neovascularisation showed similar histological findings
in all experimental groups (polymer implanted and sham
groups) (Fig. 1 and Table i). on the other hand, the degree
of fibrosis seems in favour of polymers ii, iii and iV, although no statistically significant difference was detected
when compared with the sham group (Fig. 1 and Table i).
however, the degree of fibrosis was less than sham group
for polymer i (p = 0.027) and V (p = 0.018). Therefore,
complete invasion by fibrovascular tissue at the site of
polymer implantation, especially in polymers ii, iii and
iV, was demonstrated. Sclafani et al. examined the tolerability of porous high-density polyethylene and nonporous
silicone implants in an experimental study, and observed
better fibrovascular integration with porous high-density
polyethylene2. moreover, they detected no inflammatory
cells in the periphery of implant, even though several
other studies have demonstrated a vibrant inflammatory
response with porous polytetrafluoroethylene 10-12. This
experimental study found no sign of increase in inflammatory response at the adjacent sites of polymer implantation (Fig. 1 and Table i). moreover, the presence of multinucleated foreign body giant cell, an important indicator
of vigorous inflammatory response to implants, was not
significantly different when individual comparison between polymer and sham groups was performed (Table
i). Therefore, high tolerability against all polymers was
seen, although better results were observed with polymers
iii and iV.
The moulding and fashioning of an implant is crucial, especially for facial reconstructive and aesthetic surgeries.
Softer implants are generally preferred because they can
be easily carved and structured, and have a more natural
appearance. Polymers I, II and III are softer materials; therefore, moulding and fashioning of these polymers is easier than with polymers iV and V. Finally, one of the most
important characteristics of an ideal alloplastic material
is the durability and/or firmness of an implant. An ideal
implant should preserve its integrity, which is essential
for long-term stability. in this experimental study, the durability of all synthetic polymers was acceptable, and no
significant difference was seen when a paired comparison
was performed (Fig. 1 and Table i). nevertheless, polymers III (90% intact) and IV (80% intact) demonstrated
the highest reliability.
105
E. Sahin et al.
conclusions
Five novel synthetic polymers have been developed and
introduced as potential candidates for clinical application.
in this experimental study, histopathological examination
of tissue response against these polymers demonstrated
high tolerability, especially with polymers ii, iii and iV.
in addition, polymers iii and iV had a better durability
and protected their integrity. Therefore, these synthetic
polymers may be suitable for facial plastic and reconstructive surgery; however, further studies are also required to
evaluate their biocompatibility.
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received: november 15, 2015 - Accepted: January 15, 2016
Address for correspondence: Cemal Cingi, Eskisehir osmangazi
University, ENT Department, Meselik Kampusu, Eskisehir, Turkey.
Tel. +90 532 2676616. E mail: ccingi@gmail.com
106