UHMWPE

This study evaluated the tradeoffs amongst fatigue crack propagation resistance, wear resistance, and oxidative stability in a wide variety of clinically-relevant cross-linked ultra-high molecular weight polyethylene. Highly cross-linked re-melted materials showed good oxidation and wear performance, but diminished fatigue crack propagation resistance. Highly cross-linked annealed materials showed good wear and fatigue performance, but poor oxidation resistance. Moderately cross-linked re-melted materials showed good oxidation resistance, but moderate wear and fatigue resistance. Increasing radiation dose increased wear resistance but decreased fatigue crack propagation resistance. Annealing reduced fatigue resistance less than re-melting, but left materials susceptible to oxidation. This appears to occur because annealing below the melting temperature after cross-linking increased the volume fraction and size of lamellae, but failed to neutralize all free radicals. Alternately, re-melting after cross-linking appeared to eliminate free radicals, but, restricted by the network of cross-links, the re-formed lamellae were fewer and smaller in size which resulted in poor fatigue crack propagation resistance. This is the first study to simultaneously evaluate fatigue crack propagation, wear, oxidation, and microstructure in a wide variety of clinically-relevant ultra-high. The tradeoff we have shown in fatigue, wear, and oxidation performance is critical to the material's long-term success in total joint replacements.

Taguchi methodology was implemented to optimize and evaluate the effect of process parameters such as the applied pressure and time of holding on the tribological properties of ultra-high molecular weight polyethylene (UHMWPE) nanocomposite reinforced with different loadings of silicon carbide (SiC) nanoparticles. An L 9 orthogonal array was used to design experimental matrix in terms of pressure, holding time, and the loading of SiC. UHMWPE/SiC nanocomposites were synthesized via ultrasonication and hot pressing. Pin on disk wear tests were carried out on the composites to evaluate the tribological properties such as specific wear rate and coefficient of friction. Friction and wear response were analyzed using analysis of variance and regression models. The effect of each parameter and optimal process parameters that result in minimum friction and specific wear rate were determined. The confirmation tests carried out verified the validity of the developed experimental design model.

Ultra-high molecular weight polyethylene (UHMWPE) has been used as a surface for acetabular in total joint replacements for the past 60 years. However, the performance of the implant is influenced by the increase in temperature because of the articulating motion and the contact asperities, which affects its longevity. The viscoelastic properties of multi-walled carbon nanotubes (MWCNTs) reinforced UHMWPE nanocomposites with respect to temperature and irradiation dose are not reported so far. Hence, an attempt was made to study the viscoelastic properties of UHMWPE by varying concentration of MWCNTs and intensity of irradiation dose. The test samples were subjected to sinusoidal loading in the temperature range of 30–80°C. Ultra-high molecular weight polyethylene nanocomposites were prepared at different concentrations of MWCNTs such as 0.5, 1.0, 1.5 and 2 wt-% using compression moulding process and the nanocomposites were subjected to 60Co gamma irradiation up to 100 kGy dose. The viscoelastic characteristics of UHMWPE, such as storage modulus, loss moduls and damping factor of the irradiated nanocomposites, were studied in detail. It was observed that the storage modulus of the pure UHMWPE was increased by 139% with the addition of 2 wt-% MWCNTs; however, it was found to be reduced by 83% with 100 kGy irradiation doses. The damping factor and loss modulus of the nanocomposites were reduced by 27.3 and 71.6% with 2 wt-% of MWCNTs concentration, but both were increased with 100 kGy irradiation dose by 74.7 and 69% compared to virgin UHMWPE. It is concluded that the storage modulus reduced with the increase in temperature and also irradiation dose, which may lead to higher static deformation of material. However, the presence of MWCNTs would minimise the deformation and pave way for the better functionality of the material.

Ultra-high molecular weight polyethylene (UHMWPE) reinforced with different loadings of zeolite particles were prepared using
hot compression molding. The effects of zeolite particles on the mechanical and tribological properties of the UHMWPE
composites were studied. The tribological properties were investigated using a Ducom TR-20 pin-on-disc tester under different
sliding speeds of 0.209 m/s, 0.419 m/s and 0.838 m/s with various applied loads of 10, 20, and 30 N. The worn surfaces and
transfer films of the zeolite/UHMWPE composites were observed under the scanning electron microscope (SEM). The results
showed that the addition of zeolite into UHMWPE matrix has reduced the tensile strength and elongation at break, but increased
the modulus. The 10 wt.% zeolite/UHMWPE composites showed an increase of ~25% in impact strength as compared to pure
UHMWPE. The 20 wt.% zeolite/UHMWPE composite exhibited lowest wear volume loss as compared to 10 wt.%
zeolite/UHMWPE and pure UHMWPE. In addition, the average coefficient of friction (COF) was also found to decrease with the
addition of zeolite. The lowest average COF was also obtained with the 20 wt.% zeolite/UHMWPE composite. The wear volume
loss was found to increase with increasing applied loads for all samples. Meanwhile, the average COF values have decreased
with increasing applied loads. Furthermore, shallower wear grooves and smoother worn surfaces were observed for
zeolite/UHMWPE composites as compared to pure UHMWPE. In terms of the transfer film observation, the counterface of pure
UHMWPE were partially covered, rough, and discontinuous. On the other hand, counterface of zeolite/UHMWPE composites
were fully covered, smooth, and continuous. Overall, the tribological properties showed significant improvement with the
reinforcement of zeolite in UHMWPE.

Retrieval studies of total hip replacements with highly cross-linked ultra-high-molecular-weight polyethylene liners have shown much less surface damage than with conventional ultra-high-molecular-weight polyethylene liners. A recent revision hip replacement for recurrent dislocation undertaken after only five months revealed a highly cross-linked polyethylene liner with a large area of visible delamination. In order to determine the cause of this unusual surface damage, we analysed the bearing surfaces of the cobalt-chromium femoral head and the acetabular liner with scanning electron microscopy, energy dispersive x-ray spectroscopy and optical profilometry. We concluded that the cobalt-chromium modular femoral head had scraped against the titanium acetabular shell during the course of the dislocations and had not only roughened the surface of the femoral head but also transferred deposits of titanium onto it. The largest deposits were 1.6 mum to 4.3 mum proud of the surrounding surface and could lead to increased stresses in the acetabular liner and therefore cause accelerated wear and damage. This case illustrates that dislocations can leave titanium deposits on cobalt-chromium femoral heads and that highly cross-linked ultra-high-molecular-weight polyethylene remains susceptible to surface damage.

Crosslinking of UHMWPE by gamma irradiation has been the prime choice to improve the wear resistance of the polymer. However, it is always associated with few setbacks like degradation of material properties during the shelf ageing period. In the present work, nanocomposites were prepared using ball milling process and then compression moulding process where UHMWPE was reinforced by MWCNTs with 0.20 and 0.40 wt. %. The samples were gamma irradiated using 60 Co at 25 and 50 kGy sterilizing doses in air without any post irradiative treatments and then shelf aged for 240 days. The mechanical properties of the composites were studied using small punch technique according to ASTM F2183 standards. Both toughness and hardness of the composites were found to be improved with an increase of irradiation dosage and MWCNT concentration. It is observed that the percentage reduction in Young's modulus, yield stress and % strain at fracture of 0.4% composite at 50 kGy dose are 6.4%, 8.8% and 12.7%, respectively compared to that of virgin UHMWPE irradiated at same dosage. It is concluded that presence of MWCNTs in UHMWPE prevents the degradation of material properties during the shelf ageing period after irradiation. Introduction The advent of UHMWPE as a bearing material for orthopedic applications in 1960's by sir Charnley introduced new era for materials used in total joint arthroplasty. Since then the clinical importance of UHMWPE is on rise, however the challenges like osteolysis, wear debris, property degradation due to ageing after irradiation stand high in realizing its potentiality to the fullest extent. Kurtz et al. [1] reported that the number of total joint replacements (both primary and revision) likely to be performed between 2005 and 2030 will grow by a colossal 673% in USA, which clearly reflects the severity of the problem and thus it strongly demands the necessity for development of a new material, which can overcome the above said problems. Various researchers have attempted to address the problem by crosslinking of polymer and UHMWPE composites. Suarez [2] had gamma irradiated UHMWPE from 100 kGy to 2 Mrad and reported that the ultimate tensile stress was reduced by 21% and the material became brittle. A similar study was reported by Bracco et al. [3] for 25, 50 and 100 kGy sterilizing doses and observed that both ultimate stress and strain at fracture reduced by 13.7% and 41.4%, respectively compared to unirradiated polymer at 100 kGy. Oonishi et al. [4] reported that a 100 Mrad irradiation dose on polymer reduced the wear volume by 15 % compared to unirradiated polymer, however, the elongation and tensile strength decreased to 6%, and 50%, respectively compared to that of polymer without radiation. Recent studies by Kanagaraj et al. [5] showed that addition of MWCNT into HDPE matrix can significantly improve its mechanical properties. Mehta et al. [6] reported that both Young's modulus and ultimate strength of CNT/HDPE nanocomposites were increased by 36% for 1 wt. % of CNTs in HDPE. Morlanes et al. [7] incorporated MWCNTs (1, 3 and 5 wt. %) in UHMWPE and irradiated at 90kGy. It was reported that Young's modulus of irradiated nanocomposites was increased by 71% at 3 wt.% compared to unfilled irradiated polymer in addition to significant improvement of thermal stability of composites. However, a detailed study on the role of MWCNTs in preventing the loss of mechanical properties of UHMWPE during the period of shelf ageing after irradiation is very much limited. Thus, an attempt is made in this direction.

— A knee replacement surgery has become popular worldwide and has a high success rate. In some cases, the degradation of the implant can happen due to the decoration of ultrahigh molecule weight polyethylene (UHMWPE). To overcome these problems the paper describe a possible solution for monitoring implant integrity. An implant material has encased the magneto elastic property of amorphous ribbon with UHMWPE. To stimulate knee insert, they were subject to various tensile stresses by applying AC magnetic field. This resulted in the stress caused to produce an inductance changes nearby magnetizing winding. These implant were designed according to the complexity, durability, biocompatibility and tensile strength, etc. The result obtained describes that the proposed sensor has sufficient sensitivity for measuring stress level, flexibility and weight of the implant associated in tibia inserts.

Taguchi design techniques have been applied to investigate the significant influence of various operating and design parameters,
such as contact load, rotational sliding speed, and carbon nanotubes (CNTs) concentration on the tribological properties of
ultra-high molecular weight polyethylene nanocomposites. Analysis of variance was conducted to discuss the significance of each of
the parameters. Simple regression models were developed for wear rate as well as for the coefficient of friction (COF) of the nanocomposite.
Applied normal force was found to be the dominant factor controlling the wear rate and friction coefficient. The significance
of CNTs concentration on both COF and wear rate closely follow that of applied load. Rotational sliding speed has the least
influence on the tribological properties of the nanocomposite. The developed model for predicting wear rate and the COF was found
to give very good predictions against the experimental data.

In this work, the wear behavior of the mechanical coupling between the biomedical polymer ultrahigh molecular weight polyethylene (UHMWPE) and the titanium-aluminum-vanadium alloy pin (Ti4Al6V) manufactured by electron beam melting (EBM) is investigated. Pure and oxidized graphite fillers is added to the UHMWPE matrix to boost the wear resistance. The tribological test is performed in dry and under the action of various lubricating media (distilled water [DW], simulated synovial fluid [SSF], and natural bovine serum [NBS]) in order to investigate their effects on wearing. The physical-mechanical characterization results show a progressive increase in wear resistance of more than 60% in the nanocomposite (UHMWPE/GO) with the addition of paraffin oil (PO) compared to the UHMWPE and higher under NBS lubricant (more than 80%). The observed wear action is reduced in the order Dry > DW > SSF ≥ NBS, thereby lowering the debris production.

Total hip arthroplasty represents an effective solution for bone and joint diseases. Nevertheless, the hip prosthesis has a limited lifetime, in the average around fifteen years. Their improvement, especially their dual mobility is the objective of this study. Therefore, our strategy is focused on improving the material by comparing three types of polyethylene to determine the best one from a friction mechanism and wear rate minimization standpoint. A dual mobility hip prosthesis, containing a two-sided steel and cobalt chrome cup, was tested with a TORNIER hip joint simulator in calf serum. The rubbed surfaces were characterized using scanning electron microscopy (SEM), contact angle measurements, atomic force microscopy (AFM) and confocal fluorescence microscopy. All these multiscale characterization techniques (from nanoscale to millimeter and micro- scale) showed that the velocity accommodation mechanism is different from one type of polyethylene to another. The wear in the case of standard polyethylene was noticeable and the particles were large and scattered between the surface of polyethylene, the surface of the cup and in the calf serum. For the crosslinked polyethylene, the particles coming from the wear, were not as large, but they were spread the same way as the first case. Even though it shares the same accommodation principle on the detachment of the material with the crosslinked polyethylene the wear particles for the crosslinked vitaminized polyethylene were large and they were only found on the surface of the polyethylene.

We studied the fracture surface evolution of ultra high molecular weight polyethylene (UHMWPE) specimens, manufactured from GUR 1050 compression moulded sheets, after gamma sterilisation in air followed by different aging times after thermal treatment at 120 C. Degradation profiles were obtained by FTIR and DSC measurements after 0, 7, 14, 24 and 36 h aging. We observed by SEM the morphology patterns at these aging times, in surface fractographies after uniaxial tensile test of standardised samples. The results pointed out clear differences between short and long aging times. At shorter times, 7 h, the behaviour was similar to non-degraded UHMWPE, exhibiting ductile behaviour. At longer times, 24–36 h, this thermal protocol provided a highly degraded zone in the subsurface, similar to the white band found after gamma irradiation in air followed by natural aging, although closer to the surface, at 150–200 mm. The microstructure of this oxidation zone, similarly found in gamma irradiated samples shelf-aged for 6–7 years, although with different distribution of microvoids, was formed by fibrils, associated with embrittlement of the oxidised UHMWPE. In addition, the evolution of the oxidation index, the enthalpy content, the mechanical parameters, and the depth of the oxidation front deduced from the fractographies versus aging time showed that a changing behaviour in the degradation rate appeared at intermediate aging times.

Composite laminates are considered one of the most popular damage-resistant materials when exposed to impact force in civil and military applications. In this study, a comparison of composites 12 and 20 layers of fabrics Kevlar and ultrahigh-molecular-weight poly ethylene (UHMWPE)-reinforced epoxy under low-velocity impacts represented by drop-weight impact and Izod pendulum impact has been done. During the Izod test, Kevlar-based composite showed damage at the composite center and fiber breakages. Whereas delamination was observed for UHMWPE reinforced epoxy (PE). The maximum impact strength was for Kevlar-reinforced epoxy (KE) and increases with the number of laminates. Drop-weight impact test showed the highest absorbed energy for (KE) composites. The results revealed that different behavior during the impact test for composites belongs to the impact mechanism in each test.

— Previous researches were made on UHMWPE (Ultra-High-Molecular-Weight-Polyethylene) based implant material and its fusion with Ca-alginate. New methods were made for preparing UHMWPE-Ca-alginate blends. If the coating Ca-alginate salt can be achieved on the surface of UHMWPE, it might lead to an implant material which could promote the bone formation. Earlier results show that we can make the coating layer on the polymer powder surface. Our new approach is to modify the method we made earlier, and this way the alginate layer can withstand washing and sterilization as it's shown in the paper. We also realized that the layer slowly can give off Ca2+ ions which can be absorbed with specific cells. Since we modified the surface structure of the UHMWPE samples we carried out wear testing of the new prepared samples. All of these measurements and experiments have been done as preparative ones to make one time real prosthetic material.

Retrieval studies of total hip replacements with highly cross-linked ultra-high-molecular-weight polyethylene liners have shown much less surface damage than with conventional ultra-high-molecular-weight polyethylene liners. A recent revision hip replacement for recurrent dislocation undertaken after only five months revealed a highly cross-linked polyethylene liner with a large area of visible delamination. In order to determine the cause of this unusual surface damage, we analysed the bearing surfaces of the cobalt-chromium femoral head and the acetabular liner with scanning electron microscopy, energy dispersive x-ray spectroscopy and optical profilometry. We concluded that the cobalt-chromium modular femoral head had scraped against the titanium acetabular shell during the course of the dislocations and had not only roughened the surface of the femoral head but also transferred deposits of titanium onto it. The largest deposits were 1.6 μm to 4.3 μm proud of the surrounding surf...

The use of artificial fiber reinforced composites are widely used in many applications
such as automobile, aircraft manufacturing because they are cost effective and offers high
strength, and weight ratio compared to other composites with similar applications. In this
work, epoxy was selected as a matrix material to prepare a composite specimens
reinforced with UHMWPE fabric with varying layers. Composite specimens are prepared
by varying the number of fabric layers and Taguchi’s L9 orthogonal array method is used
to study the Tribological behavior. The test specimen of composite material had been
prepared using hand layup technique and the samples were tested for wear properties
using the equipment DUCOM made pin on disc experimental setup. The weight was
measured before and after the experiment is conducted. The effects of the Tribological
operating parameters applied load, sliding velocity and sliding distance on the frictional
and wear performance of UHMWPE fabric reinforced composites are demonstrated.
Moreover, water absorption tests were conducted to know their effect over a period of
time for both the aerial densities 200gsm and 240gsm of the fiber mats. It was observed
that the wear response of the specimens is influenced by the applied load, sliding distance
and the speed.

The use of artificial fiber reinforced composites are widely used in many applications
such as automobile, aircraft manufacturing because they are cost effective and offers high
strength, and weight ratio compared to other composites with similar applications. In this
work, epoxy was selected as a matrix material to prepare a composite specimens
reinforced with UHMWPE fabric with varying layers. Composite specimens are prepared
by varying the number of fabric layers and Taguchi’s L9 orthogonal array method is used
to study the Tribological behavior. The test specimen of composite material had been
prepared using hand layup technique and the samples were tested for wear properties
using the equipment DUCOM made pin on disc experimental setup. The weight was
measured before and after the experiment is conducted. The effects of the Tribological
operating parameters applied load, sliding velocity and sliding distance on the frictional
and wear performance of UHMWPE fabric reinforced composites are demonstrated.
Moreover, water absorption tests were conducted to know their effect over a period of
time for both the aerial densities 200gsm and 240gsm of the fiber mats. It was observed
that the wear response of the specimens is influenced by the applied load, sliding distance
and the speed.

The aim of the study was to investigate whether a modified ceramic head surface could reduce the friction and wear rate of simulated ceramic-on-polyethylene hip joints. To address this aim, ultra-high molecular weight polyethylene (UHMWPE) was made to slide on aluminium oxide (Al2O3), dimpled Al2O3, diamond-like carbon (DLC) coated and DLC-coated dimpled substrates. The experiment condition was replicated to simulate artificial hip joints in terms of contact pressure, speed and temperature. UHMWPE on non-dimpled Al2O3 showed lower friction coefficient and wear rate compared to other advanced surfaces. Lower wettability, and higher hardness and surface adhesion of DLC resulted in increased friction and wear. The high difference in modulus of elasticity and hardness between UHMWPE and both, Al2O3 and DLC, reduced the effectiveness of textured surface techniques in friction and wear reduction. Therefore, no tribological benefit was found by fabricating either DLC coating or surface texturing on hard surface when rubbed against softer UHMWPE.

http://pij.sagepub.com/content/229/4/410