Ultra-high Molecular Weight Polyethylene Acetabular Cups Research Articles

Porous titanium layer co-immobilized with bone morphogenetic protein-2 and vancomycin for biofunctionalization of ultra high molecular weight polyethylene

Ultra high molecular weight polyethylene (UHMWPE), a common material for artificial joint linings, lacks appropriate bioactivity and antibacterial property, which could lead to prosthetic loosening and infections after surgery. Herein, a biofunctionalized UHMWPE material was developed by constructing a firmly bonded porous titanium layer on UHMWPE surface through hot-pressing. The micron-scale titanium surface was then activated by tannic acid treatment, and co-immobilized with Bone Morphogenetic Protein-2 and vancomycin. Scanning electron microscopy, mechanical testing, contact angle measurement, X-ray photoelectron spectroscopy analysis, and infrared spectrometry confirmed the successful construction of the coatings on UHMWPE without causing obvious oxidative degradation. The biofunctionalized UHMWPE surface significantly promoted cell adhesion and proliferation, and inhibited bacterial formation in vitro and in vivo. A preliminary in vivo study of canine hip replacement showed that the UHMWPE acetabular cup with the coating had good biocompatibility and promoted new bone formation and integration. These findings support the use of biofunctionalized UHMWPE as promising materials for artificial joint prostheses.

Reduced wear in vitamin E-infused highly cross-linked polyethylene cups: 5-year results of a randomized controlled trial

Background and purpose — Vitamin E-infused polyethylene is a relatively new material in joint arthroplasty; there are no long-term reports, and only few mid-term results. Using radiostereometric analysis (RSA), we primarily determined whether vitamin E-infused highly cross-linked polyethylene (HXLPE/VitE) acetabular cups show less wear than ultra-high molecular weight polyethylene (UHMWPE) acetabular cups at 5 years after total hip arthroplasty (THA). We also assessed whether wear rates correlate with increasing cup inclination angles or cup sizes. Patients and methods — This is a 5-year follow-up of our previously reported randomized controlled trial of 62 patients with 3 years’ follow-up, who received THA with either an HXLPE/VitE or a UHMWPE acetabular cup. At 5 years, 40 patients were analyzed (22 in the HXLPE/VitE and 18 in the UHMWPE group). Results — HXLPE/VitE cups continued to show less cumulative femoral head penetration than UHMWPE cups (HXLPE/VitE: 0.24 mm, UHMWPE: 0.45 mm; p < 0.001). Distribution of wear was also more even with HXLPE/VitE cups than with UHMWPE cups (p = 0.002). Moreover, the difference in PE wear between 1 and 5 years in both groups showed no statistically significant correlation with increasing cup inclination angles or cup sizes. Finally, no osteolysis and implant loosening occurred, and no revision surgeries were required. Interpretation — Wear rates continue to be lower in HXLPE/VitE cups than in UHMWPE cups at 5 years of follow-up without correlation with increasing cup inclination angles or cup sizes. Finally, HXLPE/VitE cups may have the potential to prevent osteolysis and implant loosening.

Numerical Convergence in Wear Volume Prediction of UHMWPE Acetabular Cup Paired with cp Ti Femoral Head Hip Implants

Wear is a problem for metal on polymer (MOP) hip implants to perform lifetime endurance. Polymer excessive volumetric loss leads to implant failures. Attempts to solve this problem are usually initiated with tribological tests. The method is time-consuming because the sliding speed is low. There is a faster way to use a computational method to gather wear data. This research aims to investigate the numerical convergence of predicted wear volume with the finite element method (FEM). The model is a commercially pure titanium (cp Ti) and ultra-high molecular weight polyethylene (UHMWPE) MOP hip implant. A dynamic Paul physiological load was applied to the model. Volumetric loss of the polymer was calculated with a wear equation involved nonlinear contact load and contact area. The inputs of calculation are wear factor and the computational contact mechanic performed by FEM. The wear factor was obtained by performing biotribological experiments with a multidirectional pin on disc tribotest. Predicted wear volume was validated with hip simulator experimental data from the literature. Convergences were found at the mesh density of 1.38 elements/mm3. An acceptable numerical error was obtained in the model with 1 mm element size for femoral head and 0.3 mm for acetabular cup. This model was then used for the investigation of load increment effects. The result is that load increment variations do not affect wear volume and contact mechanic numerical outputs. The calculated stresses are below the UHMWPE yield stress limit. In this elastic region, the effects of strain rate caused by load increment are negligible.

A vitamin E blended highly cross-linked polyethylene acetabular cup results in less wear: 6-year results of a randomized controlled trial in 199 patients

Background and purpose — Survivorship of total hip arthroplasty (THA) with the ultra-high molecular weight polyethylene (UHMWPE) monoblock cup has been limited due to periprosthetic osteolysis and aseptic loosening, secondary to wear of the UHMWPE. In response, a vitamin E blended highly cross-linked polyethylene (HXLPE) cup was developed. This study set out to compare the wear and clinical 6-year outcomes of vitamin E blended HXLPE with UHMWPE in an isoelastic monoblock cup in patients with hip osteoarthritis who underwent uncemented THA. The 2-year results have been reported previously. Patients and methods — For this randomized controlled trial 199 patients were included. 102 patients received the vitamin E blended HXLPE uncemented acetabular cup and 97 patients the uncemented UHMWPE monoblock cup. Clinical and radiographic parameters were obtained preoperatively, directly postoperatively, and at 3, 12, 24, and 72 months. Wear rates were compared using the femoral head penetration (FHP) rate. Results — 173 patients (87%) completed the 6-year follow-up. The mean NRS scores for rest pain, load pain, and patient satisfaction were 0.3 (SD 1), 0.6 (SD 1), and 8.6 (SD 1) respectively. The mean Harris Hip Score was 93 (SD 12). The FHP rate was lower in the vitamin E blended HXLPE cup (0.028 mm/year) compared with the UHMWPE cup (0.035 mm/year) (p = 0.002). No adverse reactions associated with the clinical application of vitamin E blended HXLPE were observed. 15 complications occurred, equally distributed between the two cups. The 6-year survival to revision rate was 98% for both cups. There was no aseptic loosening. Interpretation — This study shows the superior performance of the HXLPE blended with vitamin E acetabular cup with clinical and radiographic results similar to the UHMWPE acetabular cup.

2-year results of an RCT of 2 uncemented isoelastic monoblock acetabular components: lower wear rate with vitamin E blended highly cross-linked polyethylene compared to ultra-high molecular weight polyethylene

Background and purpose — The long-term survival of arthroplasty components may be limited by polyethylene wear-related problems such as periprosthetic osteolysis and aseptic loosening. Highly cross-linked polyethylene (HXLPE) blended with vitamin E was introduced to improve oxidative stability and to avoid long-term embrittlement. This study clinically compares the tribological behavior and clinical outcome of vitamin E blended HXLPE with ultra-high molecular weight polyethylene (UHMWPE) in an isoelastic monoblock cup for uncemented total hip arthroplasty.Patients and methods — In this randomized controlled trial (RCT), 199 patients were included: 102 patients received the vitamin E blended HXLPE cup, 97 patients the UHMWPE cup. Clinical and radiographic parameters were obtained preoperatively, directly postoperative and at 3, 12, and 24 months. Wear rates were compared using the mean linear femoral head penetration (FHP) rate.Results — 188 patients (94%) completed the 2-year follow-up. Mean patient satisfaction was higher in the vitamin E blended HXLPE group (8.9 [1]) than in in the control group (8.5 [2], p = 0.03). The Harris Hip Score (HHS) was higher in the vitamin E blended HXLPE group (95 [8]) than in the control group (92 [11], p = 0.3). The FHP rate was lower in the vitamin E blended HXLPE group: 0.046 mm/year compared with 0.056 mm/year in the control group (p = 0.05). No adverse reactions associated with the clinical application of vitamin E blended HXLPE were observed during follow-up, with an excellent 2-year survival to revision rate of 98% for both cups.Interpretation — This study shows the superior performance of the HXLPE blended with vitamin E acetabular cup with lower linear femoral head penetration rates and better clinical results compared with the UHMWPE acetabular cup after 2 years.

Wear Prediction of UHMWPE Acetabular Cup against CP Titanium Femoral Head in a Hip Joint Simulator

Ultra high molecular weight polyethylene (UHMWPE) is a biomaterial used for the human hip joint prosthesis bearings for decades. The main disadvantage is the wear resistant. The products should be in service in the lifetime of the patients. Tribological assessments by experiments and computations should be made to solve that problem. The aim of this research is to predict the UHMWPE acetabular cup wear volume sliding against commercially pure titanium (cp Ti) femoral head in a hip simulator. The cp Ti has the highest biocompatibility compared with other femoral head metals such as cobalt chrome, titanium alloy and 316L stainless steel. Computation processes use the Abaqus contact mechanics algorithm followed by a custom made Python script for the data extractions and Archard wear model calculations. Models were an assembly of the UHMWPE acetabular cup and 32 mm cp Ti femoral head in a biaxial rocking motion hip simulator. Sliding between the models was a 60 cycles per minute rotation. Calculations conducted for one million cycles cumulative polymer wear volume in five steps of 200,000 cycles. The geometries of the models were updated in every step. Experimental pin on disc tests conducted to obtain the wear factor and coefficient of friction. Those data support the input of computations. Wear volume verification use the experimental data from Röstlund. Results show a numerical error at 31.42 percents.

Wear Behaviours and Oxidation Effects on Different UHMWPE Acetabular Cups Using a Hip Joint Simulator.

Given the long-term problem of polyethylene wear, medical interest in the new improved cross-linked polyethylene (XLPE), with or without the adding of vitamin E, has risen. The main aim of this study is to gain further insights into the mutual effects of radiation cross-linking and addition of vitamin E on the wear performance of ultra-high-molecular-weight polyethylene (UHMWPE). We tested four different batches of polyethylene (namely, a standard one, a vitamin E-stabilized, and two cross-linked) in a hip joint simulator for five million cycles where bovine calf serum was used as lubricant. The acetabular cups were then analyzed using a confocal profilometer to characterize the surface topography. Moreover; the cups were analyzed by using Fourier Transformed Infrared Spectroscopy and Differential Scanning Calorimetry in order to assess the chemical characteristics of the pristine materials. Comparing the different cups’ configuration, mass loss was found to be higher for standard polyethylene than for the other combinations. Mass loss negatively correlated to the cross-link density of the polyethylenes. None of the tested formulations showed evidence of oxidative degradation. We found no correlation between roughness parameters and wear. Furthermore, we found significantly differences in the wear behavior of all the acetabular cups. XLPEs exhibited lower weight loss, which has potential for reduced wear and decreased osteolysis. However, surface topography revealed smoother surfaces of the standard and vitamin E stabilized polyethylene than on the cross-linked samples. This observation suggests incipient crack generations on the rough and scratched surfaces of the cross-linked polyethylene liners.

Comparison of wear of ultra-high molecular weight polyethylene acetabular cups against surface-engineered femoral heads

Alumina ceramic heads have been previously shown to reduce polyethylene wear in comparison to cobalt chrome (CoCr) heads in artificial hip joints. However, there are concerns about the brittle nature of ceramics. It is therefore of interest to investigate ceramic-like coatings on metallic heads. The aim of this study was to compare the friction and wear of ultra-high molecular weight polyethylene (UHMWPE) against alumina ceramic, CoCr, and surface-engineered ceramic-like coatings in a friction simulator and a hip joint simulator. All femoral heads tested were 28 mm diameter and included: Biolox Forte alumina, CoCr, arc evaporative physical vapour deposition (AEPVD) chromium nitride (CrN) coated CoCr, plasma-assisted chemical vapour deposition (PACVD) amorphous diamond-like carbon (aDLC) coated CoCr, sputter CrN coated CoCr, reactive gas controlled arc (RGCA) AEPVD titanium nitride (TiN) coated CoCr, and Graphit-iC coated CoCr. These were articulated against UHMWPE acetabular cups in a friction simulator and a hip joint simulator. Alumina and CoCr gave the lowest wear volumes whereas the sputter coated CrN gave the highest. Alumina also had the lowest friction factor. There was an association between surface parameters and wear. This study indicates that surface topography of surface-engineered femoral heads is more important than friction and wettability in controlling UHMWPE wear.

Isolation and characterization of UHMWPE wear particles down to ten nanometers in size from in vitro hip and knee joint simulators

There is currently considerable interest in the wear debris and osteolytic potential of different types of bearings used in total joint replacements. The biological activity of the wear debris is dependent on the size and volume of the particles produced. Wear volume also plays an important role in the functional biological activity of a joint replacement. In vitro studies have shown that crosslinking of ultra high molecular weight polyethylene (UHMWPE) acetabular cups and tibial trays produces a reduction in wear volume, and crosslinking has now been introduced clinically for both types of prostheses. Previous studies have identified both micron and submicron-sized polyethylene wear particles. The aim of this study was to characterize the wear and wear particles generated from moderately crosslinked GUR 1,020 GVF UHMWPE acetabular cups and tibial trays in hip and knee joint wear simulators down to 10 nanometers in size. The wear rates of the two prosthesis types were very similar at 25.6 +/- 5.3 mm(3) per million cycles for the hip prostheses and 22.75 +/- 5.95 mm(3) per million cycles for the knee prostheses. Nanometer-sized wear particles were isolated and characterized from both hip and knee simulator lubricants for the first time. Significantly higher numbers (p < 0.05) of particles in the nanometer (<0.1 microm) size range were produced by the hip prostheses compared to the knee prostheses. The knee prostheses produced larger particles, with the mode of particle size in the 0.1-1.0 microm size range, compared to <0.1 microm size range for the hip prostheses. In addition, the knee prostheses produced a greater volumetric concentration of wear particles in the 1.0-10 microm size range, and consequently lower specific biological activity and functional biological activity indices. These results indicated that the knee prostheses had a lower osteolytic potential compared to the hip prostheses.

Elastohydrodynamic Lubrication Modeling of Artificial Hip Joints Under Steady-State Conditions

A general steady-state elastohydrodynamic lubrication model was developed for artificial hip joints, with particular reference to the effect of the anatomical position of the cup and the three-dimensional physiological loading and motion experienced during walking. Appropriate spherical coordinates and mesh grids were employed to facilitate the numerical solution. A specific hip implant employing an ultrahigh molecular-weight polyethylene acetabular cup against a metallic femoral head was chosen to demonstrate the general applicability of the lubrication model and the effects of both the cup inclination angle and the combined flexion-extension and internal-external rotation on the lubrication were analyzed.

The influence of gamma irradiation and aging on degradation mechanisms of ultra-high molecular weight polyethylene.

The aging behavior of ultra-high molecular weight polyethylene (UHMWPE) has been studied following gamma irradiation in air. Accelerated aging procedures used elevated temperature (70 degrees C), pressurized oxygen (5 bar) and applied stress. Shelf and in vivo aged components have also been investigated. The variation in polymer properties with depth into the polymer was determined using density measurements, infra-red spectroscopy and differential scanning calorimetry. Accelerated aging in pressurized oxygen resulted in peaks in polymer density and degree of oxidation up to 500 microm below the polymer surface. Shelf and in vivo aging was also found to result in increased density at or below the component surfaces. Changes in density were mainly due to changes in crystallinity within the UHMWPE and, to a smaller extent, due to oxygen incorporation within the polymer. The application of stress did not appear to influence the accelerated aging of UHMWPE. A method for estimating the residual stress distribution in the UHMWPE using the measured changes in density is proposed. This study has indicated that oxidation of UHMWPE may lead to the development of tensile residual stresses, near the component surface, in the region of 1.7 MPa. These stresses may contribute to the failure mechanism of UHMWPE acetabular cups or knee tibial trays during service.

Lubrication and wear of ultra-high molecular weight polyethylene in total joint replacements

This paper reviews recent advances in the tribology of artificial joints. Emphasis is placed on the latest developments in understanding wear mechanisms and in wear testing of ultra-high molecular weight polyethylene (UHMWPE) materials and components. Two major advances have been made. One is the discovery and recognition of the importance of multidirectional motion in wear mechanisms and wear testing of UHMWPE. The other is the development of an orientation-softening wear concept. The significance of joint kinematics in wear of acetabular and tibial components is discussed. New ways of improving the wear resistance of UHMWPE are proposed based upon the theory of orientation softening. Crosslinking of UHMWPE by ionizing radiation has been shown to significantly improve the wear resistance. The degree of improvement is greater with higher doses of irradiation and is much more effective for the hip than for the knee. A starved lubrication mechanism is proposed for the conforming contact between an UHMWPE acetabular cup and a CoCr or alumina ceramic head. Soluble proteins are found not to be an effective boundary lubricant for UHMWPE. Criteria for validating wear and joint simulator testing are discussed. The paper focuses on the choice of lubricant, the degree of motion and the positioning of components in joint simulator testing.

A parametric analysis of the contact stress in ultra-high molecular weight polyethylene acetabular cups

It is well known that the wear factor for ultra-high molecular weight polyethylene (UHMWPE) sliding on metallic or ceramic counterfaces is largely independent of contact stress for modest loading conditions and sliding distances. However, it is now recognized that under more severe stress levels and with sliding distances comparable to those encountered in current replacement synovial joints, subsurface fatigue contributes to the volume of wear debris. Since the fatigue process is influenced by surface stress levels it is becoming increasingly important to limit the contact stress through design in order to minimize the volume of UHMWPE wear debris in implants. The contact pressure in UHMWPE acetabular cups has been predicted using both the simple elasticity analysis and the finite element method. It has been shown that the radial clearance between the femoral head and the socket is the dominant parameter in determining the contact stress. Thus, the radial clearance should be controlled so the contact half width is close to the femoral head radius (a total included angle of contact of 120°) to minimize the contact pressure. There is little benefit to be gained by increasing the contact half width greater than the femoral head radius. This is consistent with the geometrical constraint of the anatomical position and the direction of loading. It has been shown that the radius of the femoral head has the most significant effect on the maximum contact pressure for these closely conforming contacts where the contact half width is close to the femoral head radius. The effect of the elastic modulus and the thickness of UHMWPE is relatively small under these contact conditions. However, an increase of the elastic modulus and a decrease of the layer thickness both result in a decrease of the radial clearance required to minimize the contact stress and this may prove to be impractical. This places a further constraint on the design of the contact. This paper demonstrates that with careful selection of the tribological design parameters, contact stress on acetabular cups can be reduced and this is more easily achieved with larger diameter femoral heads.

Fabrication and Wear Test of a Continuous Fiber/Particulate Composite Total Surface Hip Replacement

Continuous fiber woven E-glass composite femoral shells having the ame elastic properties as bone were fabricated. The shells were then encrusted with filled epoxy wear resistant coatings and run dry against ultrahigh molecular weight polyethylene acetabular cups in 42,000 and 250,000 cycle were tests on a total hip simulator. The tribological characteristics of these shells atriculating with the acetabular cups are comparable to a vitallium bal articulating with an ultrahigh molecular weight polyethylene cup.