Soluble Polyimide Coated UHMWPE Fibers with Multiple Property Enhancements: Surface Activity, Tensile Strength, Heat Resistance, Acid Resistance, and Erasability.

Ultrahigh molecular weight polyethylene (UHMWPE) fibers possess excellent mechanical properties, yet their applications are severely limited by surface inertness and low melting points. To enhance surface activity and temperature resistance, soluble polyimide (PI) is applied to the surface of UHMWPE fibers. A mussel-inspired biomimetic polycatechol/polyamine (PA) coating is initially constructed on the UHMWPE fiber surface by oxidative self-polymerization, serving as a secondary reaction platform. Subsequently, multifunctional UHMWPE-PA-PI fibers are prepared by depositing soluble PI on the fiber surface via impregnation. The PA and PI layers are firmly bonded by hydrogen bonding interactions and physical adhesion. The results show that the PI-coated UHMWPE fiber surface exhibits enhanced chemical activity, hydrophilicity, and thermal stability, with an increased thermal decomposition temperature of approximately 30 °C. Compared to pristine UHMWPE, the breaking force of UHMWPE-PA-PI fibers increases by 14.9%, and the interfacial adhesion strength between the fiber and rubber improves by 65.5%. The PI coatings also provide thermal insulation, acid resistance, and erasability functionalities. This modification strategy is highly efficient, simple, and less damaging, offering a novel solution to address UHMWPE fibers' surface inertness and temperature intolerance.

A review of wear debris in thumb base joint implants.

AIM: Polymers and metals, such as polyethylene (PE) and cobalt chrome (CoCr), are common materials used in thumb-based joint implants, also known as CMC (Carpometacarpal) arthroplasty. The purpose of this review was to investigate the reported failure modes related to wear debris from these type of materials in CMC implants. The impact of wear debris on clinical outcomes of CMC implants was also examined. Potential adverse wear conditions and inflammatory particle characteristics were also considered. METHOD: A literature search was performed using PRISMA guidelines and 55 studies were reviewed including 49 cohort studies and 6 case studies. Of the 55 studies, 38/55 (69%) focused on metal-on-polyethylene devices, followed by metal-on-metal (35%), and metal-on-bone (4%). RESULTS: The summarized data was used to determine the frequency of failure modes potentially related to wear debris from metals and/or polymers. The most commonly reported incidents potentially relating to debris were implant loosening (7.1%), osteolysis (1.2%) and metallosis (0.6%). Interestingly the reported mechanisms behind osteolysis and loosening greatly varied. Inflammatory reactions, while rare, were generally attributed to metallic debris from metal-on-metal devices. Mechanisms of adverse wear conditions included implant malpositioning, over-tensioning, high loading for active patients, third-body debris, and polyethylene wear-through. No specific examination of debris particle characterization was found, pointing to a gap in the literature. CONCLUSION: This review underscores the types of failure modes associated with wear debris in CMC implants. It was found that failure rates and adverse wear conditions of CMC implants of any design are low and the exact relationship between wear debris and implant incidences, such as osteolysis and loosening remains uncertain. The authors note that further research and specific characterization is required to understand the relationship between debris and implant failure.

A 3-Dimensional Suture Technique for Flexor Tendon Repair: A Biomechanical Study.

PURPOSE: Flexor tendon injury continues to pose a number of challenges for hand surgeons. Improving mechanical properties of repairs should allow for earlier and unprotected rehabilitation. A 3-dimensional (3D) 4-strand suture technique has been proposed to combine high tensile strength and low gliding resistance without causing suture pullout due to tendon delamination. Our hypothesis is that the 3D technique can result in better mechanical properties than the Adelaide technique. METHODS: Four groups of 10 porcine flexor tendons were sutured using the 3D or Adelaide technique with a 3-0 polypropylene or ultrahigh molecular weight polyethylene (UHMWPE) suture. The axial traction test to failure was performed on each tendon to measure 2-mm gap force and ultimate tensile strength. RESULTS: The mean 2-mm gap force was 49 N for group A (3D + polypropylene), 145 N for group B (3D + UHMWPE), 47 N for group C (Adelaide + polypropylene), and 80 N for group D (Adelaide + UHMWPE). Failure mode was caused by suture breakage for group A (10/10) and mainly by suture pullout for the other groups (8/10 up to 10/10). With the UHMWPE suture, the mean ultimate tensile strength was 145 N for the 3D technique and 80 N for the Adelaide technique. CONCLUSIONS: Porcine flexor tendons repaired using the 3D technique and UHMWPE suture exceeded a 2-mm gap force and tensile strength of 140 N. The ultimate tensile strength was superior to that of the Adelaide technique, regardless of the suture material. CLINICAL RELEVANCE: This in vitro study on porcine flexor tendon suture highlights that the mechanical properties of 3D repair are better than those of 3D repair using the Adelaide technique when a UHMWPE suture is used.

In Vivo Performance of Vitamin E Stabilized Polyethylene Implants for Total Hip Arthroplasty: A Review.

BACKGROUND: Vitamin E stabilization was introduced to improve the oxidative stability, wear resistance, and mechanical properties of highly crosslinked polyethylene (HXLPE). In this literature review, we asked: (1) How has vitamin E-stabilized HXLPE (VEPE) performed in vivo for total hip arthroplasty (THA) and how does it compare with conventional ultra-high molecular weight polyethylene (UHMWPE) and HXLPE without vitamin E; and (2) Is there an apparent difference in the clinical performance of VEPE created by blending versus diffusion? METHODS: We performed a systematic search of the literature according to the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines using PubMed and Embase. Included studies reported the in vivo behavior of VEPE in THA. We reviewed 41 studies. RESULTS: For all studies that compared polyethylene with and without VE stabilization, outcomes for VEPE were either equivalent or superior to the control group (for HXLPE without VE and conventional UHMWPE controls, respectively). Hip insert wear rates were generally less than 0.1 mm/year and in most cases were less than 0.05 mm/year. No VEPE components were revised for osteolysis or adverse outcomes specific to VE incorporation. CONCLUSION: Across the literature, we found that VEPE was reported to be clinically effective for THA applications, with much of the research indicating positive clinical outcomes and lower or equivalent wear rates compared to conventional UHMWPE and HXLPE controls without VE. Instances of early component fracture were reported, but have multiple potential causes. There is a gap in the literature for comparison of blended and diffused components, so the in vivo impact of VE incorporation method remains to be seen. Overall, this study provides a comprehensive summary of VEPE clinical performance for THA and may serve as a resource for future investigations.

Insight into the Molecule Impact of Critical-Sized UHMWPE-ALN Wear Particles on Cells by the Alginate-Encapsulated Cell Reactor.

Wear particles of ultra-high molecular weight polyethylene (UHMWPE) are inevitable during service as joint prosthesis, and particles ≤ 10 µm with critical size could cause serious osteolysis and aseptic loosening of joint prosthesis. The aim of this study is to adopt the alginate-encapsulated cell reactor to investigate the molecular impact of critical-sized wear particles of UHMWPE loaded with alendronate sodium (UHMWPE-ALN) on cells. Results showed that compared with UHMWPE wear particles, UHMWPE-ALN wear particles inhibited the proliferation of macrophages significantly after being co-cultured for 1, 4, 7, and 14 d. Furthermore, the released ALN promoted early apoptosis, suppressed the secretion of TNF-α and IL-6 of macrophages, and down-regulated relative gene expressions of TNF-α, IL-6, and IL-1ß and RANK. In addition, compared with UHMWPE wear particles, UHMWPE-ALN wear particles promoted the ALP activity of osteoblasts, down-regulated the gene expression of RANKL, and up-regulated gene expression of osteoprotegerin. There were mainly two approaches of the effects of critical-sized UHMWPE-ALN wear particles on cells, one of which was cytology and the other was cytokine signal pathway. The former mainly affected the proliferation and activity of macrophages and osteoblasts. The latter would inhibit osteoclasts via cytokine and RANKL/RANK signal pathway. Thus, UHMWPE-ALN had the potential application in clinics to treat osteolysis induced by wear particles.

Cup positioning and its effect on polyethylene wear of vitamin E- and non-vitamin E-supplemented liners in total hip arthroplasty: radiographic outcome at 5-year follow-up.

BACKGROUND: Aseptic loosening remains a challenging problem after total hip arthroplasty. Accurate cup placement and supplementation of antioxidants in acetabular liners might reduce material failure rates. The aim of this study is to assess the effect of the cup position on the wear behaviour of UHMWPE-XE and UHMWPE-X liners in vivo using virtual radiographs. METHODS: We conducted a prospective, randomized, controlled, multicenter trial. Clinical data of 372 probands were analyzed. Anteroposterior pelvic X-rays of 324 patients immediately postoperatively and after 1 and 5 years were evaluated by the RayMatch® analysis software regarding cup position and wear behaviour. RESULTS: Mean cup anteversion was 20.3° (± 7.4) and inclination was 41.9° (± 7.0) postoperatively. 62.3% of all patients had an anteversion and inclination within the Lewinnek safe zone. Anterior and anterolateral approaches led to significantly higher cup anteversion compared to lateral approaches (27.3° ± 5.5; 20.9° ± 7.2; 17.5° ± 6.6; p < 0.001 and p = 0.001, respectively). Mean anteversion increased to 24.6° (± 8.0) after 1 year (p < 0.001). Only one revision occurred because of implant dislocation. Wear rates from UHMWPE-X and UHMWPE-XE did not differ significantly. Anteversion angles ≥ 25° correlated to increased polyethylene wear (23.7 µm/year ± 12.8 vs. 31.1 µm/year ± 22.8, p = 0.012) and this was amplified when inclination angles were ≥ 50° (23.6 µm/year ± 12.8 vs. 38.0 µm/year ± 22.7, p = 0.062). CONCLUSION: Anterior approaches lead to the highest inaccuracy of cup placement, but cup positioning outside the Lewinnek safe zone does not necessarily cause higher dislocation rates. Moreover, mean anteversion increased by approximately four degrees within the first year after operation, which is expected to be functional due to a regularization of pelvic tilt after intervention. Mid-term wear rates of UHMWPE-X and UHMWPE-XE liners are comparable, but steep cup positions lead to significantly increased polyethylene wear. In summary, a re-evaluation of target zones for intraoperative cup positioning might be considered. In the long-term reduced oxidative embrittlement could lead to superior wear behaviour of vitamin E-blended liners.

Access to Disentangled Ultrahigh Molecular Weight Polyethylene via a Binuclear Synergic Effect.

Disentangled ultrahigh molecular weight polyethylene (dis-UHMWPE) has excellent processability but can be achieved under extreme conditions. Herein, we report ethylene polymerization with the binuclear half-sandwich scandium complexes C1-Sc2 and C2-Sc2 to afford UHMWPE. C1-Sc2 bearing a short linker shows higher activity and gives higher molecular weight PEs than C2-Sc2 containing a flexible spacer and the mononuclear Sc1 . Strikingly, all UHMWPEs isolated from C1-Sc2 under broad temperature range (25-120 °C) and wide ethylene pressures (2-13 bar) feature very low degree of entanglement as proved by rheological test, DSC annealing study and SEM. These dis-UHMWPEs are facilely mediated solid-state-process at 130 °C and their tensile strength and modulus reach up to 149.2 MPa and 1.5 GPa, respectively. DFT simulations reveal that the formation of dis-UHMWPE is attributed to the binuclear synergic effect and the agostic interaction between the active center and the growing chain.

Development and Validation of a Finite Element Model of Wear in UHMWPE Liner Using Experimental Data From Hip Simulator Studies.

The wear of acetabular liner is one of the key factors determining osseointegration and long-term performance of total hip joint replacement implants. The experimental measurements of wear in total hip replacement components are time and cost-intensive. While addressing this aspect, a finite element model of a hip joint bearing consisting of zirconia-toughened alumina femoral head and ultrahigh molecular weight polyethylene liner was developed to predict the dynamic wear response of the liner. The Archard-Lancaster equation, consisting of surface contact pressure, wear rate, and sliding distance, was employed to predict the wear of the acetabular liner. The contact pressure and wear at the articulating surface were found to decrease over time. A new computational method involving three-dimensional point clouds from the finite element analyzed results were used to construct wear maps. The model was able to predict the linear wear, over 2 × 106 cycles with relative errors ranging from 9% to 36% when compared to the published results. The increasing error percentage occurring primarily from the use of a constant wear rate was reduced to a maximum of 17% by introducing a correction factor. The volumetric rate was predicted with a maximum relative error of 7% with the implementation of the correction factor. When the model was implemented to study acetabular liners of diameters ranging from 28 to 36 mm, the linear wear was seen to decrease with an increase in femoral head diameter, which is in agreement with the clinical data. This study emphasizes the need to develop more such FEA-based computational studies to reliably predict and correlate with experimentally measured temporal evolution of wear of load-bearing articulating joints.

Accelerated neutral atom beam (ANAB) modified polyethylene for decreased wear and reduced bacteria colonization: An in vitro study.

Ultra-high molecular weight polyethylene (UHMWPE) model implants were modified using accelerated neutral atom beam (ANAB) technology and tested for in vitro wear properties and bacteria colonization. Material characterization studies using atomic force microscopy (AFM), surface energy, and in vitro protein adsorption events were also conducted to better understand the mechanism behind such wear properties and bacteria colonization. ANAB modified UHMWPE showed significantly reduced wear properties compared to controls due to nanostructured features, greater surface energy, and improved adsorption of lubricin, a synovial fluid lubricating protein. There was significantly greater adsorption of proteins known to reduce bacteria colonization (specifically, mucin, casein, and lubricin) after 4 h on UHMWPE after ANAB treatment. Such changes in initial protein events led to significantly decreased bacteria (including methicillin resistant Staph. aureus (or MRSA), Staph. aureus, E. coli, multi-drug resistant E. coli, Pseudomonas aeruginosa and Staph. epidermidis) colonization after 24 h without resorting to antibiotic use.

Comparable results between crosslinked polyethylene and conventional ultra-high molecular weight polyethylene implanted in total knee arthroplasty: systematic review and meta-analysis of randomised clinical trials.

PURPOSE: Total knee arthroplasty (TKA) has experienced exponential growth over the last decade, including increasingly younger patients with high functional demands. Highly crosslinked polyethylene (HXLPE) has been proven effective in reducing osteolysis and loosening revisions while improving long-term survival and performance in total hip arthroplasty; nevertheless, this superiority is not demonstrated in TKA. The aim of this systematic review and meta-analysis was to examine whether HXLPE improved overall survival and postoperative functional and radiological outcomes compared to conventional polyethylene (CPE) in TKA. METHODS: According to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline, a literature search of five databases (PubMed, Medline, Scopus, Science Direct and Embase) was made. A PICOS model was performed. The initial screening identified 2541 studies. Each eligible clinical article was analysed according to the Oxford Centre for Evidence-Based Medicine 2011 Levels of Evidence (LoE). Only randomised clinical trials (RCTs) of LoE 1 and 2 were included. The methodological quality of the articles was assessed using the Risk of Bias 2 (RoB 2) tool. RESULTS: Six clinical studies were included in the final study. This systematic review and meta-analysis were registered on the International Prospective Register of Systematic Reviews (PROSPERO). A total of 2285 knees were included. Eight outcomes (total reoperations, reoperations for prosthesis loosening and infections, radiolucent lines, osteolysis, mechanical failure, postoperative KSS knee score and function score) were analysed. For none of them, a statistically significant difference was found about the superiority of HXLPE over CPE (p > 0.05). CONCLUSIONS: There were no statistically significant differences between HXLPE and CPE for TKA concerning clinical, radiological, and functional outcomes; nevertheless, HXLPE did not show higher failure rates or complications and can be safely used for TKA. LEVEL OF EVIDENCE: II.

Prediction of Elastic Properties Using Micromechanics of Polypropylene Composites Mixed with Ultrahigh-Molecular-Weight Polyethylene Fibers.

In this study, we calculated the elastic properties of polypropylene composites mixed with ultrahigh-molecular-weight polyethylene (UHMWPE) fibers. We applied micromechanics models that use numerical analysis, conducted finite element analysis using the homogenization method, and comparatively analyzed the characteristics of polypropylene (PP) containing UHMWPE fibers as reinforcement. The results demonstrate that elastic properties improved as the volume fraction of UHMWPE fiber increased. It was confirmed that the fibers had anisotropic elastic properties due to the shape of the fibers. In addition, it is necessary to compare these findings with future experimental results to obtain data for developing UHMWPE-PP composites.

3D Neuronal Cell Culture Modeling Based on Highly Porous Ultra-High Molecular Weight Polyethylene.

Cell culturing methods in its classical 2D approach have limitations associated with altered cell morphology, gene expression patterns, migration, cell cycle and proliferation. Moreover, high throughput drug screening is mainly performed on 2D cell cultures which are physiologically far from proper cell functions resulting in inadequate hit-compounds which subsequently fail. A shift to 3D culturing protocols could solve issues with altered cell biochemistry and signaling which would lead to a proper recapitulation of physiological conditions in test systems. Here, we examined porous ultra-high molecular weight polyethylene (UHMWPE) as an inexpensive and robust material with varying pore sizes for cell culturing. We tested and developed culturing protocols for immortalized human neuroblastoma and primary mice hippocampal cells which resulted in high rate of cell penetration within one week of cultivation. UHMWPE was additionally functionalized with gelatin, poly-L-lysine, BSA and chitosan, resulting in increased cell penetrations of the material. We have also successfully traced GFP-tagged cells which were grown on a UHMWPE sample after one week from implantation into mice brain. Our findings highlight the importance of UHMWPE use as a 3D matrix and show new possibilities arising from the use of cheap and chemically homogeneous material for studying various types of cell-surface interactions further improving cell adhesion, viability and biocompatibility.

The Stronger the Better: Donor Substituents Push Catalytic Activity of Molecular Chromium Olefin Polymerization Catalysts.

The donor strength of bifunctional pyridine-cyclopentadienyl ligands was altered systematically by the introduction of donating groups in the para-position of the pyridine. In the resulting chromium complexes an almost linear correlation between donor strength and the nitrogen-chromium distance as well as the electronic absorption maximum is experimentally observed. The connection of electron-donating groups in the ligand backbone leads to an efficient transfer of the electronic influences to the catalytically active metal centre without restricting it through steric effects. Therefore, catalytic olefin polymerization activity, which is already very high for the previously studied catalysts, increase considerably by attaching para-amino groups to the chelating pyridine or quinoline, respectively. Combining electron-rich indenyl ligands with para-amino substituted pyridines lead to the highest catalytic activities observed so far for this class of organo chromium olefin polymerisation catalysts. The resulting polymers are of ultra-high molecular weight and the ability of the catalysts to incorporate co-monomers is also very high.

Fluorinated α-Diimine Nickel Mediated Ethylene (Co)Polymerization.

Fluorine substituents in transition metal catalysts are of great importance in olefin polymerization catalysis; however, the comprehensive effect of fluorine substituents is elusive in seminal late transition metal α-diimine catalytic system. In this contribution, fluorine substituents at various positions (ortho-, meta-, and para-F) and with different numbers (Fn ; n=0, 1, 2, 3, 5) were installed into the well-defined N-terphenyl amine and thus were studied for the first time in the nickel α-diimine promoted ethylene polymerization and copolymerization with polar monomers. The position of the fluorine substituent was particularly crucial in these polymerization reactions in terms of catalytic activity, polymer molecular weight, branching density, and incorporation of polar monomer, and thus a picture on the fluorine effect was given. As a notable result, the ortho-F substituted α-diimine nickel catalyst produced highly linear polyethylenes with an extremely high molecular weight (Mw =8703 kDa) and a significantly low degree of branching of 1.4/1000 C; however, the meta-F and/or para-F substituted α-diimine nickel catalysts generated highly branched (up to 80.2/1000 C) polyethylenes with significantly low molecular weights (Mw =20-50 kDa).

Tensile response of Ultra High Performance PE Fiber Reinforced Concretes (PE-UHPFRC) under imposed shrinkage deformations.

PE-UHPFRC is a new Ultra High-Performance Fiber Reinforced Concrete (UHPFRC), which is developed to reduce the environmental impact of conventional UHPFRC by replacing the steel fibers with synthetic ones and reducing the clinker content in the mix. The development of the dynamic elastic modulus, the evolution of free autogenous deformations and the eigenstresses development with age, under full and partial restraint conditions, were investigated for PE-UHPFRC and the results were put into perspective with that for conventional UHPFRC with steel fibers. Furthermore, the tensile responses of different mixes under imposed shrinkage were compared and discussed. The results showed a shorter setting time and consequently an earlier initiation of elastic modulus development for PE-UHPFRC compared with that of conventional UHPFRC. Furthermore, the developed eigenstresses under full restraint conditions in a PE-UHPFRC layer compared with that for conventional UHPFRC were reduced by more than 70%, which is highly beneficial especially for cast-in-place rehabilitation applications.

Efficient Suppression of Chain Transfer and Branching via Cs -Type Shielding in a Neutral Nickel(II) Catalyst.

An effective shielding of both apical positions of a neutral NiII active site is achieved by dibenzosuberyl groups, both attached via the same donors' N-aryl group in a Cs -type arrangement. The key aniline building block is accessible in a single step from commercially available dibenzosuberol. This shielding approach suppresses chain transfer and branch formation to such an extent that ultrahigh molecular weight polyethylenes (5×106  g mol-1 ) are accessible, with a strictly linear microstructure (<0.1 branches/1000C). Key features of this highly active (4.3×105  turnovers h-1 ) catalyst are an exceptionally facile preparation, thermal robustness (up to 90 °C polymerization temperature), ability for living polymerization and compatibility with THF as a polar reaction medium.

Quantitative ultrahigh-molecular-weight polyethylene wear in total elbow retrievals.

BACKGROUND: The purpose of this study was to evaluate ultrahigh-molecular-weight polyethylene (UHMWPE) wear and damage from retrieved total elbow arthroplasty components and compare in vivo wear with wear produced in vitro. METHODS: Explanted total elbow components were collected at revision surgery. UHMWPE damage was characterized visually, whereas penetration and wear were quantified using micro-computed tomography and gas pycnometry. Volumetric wear rates were compared with historical hip data, and wear data were compared with reported in vitro wear test data. RESULTS: Humeral bushing damage primarily occurred in the form of burnishing, scratching, and pitting at the articular face in the region of contact with the ulnar component. Wear of the ulnar bushings was concentrated on the edge of the component at the point of contact with the axis pin. Pitting and embedded debris were dominant damage modes, in addition to burnishing and delamination. Backside wear was negligible. The median linear penetration rates of the lateral, medial, and ulnar bushings were 0.14 mm/yr (range, 0.01-0.78 mm/yr), 0.12 mm/yr (range, 0.03-0.55 mm/yr), and 0.11 mm/yr (range, 0.01-0.69 mm/yr), respectively. The volumetric wear rates of the lateral, medial, and ulnar bushings were 5.5 mm3/yr (range, 0.7-37.2 mm3/yr), 5.9 mm3/yr (range, 0.6-25.5 mm3/yr), and 5.5 mm3/yr (range, 1.2-51.2 mm3/yr), respectively. CONCLUSIONS: The observed wear rates were similar to those reported in well-functioning total hip replacement patients with conventional UHMWPE bearings. We found limitations in reported in vitro testing resulting in wear that was not consistent with our retrieval data. We recommend further investigation to clinically validate in vitro simulation to provide appropriate loading protocols for elbow wear simulation.

Comparison of In-Vivo Performance Characteristics of First-Generation and Second-Generation Cross-Linked and Conventional Explants.

BACKGROUND: Implants made of ultra high molecular weight polyethylene (UHMWPE) has been used for almost 60 years in hip joint arthroplasty as articulating surface. UHMWPE implants have evolved over time from conventional to cross-linked implants. Chemical, morphologic, and micromechanical characteristics play important roles in overall in vivo performance. METHODS: This study aimed at comparing chemical, morphologic, and micromechanical in vivo performance characteristics of conventional and cross-linked explants. Optical damage scoring, Fourier transform infrared spectroscopy, differential scanning calorimetry, and depth sensing indentation techniques were used for the measurements. The measurement results were used to correlate oxidation index, degree of crystallinity, E-Modulus, and hardness. RESULTS: Different manufacturing processes directly affect implants' in vivo performance. Conventional explants are more susceptible to oxidation in the absence of thermal treatment and air ambient gamma irradiation sterilization, whereas they have higher degree of crystallinity and E-Modulus values. Introduction of a thermal treatment step to first-generation cross-linked explants has decreased the oxidation susceptibility but degraded the crystalline structure however, such explants manufactured with moderate total cross-linking irradiation dose and a combination of both remelting and annealing thermal treatment methods are the exceptions. The second-generation cross-linked explants in general have much better E-Modulus, that is, hardness values over all other types of explants and are least susceptible to oxidation. CONCLUSION: The results suggest that in vivo performances of explants could benefit from the hybrid UHMWPE implant manufacturing techniques, such as moderate cross-linking irradiation doses, remelting, followed by annealing and ethylene oxide or gas plasma sterilization.

Vitamin E-blended highly cross-linked polyethylene liners in total hip arthroplasty: a randomized, multicenter trial using virtual CAD-based wear analysis at 5-year follow-up.

BACKGROUND: Progressive oxidation of highly cross-linked ultra-high molecular weight (UHMPWE-X) liners is considered to be a risk factor for material failure in THA. Antioxidants such as vitamin E (alpha-tocopherol) (UHMWPE-XE) were supplemented into the latest generation of polyethylene liners. To prevent inhomogenous vitamin E distribution within the polymer, blending was established as an alternative manufacturing process to diffusion. The purpose of the present study was to investigate the in vivo wear behavior of UHMWPE-XE in comparison with conventional UHMWPE-X liners using virtual CAD-based radiographs. METHODS: Until now, 94 patients from a prospective, randomized, controlled, multicenter study were reviewed at 5-year follow-up. Of these, 51 (54%) received UHMWPE-XE and 43 (46%) UHMWPE-X liners. Anteroposterior pelvic radiographs were made immediately after surgery and at 1 and 5 years postoperatively. The radiographs were analyzed using the observer-independent analysis software RayMatch® (Raylytic GmbH, Leipzig, Germany). RESULTS: The mean wear rate was measured to be 23.6 µm/year (SD 13.7; range 0.7-71.8 µm). There were no significant differences between the two cohorts (UHMWPE-X: 23.2 µm/year vs. UHMWPE-XE: 24.0 µm/year, p = 0.73). Cup anteversion significantly changed within the 1st year after implantation independent from the type of polyethylene liner [UHMWPE-X: 18.2-23.9° (p = 0.0001); UHMWPE-XE: 21.0-25.5° (p = 0.002)]. No further significant changes of cup anteversion in both groups were found between year 1 and 5 after implantation [UHMWPE-X (p = 0.46); UHMWPE-XE (p = 0.56)]. CONCLUSION: The present study demonstrates that the addition of vitamin E does not adversely affect the midterm wear behavior of UHMWPE-X. The antioxidative benefit of vitamin E is expected to become evident in long-term follow-up. Cup anteversion increment by 5° within the 1st year is likely a result of the released hip flexion contracture resulting in an enhanced posterior pelvic tilt. Therefore, a reassessment of target values in acetabular cup placement might be considered.

Effects of vitamin E incorporation in polyethylene on oxidative degradation, wear rates, immune response, and infections in total joint arthroplasty: a review of the current literature.

Highly cross-linked ultrahigh molecular weight polyethylene (UHMWPE) was introduced to decrease wear debris and osteolysis. During cross-linking, free radicals are formed, making highly cross-linked polyethylene vulnerable to oxidative degradation. In order to reduce this process, anti-oxidant vitamin E can be incorporated in polyethylene. This review provides an overview of the effects of vitamin E incorporation on major complications in total joint arthroplasty: material failure due to oxidative degradation, wear debris and subsequent periprosthetic osteolysis, and prosthetic joint infections. Secondly, this review summarizes the first clinical results of total hip and knee arthroplasties with vitamin E incorporated highly cross-linked polyethylene. Based on in vitro studies, incorporation of vitamin E in polyethylene provides good oxidative protection and preserves low wear rates. Incorporation of vitamin E may have the beneficial effect of reduced inflammatory response to its wear particles. Some microorganisms showed reduced adherence to vitamin E-incorporated UHMWPE; however, clinical relevance is doubtful. Short-term clinical studies of total hip and knee arthroplasties with vitamin E-incorporated highly cross-linked UHMWPE reported good clinical results and wear rates similar to highly cross-linked UHMWPE without vitamin E.