Study On Biocompatibility, Tribological Property And Wear Debris Characterization Of Ultra-low-wear Polyethelene As Artificial Joint Materials

Background and ObjectivesArtificial joint replacement is the main therapeutic method for advanced severe osteoarthritis of hip and knee joint, which can effectively alleviate joint pain, improve deformity and restore joint function. However, prosthesis loosening limits life span of artificial joint. Artificial joint friction wear debris especially polyethylene wear debris, extremely easy to cause the biological reaction, secondary periprosthetic osteolysis and eventually lead to aseptic loosening of the prosthesis, becoming the main factor limiting prosthesis longevity. How to improve the prosthesis materials especially the wear resistance of polyethylene components becomes the research focus of artificial joint materials.Ultra-high-molecular weight polyethylene (UHMWPE) is the main load materials of artificial joint for its excellent biocompatibility, mechanical properties and wear resistance. By radiation cross-linked and vitamin E added, UHMWPE abrasion performance was further improved. But the preparation of implanted-grade UHMWPE is not only complex, expensive and imported, but also it can’t be direct injection molding, the cost is and excessive cross-linking also leads to decrease of its mechanical strength. Seeking better polyethylene alternative materials for artificial joint and localization is an urgent item.Ultra-low-wear polyethylene (ULWPE) is a new type polyethylene material made by domestic experts, which is easy to process and inject. Preliminary test showed it was more resistant to wear than that of UHMWPE. The purpose of the research is to study biocompatibility and biotribological properties of ULWPE. When extracting debris to analyze preliminary characterization, it would provide the experimental basis for the clinical application to possible future.Methods1. Cytotoxicity test in vitro (CCK-8assay), hemolysis test, acute/chronic toxicity test, muscular implantation test were conducted according to national standard GB/T-16886/ISO-10993for evaluation requirements of medical surgical implants.2. Simulating in vivo lubrication condition(50%calf serum),2000000circles of pin- on-disc friction and wear test were done for ULWPE, HXLPE, CPE pin sample and CoCrMo disc friction pairs on the BiotriboPOD Type Zero friction wear testing machine. The pin surface abrasion morphology were observed and wear loss,wear rate and wear factor were measured and calculated.3. Hydrochloric acid digestion and vacuum freeze drying technology were used to extract ULWPE wear debris. Debris morphology and particle size characterization were analyzed by scanning electron microscopy (SEM).Results1. Biocompatibility test results showed as follows:1) Cytotoxicity test in vitro:no cytotoxicity was exhibited as relative growth rate of experimental group L929cells after cultured24h,48h,72h were95.25%、104.96%、102.81%;2) Hemolysis test:the hemolysis rate was0.81%, suggesting no hemolysis effect;3) Acute toxicity test:compared with control group, mice in experimental group showed no special behavior and no statistical difference of weight gain by t-test (P>0.05);4) Muscular implantation test:postoperative pathological examination showed the inflammatory reaction after material implantation in rats reduced gradually, accompanied by gradually thickening of surrounding tissue fibrous wall; wrapped around the material complete dense fibrous connective tissue;5) Chronic toxicity test:no significant pathological changes were found in liver and kidney of experimental animals;2. The wear rates of ULWPE, HXLPE, CPE pin were0.428mm3/million,0.915mm3/million and1.912mm3/million, the friction factors were1.945×10-6mm3/N·m,4.16×10-6mm3/N·m and8.62×10-6mm3/N·m, the wear rate of ULWPE was the lowest;3. ULWPE morphology of worn surface to surface scratch furrow and shallow;4. Hydrochloric acid digestion and vacuum freeze drying technology can extract ULWPE wear debris effectively; 5. ULWPE wear debris has many forms such as granular, flake, block, fibrous and rod, the granular debris most, flake debris times. The particle size of each are not identical, to more than200μm, small to below1μm.Conclusions1. ULWPE material has great biocompatibility and biological safety without acute cell toxicity, no hemolytic, no acute or chronic toxicity, materials implanted in muscle local inflammatory reaction disappeared gradually, meeting the basic requirements of medical implant materials.2. ULWPE morphology of worn surface and wear rate shows the mildest wear,abrasion resistant performance, better than HXLPE and CPE, having the possibility to replace the existing UHMWPE from bio-tribology angle.3. Hydrochloric acid digestion and vacuum freeze drying technology can extract ULWPE debris without destroying the surface morphology and particle size, which is a kind of effective and feasible method and no pollution.4. ULWPE debris are granular, flake, block, fibrous and rod-shaped, form different patterns, the largest number of granular debris, flake debris times; particle size also each are not identical, wide distribution.5. ULWPE morphology of worn surface and wear debris analysis showed that the adhesive wear, abrasive wear and fatigue wear of three wear mechanism.