Improved performance of ultra-high molecular weight polyethylene for orthopedic applications

摘要

A considerable number of total-joint replacement devices used in orthopedicmedicine involve articulation between a metallic alloy and ultra-high molecular weightpolyethylene (UHMWPE). Though this polymer has excellent wear resistance, the wearparticulate produced leads to the limited lifetime of the devices ? osteolytic bone loss.Crosslinking has been shown to reduce the wear rate of UHMWPE, but can cause areduction in various mechanical properties such as impact toughness. This studypresents two alternate approaches to improving the wear performance of UHMWPE inorthopedic applicationsPrevious work has shown that UHMWPE-based composites have wear resistancecomparable to the irradiation-crosslinked polymer. Zirconium has been shown to haveexcellent corrosion resistance and biocompatibility, and the authors have used thematerial as reinforcing filler in UHMWPE with promising results. Compression-moldedUHMWPE composites with up to 20 weight percent (wt%) of micro-sized zirconiumparticles were investigated with regards to wear behavior and impact toughness. These composites showed a significant reduction in wear compared to unfilled polymer whilestill maintaining impact toughness. These results reinforce the paradigm of usingpolymer composites for orthopedic applications and may provide a viable alternative tothe property tradeoffs encountered with irradiation crosslinking.Apart from UHMWPE, novel materials including hydrogels and bio-derivedpolymers show great potential in orthopedics, but such materials require thedevelopment of innovative fixation techniques [1-3]. The development of controlledporous UHMWPE morphologies offers the opportunity to utilize and expand thesedeveloping technologies. Interconnected porous structures were prepared by drymechanical mixing of NaCl particles and UHMWPE powders followed by compressionmolding. Samples were soaked in water to remove the embedded salt, leaving a porousUHMWPE structure. Computational simulations of porogen distribution and leachingpredicted leaching to be 95% effective when initial salt concentrations were 60wt% andhigher, which was found to match very well with the experimental data. It was foundthat varying the concentration and particle size of the porogen can tailor the final poremorphology to a specific application, while DMA results showed that storage and lossmoduli depend greatly on porosity, but not on pore size. Finally, porous UHMWPEscaffolds were successfully impregnated with gelatin, confirming the compatibility ofUHMWPE with hydrogel-based fillers.