Improving the Long-term Mechanical and Tribological Performances of Polymers for Total Joint Replacement Applications

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PROJECT SUMMARY Joint replacement is one of the most demanding of all the implant applications in our body. The most commonly used artificial joints are total hip replacement (THR) and total knee replacement (TKR), with over 285,000 THR surgeries performed every year in the USA. A variety of polymers, such as ultra high molecular weight polyethylene (UHMWPE), polyetheretherketone (PEEK), and high density polyethylene (HDPE) have been used for THR and TKR prostheses. Although there are many advantages, polymers may absorb liquid, which becomes a major issue in the lubricated environment of the joints. The wetting of the polymer surface due to lubrication can reduce the wear initially; however, in the long run, it may deteriorate the mechanical properties and increase the wear rate significantly. The wear debris can incorporate into the surrounding tissues, and can cause tissue irritation and inflammation, leading to bone resorption, bone loss, implant loosening, and fracture of bone. The short lifespan of implants necessitates revision surgery, which is more expensive, has lower success rates, and may induce additional tissue damage. Therefore, the long-term mechanical and tribological behaviors of polymers under extended exposure to lubricated environment are major concerns in TJR (total joint replacement) prostheses. The overarching goal of this project is to increase the longevity of TJR prostheses, specifically THR and TKR, by improving the long-term mechanical and tribological behaviors of polymers. It is hypothesized that increasing the hydrophobic properties of a polymer can improve its long-term mechanical and tribological behaviors in a lubricated environment. To improve the hydrophobic properties, micro-texture will be applied on the polymer surface. Surface texture can be formed as micro-pit (cavity or dimple) or micro-pillar (protrusion). An array of dimples can improve the tribological performance by acting as lubricant reservoirs; however, it can deteriorate the long-term mechanical and tribological performances of a polymer due to wetting of the surface for an extended period of time. Protruding micro-texture has shown to improve the hydrophobic properties of polymers significantly. However, such surface textures are highly prone to wear and abrasion. The specific aims of the proposed project are to: 1) establish relationship between surface texture and hydrophobic properties of polymers; 2) study the effect of hydrophobicity on long-term mechanical behavior in various environmental conditions; 3) investigate the relationship between surface texture and tribological performance of polymers under various lubricated conditions; 4) analyze the contact mechanics of textured surfaces using numerical modeling; and 5) design optimum surface texture for polymers to improve hydrophobicity, and long-term mechanical and tribological performances in various lubricated environments. The proposed project will enhance the research capabilities of the PI and his institution, Texas A&M University-Kingsville, which is a Hispanic serving institution. The project will also encourage the underrepresented students to pursue career in the biomedical field.