Biomimetic Design of Poly(ether ether ketone) Composites for Bone Replacement

Abstract

Hip and knee replacements are a common solution for patients whom have experienced loss in knee cartilage or have fractured their bones due to the weakening of the bone from osteoporosis. The number of bone replacements continues to rise as the number of ACL and meniscus repair surgeries increases. These surgeries accelerate the loss of cartilage especially at the knee. Current materials in use are nickel-cobalt alloys, titanium, and high-density polyethylene. These replacements have a lifespan of 10-20 years with a 10% risk of rejection from the body. Rejection can be caused by metal leeching into the bloodstream, growth of bacteria on the surface of the material, and the weakening of bone at the interface due to a large difference in young’s modulus between the replacement material and bone. Additionally, today’s bone replacement does not replicate the porous structure of bone to allow for the growth of bone cells. This research expands on a potential new material for bone replacement, poly(ether ether ketone) or PEEK. PEEK is a polymer that can be introduced to the body without rejection, and has been used as a material for spinal fusions and partial skull replacements. Additionally, not being a metal, PEEK avoids the risk of the introduction of metals into the bloodstream and weakening of surrounding bone due to its young’s modulus being lower than bone. However, traditional processing methods of injection or compression molding require high heat for melt resulting in a restriction of the structure and narrowing additives to inorganics. We introduce a unique solvent casting process with the use of chlorophenol dissolving PEEK at 150 °C. The process varies average pore sizes and allows for the introduction of organic and inorganic additives, cellulose nanocrystals and hydroxyapatite, to change the mechanical properties as well as provide a foundation for bone cell growth. We analyze the properties of the PEEK and PEEK composites through SEM imaging, thermal analysis, and mechanical testing. SEM imaging displays pore sizes in the nanometer ranges which are too small for cellular growth but small enough for mineralization. Thermogravimetric analysis confirms a proper distribution of additives within the PEEK. From differential scanning calorimetry, residual solvent remains from the processing. For mechanical testing, the additives’ significance on the PEEK composites could not be determined. However, evidence points towards higher drying temperatures, for solvent removal, increasing the modulus and yield strength of the PEEK and PEEK composites. Future research should be conducted to increase the pore size to allow for cell growth as well as cell culture studies to look at the degree of cell growth on the samples. Also, experiments should be performed to fully remove solvents and the understand the effect of drying temperatures on the PEEK composites’ structure and properties.