Polyanhydride copolymer and bioceramic composites as bone substitutes

Background/Purpose: Durable mechanical strength and biocompatibility are the two major requirements for osteogenic scaffolds. Polyanhydrides are a class of biodegradable polymers characterized by anhydride bonds that connect repeating units of the polymer backbone chain. Hydroxyapatite (HAP) is the main component of human bone and is a good osteoinductive factor that promotes bone mineralization. This work validates the combination of polyanhydrides and HAP for biomedical application. Methods: Polyanhydride copolymers were fabricated from sebacic acid (SA) and 1,6-bis(p-carboxyphenoxy)hexane (CPH). HAP was surface-modified by polycaprolactone (PCL), and testing tablets were made using different ratios of copolymers and surface-grafted HAP (g-HAP). Degradation tests were performed to evaluate mechanical strength, pH, and weight loss. Biocompatibility was assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and live/dead stain test. Cell affinity was measured using scanning electronic microscopy (SEM). Results: The favorable surface erosion property of polyanhydrides prevented marked changes in the mechanical properties over time. In addition, the degradation byproducts of the copolymer did not cause a serious decline in pH and were less harmful to the cells. g-HAP increased cell affinity for the polymer surface. Conclusion: The research team synthesized polyanhydride/g-HAP composites with high mechanical strength, slow degradation, and excellent biocompatibility. The result showed that a CPH/SA ratio of 7:3 in combination with 10 wt% g-HAP was optimal as bone substitute.