Abstract
Skeletal defects require surgery via using bone grafts. Autografts are the gold standard for bone grafting; however donor site morbidity limits the application. Allografts have the risk of disease transmission. These disadvantages of natural bone grafts have given rise to the development of various synthetic materials for bone substitutes. Ideal bone substitutes should be characterized with osteoconductivity and osteoinductivity. Biodegradable synthetic polymers, such as polyanhydride, polycaprolactone (PCL), polylactide, polyglycolide, and associated copolymers express different degradation times, mechanical strengths and byproducts. Bioceramics, such as SiO2, TiO2, SrO, tricalcium phosphate (TCP) and hydroxyapatite (HAP) have been researched for osteogenesis. But these ceramics tend to break because of their brittle nature. The combination of bioceramics and polymers as composites increases their bioactivity and biocompatibility. However, defects and cracks can form at the polymer/ceramic interface, resulting in uneven distribution of stress and subsequent inferior mechanical strength. A ring-opening polymerization method was adopted to graft short chain PCL onto the surfaces of four nanoparticles (SiO2, TiO2, SrO and HAP), and the resulting surface-modified nanoparticles were then mixed with melted PCL matrices to form bioceramic-polymer composites. The composites with surface-modified SiO2, TiO2, and HAP exhibited superior mechanical strength, slower degradation rate, less acidic environment and better biocompatibility. Moreover, the surface-modified HAP composite yielded the best cell proliferation and attachment as determined by the ALP activity and calcium deposition. The grafting of PCL on HAP particles leads to a better polymer/ceramic interface and subsequently to more stable composites. The bioactivity of the composite with 10 wt% surface-modified HAP had the best osteogenic bioactivity. The result suggested that the surface-modified HAP/PCL matrix composite is potential as bone substitute. Keywords: bone substitute, hydroxyapatite polycaprolactone, surface modification