Development of Biodegradable Poly(Ε-Caprolactone)/Calcium Phosphate Ceramic Composite Screw for Osteofixation Device in Craninoxaxillofical Surgery

Orthopaedic fixation device, such as bone screw and plate, is applied in maxillofacial fracture frequently. Most of these kind devices are made of stainless steel or alloy. In spite of with good mechanical properties and biocompatibility, patient need second surgery to remove the implant. Moreover, fractured bone fixated with a rigid stainless steel implant has a tendency to re-fracture upon removal of the implant. As the development of polymer science, biodegradable polymers are used to fabricate orthopaedic fixation devices. Some commercial products constructed of polyglycolic acid (PGA), polylactic acid (PLA), or PLGA are available currently. However, disadvantage of these products include: inappropriate degradation time, insufficient mechanical properties, and resulting acidic environment after degradation, and these disadvantages all limit the application in clinic. In this study, polycaprolactone (PCL) is used to prepare new biodegradable orthopaedic fixation devices. PCL has better mechanical properties when compared with PGA or PLA. In the meantime, tetracalcium phosphate/dicalcium phosphate anhydrous (TTCP/DCPA) powder is added to reinforce the mechanical strength of PCL. The hydration product of TTCP/DCPA is calcium-deficiency hydroxyapatite which has osteoconductive property that may improve the bone tissue ingrowth. Different weight ration of TTCP/DCPA are planning to be added to PCL; the mechanical properties, microstructure, and degradation time would be examined. After the preliminary study, a formula of TTCP/DCPA/PCL will be used for further studies. The material-mediated cytotoxicity will be evaluated. The gene expression profiles and protein secretion of osteocytes cultured with TTCP/DCPA/PCL composite will be demonstrated. Finally, orthopaedic fixation devices made of TTCP/DCPA/PCL composite will be implanted to rabbit femur. Computerized tomography and histological examination will be applied to evaluate the in vivo performances of this new implant.