Silk Fibroin and Hydroxyapatite Composites for Bioresorbable Bone Fixation Devices

Every year there are approximately 9 million bone fractures in the United States, and 30% of these require an internal fixation device to help heal. Currently, the gold standard for fixation devices relies on the use of metals because of their high mechanical properties and bioinertness. However, metal implants often require a second surgery to remove them because they cause stress shielding and metal ion leaching. Current bioresorbable fixation devices on the market have poor mechanical properties and are limited to use in non-load-bearing applications (i.e. maxillofacial fractures). As such, there remains a gap in the fracture fixation devices on the market, where a bioresorbable, high-performance device could provide the mechanical stability of metal devices, while safely degrading in vivo. The present study focuses on the development of such a device by fabricating a composite material containing both long-fiber and particle reinforcement. Using novel processing techniques, a composite consisting of PLLA fibers, HA nanorods, and PCL matrix was fabricated and had a bending modulus and strength of 9.2 Gpa and 187 MPa, respectively. To increase the mechanical properties, statistically designed experiments (DOE) were employed to home in on an ideal material composition of the composite material, resulting in the use of SF fibers, HA nanowhiskers, and a PLA matrix. The final composite possessed a bending modulus and strength of 21.3 GPa and 531 MPa, respectively. This composite material was formed into a curved device and contained screw holes, resembling current metal fixation plates. These devices underwent an accelerated 8-week in vitro degradation study, in which the samples lost a total of 5 wt%. Additionally, cell proliferation studies showed cells increase proliferation through 7 days of culturing on the plates, and a cell viability assay revealed the samples have good in vitro biocompatibility after 14 days of culturing. Overall, the mechanical properties, degradation trend, and biocompatibility of the fabricated composites in this study show great promise for future use as a degradable load-bearing bone fixation device, in which in vivostudies will be needed to verify the efficacy of the composite material as a bone fixation device.