Silk Composites: Apatite Coated Electrospun Silk Fibers

초록

Human bone is a three-dimensional composite made of inorganic apatite crystals and organic collagen fibers. Mimicking this composite structure and composition has attracted interest for bone biomaterial substitutes and well as for materials design strategies in general. An attractive strategy to fabricate this kind of composite is to grow a layer of bone-like apatite on polymeric materials to generate osteoconductive features combined with good mechanical strength. Recent interest in the use of silk in biotechnological materials and in biomedical applications has derived from the unique mechanical properties, biocompatibility and biodegradability. For example, we have reported silk protein-based matrices for ligament and bone tissue engineering. Electrospinning offers an alternative approach to protein fiber formation that can potentially generate nanometer scale diameter fibers, a useful feature in some biomaterial and tissue engineering applications. In the present study, we explored the preparation of apatite-silk composites by growing apatite on functionalized nanodiameter silk fibers prepared by electrospinning. Functionalized fibers were spun from an aqueous solution of silk/PEO (80/20, wt/wt) containg poly-L-aspartic acid. An alternate soaking process was used to grow apatite on the fibers. The deposited apatite was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and X-ray Energy-Dispersive Spectroscopy (EDS). The amount of apatite deposited increased with increased soaking cycles and length of soaking. The aligned growth of hydroxyapatite preferentially parallel to the longitudinal direction of fibers was obtained when PA was blended concentration at 200mg/g silk. EDS and XRD analysis showed that the mineral deposits were hydroxyapatite. The aligned growth of hydroxyapatite was probably due to the formation of banded gel-like structures of silk-PA complexes along the fiber axis.