Silk apatite composites from electrospun fibers

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Abstract
Human bone is a three-dimensional composite structure consisting of inorganic apatite crystals and organic collagen fibers. An attractive strategy for fabricating mimics of these types of composite biomaterials is to selectively grow apatite on polymers with control of structure, mechanical properties, and function. In the present study, silk/apatite composites were prepared by growing apatite on functionalized nanodiameter silk fibroin fibers prepared by electrospinning. The functionalized fibers were spun from an aqueous solution of silk/polyethylene oxide (PEO) (78/22 wt/wt) containing poly(L-aspartate) (poly-Asp), which was introduced as an analogue of noncollageous proteins normally found in bone. Silk fibroin associated with the acidic poly-Asp and acted as template for mineralization. Apatite mineral growth occurred preferentially along the longitudinal direction of the fibers, a feature that was not present in the absence of the combination of components at appropriate concentrations. Energy dispersive spectroscopy and x-ray diffraction confirmed that the mineral deposits were apatite. The results suggest that this approach can be used to form structures with potential utility for bone-related biomaterials based on the ability to control the interface wherein nucleation and crystal growth occur on the silk fibroin. With this level of inorganic–organic control, coupled with the unique mechanical properties, slow rates of biodegradation, and polymorphic features of this type of proteins, new opportunities emerge for utility of biomaterials.

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