Development of Keratin Based Organo-Apatites as Bone-Mimetic Biomaterials

Abstract

The bone is a hierarchically built organ by a bottom-up approach consisting of organo-apatite building blocks of mineralized collagen. In order to develop a bone-mimetic material, hard a-keratin a structural protein extracted from human hair was used as a template for the synthesis of keratin based organo-apatites in this study. A comparative study was done to analyze the stability of the keratin extracted by two different methods namely Shindai and sodium sulfide methods. It was found that the sodium sulfide method was relatively better for extraction of keratin because of its enhanced yield, ease of extraction, stability of the extracted protein and conservation of structural integrity of the extracted keratin. The keratin extracted by sodium sulfide method was used as a template for the synthesis of 5 different organo-apatites namely HAP-K50, HAP-K75, HAP-K100, HAP-K125 and HAP-K150 with different concentrations of keratin through co-precipitation method. The phase analysis of the synthesized keratin based organo-apatites was done using XRD which revealed the keratin in the composites decreased the crystallinity and size of the apatite formed. The functional analysis done using FTIR and CD and the morphological observation using FESEM showed heterogeneous nucleation and growth of 20-30nm apatite crystals along the keratin fibril. The thermal analysis helped to determine the ratio of organics and inorganics present in the composites. The composites HAP-K100 and HAP-K125 which had a ratio of organics to inorganics similar to that of the bone, showed higher bio-activity, superior cell viability and cell spreadability as compared to the other composites used under study. The enhanced osteogenic differentiation potential of these composites assessed through alizarin red assay, ALP assay and Runx2 and osteocalcin expression demonstrated that the composites HAP-K100 and HAP-K125 can be used as bone-mimetic biomaterials for bone tissue engineering applications