Biomimetic Mineralization of Hierarchical Nanofiber Shish-Kebabs in a Concentrated Apatite-Forming Solution

Recently, hierarchical polymer nanostructures called nanofiber shish-kebabs (NFSKs) have shown great potential in directing the distribution of minerals for biomineralization. In this work, we report controlled biomimetic mineralization in block copolymer-containing NFSKs. NFSKs were formed by crystallizing polycaprolactone-block-poly(acrylic acid) (PCL-b-PAA) kebabs on PCL fiber backbones. The block copolymer kebabs were periodically distributed on PCL nanofibers with a spacing of similar to 100-300 nm. Free ions could infiltrate into anionic PAA nanodomains and initiate the NFSK-templated biomimetic mineralization process. A concentrated calcium phosphate solution was used in the present study, which led to significantly accelerated mineralization kinetics compared with the previously studied simulated body fluid systems. Electron microscopy, Fourier-transform infrared spectroscopy, and wide-angle X-ray diffraction were used to characterize the structure and morphology of the mineralized NFSKs. A three-stage mineralization process was identified, and carbonated nonstoichiometric hydroxyapatite was observed after stage 2 with the mineral location templated within kebabs. This accelerated mineralization process yielded a periodic mineral distribution of a biomimetic calcium phosphate phase along the fibers, and the decrease in mineral formation time allows for more efficient biomineralization study and composite formation.