Biological and biomimetic mineralization via protein nanoribbon scaffolds

Abstract

Understanding how protein scaffolds direct mineral morphogenesis is crucial for engineering bone and tooth and would open new vistas in hybrid materials design. In the case of tooth enamel, which is the hardest tissue in the body and consists of organized bundles of coaligned filamentous apatite crystals, co-aligned amyloid-like amelogenin nanoribbons (Amel NR) are hypothesized to provide the scaffold for amorphous calcium phosphate (ACP) precursor to apatite. From quantitative analysis of ACP nucleation rates on Amel NRs as a function of chemical potential, we see phosphorylated Amel NRs (pAmel NRs) are far more potent calcium phosphate nucleators than other amelogenin motifs or collagen, which provides the scaffold for bone. This potency stems from a periodic array of charged sites that provide a template for calcium phosphate ion binding on a low-energy interface. To extend this knowledge towards templating substrates on which pAmel NRs can be patterned for tissue engineering of synthetic bone or tooth, we employed block copolymer (BCP) lamellae. From these studies, we see bottom-up, biomimetic fabrication of filamentous mineral on substrates with high-fidelity may be possible through a combination of low surface energy, high nucleation rate, low growth rate and spatially separated discrete domains generated by aligned arrays of pAmel NR.