Organic/inorganic hydrogels by simultaneous self-assembly and mineralization of aromatic short-peptides

Abstract

Self-assembled peptides and proteins have turned out to be excellent templates for the growth of inorganic minerals and can be used to emulate natural biomineralization processes. Doing this, researchers have developed complex sophisticated materials with properties, in some cases, similar to those found in nature. Of special interest is the development of scaffolds able to guide bone regeneration. The bone tissue comprises an organic matrix composed of aligned collagen fibers containing nanoapatite crystals oriented along the fiber direction. During bone mineralization, both processes, the self-assembly of collagen fibrils and mineralization occur simultaneously. Collagen fibers are able to control calcium phosphate nucleation and subsequent apatite crystal growth at a very limited range of collagen density and ionic concentration. In this study, we reproduced the simultaneity of both processes using an artificial peptide fluorenylmethoxycarbonyl-diphenylalanine (Fmoc-FF) that has the ability to self-assemble in water after the addition of Ca²⁺ ions. Therefore, the peptide self-assembly process and the mineralization of apatite are Ca-demanding processes and occur simultaneously. The role of peptide and ionic concentrations has been investigated affording organic/inorganic hybrid hydrogels with different degrees of homogeneity and mineralization. Interestingly, at very low Ca²⁺ concentrations, we found that apatite nanocrystals are integrated into Fmoc-FF fibrils and oriented as in biologically mineralized collagen fibrils, the basic building blocks of bone.