Ordered Multi-Hierarchical Intrafibrillar Mineralization as a Result of In-Situ Intrafibrillar Apatite Formation Accompanied by the Disassembly and Re-Self-Assembly of Collagen

Abstract

Mineralized collagen with stable and multi-hierarchical intrafibrillar mineralized (multi-HIM) structure is more suitable for mechanical adaptation of bone. However, the existing mineralized collagen prepared by in vitro biomineralization only has a single-layer gap zone mineralization, and this single-layer gap mineralization structure formed by the external entry of minerals is unstable. Here, a new stable multi-HIM collagen was successfully induced and prepared in vitro using polyphosphate with high reactivity and protein like assembly activity. The results indicate that the formation of stable multi-HIM collagen directed using polyphosphate is a kind of fully in-situ mineralization, including the process of collagen fiber disassembly and re-self-assembly, and intrafibrillar mineral formation. Experiments results infer that high reactivity of polyphosphate helps form new nucleation sites, thereby directing mineral nucleation and formation intrafibrillar. With the in-situ collagen fibers disassembly and re-self-assembly, multi-HIM collagen with double-band and a uniform fiber diameter is formed. Molecular dynamics simulation results validated that polyphosphate can react with specific amino acids on collagen fibers, Van der Waals forces and electrostatic attraction provides the energy source that inducing the multi-HIM formation. This study about in vitro fully in-situ mineralization of multi-HIM collagen provides important basis for further understand the bone formation from a new perspective and is expected to promote preparation of ideal bone repair materials.

Keywords: Collagen, Multi-hierarchical intrafibrillar mineralization, In-situ, self-assembly, Intrafibrillar mineral formation