# A Novel Biomineralized Collagen Liquid Crystal Hydrogel Possessing Bone-like Nanostructures by Complete In Vitro Fabrication

## TL;DR

This paper presents a new method to create a bone-like material in the lab by combining collagen and mineralization techniques to mimic the structure of natural bone.

## Contribution

The study introduces a complete in vitro fabrication method to produce a biomineralized collagen hydrogel with bone-like nanostructures.

## Key findings

- Collagen liquid crystal hydrogel (CLCH) was formed by pH elevation, creating highly oriented fibril bundles.
- PILP mineralization and phase transformation produced a bone-like inorganic component with nano-HA crystals.
- The combined method successfully mimics both organic and inorganic components of bone ECM in vitro.

## Abstract

The microstructure of bone consists of nano-hydroxyapatite (nano-HA) crystals aligned within the interspaces of collagen fibrils. To emulate this unique microstructure of bone, this work applied two biomimetic techniques to obtain bone-like microstructures in vitro, that is, combining the construction of collagen liquid crystal hydrogel (CLCH) with the application of a polymer-induced liquid precursor (PILP) mineralization process. Upon the elevation of pH, the collagen macromolecules within the collagen liquid crystal (CLC) were activated to self-assemble into CLCH, whose fibrils packed into a long and dense fiber bundle in high orientation, emulating the dense-packed matrix of bone. We demonstrated that the fibrillar mineralization of CLCH, leading to a bone-like nanostructured inorganic material part, can be achieved using the PILP crystallization process to pre-mineralize the dense collagen substrates of CLCH with CaCO3, immediately followed by the in situ mineral phase transformation of CaCO3 into weak-crystalline nano-HA. The combination of CLCH with the biomineralization process of PILP, together with the mineral phase transformation, achieved the in vitro simulation of the nanostructures of both the organic extracellular matrix (ECM) and inorganic ECM of bone. This design would constitute a novel idea for the design of three-dimension biomimetic bone-like material blocks for clinical needs.