Source: Department of Engineering and Materials Sciences

Authors: Yeqiang Tan, Yanan Hao, Yinan Lai

Supported by the project of National Natural Science Foundation of China (Grant No. 51832003) and other projects, Prof. Zhengyi Fu’s group from Wuhan University of Technology, China, and Peter Fratzl’s group from Max Planck Institute of Colloids and Interfaces, Germany, have achieved progress in bioprocessing-inspired fabrication for new materials. The research result was published in the journal Science on April 8, 2022, with a title of "Mineralization Generates Megapascal Contractile Stresses in Collagen Fibrils". Website Link: https://www.science.org/doi/10.1126/science.abm2664. Science also published a related perspective highlighting the creative work in the same issue entitled "Enhancing Strength in Mineralized Collagen" by Prof. Fabio Nudelman from University of Edinburgh, UK.

Natural biological matters are manufactured as a result of evolution and natural selection for billions of years, and the structure formation process can be accomplished at ambient temperature, resulting in unique microstructures and excellent properties (e.g. shells, teeth, bones, etc.). The research team proposed a new research direction of "Bioprocessing-inspired fabrication" by learning the exquisite bioprocessing of natural biological matters, so as to develop a new technology of materials fabrication. The main idea is inspired from the bioprocessing, or the relationship between bioprocessing and biological structure, to develop the new technology of material synthesis and fabrication.

Bone formation is a typical bio-manufacturing process. Mineralized collagen fibrils are basic structural units of bone, and hydroxyapatite is directionally deposited inside the collagen fibrils and form a particular structure that makes bone possessing excellent mechanical and functional properties. Inspired by the bone structural formation process, the team designed a confined synthesis within collagen fibrils with an in situ experimental system. The system is based on tendon tissue with continuously oriented collagen fibrils and the synthesis of strontium carbonate crystals within collagen fibrils is realized. It was found and confirmed for the first time that the synthetic products generated megapascal contractile stresses, and the prestressed composite microfibrils were prepared (Figure 1). Meanwhile, the kinetic process of structural formation of strontium carbonate crystals in the confined space of collagen fibrils and the mechanism of prestress formation were revealed (Figure 2). This method is general and can synthesize different inorganic materials in collagen by changing the chemical composition and other conditions of the mineralized solution, all of which can generate megapascal contractile stresses.

This study provides direct evidences for revealing the origin of prestress in biological minerals and biological references for revealing the process of bone formation, as well as an effective path for the design and controllable preparation of multifunctional composite materials.

Figure. 1 Synthesis of materials within collagen generates megapascal contractile stresses

Figure. 2 Formation mechanism of prestressed composite microfibrils