Huge contractile stresses are generated in collagen-based matrices via the precipitation of various minerals within the collagen fibrils. However, how to regulate the level of prestress via intrafibrillar mineralization remains unclear. Here, it is demonstrated that both, the polymorph selection and the deposition rate of mineral, are modified by proteoglycans that are naturally present in native collagen fibrils. The results show a 50% higher mineralization rate, possibly due to a reduction in the interfacial energy between collagen and precursors. While calcite particles nucleate in pure collagen, the additional presence of glycosaminoglycans leads to the intrafibrillar nucleation of vaterite in both collagen films and native tendons, resulting in contractile stress of more than 10 MPa after 72 h in tendons. Moreover, the stress generation rate can be adjusted by changing the pH values, temperature, and concentration of the mineralizing solution. The conversion of chemical energy to mechanical energy endows tendons with an energy density of 90 J kg −1 , more than twice that of biological muscle. By controlling the generation and release of the contractile stress induced by mineralization and demineralization, the designed collagen-based actuator demonstrates excellent actuation performance. The observed chemo-mechanical effect is expected to inspire the design of prestress-reinforced high-performance composites.
Qianshen Tang,Jiawei Nie,Weijian Fang,Hao Xie,Weimin Wang,Hao Wang,Hang Ping,Bin Li,Zhengyi Fu
Mineralized collagen fibrils are the building blocks of bone, and the mineralization of collagen fibrils is generally regulated by noncollagenous proteins (NCPs). However, the functions of NCPs are difficult to investigate in vivo. Here, we use poly(acrylic acid) (PAA) with different molecular weights (5, 50, 450, and 4000 kDa) as analogs of NCPs and explore their effects on collagen mineralization in vitro. All the PAA molecules can promote the intrafibrillar mineralization of calcium carbonate (CaCO3) following these steps: the precursors infiltrate the gap zones of collagen, and transform into organized calcite nanocrystals within collagen. An increase in molecular weight significantly accelerates the mineralization rate of collagen films, approximately 0.67 μm min–1 at 4000 kDa, four times that of 5 kDa (0.16 μm min–1). However, the generation of contractile stress via intrafibrillar mineralization in tendons exhibits a contrary tendency. It reaches 24.2 MPa at 5 kDa, much higher than that of 4000 kDa (8.3 MPa), due to rapid mineralization causing severe extrafibrillar precipitation around the tendon. The controllable mineralization of collagen matrices may inspire the development of bone repair and regeneration in the future.
Previous electrochemically powered yarn muscles cannot be usefully operated between extreme negative and extreme positive potentials, since generated stresses during anion injection and cation injection partially cancel because they are in the same direction. We here report an ionomer-infiltrated hybrid carbon nanotube (CNT) yarn muscle that shows unipolar stress behavior in the sense that stress generation between extreme potentials is additive, resulting in an enhanced stress generation. Moreover, the stress generated by this muscle unexpectedly increases with the potential scan rate, which contradicts the fact that scan-rate-induced stress decreases for neat CNT muscles. It is revealed by the electro-osmotic pump effect that the effective ion size injected into the muscle increases with an increase in the scan rate. We demonstrate an electrochemically powered gel-elastomer-yarn muscle adhesive that generates and delivers muscle-contraction-mimicking stimulation to a target tissue.
危险品化学品经营许可证（带存储）