Illustrations depict the collagen fibrils, with their triple-helix structure, surrounded by water molecules. The three different chains of the triple helix are depicted in different colors. Water molecules are shown in red and gray.
Research combining experimental work and detailed molecular simulations has revealed, for the first time, the complex role that water plays in collagen - a protein that is a component of tendons, bone, skin and other structural tissues in the body. The new analysis reveals an important mechanism that had never been observed before: Adding even small amounts of water to, or removing water from, collagen in tendons can generate surprisingly strong forces, as much as 300 times stronger than the forces generated by muscles. "We don't really know the physiological role of water" in the human body's collagen-based tissues, explains Professor Markus Buehler, head of MIT's Department of Civil and Environmental Engineering and a co-author of the paper. "Here we show that it can develop significant forces, especially in tendons, which are thought of as a passive material." One of the challenges in previous studies has been that natural biological samples are all different, Buehler says - so trying to determine the underlying causes of variability is tricky. In the new work, the team was able to study the same samples under a variety of conditions, enabling them to probe the causes of variations. Then, these same materials were analyzed using an atom-by-atom computer model that can simulate the structure down to the level of individual molecules, providing a detailed view of the underlying mechanisms. The molecular simulations, carried out at MIT by Buehler and postdoc Shu-Wei Chang, matched and complemented the experimental results observed by the team members in Germany, led by Professor Peter Fratzl.
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