Collagen can generate immense force, study says

Brett Smith for redOrbit.com – Your Universe Online
Found in bones, tendons and skin – collagen is a fibrous protein that plays a crucial role in the structural make-up of the human body.
New research recently published by a team of German and American scientists has revealed that removing a large amount of water from collagen fibers caused them to contract and generates forces up to 300 times greater than those generate by human muscles.
Published in the journal Nature Communications, the new research could lead to the development of novel materials and orthopedic treatments, the study team said.
The collagen molecule is like a rope, with three string-like proteins draped around one another to create a triple-helical structure. Several of these “ropes” in turn merge to form heavier “coils”, referred to as collagen fibrils. Being only 100 to 500 nanometers thick, the fibrils are still 100,000 slimmer than common rope.
Inside the fibrils, adjoining collagen molecules are not stacked next to one another, but they are arranged in a staggered set up. This results in switching denser and thinner areas over the length of the fibrils. Finally, many fibrils blend together to create collagen fibers.
In the new study, the researchers were able to show that how different collagen structures are affected by changed in water content: from the molecular level, all the way up to the fiber level. The study team both conducted water-based experiments with collagen in a special experimental chamber, and generated a series of computer models that replicated the behavior of collagen fibrils.
“Water is an integral component of collagen,” said study author Admir Masic, a bio-materials researcher at the Max Planck Institute of Colloids and Interfaces in Germany.
Water makes up about 60 percent of natural collagen’s weight and its molecules attach tightly to collagen along its helical shape, the latter of which the team was able to show using X-ray diffraction. The study team was also able to show the angle of the turns and the width of the helix.
In the drying experiments, the researchers found that when the relative humidity drops from 95 to 5 percent, collagen molecules dry out and shrink in length by 1.3 percent.  The corresponding fibrils shrink by 2.5 percent.
This decrease in length causes increased tension in collagen structures of around 100 megapascals, or 300 times the forces generated by human muscle.
Using an imaging technology called Raman spectroscopy, the researchers found that the contraction is caused by conformational changes to collagen that resemble a rope shortening by forming wave-like patterns. Interestingly, this phenomenon caused the thicker regions of the fibrils to stretch and the thinner regions to shorten.
“With this knowledge, researchers could develop materials that behave in a opposite ways when water is removed from them,” noted study author Luca Bertinetti, a materials scientist from Max Planck.
The study team noted that their findings also suggest that the high tensile strength of dried collagen could play an active structural role in the human body, such as during bone formation. The research said dried-out collagen may act like rebar in a concrete foundation.
“During bone synthesis, water may be removed from collagenous matrix so that the tissue contracts” said study author Peter Fratzl, a director at the institute.
The study team said they now plan to look into the role of collagen in bone and other tissue.
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