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April 24th 2019

Living tissues, such as skin and cartilage, owe their structure and stiffness to the fact that they are constructed from an elastic network of collagen fibres. Collagen is a protein that forms an important component of connective tissue. Each fibre in the network is made up from several of these proteins, which are layered in a sort of crystal structure. The researchers from this FOM Industrial Partnership Programme 'Bio(-related) materials', study how this ordered structure can cause the high stiffness and mechanical tensile strength of collagen fibres.

For the research they use purified collagen, which spontaneously forms fibres in a salt solution. The researchers initiate this process by warming the salt solution from 4 to 37°C. The rising temperature ensures that the collagen molecules align side to side with each other to form long fibres.

Not forgetful
Up until now, physicists assumed that the fibres fell apart again when the solution cooled down because the driving force for molecular association then disappears. However, through a combination of light diffraction and microscopy they discovered that collagen fibres exhibit a memory. If the solution cools down the fibres become thinner but otherwise remain intact. If the solution is reheated, the thickness of the fibres once again increases.

The longer the fibres remain at a temperature of 37°C, the less mass they lose when the temperature decreases. This means that the fibres exhibit a thermal memory. The exact cause of this is not yet known, but the researchers suspect that it has something to do with the special structure of collagen. In a newly formed fibre, the collagen proteins probably still form a somewhat loose, disorganised structure. As the fibres become older, collagen proteins fall into place better as result of which they disassociate from each other less easily.

The unexpected high stability of collagen fibres is relevant in the initial phase of collagen formation during the development of tissues in embryos, wound healing and fibrosis (during which the quantity of connective tissue in organs increases). Furthermore it is important to take the stability of collagen into consideration when it is used, for example, in tissue restoration and medicine transport.