Thermal (in)stability of type I collagen fibrils

We measured Young's modulus at temperatures ranging from 20 to 100 ^{\circ}$C for a collagen fibril taken from rat's tendon. The hydration change under heating and the damping decrement were measured as well. At physiological temperatures $25-45^{\circ}$C Young's modulus decreases, which can be interpreted as instability of collagen. For temperatures between $45-80^{\circ}$C Young's modulus first stabilizes and then increases with decreasing the temperature. The hydrated water content and the damping decrement have strong maxima in the interval $70-80^{\circ}$C indicating on complex inter-molecular structural changes in the fibril. All these effects disappear after heat-denaturating the sample at $120^\circ$C. Our main result is a five-stage mechanism by which the instability of a single collagen at physiological temperatures is compensated by the interaction between collagen molecules within the fibril.