Mechanical properties measurements

We measure the longitudinal component of the elastic modulus of type I rat-tail collagen using laser tweezers. All experiments were performed in buffer and with freshly extracted samples to avoid structural changes due to drying or loss of proteoglycans. Keeping fibril in its natural condition, we use a combination of optical tweezers and AFM techniques on single fibrils, and exploit Euler-Bernoulli elasticity theory. With statistics of 10 measured samples we estimate the longitudinal component of Young’s modulus to be 230±130MPa. We found variations in the fibril diameter of 325±40 nm. Since bending forces depend on the diameter to the fourth power, these variations are important for estimating the modulus. However, there still exist sources of variation that are not yet accounted for.