Micromechanical bending of single collagen fibrils using atomic force microscopy

A new micromechanical technique was developed to study the mechanical properties of single collagen fibrils. Single collagen fibrils, the basic components of the collagen fiber, have a characteristic highly organized structure. Fibrils were isolated from collagenous materials and their mechanical properties were studied with atomic force microscopy (AFM). In this study, we determined the Young's modulus of single collagen fibrils at ambient conditions from bending tests after depositing the fibrils on a poly(dimethyl siloxane) (PDMS) substrate containing micro-channels. Force-indentation relationships of freely suspended collagen fibrils were determined by loading them with a tip-less cantilever. From the deflection-piezo displacement curve, force-indentation curves could be deduced. With the assumption that the behavior of collagen fibrils can be described by the linear elastic theory of isotropic materials and that the fibrils are freely supported at the rims, a Young's modulus of 5.4 +/- 1.2 GPa was determined. After cross-linking with glutaraldehyde, the Young's modulus of a single fibril increases to 14.7 +/- 2.7 GPa. When it is assumed that the fibril would be fixed at the ends of the channel the Young's moduli of native and cross-linked collagen fibrils are calculated to be 1.4 +/- 0.3 GPa and 3.8 +/- 0.8 GPa, respectively. The minimum and maximum values determined for native and glutaraldehyde cross-linked collagen fibrils represent the boundaries of the Young's modulus.