Elastic moduli of collagen fibrils measured by nanoindentation test using atomic force microscope (AFM) and tensile test

Fibrils were isolated from rat tail tendons and the nanoindentation tests and tensile tests of these fibrils were performed in air (dry condition). In the nanoindentation test using atomic force microscope (AFM), the indentation depth and force of the AFM tip were determined by the force curve measurement. Elastic modulus was calculated from these data using Hertzian contact theory. In the tensile test, the both ends of the fibril were wound on to the tips of microneedles and the fibril was stretched to failure by moving the microneedle under dark-field observation. Elastic modulus was determined as the slope of the approximate line of the measured stress-strain relation. Elastic moduli measured by the nanoindentation tests and tensile tests were 0.97 ± 0.55 GPa and 0.90 ± 0.39 GPa (Mean ± S.D.), respectively. There was no significant difference between the two values. These results indicate that the elastic modulus of the sub-fibrils in the surface layers of fibrils may not be significantly different from that of whole fibrils in the longitudinal direction.