Tensile Mechanical Measurements on Individual Collagen Fibrils

Abstract

Introduction: There is a hierarchical order in tendon ranging from the collagen molecule to the whole tendon. We have developed a method using the atomic force microscope (AFM) together with a novel data acquisition technique to quantify the sub-failure mechanical properties of individual collagen fibrils. Here we use this method to investigate how the saline environment affects tensile force transmission. Methods: Human patellar tendon tissue was obtained from a healthy young male. Six fascicles and six fibrils were mechanically tested sub-failure to determine modulus and relative energy dissipation in PBS solutions of 0.02, 0.15 and 1 M concentration as well as two HEPES buffers containing NaCl or NaCl+CaCl2. Mechanical testing was performed to 4% strain. Results: The tensile properties of collagen fibrils are highly resistant to changes in their saline environment. The only consistent response to environment composition was a minor (<5%) increase in relative energy dissipation in 1 M PBS. This is in sharp contrast to previous reports of more than 100% increase in radial compressive modulus of fibrils in 1 M salt solution, and more than 100% increase in energy dissipation of AFM pulling experiments in the presence of Ca2+.