Mechanical Testing of Hydrated Collagen Nanofibrils Using MEMS Technology

A novel technology has been developed to perform mechanical testing on nanoscale biological materials in a hydrated state. Microelectromechanical systems (MEMS) devices have been designed and fabricated specifically to test type I collagen nanofibrils. Fluorescent antibody labeling was used to visualize the fibrils in solution. Pulled glass micropipettes attached to micromanipulators were used to extract single fibrils from a solution droplet and to place them on the MEMS devices. An etched tungsten probe was used to place small drops of epoxy to fix the fibrils to the devices. Tensile testing was performed successfully on four isolated hydrated fibrils to generate stress-strain curves which produce the elastic moduli. In addition, cyclic loading was performed to investigate the fatigue properties of the fibrils. One fibril broke in the middle of the gauge length under tensile load after cycling indicating these nanofibrils are susceptible to fatigue. This technique can make quantitative reproducible mechanical measurements on specimens with characteristic dimensions in the range of 10-1000 nm, an experimental capability which has previously been lacking. With better understanding of the mechanical properties of collagen fibrils, investigators can develop more realistic multiscale computational models to predict bone fracture, put better design constraints on synthetic bone substitutes and help develop treatments for bone diseases. With minor modifications, the MEMS platform may be used to measure the mechanical properties of other nanoscale fibers and membrane structures.