2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

Mechanical Properties of Single Collagen Nanofibrils Measured Using MEMS Technique

Z. Liu, B.N. Smith, H. Kahn, R. Ballarini, S.J. Eppell
Case Western Reserve University, US

Keywords:
mechanical properties, collagen, fibril, MEMS

Abstract:
Understanding the mechanical behavior of hierarchical materials like bone and tendon using multiscale models requires mechanical testing from molecular scales to macroscopic scales. Little has been studied on collagen fibrils with diameters around a hundred nanometers. To address this lack of experimental data, we used a method based on Microelectromechanical Systems (MEMS). Quantitative reproducible mechanical measurements on eight collagen fibrils with diameters of 120-950 nm were made. Three fibrils with relatively large diameters (>= 700 nm) show low elastic moduli around 0.5 GPa. The other five fibrils with relatively small diameters (<= 450 nm) displayed a nonlinear hardening behavior with a low strain modulus ~0.5 GPa and a high strain modulus ~5 GPa. Due to the limited force (< 35 µN) generated by this generation of MEMS devices, we could not break fibrils under low cycle monotonic tensile testing. Some of the fibrils withstood tensile stress up to 900 MPa without fracture indicating a collagen fibril tensile strength > 900 MPa. Two fibrils were broken after cyclic loading and all fibrils could be broken after dehydration in the SEM chamber. This shows that collagen structures at the level of single nanofibril are susceptible to cyclic fatigue and plasticization by water.

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