Meeting Abstract

S7.4  Tuesday, Jan. 6  Nonlinear viscoelastic biomaterials: meaningful characterization and engineering inspiration EWOLDT, R.H.*; HOSOI, A.E.; MCKINLEY, G.H.; MIT, Cambridge, MA; MIT, Cambridge, MA; MIT, Cambridge, MA ewoldt@mit.edu

Nonlinear mechanical properties play an important role in numerous biological functions. For example, the strain-stiffening of artery walls enables stability to inflation over a range of pressures (Shadwick, J. Exp. Biol. 1999), and the dramatic viscous shear-thinning of gastropod pedal mucus enables the wall-climbing abilities of adhesive locomotion (Denny, Nature 1980). Purely elastic and purely viscous nonlinearities are amenable to standard characterization techniques. However, biomaterials are often viscoelastic, exhibiting both elastic and viscous nonlinear responses simultaneously, requiring more advanced characterization techniques. Here we discuss a new framework for describing and understanding such nonlinear viscoelastic behavior, outlining new material measures and clearly defining commonly used but previously ambiguous language such as strain-stiffening/softening and shear-thickening/thinning. This framework enables a meaningful physical interpretation of nonlinear viscoelastic material responses which before could only be described mathematically. Interest in soft materials is increasing within the engineering field, for example with the use of complex fluids and smart materials for mimicking natural systems. The wall-climbing ability of gastropods has motivated our pursuit of an engineered system which imitates native pedal mucus. Furthermore, soft-bodied animals give inspiration for soft robots which can actively control their shape and/or mechanical properties. A better understanding of complex viscoelastic biomaterials will help the engineering community integrate soft solids and complex fluids into the working components of devices.