Nonlinear Viscoelastic Biomaterials: Meaningful Characterization and Engineering Inspiration
by Ewoldt, R.H., Hosoi, A.E., McKinley, G.H.

Nonlinear mechanical properties play an important role in numerous biological functions, for
instance the locomotion strategy used by terrestrial gastropods. We discuss the progress made
toward bioinspired snail-like locomotion and the pursuit of an engineered fluid that imitates the
nonlinear viscoelastic properties of native gastropod pedal mucus. The rheological behavior of
native pedal mucus is characterized using an oscillatory deformation protocol known as large
amplitude oscillatory shear (LAOS), and we review recently-developed techniques for
appropriately describing nonlinear viscoelastic behavior. Whereas materials that exhibit purely
elastic and purely viscous nonlinearities are amenable to standard techniques for characterization,
pedal mucus samples (and biomaterials in general) are viscoelastic, exhibiting both elastic and
viscous nonlinear responses simultaneously and requiring advanced techniques for
characterization. We reveal the utility of these new methods by examining trail mucus from the
terrestrial slug Limax maximus using oscillatory shear rheology. Material responses which
previously could only be described mathematically, with little physical insight, can now be
interpreted with familiar language such as strain-stiffening/softening and shearthickening/
thinning. The new methodology is applicable to any complex material that can be
tested using imposed oscillatory deformations. We have developed data-analysis software to
enable wider use of this framework within and beyond the biomaterials community. The
functionality of this software is outlined here.