Gels are solids that are composed of a dilute network of material within a liquid domain. Examples range from familiar items like Jell-O to biomaterials, like the the lens of an eye, to hydrogels, like those found in absorbant diapers. The mechanical behavior of these materials is key to their utilization in both nature and new technology and is a function of the microstructural make-up of the material. Currently, our group characterizes this microstructure/property relationship from both design and property measurement perspectives. To this end, we have developed a novel characterization technique we call Cavitation Rheology that is capable of locally quantifing the mechanical properties of soft materials, such as hydrogels.
Cavitation Rheology takes advantage of the unique elastic instability associated with non-linear elastic materials. This instability is the result of favorable growth for a bubble, or cavity, at some critical pressure related to the local elastic modulus combined with the energetic cost associated with the surface energy of the growing bubble. We are utilizing this technique to probe the mechanical properties of varieties of synthetic materials as well as living tissues. An example of the latter is shown in the image on the right in which cavitation measurements are being performed in order to correlate disease in mouse skin with mechanical response. Simultaneously, we characterize the fundamental principles governing a cavitation event under changes in local geometry (e.g.., confinement of the material being tested) and loading conditions (e.g., loading rate) in synthetic hydrogels and soft polymers.