Visualizing mechanical stress in artificial protein hydrogels

Soft materials with made-to-order chem. and phys. properties have significant potential value in fields ranging from regenerative medicine and in vitro cell culture to soft robotics and drug delivery. Artificial protein hydrogels (APHs) are uniquely suited to be designer materials via exploitation of the near limitless possible combinations of functional protein domains that can be used to create novel polymer building blocks with tailored properties. Recent work in model systems has demonstrated APHs can be engineered to improve wound healing, for controlled drug delivery and for the creation of materials with programmed characteristic relaxation times. However, engineering APHs to have enhanced mech. strength and toughness has so far not been possible and remains a crit. obstacle for their clin. deployment and use in other applications. One potential approach to make tougher APHs is by creating them from protein structures encoded with a higher propensity to dissipate energy through unfolding in response to mech. stress. This approach seems promising; however, it is not currently understood how features at the mol. level permeate to the bulk phys. properties of APHs. I will discuss our efforts to address this gap through the development of a fluorescence microscopy method for real-time visualization of protein conformational changes that result from mech. stress induced on an APH. The talk will focus on two key points: (1) Design and synthesis of a tunable force-responsive single-mol. FRET sensor that can be readily incorporated into APHs and other types of hydrogels; and (2) fundamental insights on the mechanism of energy dissipation in protein hydrogels gained from visualizing spatially resolved mech. stress. Lastly, I will briefly discuss an application of visualizing mech. stress in APHs - quantifying cell traction forces in three-dimensional cell culture systems