(267g) Gas-Filled Nanoscale Additives for Acoustically Responsive Hydrogel

The ability to spatially and temporally control the porosity and diffusivity of hydrogels would be desirable in multiple areas of regenerative medicine. Here, we describe an approach to enable control of hydrogel bulk properties using ultrasound via the introduction of “acoustic nanoadditives”. These additives are based on gas vesicles (GVs), which are gas-filled protein nanostructures found in cyanobacteria whose native function is to regulate cellular buoyancy. GVs can undergo pressure-induced collapse, instantaneously reducing their volume by nearly 10-fold. Due to their rapid and drastic volume reduction in response to pressure, we hypothesized that GVs could serve as nanoadditives in materials to influence bulk properties in a stimulus-responsive manner. In this work, we show that GVs act as stable inclusions when embedded in polyacrylamide hydrogels, without compromising gel integrity. In addition, we observed that GVs can be acoustically collapsed by ultrasound in situ, forming nanoscale pores within the polymeric network. Furthermore, we show that GVs, in their intact form, can impede the diffusion of proteins through the hydrogel, and upon in situ collapse, increase the diffusivity of the hydrogel material. This work demonstrates the ability of GVs to serve as nanoadditives to enable acoustically responsive polymeric materials with locally tunable porosity and diffusivity, and could open the door to applications in drug delivery and tissue engineering in a broad range of in vitro and in vivo contexts.