CBE Doctoral Dissertation Defense: “Gas Encapsulating Microcapsules (GEMs)” (CK Yeh)

Microcapsules that can respond under hydrostatic pressure would open a new avenue of application in ultrasound- or impact-induced release of therapeutic agents. While microcapsules that are designed to release cargo under uniaxial compressive loadings have been developed, they are filled with liquid, rendering them insensitive to hydrostatic pressure. To overcome this limitation, bubbles can be introduced into the core of the capsule that can impart hydrostatic pressure sensitivity. Although microcapsules that contain bubbles have been reported, the methods for their fabrication make it difficult to control the size of the bubble and microcapsule. In this work, we use microfluidics to create uniform microcapsules while also utilizing osmosis-induced-cavitation to convert microcapsules into gas-encapsulating microcapsules (GEMs). Following GEMs formation under high salt concentrations, the size of the bubble can be modulated by placing the GEMs back into relatively lower salt concentrations. GEMs with a well-defined thickness to diameter ratio (t/D) and volume fraction of gas are subjected to a known hydrostatic pressure through the means of a drop tower. These data establish a relationship between how the thickness to diameter ratio and volume fraction of bubble influence the rupture pressure and drug release, helping to establish the foundation for a new class of on-demand therapeutics that take advantage of pressure inputs.