(333d) Encapsulation of Single ß Cells in Microgels Via Integrated Microfluidic Flow Focusing and Photopolymerization

Encapsulation of ß cells in biocompatible hydrogels is a highly promising therapy for Type 1 Diabetes Mellitus, which avoids  post-transplantation immunorejection. Many factors affect post-encapsulation cell viability and function, including monomer molecular weight and concentration, solution composition, and cell-cell interactions, among others. The described microfluidic droplet generation technology provides a platform for the encapsulation of single cells and the high throughput screening of cell response to encapsulation. Polyethylene glycol diacrylate (PEGDA), a versatile and widely used hydrogel-forming macromer, is employed as the encapsulating phase and is photopolymerized in situ immediately following droplet formation. However, atmospheric oxygen inhibits the photo-polymerization of PEGDA, an issue that is dramatically exacerbated at the microscale, and particularly so when using a fluorinated oil carrier phase within channels fabricated from oxygen permeable poly(dimethylsiloxane) (PDMS). To overcome the challenge, we present a nitrogen micro-jacketed microfluidic device to locally control the oxygen concentration in the system.  The reduction of oxygen allowed free radical polymerization to proceed while also mitigating the production of deleterious reactive oxygen species, with which cell laden hydrogel microparticles can be produced.  Employing the oxygen-controllable microfluidic device, we were able to encapsulate single cells within photopolymerized microscale (~25 µm) droplets with high post-encapsulation cell viability.  This platform was successfully used for 𝛽-cell encapsulation and matrix parameter screening.