A Microfluidic-Based Cell Encapsulation Platform to Achieve High Long-Term Cell Viability in Photopolymerized Pegnb Hydrogel Microspheres

Cell encapsulation within photoinitiated polyethylene glycol (PEG) hydrogel scaffolds has been demonstrated as a robust strategy for drug delivery, tissue engineering, high throughput screening, and developing platforms to study cellular behavior and fate. The spatially and temporally specify PEG hydrogel properties, chemical functionalization, and cytocompatibility has advanced in recent years. Recent development in microfluidics has recently enabled the miniaturization of PEG hydrogels, thus making the fabrication of miniaturized cell-laden vehicles possible. However, the presence of oxygen dramatically inhibits the chain growth photopolymerization of polyethylene glycol diacrylate (PEGDA), thus limiting its application in microfluidics. Another promising PEG-based scaffold material, PEG norbornene (PEGNB), is formed by a step growth photopolymerization, which is not inhibited by oxygen. PEGNB is also more cytocompatible than PEGDA and allows for orthogonal addition reactions. The step-growth kinetics, however, are slow and therefore present a challenge to achieving fully polymerized microgel droplets within microfluidic devices. Here, we describe a microfluidic-based droplet fabrication platform that consistently generates monodisperse cell-laden water-in-oil emulsions. PEGNB droplets are collected and photopolymerized under UV exposure in bulk. In this work, we compare this microfluidic-based cell encapsulation platform with a vortex-based method in terms of controlling microgel size, uniformity, post-encapsulation cell viability and long-term cell viability. Several factors that potentially influence post-encapsulation cell viability are investigated. Finally, this platform is compared with a similar cell encapsulation platform using PEGDA in term of long-term cell viability. We show that this PEGNB microencapsulation platform is capable of generating cell-laden hydrogel microspheres at high rates with well-controlled size distribution and high long-term cell viability.