Cytocompatible cell encapsulation via hydrogel photopolymerization in microfluidic emulsion droplets

Abstract

Encapsulating cells within biocompatible materials is a widely pursued and promising element of tissue engineering and cell-based therapies. Recently, extensive interest in microfluidic-enabled cell encapsulation has emerged as a strategy to structure hydrogels and establish custom cellular microenvironments. In particular, it has been shown that the microfluidic-enabled photoencapsulation of cells within PEG diacrylate (PEGDA)-based microparticles can be performed cytocompatibly within gas-permeable, nitrogen-jacketed polydimethylsiloxane microfluidic devices, which mitigate the oxygen inhibition of radical chain growth photopolymerization. Compared to bulk polymerization, in which cells are suspended in a static hydrogel-forming solution during gelation, encapsulating cells via microfluidic processing exposes cells to a host of potentially deleterious stresses such as fluidic shear rate, transient oxygen depletion, elevated pressures, and UV exposure. In this work, we systematically examine the effects of these factors on the viability of cells that have been microfluidically photoencapsulated in PEGDA. It was found that the fluidic shear rate during microdroplet formation did not have a direct effect on cell viability, but the flow rate ratio of oil to aqueous solution would impart harmful effects to cells when a critical threshold was exceeded. The effects of UV exposure time and intensity on cells, however, are more complex, as they contribute unequally to the cumulative rate of peroxy radical generation, which is strongly correlated with cell viability. A reaction-diffusion model has been developed to calculate the cumulative peroxy radical concentration over a range of UV light intensity and radiation times, which was used to gain further quantitative understanding of experimental results. Conclusions drawn from this work provide a comprehensive guide to mitigate the physical and biochemical damage imparted to cells during microfluidic photoencapsulation and expands the potential for this technique.

Manufacturing of poly(ethylene glycol diacrylate)-based hollow microvessels using microfluidics

“…The cytocompatibility and biomaterial properties of PEGDA enable it to be photopolymerized into a hydrogel that is resistant to protein absorption, and that can be lithographically modeled and spatially controlled, proving useful for tissue and bioengineering. [43][44][45][46] Other research groups, including Uwamori et al 40 and Daniele et al, 47 have used brin gel and poly(ethylene glycol) dimethacrylate (PEGDMA) for the polymer-based foundations of their microvessels. However, based on the literature, [44][45][46] PEDGA may behave more suitably as the tissue foundation for our synthetic microvessels, due to the molecular toughness and dened permeability of the polymer.…”

Comparative cytocompatibility of multiple candidate cell types to photoencapsulation in PEGNB/PEGDA macroscale or microscale hydrogels

“…As the same concentration of LAP and total dose UV was used for polymerizing PEGDA hydrogels in each parallel experiment, the difference in cell viability is solely attributable to the elevated cumulative production of ROS. As previously shown[102], the rate of ROS production is governed by UV exposure time, and is independent of UV intensity. Increased exposure time allows consumed oxygen to be replenished by diffusion into hydrogels, where it inhibits initiator and monomer radicals and is quickly converted into ROS[102].…”

“…As previously shown[102], the rate of ROS production is governed by UV exposure time, and is independent of UV intensity. Increased exposure time allows consumed oxygen to be replenished by diffusion into hydrogels, where it inhibits initiator and monomer radicals and is quickly converted into ROS[102]. However, cells in PEGNB hydrogels can tolerate high UV intensity as well as long UV exposure time, indicating the deleterious effect of ROS must be mitigated during PEGNB polymerization[87].…”

Moving Towards a Finer Way of Light-Cured Resin-Based Restorative Dental Materials: Recent Advances in Photoinitiating Systems Based on Iodonium Salts

“…Photopolymerization processes play an increasingly important role in biomedical applications, for instance, in obtaining hydrogel polymer materials [45][46][47][48][49][50][51][52][53][54] or in vivo photocurable dental composites [55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73]. Applying photochemically initiated polymerization for obtaining dental polymer composites enables the use of unique and innovative features.…”