PEG hydrogels formed by thiol-ene photo-click chemistry and their effect on the formation and recovery of insulin-secreting cell spheroids.

Hydrogels provide three-dimensional frameworks with tissue-like elasticity and high permeability for culturing therapeutically relevant cells or tissues. While recent research efforts have created diverse macromer chemistry to form hydrogels, the mechanisms of hydrogel polymerization for in situ cell encapsulation remain limited. Hydrogels prepared from chain-growth photopolymerization of poly(ethylene glycol) diacrylate (PEGDA) are commonly used to encapsulate cells. However, free radical associated cell damage poses significant limitation for this gel platform. More recently, PEG hydrogels formed by thiol-ene photo-click chemistry have been developed for cell encapsulation. While both chain-growth and step-growth photopolymerizations offer spatial-temporal control over polymerization kinetics, step-growth thiol-ene hydrogels offer more diverse and preferential properties. Here, we report the superior properties of step-growth thiol-ene click hydrogels, including cytocompatibility of the reactions, improved hydrogel physical properties, and the ability for 3D culture of pancreatic β-cells. Cells encapsulated in thiol-ene hydrogels formed spherical clusters naturally and were retrieved via rapid chymotrypsin-mediated gel erosion. The recovered cell spheroids released insulin in response to glucose treatment, demonstrating the cytocompatibility of thiol-ene hydrogels and the enzymatic mechanism of cell spheroids recovery. Thiol-ene click reactions provide an attractive means to fabricate PEG hydrogels with superior gel properties for in situ cell encapsulation, as well as to generate and recover 3D cellular structures for regenerative medicine applications.