FIG. 1.

A schematic of the process for fabricating hydrogels by photopolymerization, which are used in cell encapsulation strategies. The photopolymerization process occurs via a photoinitiated free radical chain polymerization involving initiation, propagation, and termination. Photoinitiator molecules (In) absorb photons of light energy (hv) and dissociate into radicals (R•) (initiation). The initiator radicals react with unreacted double bonds (C = C) on macromolecular monomers [e.g., poly(ethylene glycol) dimethacrylate] to form growing kinetic chains (propagation). Termination occurs through either bimolecular termination or chain transfer between two propagating chains.