Choi, M. et al. Nat. Photonics doi:10.1038/nphoton.2013.278 (20 October 2013).

Hydrogel polymers have properties well suited for cell encapsulation and are increasingly being used for cell transplantation experiments in animal models. Tailoring hydrogels so that their light-transmission capabilities can be exploited adds new functionality. As shown by Choi et al., modifications of the shape and structure of poly(ethylene glycol)-based hydrogels can improve their light-guiding properties. The authors found that longer polymers yielded a higher transparency after cross-linking. They implanted patches of hydrogels containing cells in awake, freely moving mice for several days to characterize the long-term transparency, biocompatibility, cell viability and light-guiding properties. They then used these light-guiding hydrogels for optogenetic stimulation of glucagon-like peptide 1–secreting cells in a mouse model of diabetes and for real-time in vivo readouts of quantum-dot toxicity in reporter cells.