In this paper, Tobin Brown and I developed and characterized a synthetically tractable photodegradable hydrogel and demonstrated the ability to control the extension of motor axons. Check it out at http://pubs.acs.org/doi/abs/10.1021/bm500731b. The abstract appears below:

Hydrogels with photocleavable units incorporated into the cross-links have provided researchers with the ability to control mechanical properties temporally and study the role of matrix signaling on stem cell function and fate. With a growing interest in dynamically tunable cell culture systems, methods to synthesize photolabile hydrogels from simple precursors would facilitate broader accessibility. Here, a step-growth photodegradable poly(ethylene glycol) (PEG) hydrogel system cross-linked through a strain promoted alkyne–azide cycloaddition (SPAAC) reaction and degraded through the cleavage of a nitrobenzyl ether moiety integrated into the cross-links is developed from commercially available precursors in three straightforward synthetic steps with high yields (>95%). The network evolution and degradation properties are characterized in response to one- and two-photon irradiation. The PEG hydrogel is employed to encapsulate embryonic stem cell-derived motor neurons (ESMNs), and in situ degradation is exploited to gain three-dimensional control over the extension of motor axons using two-photon infrared light. Finally, ESMNs and their in vivo synaptic partners, myotubes, are coencapsulated, and the formation of user-directed neural networks is demonstrated.