A strategy for making light-responsive hydrogels is reported in Nature Communications this week. The gels expand and contract upon exposure to ultraviolet or visible light in ways that mimic muscles, and may pave the way for further development of “soft robotics”.

Materials that perform muscle-like movements upon external stimulation are important targets in a range of research fields. Akira Harada and his colleagues report a gel consisting of polymers containing azobenzene and cyclodextrin groups, where the “host-guest” interactions between the two polymers are tuned by exposure to different wavelengths of light. This then results in the controllable expansion and contraction of the gel. The authors demonstrate that plates and coils made of these gels and suspended in solution can be deformed at will by shining light from different positions.