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Electrically collapsible hydrogels with enhanced mechanical toughness

Harvard MRSEC team led by Clarke, Mooney, Parker, Suo, and Vlassak has developed new hydrogels
that are both electrically responsive and mechanically tough. Poly(acrylic
acid) hydrogels can be made to be macroporous and therefore capable of rapid
volumetric collapse (top left image sequences). These electrically
responsive hydrogels can be integrated into systems capable of rapid
configurational changes using simple and inexpensive electronics (top right
).  However, these
electrically responsive hydrogels are not very mechanically tough, limiting
their broad applicability. When they are interpenetrated with an ionically
cross-linked network such as calcium cross-linked alginate, they become more
mechanically tough and stretchable (bottom left image sequence). This
enhancement in toughness (6-fold increase from 0.1 to 30 mM calcium, bottom
right graph
) only moderately reduces the ability of the gel to be electrically
collapsed. These mechanical enhancements may enable electrically responsive
hydrogel materials to be used as actuators and artificial muscles.