​Sub-gram Scale Robot

We mimicked this action by creating curved geometries (applying a mechanical constraint to the material) encoded with molecular-level programming that when exposed to a thermal stimulus, evolve and snap between discrete shapes. The LCE/PET tape spring encapsulates a microfabricated electrode that delivers Joule heating from low-voltage sources using pulsed power of ≈200 mW. The lightweight actuators are harnessed in a water strider that floats via surface tension. Actuation results in translation across the surface. The actuation profiles are also harnessed in terrestrial motility. This includes motility on surfaces with arbitrary topographies that are compliant (loose sand) and those which are firm, but slippery (lab table).

While responsive materials (LCEs in particular) offer compliant structures capable of work-dense actuation, thermomechanical actuation in soft materials is characteristically slow and the displacement speeds are not scalable to enable impulsive actuation at speeds >>100 mm s−1. The challenge is that while we could get some movement and actuation with light-driven polymers, it was too slow of a response to be practical. If you want to move something, like flip a switch or move a lever, you need something that will react quickly and with enough power.