The development of untethered soft robots that mimic natural biological systems has been constrained by soft actuator technologies based on pneumatic or hydraulic inflation of elastomer skins that expand when air or liquid is supplied to them. These systems lack the desired properties of high actuation stress and high strain. In addition, the external compressors and pressure-regulating equipment required for such technologies prevent miniaturization and the creation of robots that can move and work independently.
Mechanical engineers at Columbia University report overcoming this impediment to the realization of more lifelike robots with the development of a 3D-printable synthetic soft muscle. The artificial active tissue features intrinsic expansion ability, eliminating the need for an external compressor or high voltage equipment.
The material also has a strain density (expansion per gram) that is 15 times larger than natural muscle and can lift 1,000 times its own weight. Researchers used a silicone rubber matrix with ethanol distributed throughout in micro-bubbles to fabricate an actuator with high strain and high stress coupled with low density.
After being 3D-printed into the desired shape, the artificial muscle was electrically actuated using a thin resistive wire and low-power (8-volt). Tests in different robotic applications demonstrated significant expansion-contraction ability: expansion up to 900 percent when electrically heated to 80 degrees Celsius was observed. The autonomous unit is capable of performing motion tasks, by use of computer controls, in almost any design.
The researchers plan to incorporate conductive materials to replace the embedded wire, accelerating the muscle's response time and increasing its shelf life. Artificial intelligence technology will also be applied to learn muscle control.