Miniature mechanical actuators measuring a fraction of a millimeter thick can deliver three to six times more torque than comparable electric motors at 1/20th the weight, according to scientists at MIT (Cambridge, MA). The actuators could someday be used in applications that are too small to accommodate current motor designs, including components of minimally invasive surgical devices.While other experimental actuators have incorporated springs made from shape-memory alloys, the MIT mechanical muscle is constructed entirely from a shape-memory alloy. In addition to being easier to manufacture, it also features only a small section of the device that heats up when electrically charged.To increase electrical resistance, the scientists carved rectangular notches into the alloy so that only the material surrounding the notches heats up in response to an electrical current passing through the device, according to the scientists. As a result, heat should dissipate more easily and the actuator should be more energy efficient.The actuators can be arranged in an array of configurations; different configurations of the actuators on a device can induce different types of motion. View MIT's informative slideshow on the actuators for more information.