Traditional robots are made of components and rigid materials like you might see on an automotive assembly line - metal and hydraulic parts, harshly rigid, and extremely strong. But away from the assembly line, for robots to harmoniously assist humans in close-range tasks scientists are designing new classes of soft-bodied robots. Yet one of the challenges is integrating soft materials with requisite rigid components that power and control the robot's body. At the interface of these materials, stresses concentrate and structural integrity can be compromised, which often results in mechanical failure. But now, by understanding how organisms solve this problem by self-assembling their bodies in a way that produces a gradual transitioning from hard to soft parts, a team of Wyss Institute researchers and their collaborators have been able to use a novel three-dimensional printing strategy to construct entire robots in a single build that incorporate this biodesign principle. The strategy permits construction of highly complex and robust structures that can't be achieved using conventional nuts and bolts manufacturing. A proof-of-concept prototype- a soft-bodied autonomous jumping robot reported in the July 10 issue of Science - was 3D printed layer upon layer to ease the transition from its rigid core components to a soft outer exterior using a series of nine sequential material gradients.

"We leveraged additive manufacturing to holistically create, in one uninterrupted 3D printing session, a single body fabricated with nine sequential layers of material, increasing in stiffness from rigid to soft towards the outer body," said the study's co-senior author Robert Wood, Ph.D, who is a Core Faculty member and co-leader of the Bioinspired Robotics Platform at the Wyss Institute for Biologically Inspired Engineering at Harvard University, the Charles River Professor of Engineering and Applied Sciences at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), and Founder of the Harvard Microrobotics Lab. "By employing a gradient material strategy, we have greatly reduced stress concentrations typically found at the interfaces of soft and rigid components which has resulted in an extremely durable robot."