Traditional robots are made of components¹ and rigid² materials like you might see on an automotive assembly line - metal and hydraulic³ parts, harshly rigid, and extremely strong. But away from the assembly line, for robots to harmoniously⁴ 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 requisite⁵ rigid components that power and control the robot's body. At the interface⁶ of these materials, stresses concentrate and structural⁷ 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 robust⁸ structures that can't be achieved using conventional nuts and bolts manufacturing. A proof-of-concept prototype- a soft-bodied autonomous⁹ 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 exterior¹⁰ using a series of nine sequential material gradients.