Tiny, flexible robotic spider could aid future surgeries
Scientists have developed a flexible, soft robotic spider – about as big as a coin – that could help assist delicate surgical procedures or access areas too difficult for humans or rigid robots to reach. Roboticists are envisioning a future in which soft, animal-inspired robots could be safely deployed in difficult-to-access natural and human-made environments. Centimeter-sized soft robots have been created, but thus far it has not been possible to fabricate multifunctional flexible robots that can move and operate at smaller size scales. Researchers at from Harvard University and Boston University in the US overcame this challenge by developing an integrated fabrication process that enables the design of soft robots on the millimetre scale with micrometer-scale features. To demonstrate the capabilities of their new technology, they created a robotic soft spider – inspired by the millimetre-sized colourful Australian peacock spider – from a single elastic material with body-shaping, motion, and colour features. “The smallest soft robotic systems still tend to be very simple, with usually only one degree of freedom, which means that they can only actuate one particular change in shape or type of movement,” said Sheila Russo, an assistant professor at Boston University in the US. “By developing a new hybrid technology that merges three different fabrication techniques, we created a soft robotic spider made only of silicone rubber with 18 degrees of freedom, encompassing changes in structure, motion, and colour, and with tiny features in the micrometer range,” said Russo, who was a postdoctoral fellow at Harvard at the time of the study. In their Microfluidic Origami for Reconfigurable Pneumatic/Hydrolic (MORPH) devices, researchers first used a soft lithography technique to generate 12 layers of an elastic silicone that together constitute the soft spider’s material basis. Each layer is precisely cut out of a mold with a laser micromachining technique, and then bonded to the one below to create the rough 3D structure of the soft spider. Key to transforming this intermediate structure into the final design is a pre-conceived network of hollow microfluidic channels that is integrated into individual layers. With a third technique known as injection-induced self-folding, pressurized one set of these integrated microfluidic channels with a curable resin from the outside. This induces individual layers, and with them also their neighbouring layers, to locally bend into their final configuration, which is fixed in space when the resin hardens. This way, for example, the soft spider’s swollen abdomen and downward-curved legs become permanent features. “We can precisely control this origami-like folding process by varying the thickness and relative consistency of the silicone material adjacent to the channels across different layers or by laser-cutting at different distances from the channels,” said Tommaso Ranzani, first author of the study published in the journal Advanced Materials. “During pressurisation, the channels then function as actuators that induce a permanent structural change,” said Razani, an assistant professor at Boston University. The remaining set of integrated microfluidic channels were used as additional actuators to colourise the eyes and simulate the abdominal colour patterns of the peacock species by flowing coloured fluids; and to induce walking-like movements in the leg structures. “This first MORPH system was fabricated in a single, monolithic process that can be performed in few days and easily iterated in design optimisation efforts,” said Ranzani.