The emerging field of soft robotics holds great potential for the medical world, with flexible and forgiving parts that are a lot more agreeable with our squishy tissue and organs than moving pieces of metal. And when it comes to materials, the high water content of hydrogels make them a suitable candidate for use in the human body. With this goal in mind, MIT engineers have developed new hydrogel-based robots capable of generating enough force to "kick" balls and catch and release live fish.
Over the past few years we've seen a number of hydrogel-based soft robotic devices in development, ranging from swimming bots on the micron scale to grippers that dissolve in the body after performing surgery or delivering drugs. But in the view of the MIT team, typical hydrogels could do with some more durability.
"Conventional hydrogels are weak and brittle, so they crack or burst easily under loads," Professor Xuanhe Zhao, who led the new research, explains to New Atlas. "We design biocompatible hydrogels that integrate mechanisms of high stretchability and mechanical dissipation to achieve high toughness and robustness. We further make the robust hydrogel into structures capable of hydraulic actuation."
This hydraulic actuation comes courtesy of rubbery tubes, which attach to the hydrogel robots and can be used to pump them full of water. The robots consist of hollow, interlocking hydrogel cubes, arranged in such a way that when pumped full of water they curl up or stretch out. So much so, that they can produce a few newtons of force in one second. Comparably, the team says similarly actuated hydrogel robots have only been able to generate millinewton forces over minutes or hours.
This method was used to create a fin-like device that flaps back and forth, an articulated appendage that simulates a kicking action and a hand-shaped gripper. In their experiments, the researchers found that their hydrogel robots could endure up to 1,000 cycles of repeated use without rupturing. And for one of their more impressive tests, the team submerged the gripper in a tank with a gold fish and managed to grab a hold of it as it swam past, before releasing it again.
"[The robot] is almost transparent, very hard to see," Zhao says. "When you release the fish, it's quite happy because [the robot] is soft and doesn't damage the fish. Imagine a hard robotic hand would probably squash the fish."
So what you've got there is a clever little robot that is not only made mostly from water, but is powered by water as well, meaning that if used underwater they appear almost invisible like a jellyfish. But for now, the team is focusing on medical applications and tailoring the approach to specific-use cases.
"The hydrogel actuators and robots may be used to interact with soft and delicate tissues and organs in human body, for example, or assist heart beating by applying pressuring through hydrogel," Zhao tells us. "Since hydrogels are soft, wet and biocompatible, they can fit inside human body well. The gel actuators or robots will be controlled by pumping water into the designed chambers for controlled motion."
The team has published its research in the journal Nature Communications, and you can see more of the robots in action in the video below.
(Video produced and edited by: Melanie Gonick/MIT; Hydrogel robot footage: Hyunwoo Yuk/MIT Soft Active Materials Lab)