Go Fish: A hydrogel hand, shown here delicately grasping a goldfish, could one day be used as a surgical tool. Photo: Hyunwoo Yuk/MIT
The inside of the human body is mostly squishy (that’s a technical term), and our soft innards don’t always fare well when hard objects are placed inside. Not only can sharp edges damage organs and blood vessels, but the body’s defense system can also surround the foreign object with scar tissue and interfere with its intended function. So researchers are working on soft robots that may be better tolerated within the body, permitting machines to make intimate contact with human tissue without jeopardizing safety.
These three experimental bots are designed for different purposes—two are implants, one is a potential surgical tool—but they all showcase a gentler kind of robotics, enabled by new materials and flexible actuators.
Twist and Squeeze: A rubbery sleeve that fits over the heart rhythmically compresses it in two directions to mimic the natural actions of cardiac muscles. Photo: Ellen Roche/Harvard University
Inside the chests of 41 million people around the world, failing hearts gradually become less effective at the vital task of pumping blood. Some heart failure patients get on the list for a transplant, while others receive metallic pumps called ventricular assist devices (VADs) to help their faltering organs. But VADs increase the risk of blood clots, which can form as the liquid flows over surfaces made of metal and plastic.
In search of a better pumping assistant, an international team of researchers invented a silicone sleeve that slips over the heart’s exterior, thus keeping the robot from contact with flowing blood as it rhythmically squeezes the organ. The sleeve’s design is inspired by the arrangement of real heart muscles, with an inner layer of material that contracts using concentric rings and an outer layer that contracts in a helical fashion. The early-stage device uses 14 pneumatic actuators (6 in the concentric layer, 8 in the helical layer), which the team can activate individually by filling them with air, allowing for experimentation with different patterns of contractions. In experiments with live pigs, the researchers demonstrated that the device can either detect and match the natural rhythm of the heart or override a faulty rhythm with a steady beat.
Soft robots have the potential to do more than supplement a failing body, says study coauthor Ellen Roche, a postdoctoral researcher at the National University of Ireland, Galway, who will move to MIT in September to start as an assistant professor of mechanical engineering. “If you can match the organ’s native properties, you’re going to do a better job of aiding it—and maybe you can try to rehabilitate it or help it recover function,” she says. “If you just take over its function, it’s not going to get better.”
When you think of Swiss clockwork, “soft” and “yielding” may not be the first adjectives that come to mind, so researchers at Columbia University get full marks for creativity. By replicating a watch mechanism called the Geneva drive in a soft hydrogel, they created a biocompatible robot that could tick along to release doses of drugs from inside the body.
Samuel Sia, a Columbia University professor of biomedical engineering, created the watch-inspired biobot with one simple hydrogel gear that’s embedded with iron nanoparticles, enabling researchers to turn it with an external magnet. Each click forward brings a hollow chamber into line with an opening so a dose of liquid can flow out. Sia suggests that in cancer care such implants could enable the localized delivery of a chemotherapy drug and spare the rest of the body from the drug’s toxic effects. When he tested his device in mice with bone cancer, he found that drug doses delivered by the biobot killed more tumor cells and spared more cells elsewhere in the body than a typical systemic chemo treatment. What’s more, with an external controller to trigger the device’s every tick, doses could be delivered only when a doctor sees fit.
The trickiest part of the design process was getting the material just right, Sia says, not too soft, but not too hard. “You don’t want to lose the nice properties of hydrogels, but if your material is collapsing like Jell-O, it’s hard to make robots out of it,” he says. “It has to be stiff enough to work like a tiny implantable machine.”
Today’s surgeons use various gripping tools to wrangle with your viscera; they may use one tool to nudge aside fat tissue, for example, while using another to cut away tumors on the kidney. While surgeons are scrupulous in their attempts to avoid unnecessary harm to the tender flesh, they might have an easier time with Xuanhe Zhao’s soft tools.
Zhao, an MIT associate professor in the mechanical as well as the civil and environmental engineering departments, devised a series of robotic gadgets made of hydrogel, each fabricated in the form of interlocking cubes with hollow interiors. To activate a device, a syringe pump injects water into the robot in certain combinations to make it curl up or stretch out, producing fast and forceful movements. One grabber bot, which resembles a five-fingered hand, demonstrated its deftness by seizing hold of a swimming goldfish—and then releasing it unharmed. Zhao’s team is now collaborating with medical groups on hydrogel “hands” that could grasp organs in robotic surgeries.
Another application could be a soft robot that wraps around the intestines and contracts rhythmically, mimicking the wavelike peristalsis process that moves food through the digestive tract. For tomorrow’s soft robots, it seems that everything inside the body is up for grabs.
This article appears in the April 2017 print issue as “Medical Robots Go Soft.”