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Soft Robots

By Joe Sugarman
Rebecca Schulman, David H. Gracias, and Thao Nguyen are faculty members in the Johns Hopkins Whiting School of Engineering.
George Wylesol

One of the challenges with even the most advanced medical implants is that they’re often static, sometimes bulky affairs, whose inorganic components can be rejected by the body. But what if you could implant a smart device capable of interacting with a person’s own cells, one that did not rely on cumbersome wires, batteries, or tethers? Imagine that it could work autonomously to diagnose an issue and adapt to correct a health problem. Imagine, in other words, if a medical implant was a “soft robot” instead— composed of a material that’s extremely pliant, biocompatible, and with the smarts of a computer.

Three faculty members in the Johns Hopkins Whiting School of Engineering—Rebecca Schulman, David H. Gracias, and Thao “Vicky” Nguyen— have taken the first baby steps in achieving such a technology by successfully altering the size of a hydrogel, a jellylike material composed mainly of water, and implanting it with DNA.

The researchers created a variety of wafer-thin hydrogels and exposed the material to several sequences of DNA in petri dishes. Over the course of hours, they watched as the roughly 1-millimeter-square gels grew in volume a hundredfold and then halted the growth, as instructed by the DNA sequence. These special DNA sequences are analogous to a computer code, working to alter the material. And while materials scientists have long been able to influence the size and shape of gels by changing temperature or pH, this was the first time that researchers have been able to cause the material to grow—and cease growing— by using DNA.

“There has been a lot of effort within the scientific community to make materials that can be programmed with the same level of programmability as software code,” Gracias says. “DNA is like a computer code. You can change the sequences to get the material to respond how you want. Just as computer software can direct specific tasks, DNA sequences can cause a material to bend or expand in a certain way at a specific site.”

What this experiment means is that researchers may someday be able to use DNA to program flexible materials— what are called soft robots—to carry out tasks in intelligent ways in the body. Applications in the field of medicine range from smart implants, such as heart valves and stents that swell or close on their own based on biological stimuli, or jellylike bandages that control the spread of infection. “My dream is to have a soft robot that acts like an immune cell,” Gracias says. “It would sense the pathogen and gobble it up.”

Now that the researchers have proved they can make a gel grow substantially in volume and then stop, the team plans to work on achieving the opposite effect. “We showed that hydrogels can grow, but the thing everyone wants to know is, Can they shrink back down? That’s the next big question,” says Schulman, an expert in nanotechnology.

Schulman also points out that the technology could be used as a diagnostic tool, programming the particle-sized robots to look for abnormalities in the body. “Perhaps you could have them detect inflammation or forms of cancer at developmental stages by reading RNA,” Schulman says (RNA, or ribonucleic acid, effectively carries messages from our DNA). “These robots would do the diagnosis and then carry out the response. That’s a very new idea, and we’re that much closer to it.”

robot activity
Dalbert Vilarino

Using hydrogels exposed to sequences of DNA, researchers were able to program the material to respond as desired. “Just as computer software can direct specific tasks, DNA sequences can cause a material to bend or expand in a certain way at a specific site,” David Gracias says. This could lead to smarter medical implants.

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