Creating swarms of soft, robotic hands that can safely dissolve within a living body once they've performed surgical procedures or delivered drugs just got a step closer thanks to work done by John Hopkins University scientists. They've created minute biodegradable microgrippers by adding stiff polymers containing magnetic nanoparticles to soft hydrogels, allowing them be magnetically guided to any location in the body.
Earlier Dr David Gracias demonstrated how the 300-micrometer microgrippers were able to retrieve tissue samples from the bile duct of a live pig. While the tests were successful, the microgrippers they used were metallic in nature. That posed a problem of retrieval. Even when drawn out with magnets there was a chance that some microgrippers might be left behind within the body.
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To tackle that problem, the researchers decided to make the microgrippers out of biodegradable materials. They created a thin layer of rigid polymers, embedded with magnetic nanoparticles that they could substitute for metal. These stiff polymers were integrated into soft hydrogels to create tiny robotic hands that could be magnetically guided with a magnetic probe. They're also strong enough to wrap around cells, enabling them to perform biopsies or deliver drugs in previously inaccessible areas.
"The use of a swellable hydrogel and a very stiff non-swellable polymer backbone is a unique design principle, and achieves a balance between large strain derived from the hydrogel and relatively high strength from the polymer which are both needed to actuate and securely grasp cargo or excise soft matter," Gracias tells Gizmag.
To get the microgrippers to work without the need for any wires, tethers, batteries or external power sources, the team focused on making them responsive to temperature. In a cold state, they are quite compact and can pass through small catheters easily into the body. Once they reach the desired location, and warm up to the body's temperature, they activate and unfold. They can then fold in the opposite direction to grip tissue; the goal is to have them carry out tasks entirely by themselves, without human direction.
"They could perform robotic tasks such as cell capture autonomously in response to variable thermal environments," says Gracias.
The team's work addresses some of the biggest issues in creating viable mechanized nanostructures, the questions of how to mass-produce and power them. Envision the challenges involved in creating, powering and operating tens of thousands of dust-sized surgical tools, each smaller than a millimeter, with precision.
"Using the approaches we discuss, this would no longer be a challenge," Gracias tells us. "We have already shown that we can mass-produce such structures and since they are actuated by swelling on cue from the environment, they can also be powered and operated in unison at small size scales."
The scientists plan to tailor the properties of the biodegradable polymers further, evaluate safety and also modify them for specific surgical applications. They'll also optimize the overall design of the microgrippers for more force, momentum and speed. Gracias believes that origami-inspired, polymer-based micogrippers are key to creating tiny, autonomous, bio-dissolvable surgical devices.
"I'd love to be able to create mimics of the sophisticated machines seen in insects and other microorganisms that are inherently made of polymer based (soft) materials and can perform amazing mechanized feats at small size scales," says Gracias.
A paper detailing the development was recently published in the journal ACS Applied Materials & Interfaces.
Check out a video of the microgrippers below.