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Steerable soft 'fiber' robots could enhance medical applications

29 Nov 2022

Using optical fiber making ideas enables development of soft robots with advanced motion control.

Researchers from EPFL, Lausanne, Switzerland, and Imperial College, London, have created fiber-based soft robots with advanced motion control that integrate other functionalities, such as electric and optical sensing and targeted delivery of fluids.

In recent years, catheter-based surgery has transformed medicine, giving doctors a minimally invasive way to do anything from placing stents and targeting tumors to extracting tissue samples and delivering contrast agents for medical imaging.

While today’s catheters are highly engineered robotic devices, in most cases, the task of pushing them through the body to the site of intervention continues to be a manual and time-consuming procedure.

Combining advances in the development of functional fibers with developments in smart robotics, researchers from the Laboratory of Photonic Materials and Fiber Devices in EPFL’s School of Engineering have created multifunctional catheter-shaped soft robots that, when used as catheters, could be remotely guided to their destination or possibly even find their own way through semi-autonomous control.

“This is the first time that we can generate soft catheter-like structures at such scalability that can integrate complex functionalities and be steered, potentially, inside the body,” said Fabien Sorin, the study’s principal investigator. The work is described in Advanced Science.

The researchers created the fibers with the thermal drawing process commonly used to produce fiber optic cables. Material choice was critical, with elastomers being the preferred candidate.

But, said Andreas Leber, the first author of the study, “Historically, thermal drawing has been restricted to hard materials. Fortunately, our group had identified a class of thermoplastic elastomers that can be drawn and maintain their elastomeric properties after drawing.”

Motion control, sensing, and drug delivery

To generate long fibers featuring multiple channels along their entire length, the researchers had to fine-tune the drawing process parameters. “An important characteristic of the process is the interplay between the viscosity of the material, which lets you draw a continuous fiber, and the surface tension, which can cause the channels within them to collapse,” said Fabien Sorin.

By optimizing the material properties, drawing speed, and fabrication temperature, the team could reliably produce the continuous channels, arranged within the fibers at a micrometer scale, needed to give the fiber its robotic capabilities. For example, by using a motor to pull on one or several tendons introduced into channels, doctors could control the orientation of the end of the fiber to guide it through the body.

Besides channels, the fibers can be equipped with a variety of elements using the thermal drawing process. “In addition to the tendons, the fibers can integrate optical guides, electrodes, and microchannels that enable drug delivery, imaging, electrical recording and stimulation, and other tools commonly used in robotics and medical applications,” said Leber.

These functional elements also open the door to autonomous fiber-shaped robots. “The integrated optical guides give fibers the sense of sight. They can detect and avoid obstacles in their trajectory and even find targeted objects, such as cavities, all on their own,” said Leber.

Sorin added, “We use optical fiber fabrication technology, which is very scalable. You can generate hundreds of kilometers of optical fiber overnight. As a result, our fabrication approach brings a novel, scalable way to make soft catheter-like structures with an unprecedented combination of advanced functionalities.”

Remotely controlled catheters are only one of many exciting potential applications that this new class of fiber-based soft robots could enable. “The tendon-based approach to motion control is a first step of the development of thermally drawn smart catheters.

The next step will involve moving toward electrical or magnetic actuation modes and testing the exciting opportunities of such fibers one step closer to clinical applications,” says Burak Temelkuran, co-author and group leader at the Hamlyn Center for Robotic Surgery at Imperial College.

Mattresses, prosthetics and robots

Such soft robotic fibers also have many applications outside the human body: mattresses could be equipped with them to monitor sleep quality or change their material properties in response to sensed pressure and physiological parameters.

The fibers could also be used to create soft prosthetics capable of responding to excess mechanical stress on a joint by becoming stiffer. Industrial or environmental sensing applications could include self-guiding soft robots that navigate based on information sensed by integrated heat sensors, haptic sensors, and even electrical and optical systems for vision.

Mad City Labs, Inc.AlluxaCHROMA TECHNOLOGY CORP.Universe Kogaku America Inc.TRIOPTICS GmbHABTechLASEROPTIK GmbH
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