Borrowing from methods used to produce optical fibers, researchers from EPFL and Imperial College have created fiber-based soft robots with advanced motion control that integrate other functions, such as electrical and optical sensing and targeted delivery of fluids.
In recent decades, catheter-based surgery has revolutionized medicine, providing physicians with 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 catheters today are highly engineered automated devices, in most cases the task of advancing them through the body to the site of intervention remains a manual and time-consuming procedure.
By combining advances in the development of functional fibers with advances in smart robotics, researchers from the Photonic Materials and Fiber Devices Laboratory in the College of Engineering at EPFL have created multifunctional catheter-shaped soft robots that, when used as catheters, can be remotely steered. destination or may find its own way through semi-autonomous control. “This is the first time we can create soft, catheter-like structures with such expandability that can integrate complex functions and be directed, potentially, within the body,” says Fabian Soren, the study’s principal investigator. Their work has been published in the journal advanced science.
The researchers created the fibers through a heat drawing process commonly used to produce the fibers optical cablesSimilar to pulling a long string of cheese out of the fondue and letting it harden. The choice of materials was critical, with elastomers — flexible polymers that return to their original shape when stretched — the preferred candidate: in addition to being flexible, they are soft enough to minimize lesions to the body’s soft tissues. But, says Andreas Lieber, first author of the study, “Historically, thermodrawing has been restricted to rigid materials. Fortunately, our group has identified a class of thermoplastic elastomers that can be drawn out and maintain their elastic properties after drawing.”
Integration of motion control, sensing, and drug delivery
To generate long fibers that feature multiple channels along their entire length, the researchers had to finely tune the parameters of the drawing process. An important feature of the process is the interaction between the viscosity of the material, which allows you to draw continuous fibers, and Surface tensionwhich can cause the ducts inside to collapse, ”says Fabian Soren.
By getting the material properties, drawing speed, and temperature just right, the team can reliably produce the continuous channels, carefully arranged within the fiber on a micrometer scale, that are essential to giving the fiber its robotic capabilities. For example, by using a motor to pull one or several tendons inserted into the channels—a well-established approach in smart catheters—doctors can control the direction of the end of the fibers to guide them through the body.
Besides channels, the fibers can be equipped with a variety of elements using the heat drawing process. “In addition to strings, fibers can incorporate optical guides, electrodes, and microchannels that enable drug delivery, imaging, electrical recording and stimulation, and other tools commonly used in robotics and medical applicationsLieber explains.
These functional elements also open the door for autonomous, fibrous-shaped robots. Lieber continues, “Integrated optical guides give fibers a sense of sight. They can detect and avoid obstacles in their path and even find target objects, such as cavities, all on their own.” Crucial to this effort is a complex control algorithm and software user interface that was developed from the ground up by the team in the lab.
Highly scalable manufacturing
While it may seem complicated, this multi-material fiber is remarkably easy to produce. “We use optical fiber manufacturing technology, which is very scalable. You can generate hundreds of kilometers of optical fibers overnight. As a result, our manufacturing approach provides a new, scalable way to create soft catheter-like structures with an unprecedented combination of functionality,” he says. Soren.
Remote-controlled catheters are just one of the many exciting potential applications that this new class of fiber-based soft robots could make possible. “A string-based approach to motion control is the first step in developing smart thermally drawn catheters. The next step will involve moving toward electric or magnetic modes of operation and testing the exciting opportunities of these fibers one step closer to clinical applications,” says Burak Temelkuran, co-author and group lead at Hamlin Center for Robotic Surgery at Imperial College.
Smart mattresses, soft prostheses, and industrial robots
Soft robotic fibers also have a wide range of applications beyond the human body. Mattresses can be equipped with them to monitor or alter sleep quality Material properties In response to perceived pressure and physiological parameters, giving users a better night’s sleep.
The fibers can be used to create soft prostheses that are able to respond to increased mechanical stress on the joint by becoming stiffer. Industrial or environmental sensor applications may include self-guiding Soft robots which navigates based on information sensed by built-in heat sensors, tactile sensors, and even electrical and optical systems for vision.
Andreas Leber et al, Highly Integrative Multi-Material Fibers for Soft Robotics, advanced science (2022). DOI: 10.1002/advs.202204016
Ecole Polytechnique Federale de Lausanne
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