A soft pop-up robot arm performs tissue counter-traction during an ex-vivo test on a porcine stomach. [Image courtesy of Harvard University]
Flexible endoscopes fit through narrow passages to reach difficult parts of the body. Once they reach their target, the devices need rigid surgical tools to be able to manipulate or remove tissues.
Researchers from Harvard’s Wyss Institute for Biologically Inspired Engineering and John A. Paulson School of Engineering and Applied Sciences (SEAS) developed this robotic arm using a manufacturing paradigm that involves pop-up fabrication and soft lithography. The robotic arm lies flat on an endoscope until it reaches a certain location where it pops up to help in surgical procedures.
Soft robotics are especially helpful in surgical procedures because they are able to match the stiffness of the human body. Because they’re soft, the risk of puncturing or tearing tissue is eliminated. The drawback to soft robotics, however, is that soft materials sometimes cannot perform surgical tasks because they don’t have enough force.
“At the millimeter scale, a soft device becomes so soft that it can’t damage tissue but it also can’t manipulate the tissue in any meaningful way,” Tommaso Ranzani, a Postdoctoral Fellow at the Wyss Institute and SEAS and co-author of the paper, said in a press release. “That limits the application of soft microsystems for performing therapy. The question is, how can we develop soft robots that are still able to generate the necessary forces without compromising safety.”
The researchers created a hybrid model that had a rigid skeleton encased in soft material. It was manufactured using an origami-inspired pop-up fabrication method that was developed by Robert Wood, a paper co-author.
Other pop-up manufacturing methods use actuation methods that need high voltages and temperatures to operate. Those conditions are not safe for surgical tools that manipulate biological tissues and organs. So soft actuators were the researchers’ solution.
“We found that by integrating soft fluidic microactuators into the rigid pop-up structures, we could create soft pop-up mechanisms that increased the performance of the actuators in terms of the force output and the predictability and controllability of the motion,” said Sheila Russo, postdoctoral fellow at the Wyss Institute and SEAS and lead author of the paper. “The idea behind this technology is basically to obtain the best of both worlds by combining soft robotic technologies with origami-inspired rigid structures. Using this fabrication method, we were able to design a device that can lie flat when the endoscope is navigating to the surgical area, and when the surgeon reaches the area they want to operate on, they can deploy a soft system that can safely and effectively interact with tissue.”
The soft actuators for the robot are powered using water and are connected to the rigid components of the arm using an irreversible chemical bond – no need for adhesives. The robot also had capacitive sensing that could measure forces applied to tissues to give surgeons an idea of where the arm is and how it is moving. This fabrication method allows for the surgical arm to be manufactured in bulk. All the materials used are also biocompatible.
The robotic arm features a suction cup that allows for the arm to interact with tissues safely. The researchers tested the arm ex vivo by emulating a complicated endoscopic procedure on pig tissues. It was able to successfully and safely manipulate the tissue.
“The ability to seamlessly integrate gentle yet effective actuation into millimeter-scale deployable mechanisms fits naturally with a host of surgical procedures,” Wood said. “We are focused on some of the more challenging endoscopic techniques where tool dexterity and sensor feedback are at a premium and can potentially make the difference between success and failure.”
The researchers also showed that the device was able to be scaled down to 1 mm that could be beneficial for tighter endoscopic procedures in the lungs and brain. They hope to test the device in vivo soon.
“Our technology paves the way to design and develop smaller, smarter, softer robots for biomedical applications,” Russo said.
The research was funded by the DARPA “Atoms to Product” program and the Wyss Institute for Biologically Inspired Engineering and was published in the journal Advanced Materials Technology.
