Robot arm can be soft or rigid Thursday, 03 August 2017

Endoscopes used inside the body should ideally be soft when being manoeuvred into position but rigid when conducting surgical tasks. A new hybrid rigid-soft robotic arm may offer the best of both worlds.

A team from the Harvard School of Engineering and Wyss Institute for Biologically Inspired Engineering have developed the arm with integrated sensing, flexibility, and multiple degrees of freedom.

Researcher Tommaso Ranzani said soft robots are promising for surgical applications because they can match the stiffness of the body, meaning they won’t accidentally puncture or tear tissue. However, at small scales, soft materials cannot generate enough force to perform surgical tasks.

“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,” he said.  

“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.”

Inspired by biology, the team developed a hybrid model that used a rigid skeleton surrounded by soft materials. It is based on pop-up fabrication and soft lithography so it lies flat on an endoscope until it arrives at the desired spot, then pops up to assist in surgical procedures.

Previous pop-up manufacturing techniques relied on actuation methods that require high voltages or temperatures to operate, something that wouldn’t be safe in a surgical tool directly manipulating biological tissues and organs.

So, the team integrated soft actuators into the pop-up system. These are powered by water and connected to the rigid components with an irreversible chemical bond, without the need of any adhesive.

The team demonstrated the integration of simple capacitive sensing that can be used to measure forces applied to the tissue and to give the surgeon a sense of where the arm is and how it’s moving.

[Scanning electron microscope images of the hybrid soft pop-up actuators, coloured to differentiate between the soft (in yellow) and the rigid structure (in blue). Image: Wyss Institute at Harvard University]