Minimally invasive surgeries in which surgeons gain access to internal tissues through natural orifices or small external excisions are common practice in medicine. They are performed for problems as diverse as delivering stents through catheters, treating abdominal complications, and performing trans­nasal operations at the skull base in patients with neuro­logical conditions. The ends of devices for such surgeries are highly flexible to enable the visualization and specific mani­pulation of the surgical site in the target tissue. In the case of energy-deli­vering devices that allow surgeons to cut or dry tissues, and stop internal bleeds deep inside the body, a heat-genera­ting energy source is added to the end of the device. However, presently available energy sources delivered via a fiber or electrode, such as radio frequency currents, have to be brought close to the target site, which limits surgical precision and can cause unwanted burns in adjacent tissue sections and smoke develop­ment.

Laser technology, which already is widely used in a number of external surgeries, such as those performed in the eye or skin, would be an attrac­tive solution. For internal surgeries, the laser beam needs to be precisely steered, positioned and quickly repositioned at the distal end of an endoscope, which cannot be accomplished with the currently available rela­tively bulky technology. Now, robotic engineers led by Wyss Associate Faculty member Robert Wood, post­doctoral fellow Peter York at Harvard University's Wyss Institute for Biolo­gically Inspired Engineering and John A. Paulson School for Engineering and Applied Science (SEAS) have developed a laser-steering microrobot in a minia­turized 6 x 16 millimeter package that operates with high speed and precision, and can be integrated with existing endoscopic tools. Their approach could help significantly enhance the capa­bilities of numerous minimally invasive surgeries.

“To enable minimally invasive laser surgery inside the body, we devised a micro­robotic approach that allows us to precisely direct a laser beam at small target sites in complex patterns within an anatomical area of interest,” said York. “With its large range of arti­culation, minimal footprint, and fast and precise action, this laser-steering end-effector has great potential to enhance surgical capabilities simply by being added to existing endoscopic devices in a plug-and-play fashion.” The team needed to overcome the basic challenges in design, actuation, and micro­fabrication of the optical steering mechanism that enables tight control over the laser beam after it has exited from an optical fiber. These challenges, along with the need for speed and precision, were exa­cerbated by the size constraints - the entire mechanism had to be housed in a cylindrical structure with roughly the diameter of a drinking straw to be useful for endoscopic procedures.

“We found that for steering and re-directing the laser beam, a configuration of three small mirrors that can rapidly rotate with respect to one another in a small galvano­meter design provided a sweet spot for our minia­turization effort,” said Rut Peña, a mechanical engineer with micro-manu­facturing expertise in Wood's group. “To get there, we leveraged methods from our microfabrication arsenal in which modular components are laminated step-wise onto a super­structure on the millimeter scale – a highly effective fabri­cation process when it comes to iterating on designs quickly in search of an optimum, and delivering a robust strategy for mass-manu­facturing a successful product.”

The team demons­trated that their laser-steering end-effector, miniaturized to a cylinder measuring merely 6 millimeter in diameter and 16 millimeter in length, was able to map out and follow complex tra­jectories in which multiple laser ablations could be performed with high speed, over a large range, and be repeated with high accuracy. To further show that the device, when attached to the end of a common colono­scope, could be applied to a life-like endo­scopic task, York and Peña, advised by Wyss Clinical Fellow Daniel Kent, success­fully simulated the resection of polyps by navigating their device via tele-operation in a benchtop phantom tissue made of rubber. Kent also is a resident physician in general surgery at the Beth Israel Deaconess Medical Center.

“In this multi-disci­plinary approach, we managed to harness our ability to rapidly prototype complex micro­robotic mechanisms that we have developed over the past decade to provide clinicians with a non-disruptive solution that could allow them to advance the possi­bilities of minimally invasive surgeries in the human body with life-altering or poten­tially life-saving impact,” said Wood, Charles River Professor of Engi­neering and Applied Sciences at SEAS. Wood's micro­robotics team together with techno­logy trans­lation experts at the Wyss Institute have patented their approach and are now further de-risking their medical techno­logy as an add-on for surgical endoscopes. (Source: Wyss Inst.)

Reference: P. A. York et al.: Microrobotic laser steering for minimally invasive surgery, Science Robot. 6, eabd5476 (2021); DOI: 10.1126/scirobotics.abd5476

Link: Microrobotics Lab,  Harvard John A. Paulson School of Engineering, Harvard University, Boston, USA