Engineering news
Taking up much less space than current bulky robots in operation rooms, the ‘mini-RCM’ was developed by a member of Harvard University’s Wyss Institute and a Sony robotics engineer.
The origami-inspired miniature Remote Centre of Motion manipulator is the size of a tennis ball, weighs about as much as a penny and has successfully performed a difficult mock surgical task.
Wyss Associate Faculty member Robert Wood and Sony’s Hiroyuki Suzuki used the Pop-Up MEMS manufacturing technique developed in Wood’s lab, in which materials are deposited on top of each other in layers that are bonded together, then laser-cut in a specific pattern that allows the desired three-dimensional shape to “pop up” like a child’s pop-up picture book. The technique simplifies the mass production of small, complex structures that would otherwise have to be painstakingly constructed by hand.
The team created a parallelogram shape to serve as the main structure of the robot, then fabricated three linear actuators to control its movement – one parallel to the bottom of the parallelogram that raises and lowers it, one perpendicular to the parallelogram that rotates it, and one at the tip of the parallelogram that extends and retracts the tool in use.
“The result was a robot that is much smaller and lighter than other microsurgical devices previously developed in academia,” a research announcement said.
The linear actuators are built around a piezoelectric ceramic material that changes shape when an electrical field is applied. The shape change pushes runner units along rails, and that linear motion moves the robot. Because piezoelectric materials inherently deform as they change shape, the team also integrated LED-based optical sensors to detect and correct any deviations from the desired movement, such as those caused by hand tremors.
To mimic the conditions of a teleoperated surgery, the team connected the mini-RCM to a Phantom Omni haptic device, which manipulated the mini-RCM in response to the movements of a user’s hand controlling a pen-like tool.
The first test evaluated a human’s ability to trace a tiny square smaller than the tip of a ballpoint pen, looking through a microscope and either tracing it by hand, or tracing it using the mini-RCM. The mini-RCM tests dramatically improved user accuracy, reducing error by 68% compared to manual operation – an especially important quality, given the precision required to repair small and delicate structures in the human body.
After the mini-RCM’s success on the tracing test, the researchers then created a mock version of a surgical procedure called retinal vein cannulation, in which a surgeon must carefully insert a needle through the eye to inject drugs into the tiny veins at the back of the eyeball. They fabricated a silicone tube the same size as a retinal vein – about twice the thickness of a human hair – and punctured it with a needle attached to the end of the mini-RCM without causing local damage or disruption.
As well as its ability to perform delicate manoeuvres, the mini-RCM’s small size reportedly makes it easy to set up and install. It could also be removed by hand in the event of a complication or electrical outage.
“The Pop-Up MEMS method is proving to be a valuable approach in a number of areas that require small yet sophisticated machines, and it was very satisfying to know that it has the potential to improve the safety and efficiency of surgeries to make them even less invasive for patients,” said Wood.
The researchers aim to increase the force of the robot’s actuators to cover the maximum forces experienced during an operation, and improve its positioning precision. They are also investigating using a laser with a shorter pulse during the machining process, to improve the mini-linear actuators’ sensing resolution.
The work was published in Nature Machine Intelligence.
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