Minimally invasive laparoscopic surgery, in which a surgeon uses tools and a tiny camera inserted into small incisions to perform operations, has made surgical procedures safer for both patients and doctors. Surgical robots further assist surgeons by allowing them to manipulate multiple tools at once with greater precision, flexibility, and control than is possible with traditional techniques. These robotic systems are extremely large, often taking up an entire room and their tools can be much larger than the delicate tissues and structures on which they operate.
Researchers created an origami-inspired, miniature, remote center of motion manipulator (mini-RCM) that is the size of a tennis ball, weighs about as much as a penny, and successfully performed a difficult mock surgical task. To create the miniature surgical robot, the team used the Pop-Up MEMS manufacturing technique 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.” This technique greatly simplifies the mass-production of small, complex structures that would otherwise have to be constructed by hand.
A parallelogram shape was created to serve as the main structure of the robot; the team then fabricated three linear actuators (mini-LAs) to control the robot’s 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.
The mini-LAs are built around a piezoelectric ceramic material that changes shape when an electrical field is applied. The shape change pushes the mini-LA’s “runner unit” along its “rail unit” like a train on train tracks, and that linear motion is harnessed to move the robot. Because piezoelectric materials inherently deform as they change shape, the team also integrated LED-based optical sensors into the mini-LA 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 device, which manipulated the mini-RCM in response to the movements of a user’s hand controlling a pen-like tool. Their first test evaluated a human’s ability to trace a tiny square smaller than the tip of a ballpoint pen while looking through a microscope and either tracing it by hand or tracing it using the mini-RCM. The 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 therapeutics into the tiny veins at the back of the eyeball. They fabricated a silicone tube the same size as the retinal vein (about twice the thickness of a human hair) and successfully punctured it with a needle attached to the end of the mini-RCM without causing local damage or disruption.
In addition to its efficacy in performing delicate surgical maneuvers, the mini-RCM’s small size provides another important benefit: it is easy to set up and install and, in the case of a complication or electrical outage, the robot can be easily removed from a patient’s body by hand.
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-LA’s sensing resolution.