Ideally, Okamura says, she’d like to figure out the interaction forces without using a force sensor at all, because the sensors have to be sterile and biocompatible. They also have to be small enough and cheap enough for medical applications.
If Okamura gets her way, a complex computer model would handle all the feedback by estimating the forces made by the movement of the robotic tools. “Developing some sort of generic or even surgery-specific interface that gives you many different kinds of tactile or force feedback–like textures on your fingers, fine force feedback on your fingertips, and gross force feedback on your arms–is a really huge challenge,” says Mark Ottensmeyer, lead investigator in tissue-property measurement and modeling and a developer of electromechanical systems for medical/surgical training at the Simulation Group. “You have to have some separate actuator, like a motor, electromechanical, hydraulic, or pneumatic device. Then you have to get a computer to control it all. So it really is a systems type of thing.”
Engineers at the Center for Advanced Surgical and Interventional Technology (CASIT) are developing a haptic feedback system for robot-assisted surgeries as well. Their system works by mounting arrays of pneumatic balloons onto the master robot and attaching force sensors to the patient-side robotic tools. The sensor measures the force being applied to the tissue and translates it into pressure on the actuator attached to the joystick touching the surgeon’s hand, explains Martin Culjat, the engineering research director at CASIT.
“The addition of tactile information will enable surgeons to ‘feel’ tissue characteristics, appropriately tension sutures, identify pathologic conditions, and will enable expansion of MIS to other surgical procedures and simulations,” says Culjat.
However, these technologies still need many years of research before they will be ready for commercial systems. In the interim, Okamura’s team has developed a system using visual haptics, called sensory substitution. As the surgeon ties a suture, dots on the surgical instruments change color relative to the applied force. Requiring no changes to the control system, this approach is easier to implement and will probably get into the operating room faster than devices that send haptic feedback to the surgeon’s hand, says Okamura.