Smart Cooling-Integrated End Effector for Bone Drilling in Robotic Surgery

Orthopedic surgery plays a crucial role in the treatment of fractures. When a bone breaks, fixation using screws or plates is required to ensure proper healing and stability, and the first step of this procedure is drilling precise pilot holes in the bone. In bone drilling, maintaining the temperature below 47 °C is critical to prevent thermal damage. Conventional cooling methods use continuous coolant flow, which obstructs the surgeon’s visual field. This study presents a robotic end effector with a rule-based, temperature-triggered cooling system mounted on a UR5e collaborative robot. In the first experimental campaign, a single-threshold (44 °C) ON/OFF strategy was evaluated with repeated trials. In response to the limitations identified, the controller was upgraded to (i) a three-level pulse-width-modulated (PWM) coolant law (0/30/50% at <42, 42–46 and ≥46 °C), (ii) automatic suction coupled to coolant activation, and (iii) a force-adaptive spindle-speed law driven by the robot’s wrist force–torque sensor (speed reduction when the thrust-force increase exceeds 19 N). A second campaign of 24 ex vivo femur trials (two drill diameters × three spindle-speed levels × two feed rates × with/without cooling, one hole per condition) showed that temperature-triggered cooling reduced the peak temperature measured by a thermocouple 0.5 mm from the hole from 57.5 ± 9.7 °C to 46.4 ± 3.8 °C (mean paired reduction 11.2 °C, 95% CI 5.5–16.9 °C; paired t(11) = 4.34, p = 0.001), although three of the 12 cooled holes still exceeded 47 °C, while the pumps were active for only 40.3% of the drilling time on average. An integrated suction mechanism removes debris and excess coolant, which is intended to improve visibility at the drilling site (assessed qualitatively in this study); cooling and suction were associated with a lower measured hole-diameter error in the tested samples. The cobot provides six-component wrist force–torque data as well as the position and velocity of the tool synchronously, enabling real-time monitoring of surgical drilling and acquisition of multi-sensor data useful for continuous process improvement. The results are obtained on non-perfused ex vivo bone and should be regarded as a laboratory proof of concept.