A miniature ultrasonic surgical device based on a flextensional configuration with a pre-stressed piezoelectric stack

Ultrasonic bone scalpels are known to offer benefits of low cutting force, high precision, low microdamage around the cut site, and tissue selectivity in surgical procedures. However, all current commercial devices are too large to be integrated with the flexible endo-wrist of a surgical robot, and therefore, there is a significant gap for innovation in miniature devices. Ultrasonic bone scalpels in use in clinical settings are all based on a bolted Langevin transducer (BLT), which consists of a pre-stressed piezoceramic ring stack, two end masses, and a cutting blade. The BLT-based device must operate in resonance to achieve sufficient displacement amplitude at the surgical tip to cut through bone, and this dictates its size. Flextensional transducers have emerged as an alternative, but these transducers generally contain a low volume of piezoelectric driving material, and hence cannot excite the required displacement amplitude, and their reliance on adhesive bonds in their fabrication means they fail at the excitation levels required for a bone surgery device. We present a flextensional configuration that forms an ultrasonic surgical device, where the vibration-amplifying metal caps are excited by a pre-stressed piezoelectric stack. In vitro ultrasonic bone cutting tests facilitated with a Kuka robot are performed for a range of cutting speeds and penetration rates. The results demonstrate effective integration with a Kuka robot and that bone cutting can be achieved with an extremely low cutting force ( < 1 N) and high precision (the width of the bone cut presents under 6% deviation from the thickness of the blade). The flextensional device overcomes both the large size of conventional ultrasonic osteotomy devices and the displacement amplitude limitations of other miniaturisation approaches. Integration with an articulated robotic endo-wrist is enabled, establishing a foundation for low-force and high-precision ultrasonic bone cutting in minimally invasive, anatomically constrained robotic surgical environments.