ROBOImplant II: Development of a Noninvasive Controller/Actuator for Wireless Correction of Orthopedic Structural Deformities

An implantable actuator and its accompanying driver circuit are presented for the purpose of lengthening bones and correcting skeletal deformities without requiring physical contact between the operator and the implanted device. This system utilizes magnetic coupling to form a magnetic gear, allowing an external motor to drive an implantable telescoping rod. The accompanying electronics are able to monitor the progress, in the form of turns delivered, as well as detect procedural errors, such as magnet decoupling. The force applied by the implanted telescoping rod can be accurately measured by monitoring the current necessary for the external controller to drive the extension of the implanted rod. After characterization, the system was shown to reliably deliver extension distances within 34 μm and maintain coupling out to 70 mm. The system is also able to measure torques as low as 0.12 mN m. System variability and accuracy of external monitoring are addressed.