A reliable, battery-free and implantable magnetic sensing system for wireless monitoring of spinal motion in rats and humans

Continuous monitoring of spinal and joint motions in patients allows surgeons to optimize patient rehabilitation. However, the current monitoring approaches are achieved via tethered devices, which are inconvenient and associated with a risk of infections. In this study, we developed and validated a new type of reliable wireless, battery-free, and implantable sensing system (RWBS) for the real-time monitoring of physiological bending of spines and joints. The RWBS exploits the unique movement-sensing capabilities of an implantable flexible magnetic strip, the signals from which are detected with an external receiver. We implanted this magnetic strip beneath the skins of Sprague Dawley rats and human cadavers and demonstrated that in combination with the receiver, the magnetic strip enabled real-time in vivo and wireless monitoring of motions in both rats (anesthetized/awake) and human cadavers. The adaptability of RWBS in other human bones has been verified by sensing the motions of elbow joints and knee joints. The simple design of the RWBS allowed it to continue functioning in vivo after the magnetic strip had been broken into two or more pieces, indicating its high reliability. Thus, the RWBS is biocompatible, exhibits excellent functionalities, and can be conveniently implemented in both rats and humans. This device will help to facilitate the post-surgery monitoring of spinal and joint movements of human patients.