Clinical viability of magnetic bead implants in muscle

Abstract

Human movement is accomplished through muscle contraction, yet there does not exist a portable system capable of monitoring muscle length changes in real time. To address this limitation, we previously introduced magnetomicrometry, a minimally-invasive tracking technique comprising two implanted magnetic beads in muscle and a magnetic field sensor array positioned on the body’s surface adjacent the implanted beads. The implant system comprises a pair of spherical magnetic beads, each with a first coating of nickel-copper-nickel and an outer coating of Parylene C. In parallel work, we demonstrate submillimeter accuracy of magnetic bead tracking for muscle contractions in an untethered freely-roaming avian model. Here, we address the clinical viability of magnetomicrometry. Using a specialized device to insert magnetic beads into muscle in avian and lagomorph models, we collect data to assess gait metrics, bead migration, and bead biocompatibility. For these animal models, we find no gait differences post-versus pre-implantation, and bead migration towards one another within muscle does not occur for initial bead separation distances greater than 3 cm. Further, using extensive biocompatibility testing, the implants are shown to be non-irritant, non-cytotoxic, non-allergenic, and non-irritating. Our cumulative results lend support for the viability of these magnetic bead implants for implantation in human muscle. We thus anticipate their imminent use in human-machine interfaces, such as in control of prostheses and exoskeletons and in closed-loop neuroprosthetics to aid recovery from neurological disorders.

Untethered muscle tracking using magnetomicrometry

“…In parallel work, we also demonstrate the viability of magnetic bead implants for human use, verifying comfort, lack of implant migration, and biocompatibility (Taylor, Clark, et al, 2022). Due to the untethered nature of MM, this technique has applications in prosthetic and exoskeletal control.…”

“…One pair of 3-mm-diameter Parylene-coated magnetic beads (N48SH) were implanted into the right lateral gastrocnemius muscle of each turkey, with a target magnetic bead separation distance of 3.5 cm. For details on the surgical procedure and implants, see Taylor et al, 2022 . A 1-month recovery period was given before the start of the data collection.…”

Magnetic Micro and Nano Sensors for Continuous Health Monitoring

“…An electromyography sensor system, which gathers signals from 32 implanted myoelectric sensors, was described by Weir et al, who used wireless telemetry to avoid the problems caused by percutaneous wires [93]. Taylor et al used magnetomicrometry to track muscle tissue lengths using magnetic bead implants, e.g., for the control of a prosthetic limb device or for the muscle stimulation of paralyzed muscles, as depicted in Figure 7 [94]. Magnetic implants in the lips and tongue can be used for the silent speech recognition of patients who have lost their ability to vocalize due to injury or disease [95].…”

Non-pyrogenicity and biocompatibility of parylene-coated magnetic bead implants

“…However, for magnetomicrometry to be used in humans, the clinical viability of magnetic bead implants must first be verified. In previous work, we addressed the salient aspects of the clinical viability of implanting magnetic beads in muscle ( Taylor et al, 2022b ). Namely, we described a manufacturing process for medical-grade magnetic bead implants, in which we coat 3-mm-diameter neodymium spheres in 5 µm of gold and 21 µm of Parylene C and ultrasonically-clean, magnetize, package, and gamma-sterilize them, and we also described the manufacturing of implant insertion devices that are used to deploy the magnetic bead implants from their cartridge packaging.…”