Magnetic implants in the tongue for assistive technologies: Tests of migration; oromotor function; and tissue response in miniature pigs

Abstract

Objective Uncertain biological consequences of titanium-magnet (Ti-mag) tongue implants constrain application of the Tongue Drive System (TDS), a brain-tongue-computer interface for individuals with severe physical impairment. Here we describe oromotor function and tongue tissue response following Ti-Mag implantation and explantation in the miniature pig, an animal model with a tongue similar in size to humans. Design A 1.8 × 6.2 mm Ti-mag tracer was implanted into the anterior tongue in five Yucatan minipigs. X-rays were taken immediately and >six days after implantation to evaluate tracer migration. In three minipigs, the tracer was explanted >16 days after implantation. Twenty-five days post-explantation, tongue tissue was harvested and processed for histological and immunohistochemical (IHC) markers of healing. In two minipigs tissue markers of healing were evaluated post-mortem following >12 days implantation. Drink cycle rate (DCR) was characterized to determine the impact of procedures on oromotor function. Results Neither implantation (N=5) nor explantation (N=3) changed DCR. X-rays revealed minimal tracer migration (N=4, 0–4 mm). By histology and IHC a robust capsule was present two weeks post-implantation with limited fibrosis. Explantation produced localized fibrosis and limited muscle remodeling. Conclusions These findings suggest the safety of Ti-mag anterior tongue implants for assistive technologies in humans.

Stability andin vivosafety of gold, titanium nitride and parylene C coatings on NdFeB magnets implanted in muscles towards a new generation of myokinetic prosthetic limbs

“…An asset of this study is that the tests were carried out by carefully following the medical device safety ISO, by evaluating also the toxicity induced by injections of sample extracts so as to determine the biological reactivity and the hazard potential of any substances that may be released from the device into the surrounding tissues. The low irritation score associated with the Par coated magnets paves the way towards their use as a key element in a safe myokinetic implant, 9 as well as in other biomedical applications in which a safe acute or chronic interaction of magnets with muscle tissues may be desirable, [42][43][44] with possible impacts also in the eld of muscle-based bio-hybrid robotics. 45…”

Clinical viability of magnetic bead implants in muscle

“…To provide a consistent measurement of tissue length and to ensure patient health, the magnetic implants must 1) not move relative to the surrounding tissue, 2) not move relative to one another, and 3) not migrate out of the muscle. Spherical steel beads and cylindrical titanium-encapsulated magnetic beads implanted individually into the tongue muscle in animal models proved to be stable against migration in short-term studies (6–24 days) ( Mimche et al, 2016 ; Sokoloff et al, 2017 ). In previous work, we also showed that magnetic beads implanted in pairs do not migrate over a long-term study (191 days) if sufficiently separated from one another at the time of implantation ( Taylor et al, 2021 ).…”