Tongue implant for assistive technologies: Test of migration, tissue reactivity and impact on tongue function.

OBJECTIVE: The Tongue Drive System (TDS) is a new wearable assistive technology (AT), developed to translate voluntary tongue movements to user-defined computer commands by tracking the position of a titanium-encased magnetic tracer (Ti-Mag) implanted into the tongue. TDS application, however, is constrained by limited information on biological consequence and safety of device implantation into the tongue body. Here we implant a stainless-steel pellet in the rat tongue and assay pellet migration, tongue lick function, and tongue histology to test the safety and biocompatibility of unanchored tongue implants. DESIGN: Water consumption, weight and lick behavior were measured before and for >24days after implantation of a stainless-steel spherical pellet (0.5mm) into the anterior tongue body of twelve adult male rats. X-rays were obtained weekly to assess pellet migration. Pellet location and tissue reaction to implantation were determined by post-mortem dissection and histology of the anterior tongue. RESULTS: By dissection pellets were distributed across the transverse plane of the tongue. Measures of water consumption, weight, and lick behavior were unchanged by implantation except for a decrease in consumption immediately post-implantation in some animals. By X-ray, there was no migration of the implant, a finding supported by pellet encapsulation demonstrated histologically. Measures of lick behavior were minimally impacted by implantation. CONCLUSION: A smooth spherical stainless-steel implant in the anterior tongue of the rat does not migrate, is encapsulated and does not substantially impact lick behavior. These findings support the implantation of small tracers in the anterior tongue in humans for operating wearable assistive technologies.

Three-Phase Time-Multiplexed Planar Power Transmission to Distributed Implants.

A platform has been presented for wireless powering of receivers (Rx's) that are arbitrarily distributed over a large area. A potential application could be powering of small Rx implants, distributed over large areas of the brain. The transmitter (Tx) consists of three overlapping layers of hexagonal planar spiral coils (hex-PSC) that are horizontally shifted to provide the strongest and most homogeneous electromagnetic flux coverage. The three-layer hex-PSC array is driven by a three-phase time-division-multiplexed power Tx that takes the advantage of the carrier phase shift, coil geometries, and Rx time constant to homogeneously power the arbitrarily distributed Rx's regardless of their misalignments. The functionality of the proposed three-phase power transmission concept has been verified in a detailed scaled-up high-frequency structure simulator Advanced Design System simulation model and measurement setup, and compared with a conventional Tx. The new Tx delivers 5.4 mW to each Rx and achieves, on average, 5.8% power transfer efficiency to the Rx at the worst case 90° angular misalignment, compared with 1.4% by the conventional Tx.

Optimal Design of Wireless Power Transmission Links for Millimeter-Sized Biomedical Implants.

This paper presents a design methodology for RF power transmission to millimeter-sized implantable biomedical devices. The optimal operating frequency and coil geometries are found such that power transfer efficiency (PTE) and tissue-loss-constrained allowed power are maximized. We define receiver power reception susceptibility (Rx-PRS) and transmitter figure of merit (Tx-FoM) such that their multiplication yields the PTE. Rx-PRS and Tx-FoM define the roles of the Rx and Tx in the PTE, respectively. First, the optimal Rx coil geometry and operating frequency range are identified such that the Rx-PRS is maximized for given implant constraints. Since the Rx is very small and has lesser design freedom than the Tx, the overall operating frequency is restricted mainly by the Rx. Rx-PRS identifies such operating frequency constraint imposed by the Rx. Secondly, the Tx coil geometry is selected such that the Tx-FoM is maximized under the frequency constraint at which the Rx-PRS was saturated. This aligns the target frequency range of Tx optimization with the frequency range at which Rx performance is high, resulting in the maximum PTE. Finally, we have found that even in the frequency range at which the PTE is relatively flat, the tissue loss per unit delivered power can be significantly different for each frequency. The Rx-PRS can predict the frequency range at which the tissue loss per unit delivered power is minimized while PTE is maintained high. In this way, frequency adjustment for the PTE and tissue-loss-constrained allowed power is realized by characterizing the Rx-PRS. The design procedure was verified through full-wave electromagnetic field simulations and measurements using de-embedding method. A prototype implant, 1 mm in diameter, achieved PTE of 0.56% ( -22.5 dB) and power delivered to load (PDL) was 224 µW at 200 MHz with 12 mm Tx-to-Rx separation in the tissue environment.

Enhanced Wireless Power Transmission Using Strong Paramagnetic Response.

A method of quasi-static magnetic resonant coupling has been presented for improving the power transmission efficiency (PTE) in near-field wireless power transmission, which improves upon the state of the art. The traditional source resonator on the transmitter side is equipped with an additional resonator with a resonance frequency that is tuned substantially higher than the magnetic field excitation frequency. This additional resonator enhances the magnetic dipole moment and the effective permeability of the power transmitter, owing to a phenomenon known as the strong paramagnetic response. Both theoretical calculations and experimental results show increased PTE due to amplification of the effective permeability. In measurements, the PTE was improved from 57.8% to 64.2% at the nominal distance of 15 cm when the effective permeability was 2.6. The power delivered to load was also improved significantly, with the same 10 V excitation voltage, from 0.38 to 5.26 W.