Challenges in Scaling Down of Free-Floating Implantable Neural Interfaces to Millimeter Scale

Abstract

Implantable neural interface devices are an emerging technology for continuous brain monitoring and brain-computer interface (BCI). Recording of electrical signals from neurons of interest has led to more efficient and personalized diagnosis, treatment, and prognosis of neurological disorders. It facilitates the dynamic mapping of the whole brain, improving our understanding of the links between brain functions and behaviors. Stimulation of targeted nerves and neurons has been utilized as an effective therapy for Parkinson's disease, essential tremor, dystonia, etc. It has also been developed as motor neuroprosthetic devices, improving the quality of life of many. Although initial designs were bulky, recent advances in semiconductor and nano-, micro-technology has enabled the miniaturization of such devices to the millimeter scale. Free-floating neural implants of miniature size are highly scalable to be distributed around the targeted region of interest more extensively. They are more clinically viable as they cause less disturbance to the body and induce less tissue immune response. However, these research efforts for scaling down have faced challenges resulted from decreasing the size of such implants, including issues pertaining to wireless powering, data communication, neural signal recording, and neural stimulation. Through extensive literature research and simulations, the limits and trade-offs regarding neural implant miniaturization are investigated and analyzed for each aspect of the challenges. State-of-the-art development and future trends for advanced neural interfaces are also explored. INDEX TERMS Implantable neural interface, neural signal recording and stimulation, wireless power transfer, millimeter size, free-floating neural probes.

Wirelessly-Powered Cage Designs for Supporting Long-Term Experiments on Small Freely Behaving Animals in a Large Experimental Arena

“…Although most wirelessly-powered cages provide PTE and PDL for specific experimental conditions, the physical constraints of Rx coils, coil separations, and magnetic field homogeneity over the experimental area should be compared for a more suitable choice. As the most recent class of IMDs are millimeter-sized and distributed over a large area in the brain or the rest of the body [43][44][45][46], the importance of wirelessly-powered cages for tiny multiple implants is elevated as introduced in Section 4. Hence, it is important for designers to select suitable wirelessly-powered cages, considering the practical limitations of IMD design related to key aspects, such as PTE, PDL, closed-loop power control, scalability, spatial/angular misalignment, near-field data telemetry, and safety issues against various perturbations during the longitudinal animal experiment.…”

Energy Harvesting in Nanosystems: Powering the Next Generation of the Internet of Things

“…Bio-implantable devices have much higher constraints on accessible energy sources, dimensions, and toxicity requirements. An example application with extreme requirements are floating autonomous neural sensors, where ultrasound, infrared, and RF have all been pursued (Yang et al, 2020). Micro and nanoscale sensors have tremendous opportunity to realize "body dust" for biological monitoring that extends beyond wearable and implantable devices (Carrara, 2020).…”

Securing Implantable Medical Devices Using Ultrasound Waves

“…It has also been proposed as a wireless-power-transfer (WPT) channel for recharging IMDs [23], [24]. Furthermore, it is being touted as an in-body communication and WPT channel for the next-generation mm-sized neural implants for both the Central (CNS) and Peripheral Nervous Systems (PNS) [25], [26]. This is because the size of ultrasound transceivers can be several orders smaller than their electromagnetic (EM) counterparts, which is ideal for scaling-down of IMDs.…”