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

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.