Advances in Scalable Implantable Systems for Neurostimulation Using Networked ASICs

Abstract

Neurostimulation is a known method for restoring lost functions to neurologically impaired patients. This paper describes recent advances in scalable implantable stimulation systems using networked application specific integrated circuits (ASICs). It discusses how they can meet the ever-growing demand for high-density neural interfacing and long-term reliability. A detailed design example of an implantable (inductively linked) scalable stimulation system for restoring lower limb functions in paraplegics after spinal cord injury is presented. It comprises a central hub implanted at the costal margin and multiple Active Books which provide the interface for stimulating nerve roots in the cauda equina. A 16-channel stimulation system using four Active Books is demonstrated. Each Active Book has an embedded ASIC, which is responsible for initiating stimulus current to the electrodes. It also ensures device safety by monitoring temperature, humidity, and peak electrode voltage during stimulation. The implant hub was implemented using a microcontroller-based circuit. The ASIC in the Active Book was fabricated using XFAB's 0.6-µm high-voltage CMOS process. The stimulation system does not require an accurate reference clock in the implant. Measured results are provided.

An ASIC for Recording and Stimulation in Stacked Microchannel Neural Interfaces

“…Multiplexing across electrodes within and between MNI ASICs has been demonstrated. This device only allows stimulation from one electrode, or all electrodes at the same time, not from a subset of electrodes [51]; however fast switching between electrodes can stimulate axons in different microchannels sequentially. Fast switching between recording channels is not proposed for this system.…”

“…Due to the use of passive conductors previous MNI designs have been limited in the number of channels for stimulating and recording e.g., [28], [30], [31]. Here, reducing the number of interconnect wires has the additional advantage of reducing surgical complexity and failure risk due to cable damage [51].…”

On the review of electronic technologies applied to implantable medical devices

“…With the aim to understand the evolution of IMDs in the context of electronics systems, a survey of academic journal publications was made. Based on the work presented in [3], this survey of the relevant scientific articles covers a period from 1974 to 2018. Traditionally, state of the art reviews and investigations of biomedical implants have covered limited sets of systems and cases of study, restricted to specific applications or sub-system modules common to a group of devices, for example; Point of Care (POC) monitoring systems are surveyed and reviewed in [4], where the maturity of some selected works and their suitability to become a commercial alternative in the healthcare market are evaluated.…”

A Multichannel High-Frequency Power-Isolated Neural Stimulator With Crosstalk Reduction

“…Besides conventional multichannel stimulators such as cochlear [1], [2] retinal [3], [4] and vestibular implants [5], [6] where stimulating multiple channels is necessary for creating real perceptual sensation, state-of-the-art neural stimulators for the spinal cord [7], and the peripheral nervous system [8], [9] are also enhanced with novel electrode design features such as three-dimensional [10] or microchannel arrays [8], [11] where a finer neural interface allows higher selectivity for stimulating targeted nerves. Additionally, advanced system architectures including active electrodes [7], [12] and networked topologies [13] allow localized stimulation with maximum efficiency.…”