A Fully Implantable Miniaturized Liquid Crystal Polymer (LCP)-Based Spinal Cord Stimulator for Pain Control.

Seunghyeon Yun,Sung June Kim,Hyun Ho Jung,Shinyong Shim,Chin Su Koh,Jin Woo Chang,Kyungsik Eom,Jungmin Seo,Minkyung Park

doi:10.3390/s22020501

Abstract

Spinal cord stimulation is a therapy to treat the severe neuropathic pain by suppressing the pain signal via electrical stimulation of the spinal cord. The conventional metal packaged and battery-operated implantable pulse generator (IPG) produces electrical pulses to stimulate the spinal cord. Despite its stable operation after implantation, the implantation site is limited due to its bulky size and heavy weight. Wireless communications including wireless power charging is also restricted, which is mainly attributed to the electromagnetic shielding of the metal package. To overcome these limitations, here, we developed a fully implantable miniaturized spinal cord stimulator based on a biocompatible liquid crystal polymer (LCP). The fabrication of electrode arrays in the LCP substrate and monolithically encapsulating the circuitries using LCP packaging reduces the weight (0.4 g) and the size (the width, length, and thickness are 25.3, 9.3, and 1.9 mm, respectively). An inductive link was utilized to wirelessly transfer the power and the data to implanted circuitries to generate the stimulus pulse. Prior to implantation of the device, operation of the pulse generator was evaluated, and characteristics of stimulation electrode such as an electrochemical impedance spectroscopy (EIS) were measured. The LCP-based spinal cord stimulator was implanted into the spared nerve injury rat model. The degree of pain suppression upon spinal cord stimulation was assessed via the Von Frey test where the mechanical stimulation threshold was evaluated by monitoring the paw withdrawal responses. With no spinal cord stimulation, the mechanical stimulation threshold was observed as 1.47 ± 0.623 g, whereas the stimulation threshold was increased to 12.7 ± 4.00 g after spinal cord stimulation, confirming the efficacy of pain suppression via electrical stimulation of the spinal cord. This LCP-based spinal cord stimulator opens new avenues for the development of a miniaturized but still effective spinal cord stimulator.

Highlights

The efficacy of spinal cord stimulation has been demonstrated in several clinical studies, and commercial spinal cord stimulators have been developed for human use [9,10,11,12]
We developed a fully implantable neural stimulator using liquid crystal polymer (LCP) for spinal cord stimulation
The mechanical withdrawal threshold was increased after electrical stimulation, and it even brought them back to a normal state at the certain parameter, confirming the effectiveness of the spinal cord stimulation in pain control

Summary

Introduction

Spinal cord stimulation is a therapeutic tool used to treat certain chronic pain conditions especially related to neuropathic pain caused by trauma or postoperative sequelae and sensory nerve damage [1,2,3]. The idea was to deliver electric current pulses to the spinal cord through an electrode inserted into the fat layer of the spine [4]. Based on the well-known gate control theory, the stimulation current delivered to the spinal cord inhibits the transmission of the nociceptive information as well as other sensory information [5,6,7,8]. An implantable spinal cord stimulator that allows continuous activation of the spinal cord to alleviate the pain is crucial for the patients suffering chronic neuropathic pain.

Methods

Results

Conclusion