Development of Surrogate Spinal Cords for the Evaluation of Electrode Arrays Used in Intraspinal Implants

Abstract

A surrogate spinal cord was developed to test the mechanical stability of electrode arrays for intraspinal implants. The mechanical and surface properties of candidate materials were tested. The elastic modulus was characterized using dynamic mechanical analysis. Forces required to indent the surrogate cords to specified depths was measured. Frictional forces were measured by pulling a needle out at a controlled rate. The results were compared to actual spinal cords, either to value from literature or ex vivo measurements. Surrogate cords with the most suitable properties (formaldehyde crosslinked gelatin, 12 wt% in water) were implanted with two types of intraspinal electrode arrays (one made of individual microwires and another of microwires anchored with a solid base), and an elongation was applied. Arrays with solid bases impeded the deformation of the cord suggesting that they could cause tissue damage in vivo, while arrays without a base moved freely with the cord.