The design of and chronic tissue response to a composite nerve electrode with patterned stiffness.

The design of and chronic tissue response to a composite nerve electrode with patterned stiffness.

J Neural Eng. 2017 Mar 13;:

Authors: Freeberg M, Stone M, Triolo R, Tyler D

Abstract
As neural interfaces demonstrate success in chronic applications, a novel class of reshaping electrodes with patterned regions of stiffness will enable application to a widening range of anatomical locations. Patterning stiff regions and flexible regions of the electrode enables nerve reshaping while accommodating anatomical constraints of various implant locations ranging from peripheral nerves to spinal and autonomic plexi. Introduced is a new composite electrode enabling patterning of regions of various electrode mechanical properties. The initial demonstration of the composite's capability is the composite flat interface nerve electrode (C-FINE). The C-FINE is constructed from a sandwich of patterned PEEK within layers of pliable silicone. The PEEK polymer is significantly stiffer than the silicone sheeting and the shape of the PEEK provides a desired pattern of stiffness to the electrode. The design was stiff across the width of the nerve to reshape the nerve, but flexible only the length to allow for bending with the nerve. This is particularly important in anatomical locations near joints and in constrained compartments. We tested pressure and volume design constraints in vitro to verify that the C-FINE can attain a safe cuff-to-nerve ratio (CNR) without impeding intraneural blood flow. In vitro inflation tests on showed effective CNRs (1.93 +/- 0.06) that exceeded the industry safety standard of 1.5 at an internal pressure of 20 mmHg. This is less than the 30 mmHg shown to induce loss of conduction or compromise blood flow. We measured nerve function as well as nerve and axonal morphology following 3-month implantation of the C-FINE without wires on feline peripheral nerves in anatomically constrained areas near mobile joints and other important anatomical structures in both the hind and fore limbs. Implanted cats showed no changes in physiology or electrophysiology. Behavioral signs were normal suggesting normal neural pathology. Motor nerve conduction velocity (MNCV) and compound motor action potential (CMAP) did not change significantly between implant and explant (p > 0.15 for all measures). Axonal density or myelin sheath thickness was not significantly different within the electrode compared to sections greater than 2 cm proximal to implanted cuffs (p > 0.14 for all measures). Chronic implantation of C-FINE support the hypothesis that the C-FINE design does not adversely impact nerve health.

PMID: 28287078 [PubMed - as supplied by publisher]

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