Biocompatibility of intracortical microelectrodes: current status and future prospects

Abstract

Rehabilitation of sensory and/or motor functions in patients with neurological diseases is more and more dealing with artificial electrical stimulation and recording from populations of neurons using biocompatible chronic implants. As more and more patients have benefited from these approaches, the interest in neural interfaces has grown significantly. However an important problem reported with all available microelectrodes to date is long-term viability and biocompatibility. Therefore it is essential to understand the signals that lead to neuroglial activation and create a targeted intervention to control the response, reduce the adverse nature of the reactions and maintain an ideal environment for the brain-electrode interface. We discuss some of the exciting opportunities and challenges that lie in this intersection of neuroscience research, bioengineering, neurology and biomaterials.

Keywords: brain-machine interface; coating; glial scar; neural interface; neural prosthesis.

Figure 1

Development of glial encapsulation on an intracortical microelectrode. (A) Acute neural injury caused by inserting a microelectrode into the brain cortex. Astrocytes and microglial cells become activated and migrate to the site of injury. (B) Chronic response showing a dense sheath around implanted probes, which contains fibroblasts, macrophages and astrocytes. (C,D) The reactive astrocytes, immunohistochemically labeled here for GFAP, encapsulate the neural probes forming a dense cellular sheath. Calibration bar = 50 μm.

Figure 2

Photomicrograph showing astrocytes (GFAP staining, red) and neurons (NeuN staining, green) around one microelectrode track (asterisk) following chronic implantation of a NeuroProbes multielectrode array in rabbit occipital cortex. Calibration bar = 50 μm.

Figure 3

Summary of optimum surface behavior for an implanted neural probe. (A) Surface of encapsulation and insulation material: adsorption of proteins and adhesion of fibroblast for good incorporation into the tissue, no reaction of macrophages. (B) Surface without electrodes: good contact to neurons and glial cells, no reaction of macrophages. (C) Surface of electrodes: attraction and good contact to neurons, no adhesion of fibroblasts, no macrophage reaction.