Host response to microgel coatings on neural electrodes implanted in the brain

Abstract

The performance of neural electrodes implanted in the brain is often limited by host response in the surrounding brain tissue, including astrocytic scar formation, neuronal cell death, and inflammation around the implant. We applied conformal microgel coatings to silicon neural electrodes and examined host responses to microgel-coated and uncoated electrodes following implantation in the rat brain. In vitro analyses demonstrated significantly reduced astrocyte and microglia adhesion to microgel-coated electrodes compared to uncoated controls. Microgel-coated and uncoated electrodes were implanted in the rat brain cortex and the extent of activated microglia and astrocytes as well as neuron density around the implant were evaluated at 1, 4, and 24 weeks post-implantation. Microgel coatings reduced astrocytic recruitment around the implant at later time points. However, microglial response indicated persistence of inflammation in the area around the electrode. Neuronal density around the implanted electrodes was also lower for both implant groups compared to the uninjured control. These results demonstrate that microgel coatings do not significantly improve host responses to implanted neural electrodes and underscore the need for further improvements in implantable materials.

Responsive Microgels at Surfaces and Interfaces

“…Here, reduced protein adsorption and inflammation are desired and current studies explore the applicability of microgel coated maBrought to you by | Carleton University OCUL Authenticated Download Date | 6/21/15 5:39 PM terials for this purpose [30]. Moreover, polyelectrolyte-mediated cross-linking of PNIPAM-co-AAc microgel films at Au coated substrates can resist large forces compared to their own mass and actuate in response to humidity [47].…”

Progress towards biocompatible intracortical microelectrodes for neural interfacing applications

“…However, a number of in vivo studies looking at either stiff materials or those coated with compliant polymers have indicated that haptic-mediated mechanotransduction may not play as significant a role as initially thought (see Sections 4.1.3, 4.2.1, 4.3 and 4.6.1) . (117, 195) The second, and perhaps more predominant hypothesis, is that mechanical differences between the brain and microelectrodes induce adverse strains in the surrounding tissue during regular brain micromotion. (95, 138, 196) Therefore, compliant materials that have mechanical properties closer to that of brain tissue have received extensive attention towards improving microelectrode integration within the surrounding tissue.…”

“…using conformal microgel coatings of poly(N-isopropylacrylamide) (pNIPAm) cross-linked with poly(ethylene glycol diacrylate) (PEG-DA) on silicon microelectrodes. (195) Long polyethylene glycol (PEG) chains take advantage of entropic and osmotic repulsion to prevent cell adhesion through the inhibition of protein adsorption. In vitro analyses demonstrated significantly reduced astrocyte and microglia adhesion to microgel-coated microelectrodes, compared to uncoated controls.…”

Recent advances in neural electrode–tissue interfaces

“…No differences in glial and neuronal responses have been found between Parylene C and silicon dioxide surfaces, two commonly used insulation materials [33], and polyethylene glycol based hydrogel coatings did not shown benefit [36]. These results suggest that physical chemistry alone may not be sufficient to alter the host tissue response.…”