Biocompatibility Assessment of Insulating Silicone Polymer Coatings Using an in vitro Glial Scar Assay

Abstract

Vapor-deposited silicone coatings are attractive candidates for providing insulation in neuroprosthetic devices owing to their excellent resistivity, adhesion, chemical inertness and flexibility. A biocompatibility assessment of these coatings is an essential part of the materials design process, but current techniques are limited to rudimentary cell viability assays or animal muscle implantation tests. This article describes how a recently developed in vitro model of glial scar formation can be utilized to assess the biocompatibility of vapor-deposited silicone coatings on micron-scale wires. A multi-cellular monolayer comprising mixed glial cells was obtained by culturing primary rat midbrain cells on poly(D-lysine)-coated well plates. Stainless steel microwires were coated with two novel insulating thin film silicone polymers, namely poly(trivinyltrimethylcyclotrisiloxane) (polyV(3)D(3)) and poly(trivinyltrimethylcyclotrisiloxane-hexavinyldisiloxane) (polyV(3)D(3)-HVDS) by initiated chemical vapor deposition (iCVD). The monolayer of midbrain cells was disrupted by placing segments of coated microwires into the culture followed by immunocytochemical analysis after 7 d of implantation. Microglial proximity to the microwires was observed to correlate with the amount of fibronectin adsorbed on the coating surface; polyV(3)D(3)-HVDS adsorbed the least amount of fibronectin compared to both stainless steel and polyV(3)D(3). Consequently, the relative number of microglia within 100 µm of the microwires was least on polyV(3)D(3)-HVDS coatings compared to steel and polyV(3)D(3). In addition, the astrocyte reactivity on polyV(3)D(3)-HVDS coatings was lower compared to stainless steel and polyV(3)D(3). The polyV(3)D(3)-HVDS coating was therefore deemed to be most biocompatible, least reactive and most preferable insulating coating for neural prosthetic devices.

Surface modification of neural electrodes with a pyrrole-hyaluronic acid conjugate to attenuate reactive astrogliosis in vivo

“…[19][20][21] Among them, coating the electrode surfaces with biocompatible or bio-inert polymers can be an effective strategy to shield the foreign electrode materials and reduce astrocyte activation. [22][23][24][25][26][27][28][29] However, these coatings resulted in substantial increase in electrical impedance aer the surface modication and/or did not adequately reduce the glial response. [22][23][24][25][26][27][28][29] However, these coatings resulted in substantial increase in electrical impedance aer the surface modication and/or did not adequately reduce the glial response.…”

Nebulized solvent ablation of aligned PLLA fibers for the study of neurite response to anisotropic-to-isotropic fiber/film transition (AFFT) boundaries in astrocyte–neuron co-cultures

“…While other in vitro platforms have focused on studying how neurons are affected by CSPG and laminin gradients [18], chemically activated astrocytes [45], mechanically stretched co-cultures of astrocytes and fibroblasts [46], or mixed glial cell cultures [47], this biomaterial platform was designed to specifically study how neurite extension was affected by astrocyte morphological transitions. Along with other groups, we have previously shown that astrocytes cultured on aligned substrates have altered functions that mostly appear to be supportive of neuron survival and growth when compared to astrocytes cultured on smooth, isotropic substrates [34,39–41,51–53].…”

A critical review of cell culture strategies for modelling intracortical brain implant material reactions

“…4). Direct contact models involve either seeding cells directly on a biomaterial surface (cell adhesion models) [75] or bringing a material into contact with cells grown on a control surface (implant mimicking models) [36,76,77]. Both direct contact models allow for investigation of cellular reaction to material surfaces, and of how the cell contact can modify the surface [78].…”

“…There are a number of short-term interactions that can be assessed from in vitro blood and peripheral immune cell models; these are relevant to the integration and performance of materials and microdevices within the human body and CNS [23,76]. More research into how microglia modify these reactions will give immune cell and blood studies more relevance to biomaterials and devices developed for neuroprosthetic applications.…”