Abstract
Purpose: :
New promising results of non-invasive neuronal stimulation have been reported, however, implantation of MEA with good dielectric coating provides best stimulation and is the most effective way to receive distinct responses from individual groups of neurons creating functionally useful images for a patient. Different materials and coatings were tested to reveal most biocompatible and stable of them for future long-term clinical trials. Silicon carbide (SiC) is nontoxic and effective dielectric. Thin layer of SiC is sufficient for electrode isolation. Purpose of this work was to evaluate the efficacy of the SiC coating for MEA in CVP, and compare it to standard polyethylsiloxane varnish coating.
Methods: :
MEAs (2x5 100-μm diameter electrodes with 500μm interelectrode distance) were implanted into the 4th layer of visual cortex in 8 wistar rats. Four types of electrode material were tested: stainless steel, nichrome, Tungsten (W), and Molybdenum (Mo). W and Mo were chosen due to their rigidity which is important for the thin electrodes implanted intracortically. 4 rats were implanted with different electrode material and 2-μm thick SiC coating. Other 4 rats were implanted with the same 4 types of electrode material and standard 15-μm varnish coating. Animals were followed up for 6 months. Brain tissue damage was evaluated by the extent of necrosis around the electrodes, thickness of fibrotic incapsulation, and density of macrophage accumulation.
Results: :
Mean±St.Dev. thickness of necrosis in the varnish coating group was 12±4μm for all types of the electrode material. SiC coating was associated with 9±5μm of necrosis. Mean±St.Dev. thicknesses of the fibrotic incapsulation was 3.2±0.6μm for the varnish-coated MEAs and 2.0±0.8μm for the SiC-coated MEAs (p=0.08). Density of macrophage accumulation showed no difference between the two types of coating, showing Mean of 3000 cells/mm2. SiC coating seemed to cause less damage to the neuronal tissue than the varnish coating, however, the difference was not statistically significant.
Conclusions: :
Our results suggest that SiC coating is biologically inactive, biocompatible and stable material with good dielectric properties, causing mild damage to the brain tissue after 6 months of implantation.
Keywords: visual cortex • pattern vision • perception