A Novel Dexamethasone-releasing, Anti-inflammatory Coating for Neural Implants

The long-term stability of implanted micromachined neural probes is compromised due to the glial scar formation at the insertion site. In this study, we developed a novel nitrocellulose-based coating for the sustained local delivery of the anti-inflammatory drug dexamethasone, a synthetic glucocorticoid that effectively reduces inflammation in the CNS. In vitro dexamethasone release was observed over 16 days, with a relatively high release in the first three days and a slow, stable release thereafter. When Michigan neural recording probes coated with and without dexamethasone-loaded nitrocellulose coatings were implanted into the adult rat brains, immunohistochemical evidence shows a marked reduction of reactive astrocytes (GFAP), reactive microglia (EDl), and chondroitin sulfate proteoglycans (CS56) expression around the insertion site compared to uncoated probes. Impedance spectroscopy showed that the dexamethasone-loaded nitrocellulose coatings slightly reduce the magnitude of electrode impedance at the biologically relevant frequency of 1 kHz through an increase of capacitance. In vivo acute recordings demonstrate that extracellular recordings with coated probes are akin to non-coated probes and it is anticipated that with time, the coated probes will exhibit superior performance. In conclusion, we developed a novel nitrocellulose-based, drug releasing coating for neural electrodes that can effectively reduce scar tissue formation without adversely affecting the electrical performance of the electrodes