Matrigel coatings for Parylene sheath neural probes

Abstract

The biologically derived hydrogel Matrigel (MG) was used to coat a Parylene-based sheath intracortical electrode to act as a mechanical and biological buffer as well as a matrix for delivering bioactive molecules to modulate the cellular response and improve recording quality. MG was loaded with dexamethasone to reduce the immune response together with nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) to maintain neuronal density and encourage neuronal ingrowth toward electrodes within the sheath. Coating the Parylene sheath electrode with the loaded MG significantly improved the signal-to-noise ratio for neural events recorded from the motor cortex in rat for more than 3 months. Electron microscopy showed even coverage of both the Parylene substrate and the platinum recording electrodes. Electrochemical impedance spectroscopy (EIS) of coated electrodes in 1× phosphate-buffered saline demonstrated low impedance required for recording neural signals. This result was confirmed by in vivo EIS data, showing significantly decreased impedance during the first week of recording. Dexamethasone, NGF, and BDNF loaded into MG were released within 1 day in 1× phosphate-buffered saline. Although previous studies showed that MG loaded with either the immunosuppressant or the neurotrophic factor cocktail provided modest improvement in recording quality in a 1-month in vivo study, the combination of these bioactive molecules did not improve the signal quality over coating probes with only MG in a 3-month in vivo study. The MG coating may further improve recording quality by optimizing the in vivo release profile for the bioactive molecules.

Micromachining of Parylene C for bioMEMS

“…However, pre‐treatment of the Parylene film with oxygen plasma in this case has been found to decrease protein adsorption . In cases where protein adhesion is required within Parylene lumen structures, a pre‐coating of poly(d‐lysine) was found to improve the wettability of the Parylene surface and to wick protein mixtures . Other methods for surface modification of Parylene C for biomedical applications involve UV‐induced photoxidation (1 or 2 h of treatments) to create a hydrophilic surface by producing carboxyl and aldehyde groups .…”

Mechanical flexibility reduces the foreign body response to long-term implanted microelectrodes in rabbit cortex

“…One way to mitigate the modulus mismatch between the brain and electrode materials, is to use materials with a lower Young's modulus, for example Parylene-C or Polyimide insulated thin film electrodes that have been shown to record for periods up to 4-12 weeks [16][17][18].…”

The Future of Neuroimplantable Devices: A Materials Science and Regulatory Perspective

“…In another case, Matrigel, dexamethasone (DEX), nerve growth factor (NGF), and brain-derived neurotrophic factor (BDNF) were used to coat a parylene and platinumbased probe, resulting in a higher signal-to-noise ratio (SNR), which improved device functionality. [50] Researchers have also demonstrated the feasibility of creating insertion shuttles made of bioresorbable polymers, such as polyvinyl alcohol (PVA) and poly(lactic-co-glycolic acid) (PLGA), to reduce glial scarring during implantation of rigid probes. [51] For polymer-based probes, such as those coasted parylene-C as the substrate material, that are too flexible to be implanted directly into the brain, silk coatings have been used during implantation to act as a temporary stiffening agent which dissolves in the brain afterward.…”