Surface modification of neural prosthetic devices by conducting polymers and biopolymers.

摘要

Micromachined neural prosthetic devices facilitate the functional stimulation of and recording from the peripheral and central nervous systems. The microelectrode sites on the neural probes are the actual interface to communicate with neurons. The surfaces of the devices should provide intimate interfacial contact between electrodes and neurons, facilitate the charge transport from ionically conductive tissue to electronically conductive electrode and induce selected neurons or neuron processes to attach onto the microelectrode. Traditional metal electrode materials do not fulfill these functions. Biocompatible conducting polymers were therefore used to modify the surface of the microelectrodes. An electrochemical polymerization approach was developed to directly deposit conductive polymers, such as polypyrrole and poly (3,4-ethylenedioxythiophene) (PEDOT), together with biopolymers, such as protein polymers and bioactive peptides, onto the microelectrode sites. It was found that the deposition of conducting polymer significantly lowered the electrode impedance which is beneficial to neural signal transport. The electronic properties of the conductive polymers were found to be influenced by the film morphology, which could be tailored by controlling the polymerization conditions. The incorporation of biopolymers was confirmed by microfocused Fourier-Transformed infrared (FTIR) spectroscopy. Rat glia and human neuroblastoma cells were shown to preferentially attach and grow on the coated electrode site area of the neural probes. The chemical stability of conducting polymer/biomolecule coatings was studied using FTIR, impedance spectroscopy and cyclic voltammetry. The biomolecules were stable in the film after seven weeks of soaking in deionized water, while polypyrrole underwent some subtle changes in chemical structure. PEDOT was proven to be a more stable material under potential cycling and provided even lower impedance. The adhesion between the coating and electrode sites was also important for long term applications, and a rough electroplated gold layer helped to improve the adhesion significantly. Finally, polypyrrole/peptide (CDPGYIGSR) coated probes were tested in vivo for one, two and three weeks. The PPy/peptide coating promoted the attachment of neurons. The tight connection between neurons and the polymer coated electrodes made it possible to establish more stable neural recordings.