Functional thin film polymers for biopassivation of neuroprosthetic implants

Abstract

Neuroprosthetics is the investigation of methods to control external electronic devices utilizing recorded neuronal firing patterns. These investigations are crucial to the quality of life of quadriplegic patients. Central to this field is the ability to implant neural recording probes within the brain that will remain functional over the life of the patient. In this work, two novel polymeric materials for use in biopassive neural probe coatings have been developed and validated. These polymers are synthesized by initiated chemical vapor deposition to allow conformal, pin-hole free coatings of high aspect ratio neural probe assemblies. The first developed material is an electrically insulating barrier coating for the protection of neural probe assemblies. The polymer, poly(trivinyltrimethylcyclotrisiloxane), has an electrical resistivity of 4 X 1015 Ohm-cm and has been demonstrated to be smooth (RMS roughness < 0.4 nm), adherent to silicon substrates, insoluble, and hydrolytically stable. Long term soak testing under physiological conditions has demonstrated retention of electrical properties for > 1000 days. In addition, initial cytotoxicity testing indicates that the material is biocompatible with PC 12 neurons. The second developed material, poly(pentfluorophenyl methacrylate-co-ethylene glycol diacrylate), was developed as a platform for easy surface functionalization of neural probe coatings with bioactive molecules.

(cont.) Single step chemical modification of this material is possible through nucleophilic substitution with primary amines, groups present in all relevant adhesion peptides. Patterned surface functionalization of this material, through microcontact printing, has been demonstrated along with bulk functionalization with small molecule amines from solution. In addition to material development, a novel methodology for additive patterning of CVD polymer thin films has been created. This technique utilizes microcontact printing of photo-active free radical initiator onto the substrate surface prior to polymer deposition. Features 100jIm in scale of poly(cyclohexylmethacrylate) with film thicknesses of > 200 nm have been deposited as verification of this technique.