Novel flexible Parylene neural probe with 3D sheath structure for enhancing tissue integration

Abstract

A Parylene C neural probe with a three dimensional sheath structure was designed, fabricated, and characterized. Multiple platinum (Pt) electrodes for recording neural signals were fabricated on both inner and outer surfaces of the sheath structure. Thermoforming of Parylene was used to create the three dimensional sheath structures from flat surface micromachined microchannels using solid microwires as molds. Benchtop electrochemical characterization was performed on the thin film Pt electrodes using cyclic voltammetry and electrochemical impedance spectroscopy and showed that electrodes possessed low impedances suitable for neuronal recordings. A procedure for implantation of the neural probe was developed and successfully demonstrated in vitro into an agarose brain tissue model. The electrode-lined sheath will be decorated with eluting neurotrophic factors to promote in vivo neural tissue ingrowth post-implantation. These features will enhance tissue integration and improve recording quality towards realizing reliable chronic neural interfaces.

Formation of three-dimensional Parylene C structures via thermoforming

“…A detailed account of PMP device fabrication can be found elsewhere [15,33]; the process is briefly summarized here. PMP devices were fabricated by Parylene surface micromachining; all processing was conducted at low temperatures (<90…”

“…Initially used as an encapsulation coating to protect implantable devices [6][7][8], Parylene is now a commonly used structural material in surface micromachining that can be selectively shaped using standard lithographic processes in combination with oxygen plasma-based removal [9]. More recently, the ability to form 3D Parylene structures have also contributed to the development of novel sensors [10,11], microfluidics [12][13][14], and implantable devices [15,16].…”

Perforated 2&#x00D7;2 Parylene sheath electrode array for chronic intracortical recording

“…We previously reported in detail on the fabrication of the PSE [6] as well as preliminary data demonstrating the use of this technology to record neuronal activity in vivo [7]. In this work, we present the use of our Parylene C sheath neural probe technology to develop a novel perforated 2×2 PSEA.…”

Electron-beam lithography for polymer bioMEMS with submicron features

“…The combination of low hardness and low rigidity, characteristic to polymer devices, mitigates risk of tissue damage and subsequent immune response 8 , whereas the biocompatibility afforded by several inert polymers conveys negligible cytotoxicity. Examples of implantable polymer microdevices include neural probes [9][10][11] , cochlear implants, biomedical sensors 12,13 , and drug dispensing devices 14,15 ; some, such as retinal electrodes 16,17 and peripheral nerve interfaces 18,19 , exploit polymeric flexibility to achieve nonplanar geometries. Parylene C in particular has found widespread adoption, owing to its low moisture permeability, high electrical resistivity, and designation as a USP (United States Pharmacopeia) Class VI polymer 20 .…”