Electronic implants with mechanically compliant coatings for interfacing with the nervous system

Interfacing with the nervous system holds immense therapeutic potential for the treatment of debilitating conditions such as nerve and spinal cord injury, and for restoring lost sensing modalities such as hearing or vision. Currently, there are many devices used in the clinic that can chronically stimulate the central or peripheral nervous system –deep brain stimulators, cochlear implants or retinal implants. However, devices that are able to record chronically have only been used in a very limited number of pilot studies. Such recording devices would be useful in creating closed loop stimulator systems and prosthetics with sensory feedback. However, their implementation is partly inhibited by a long-term deterioration in their performance, largely due tothe accumulation of scar tissue around the implant surface. This scar, which formed in a process called foreign body reaction (FBR), displaces nearby neurons, thus compromising electrical contact. Recent studies suggested that FBRs are triggered by the mechanical mismatch between the surface of the usually very stiff implant and the surrounding much softer tissue. The aim of this project was to develop a way to fabricate electronically active implants with soft coatings for long-term use in neural interfacing. First, I developed a soft silicone elastomeric blend with suitable mechanical properties (G~1.5 kPa), and showed its biocompatibility with cell culture studies. Subsequently, I used this material as a coating for flexible microelectrode implants. Byinkjet printing sacrificial sucrose hemispheres, I patterned the soft blend with 50 μm diameter vias, in order to expose the electrodes. I then adapted the protocol, in order to fabricate more demanding organic electrochemical transistor structures, with dimensions of a single mammalian cell (i.e. a source-drain distance of 20 μm). Finally, I present electrophysiological results from acute rat sciatic and brain recordings and histological results from chronic sciatic nerve implantations of the devices. Insummary, this study demonstrates the feasibility of constructing state-of-the art neural implants, that can be coated with a stiffness-matching coating, for FBR attenuation. In the future, this could lead to implants with significantly improved long-term performance, potentially enabling chronic recording applications, like controlled prosthetics, or adaptive, closed-loop stimulators.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2019

Author dc:creator

• Dimov, Ivan

Advisor dc:contributor.advisor

• Franze, Kristian

• Neural interface
• Neuroelectronics
• Bioelectronics
• Foreign Body Reaction

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/39fe08c1-a56f-47f2-a80d-02ae3f0c5654/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.53184

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/306106