Novel Graphene Electrode for Retinal Implants: An in vivo Biocompatibility Study

Area of Science:

• Biomaterials Science
• Neuroscience
• Ophthalmology

Background:

• Biocompatibility evaluation is crucial for neural interface materials.
• Glial scarring from foreign body reactions can impair brain-machine interface (BMI) performance.
• Graphene's electrical properties make it suitable for neural stimulation, particularly in retinal prostheses.

Purpose of the Study:

• To assess the biocompatibility of chemical vapor deposition (CVD) graphene embedded onto polyimide/SU-8 substrates for potential use in neural interfaces.
• To evaluate the *in vivo* response of retinal tissue to these graphene-based implants.

Main Methods:

• Fabrication of non-functional CVD graphene/polyimide/SU-8 devices.
• Surgical implantation of devices beneath the retina in blind P23H rats.
• Monitoring implant stability using optical coherence tomography (OCT) and eye fundus imaging for up to 3 months.
• Histological analysis, including confocal imaging for microglial reconstruction.

Main Results:

• Implants demonstrated high *in vivo* stability for up to 3 months.
• The presence of graphene on polyimide significantly reduced microglial cell density compared to polyimide alone.
• This reduction in microglial response indicates enhanced biocompatibility of the graphene-containing material.

Conclusions:

• Graphene-embedded polyimide substrates exhibit high biocompatibility in a retinal tissue model.
• This approach offers a promising strategy for developing safer and more effective neural implants.
• The retina serves as an accessible and optically/surgically tractable model for assessing central nervous system material biocompatibility.