SiC protective coating for photovoltaic retinal prosthesis.

Area of Science:

• Biomaterials Science
• Materials Science
• Ophthalmology

Background:

• Implantable electronic devices, such as retinal prostheses, require robust protective coatings to ensure long-term functionality and biocompatibility.
• Degradation of coatings can lead to device failure and adverse biological responses.
• Amorphous silicon carbide (α-SiC:H) is a promising material for protective coatings due to its chemical inertness and mechanical properties.

Purpose of the Study:

• To evaluate plasma-enhanced, chemically vapor deposited (PECVD) amorphous silicon carbide (α-SiC:H) as a protective coating for retinal prostheses and other implantable devices.
• To investigate the in vivo failure mechanisms of these coatings.

Main Methods:

• Retinal prostheses coated with α-SiC:H were implanted in rats for up to 1 year.
• Implant degradation was assessed using optical and scanning electron microscopy.
• Accelerated soaking tests at 87 °C in saline were performed to measure dissolution rates of SiC, SiNx, and thermal SiO2.
• Defects in SiC films were analyzed by selectively removing underlying materials.

Main Results:

• SiNx dissolved at 18.3 ± 0.3 nm/d, and thermal SiO2 dissolved at 0.104 ± 0.008 nm/d at 87 °C.
• α-SiC:H films exhibited superior stability, with no quantifiable degradation after 112 days of accelerated testing.
• Defects in thin SiC films were primarily observed over complex topography and rough surfaces.

Conclusions:

• α-SiC:H coatings provide effective protection against erosion, with 112 days of accelerated aging at 87 °C correlating to approximately 10 years in vivo.
• Photovoltaic retinal prostheses with PECVD α-SiC:H coatings demonstrated protection from erosion during a 4-month in vivo follow-up.
• An optimal α-SiC:H layer thickness of approximately 560 nm is recommended for anti-reflective properties and defect coverage.