Abstract
Microelectrodes for pain management, neural prosthesis or assistances have a huge medical demand, such as the application of pain management chip or retinal prosthesis addressed on age-related macular degeneration (AMD) and the retinitis pigmentosa (RP). Due to lifelong implanted in human body and direct adhesion of neural tissues, the electrodes and associated insulation materials should possess an ideal bio-compatibility, including non-cytotoxicity and no safety concern elicited by immune responses. Our goal intended to develop retinal prosthesis, an electrical circuit chip used for assisting neural electrons transmission on retina and ameliorating the retinal disability. Therefore, based on the ISO 10993 guidance for implantable medical devices, the electrode prosthesis with insulation material has to conduct bio-compatibility assessment including cytotoxicity, hemolysis, (skin) irritation and pathological implantation examinations. In this study, we manufactured inter-digitated electrode (IDE) chips mimic the electrode prosthesis through photolithography. The titanium and platinum composites were deposited onto a silicon wafer to prepare an electric circuit to mimic the electrode used in retinal prosthesis manufacture, which further be encapsulated to examine the bio-compatibility in compliance with ISO 10993 and ASTM guidance specifically for implantable medical devices. Parylene-C, polyimide and silicon carbide were selected as materials for electrode encapsulation in comparison. Our data revealed parylene-C coating showed a significant excellence on bio-insulation and bio-compatibility specifically addressed on implantable neuron stimulatory devices and provided an economic procedure to package the electrode prosthesis. Therefore, parylene C encapsulation should serve as a consideration for future application on retinal prosthesis manufacture and examination.
Highlights
The implantable medical electronics clinically are mostly related to the neuron stimulatory devices, such as electronic ear, retinal prosthesis, pain-controlled electronic devices and implantable heart de-vibration devices
We further examined the direct current resistance (DC-R) of chips collected from the saline soaking, showed diminished DC-R values in the SiC and polyimide embedded chips, but DC-R approximately = ∞ in the parylene C embedded group, and demonstrated the water-proof and electrode protection capability of embedment materials using parylene C were superior than that of the SiC and polyimide
Our study showed an affordable and facile engineering process to manufacture an inter-digitated electrode (IDE) chip through photolithography (Figure 1) and subsequently insulated with parylene-C, polyimide or silicon carbide for waterproof comparison
Summary
The implantable medical electronics clinically are mostly related to the neuron stimulatory devices, such as electronic ear, retinal prosthesis, pain-controlled electronic devices and implantable heart de-vibration devices. The implantable neuron stimulatory devices are still existing many unmet medical needs, such as insufficient bio-insulation, bio-compatibility, anti-inflammatory capability and the optimal implantation-assisted hand-helds devices. There are some problems associated with the flexible polyimide coating, such as stiffness, durability and long-termed insulation capability in vivo, and lead to need further material modification [3,4]. Another material, silicon carbide encapsulation has been widely used in the semi-conductor assembly process, and showed excellent insulation capability as described [5], which is emerging as an enabling material for biomedical microsystems due to its unique combination of electrical, mechanical and chemical properties. Surface modification with silicon carbide showed its bio-compatibility, which did not undergo consistent oxidative stress events and did not exhibit morphological modifications or adverse reactions in mitochondrial membrane potential [6]
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