Silicon carbide neural implants: In vivo neural tissue reaction

Abstract

Novel materials are needed for intracortical neural implants (INI) to extend their reliability and functionality beyond a few years. Cubic silicon carbide (3C-SiC) is a chemically inert, physically robust semiconductor that has shown, through extensive in vitro testing, a high biocompatibility with neural cells. Recently we have shown that 3C-SiC does not attract a negative immune response from microglia in vivo, but the implants size did not allow adequate investigation of tissue response [1]. We produced a passive implant to test the in vivo tissue reaction of C57BL/6J mice to 3C-SiC and compare to our positive control of silicon (Si). Dual, triangular shanks were fabricated from each material and combined into a single device which was then implanted simultaneously into three C57BL/6J mouse brains for 35 days. The mice were perfused with 4% paraformaldehyde and the brains treated using immunohistochemistry. Fluorescence microscopy indicated that Si produced the expected increased inflammatory response from both microglia/ macrophage and astrocyte cells, whereas 3C-SiC shows minimal inflammatory reaction from these glial cells. Si also created tissue voids larger than the implants themselves whereas 3C-SiC showed minimal voids and even still had neuronal processes in contact with the implant. Our conclusion is that 3C-SiC shows great potential for use within the neural environment and should be fashioned into active INI to evaluate signal quality over time.

Transmission of wireless neural signals through a 0.18µm CMOS low-power amplifier

“…In a previous study [13], it was observed that cubic silicon carbide (3C-SiC) is highly compatible with CNS tissue in a murine mouse model. Therefore, in this work, we opted for 3C-SiC as the most adequate material to define a permanent implantable neuronal prosthesis.…”

“…Our solution relies on two features: (1) we use a chip designed to operate with a power consumption that is small enough for it to be powered by radio frequency antennas, dispensing with the need for batteries; (2) we use a probe manufactured from silicon carbide (SiC), a material that demonstrated excellent neural compatibility with murine mouse brain tissue in vivo [13]. This paper presents the first version of the Cortex chip, which is a 4-channel amplifier that magnifies neural signals to levels high enough for them to be processed by a computer.…”

Silicon Carbide Materials for Biomedical Applications

“…At this stage it is useful to review some of the important biomedical devices that have been reported and use SiC materials. Indeed, SiC has been used in virtually every part of the human body, from a durable coating for bone prosthetics [38] and in dental applications [39], which cover the mechanical/structural biomedical use of SiC, to coatings for brain-machine-interface (BMI) devices [7,28,[40][41][42][43][44], myocardial heart probes [45,46] and finally non-fouling coatings for coronary heart stents [10,30,47]. A plethora of sensors have been reported and, at this point, it is sufficient to review the literature for a sampling of this important work [26].…”

“…d An incubation device with PID controlled temperature and CO 2 saturation which will allow the MEA to be used for long term neuroscience experiments material uses most of the processing techniques available from the Si semiconductor device industry. Here we report some of the initial in vivo reactions from CNS microglia to an neural implant composed of 3C-SiC(100) [41,155].…”

“…d One of the 10 µm thick 3C-SiC shanks showing the flexibility of the material under a load applied with tweezers. The thickness has since been increased to 15 µm as the 10 µm thick shanks did not easily penetrate the cortex of the mouse [155] Si simultaneously, one material in each hemisphere of the brain. The device was implanted in the area nearest the rostral mesencephalon, or mouse midbrain, where it will interact with a large area of the hippocampus as well as parts of the sensory cortex of the mouse.…”