The brain influences all aspects of our life, is the most complex organ of the body and is composed by billions of cells, mainly neurons and glia. Neurological conditions are the second leading cause of death worldwide and the leading cause of Disability Adjust Life Years, accordingly to World Health Organization. It’s key to better understand and monitor the brain in order to prevent and cure brain related diseases, such as stroke, dementia, epilepsy, depression, drug addiction, and Parkinson and Alzheimer disease. The introduction of high-density implantable neural probes based on complementary metal–oxide semiconductor (CMOS) technology, such as the SiNAPS probes developed in our lab, is a big step forward in neuroscience. These new probes provide simultaneous access to thousands of single neurons in different brain circuits, introducing hundreds of closely spaced microelectrodes into the substrate for recording extracellular bioelectrical signals. However, when a device is implanted in the brain, it triggers tissue-reactions to protect the brain from the device, called foreign body response (FBR). Such FBR leads to device loss of recording quality over time and eventually to its complete failure. An emerging hypothesis to minimize tissue-reactions and improve chronic stability of implantable probes consists in downscaling the cross-sectional sizes of their shafts (implanted part) as well as the overall system size. Downscaling the size of conventional implantable probes is at the cost of a drastically reduced number of recording sites due to technological limitations, which leads to limited information retrieved from the brain. The ChroMOS project explored the key advantages of monolithic CMOS-based neural probes together with the optimization of circuits, materials and microfabrication processes to reduce the size of the probe to micro-wire like dimensions (≈ 30 µm diameter) while maintaining a high number of recording sites.
