Characterizing deep brain biosignals: The advances and applications of implantable MEMS-based devices

The brain is the center of the nervous system controlling other organs. The brain is characterized by extreme complexity of its structure and delicate texture, which makes it difficult to investigate by invasive methods. The advances in semiconductor manufacturing technology led to the development of implantable microelectromechanical system (MEMS)-based devices that can be implanted into the brain with reduced risk of damage to the brain tissue due to their small size and low stiffness. Such devices are now widely applied in the clinic and brain research for understanding brain functions, diagnosing brain-related diseases, and pursuing innovative therapies. Inevitably, these invasive devices cause damage to the brain tissue, such as wounds, inflammation, and scars, eventually leading to dysfunction of the device. Therefore, it is vital to find an optimal design solution for such devices taking into consideration such parameters as size, stiffness and biocompatibility. In this review, we focus on three main brain applications of such devices: detection of electrical signals, intracranial pressure (ICP), and optogenetics. We summarize the current application scope of such MEMS-based devices in brain research and clinical application, and compare them based on their mechanical and biological properties. The understanding of the device design, methods of application, and current development can support neuroscientists and neurologists to make revolutionary discoveries in the brain research field.