with the outermost layer of biological tissues, often spanning a significant surface area. Devices typically have multiple electrodes that aim to monitor and modulate cells and tissues in a minimally invasive manner, using biomaterials designed to evoke minimal inflammatory responses.
Applications of Surface Electrode Arrays
RecordingBecause surface electrode arrays can record a "snapshot" of the electrical activity at distinct locations, these arrays are useful to monitor the function of a tissue. Though the recordings are typically local field potentials, with electrodes that are small enough to modulate as little of a location as possible while still maintaining a sufficiently high conductivity, single units from individual cells have been reported. Clinically, these recordings are used to map the epicardial surface to identify instances, and potentially mechanisms, of chronic atrial fibrillation, [1] dysfunction of ventricular tachycardia caused by congenital defects, [2] and other abnormal conduction conditions in the cardiac system. Clinical electrocorticogram (ECoG) is used to identify similar functional changes on the cortical surface of the brain, most commonly to identify epileptic focal center(s), or detect seizure activity. [3][4][5][6][7] Other functional uses of ECoG include intraoperative monitoring during tumor resection. [8] A surgeon can ask a patient to perform an activity such as a speech and then identify and avoid the active cortical regions during surgery, to avoid major disruptions to the patient quality of life.
StimulationInstead of passively monitoring electrical activity, multielectrode surface arrays can provide electrical current to the underlying tissue and induce a desired excitatory or inhibitory response. The applications for stimulating surface electrode arrays are often therapeutic and include implantable pacemakers, which restore a normal cardiac rhythm by providing external and overriding cues to the cardiomyocytes responsible for establishing a sinus rhythm. [9] Pulses delivered to specific regions of the spinal cord are used to manage chronic pain, [10][11][12] and more recently as a therapy to promote neuronal plasticity in Surface electrode arrays are mainly fabricated from rigid or elastic materials, and precisely manipulated ductile metal films, which offer limited stretchability. However, the living tissues to which they are applied are nonlinear viscoelastic materials, which can undergo significant mechanical deformation in dynamic biological environments. Further, the same arrays and compositions are often repurposed for vastly different tissues rather than optimizing the materials and mechanical properties of the implant for the target application. By first characterizing the desired biological environment, and then designing a technology for a particular organ, surface electrode arrays may be more conformable, and offer better interfaces to tissues while causing less damage. Here, the various materials used in each component of a surface electrode array are first r...
