Inkjet-Printed Flexible Gold Electrode Arrays for Bioelectronic Interfaces

Bioelectronic electrodes are essential in electrophysiology, the scientifi c fi eld that investigates the relationship between electricity and life. Since the advent of electrophysiology in 1783 marked by Luigi Galvani’s experiment of electrical stimulation of a frog leg, electrodes have been used to transduce the body’s ionic current to electronic current and vice versa. [ 1 ] These bioelectronic electrodes can be utilized for both bioimpedance and biopotential measurements. In the case of bioimpedance tomography, a small amount of alternating current is sourced through the tissue, and the resultant voltage signals are recorded using an array of electrodes. Then, various biological tissues are electrically differentiated depending on the complex impedance of the tissues. The contrast between two different types of tissue, for example, lean and fatty tissues, can be picked up using this technique and reconstructed graphically. [ 2 ] In biopotential measurements, differential voltage measurements are done on skin and tissue. For example, in electrocardiography (ECG), a set of electrodes are used to pick up the electrical depolarization signal of the heart that provides the cardiac rhythm of the patient. [ 3 ] For bioimpedance and biopotential measurements, the interface between the electrode and the body is crucial, any disturbance at the interface creates unwanted noise artifacts or even invalidates the measurement. [ 4 ] Flexible electronics and optoelectronics are highly promising for creating high-fi delity bioelectronic and biophotonic interfaces. [ 5–8 ] The elasticity of fl exible electronics allows skin-like devices, which are bendable and stretchable. [ 9,10 ] Hence, medical devices fabricated using fl exible materials have the potential to interface better with the human body when compared to rigid electronics. Fabrication of fl exible medical devices has heavily relied on processing techniques such as metal evaporation, atomic layer deposition, photolithography processes, and transfer printing. [ 11,12 ] In contrast, printing methods, which use relatively inexpensive tools and mild processing conditions, [ 11,13 ]