However, their low conductivity and ionic conductive nature hindered their applications in in vivo tests.Īnother important category of materials in the fabrication of bioelectronics is the amphiphilic conducting polymers, such as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS), polypyrrole (PPy), poly(3-hexylthiophene-2,5-diyl) (P3HT) and polyaniline (PANI). Theses ionic conductive hydrogels based electronics were also named as ionotronics, which have found their applications in epidermal sensors, artificial axons and soft actuators. By further dissolving electrolyte molecules such as LiCl, NaCl, KCl or even zwitterionic molecules into hydrogel matrix, ionic conductive can be achieved. Either synthetic polymers like polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyacrylamide (PAAm), poly(2-hydroxyethyl methacrylate) (PHEMA), etc., or natural macromolecules such as polysaccharides, gelatin and proteins, etc., can be utilized to synthesized biocompatible hydrogels. Hydrogels have emerged as a promising candidate for fabrication of next-generation bioelectronics, due to their similarity to biological tissues, water infiltrability and versatility in electrical, mechanical, and biofunctional engineering. However, there still could be challenges with formation of scar tissue between bioelectronics and biological tissues during long-term implantation, resulting in the increase in interfacial impedance. The employment of degradable metal and metal oxides as conducting and dielectric materials, respectively, and bioresorbable silk or poly(lactic-co-glycolic acid) (PLGA), transient bioelectronics can be manufactured. The biocompatible metals such as gold were engineered into serpentine shapes to enabling its stretchability as conducting circuit materials, by further integration of these engineered stretchable circuits with semiconductor into a thin and flexible polydimethylsiloxane (PDMS)-based encapsulations via “soft lithographic” technologies several types of bioelectronics were fabricated including epidermal tactile/chemo-sensors, implantable cardiac pacemaker, optoelectronics, etc., which demonstrated their applications in biomedical research and potential clinical treatments.

The fabrication of bioelectronics combines the careful design of deformable circuits, integration of rigid and planar semiconductor devices, and the engineering of soft and stretchable encapsulations to realize a better mechanical matching with soft biological tissues and even growing organisms, enabling their constant communication with human body. These systems which can interface with human bodies via electrical stimulation and recording of biological signals are of great interest in emerging neural science and engineering, diagnostics, therapy, and wearable and implantable devices. From materials point of view, bioelectronics and biomedical devices are mostly composed of conductive, dielectric, and semiconductor materials, as well as soft substrates/encapsulations.

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