Stretchable Electrode Using Silver Nanowires and Elastomeric Block-Copolymer Nanocomposite for Biomedical Devices

Abstract

Stretchable conductors with high conductivity and stable performance under deformation are potentially highly useful for fabricating improved stretchable and wearable devices. Stretchable conductive nanocomposites comprising a percolation network of various conductive nanomaterials are being vigorously investigated to utilize their outstanding electrical and mechanical properties. Silver nanowire-based stretchable conductor, in particular, showed stable electrical performance under extreme mechanical deformation because of its intrinsically high conductivity and high aspect ratio. This dissertation describes the synthesis of highly conductive and stretchable silver nanowire/elastomer nanocomposite and device fabrication processing to minimize strain, so as to develop stretchable bio-medical devices such as articular thermotherapy device and epicardial mesh for cardiac resynchronizing therapy. First, a soft, thin, and stretchable heater was developed by using a nanocomposite of silver nanowires and a poly(styrene-butadiene-styrene) (SBS) elastomer. A highly conductive and homogeneous nanocomposite was formed by the ligand exchange reaction of silver nanowires. By patterning the nanocomposite with serpentine-mesh structures, conformal lamination of devices on curvilinear joints was achieved, which led to effective heat transfer even during motion. The combination of a homogeneous conductive elastomer, a stretchable design, and a custom-designed electronic band helped create a novel wearable heater system that can be used for long-term and continuous articular thermotherapy. Second, the epicardial device was developed to improve the systolic function in a diseased rat heart without impeding the diastolic function by wrapping the device around the rat heart. The epicardial mesh was designed with elastic properties that are nearly identical to those of the epicardial tissue of the rat heart, and hence, the mesh functioned as a structural component by reducing the host-myocardial wall stress. In addition, the epicardial mesh was able to detect electrical signals reliably on the moving rat heart as well as activate the entire ventricular myocardium simultaneously through synchronized electrical stimulation over the ventricles. Electrically and mechanically optimized epicardial mesh using the ligand-exchanged silver nanowire and SBS nanocomposite improved the hemodynamics in experimental heart failure in the rodent. Finally, a new biocompatible and conductive nanocomposite was developed for stretchable bio-medical devices. As the stretchable conductive composites become widely available as an implantable biomedical device, its biocompatibility must be improved. To overcome the limited biocompatibility of the silver-based nanocomposite, a gold nanoshell was encapsulated on the ultra-long silver nanowire (Ag@AuNW) to prevent the toxic silver ion from leaching out. The formed novel percolation network in the fabricated Ag@AuNW and SBS composite showed stable electrical performance of stretchable conductors under extreme mechanical strain (up to 180%), resulting in high conductivity and stretchabiltiy. A 3D customized cardiac mesh-sock for the porcine heart was fabricated using the Ag@AuNW/SBS composite. In an acute-MI porcine heart, the progress of heart disease was monitored by chronological cardiac activity mapping through a customized 3D mesh sock. Multi-channel electrodes on the epicardial surface diversified the pacing sites on the dysfunctional heart, enabling disease-specific treatment by offering various electrical treatment options without any spatial limitation.