E-Sutures: Electrical and Ionic Conductive Sutures for Medicine and Bioelectronics

Metals have long served as the foundational electrode and wiring materials for implantable bioelectronics due to their high conductivity and processability to achieve the small size necessary for <i>in vivo </i>electrophysiological signal acquisition and stimulation. However, metal-based wires are susceptible to mechanical damage due to material rigidity, and in bulky, high-density systems, they may contribute to patient discomfort. The ideal bioelectronic wire is thus soft, highly conductive, mechanically and chemically resilient and biocompatible. Most importantly, such a wire should also leverage modern polymer chemistry to enable multi-modal interventions, namely mixed-conductors that facilitate delivery of positive and negative charges. In this work, we use PEDOT:PSS to turn silk sutures into flexible, mixed-conducting and biocompatible wires (e-sutures) that can be used for suturing, acquiring electrophysiological signals, delivering electrical stimulation and finally, delivering drug molecules as ion pump channels.<br/> We fabricate e-sutures by coating silk sutures with PEDOT:PSS to produce a mixed conducting suture and then create an insulation layer (jacket) on the fiber using subsequent coatings of PDMS and parylene-C to preserve the conductive properties in an ionic environment<i>.</i> We demonstrate the high conductivity and stability of e-sutures as well as their ability to form robust mechanical connections with metallic circuit components to facilitate integration to a complete bioelectronic device. Further, the conductive nature of e-sutures <i>in vivo </i>is demonstrated by recording electrocardiogram (ECG) from mouse pups, elicitation and recording of intramuscular electromyogram (EMG) in rats as well as local field potential (LFP) from the surface of a rat brain using e-sutures as electrodes. Finally, we demonstrate that e-sutures can serve as an ion pump channel and deliver positively charged molecules from a hydration reservoir to the target tissue without generating volumetric pressure in the delivery target. In summary, the work highlights the capability of PEDOT:PSS coated silk fibers to serve as a soft, biocompatible alternative to metallic wires and electrodes in a research and clinical setting while providing the additional capability of drug-delivery through ion pumping.