Biodegradable Gel Electrolyte for Self-Electrified Implantable Biomedical Devices

Gel electrolyte have attracted increasing attention as one of compartment of battery system due to their mechanical strength and high capacitance-to-volume ratio. However, the non-biodegradable gel electrolyte is still challenging to apply to various applications because of the harmfulness to environment and the toxicity to human. Here, we developed the biodegradable gel electrolyte by blending the polyvinyl alcohol (PVA) with polyethylene glycol (PEG) to enhance their mechanical, electrical, and electrochemical stability for implantable bioelectronic devices. We synthesized the different ratio of blended hydrogel (PEG:PVA = 1, 2, 5, 10, 20 %) by freezing-thawing method. The biodegradable gel electrolyte is achieved by immersing the blended hydrogel into ion-rich solution (<i>i.e.,</i> Phosphate Buffered Saline (PBS) and ionic liquid etc.). The prepared gel electrolyte exhibits better <u>mechanical strengths</u> (tensile strength of ~30 kPa under 120 % of strain) and high <u>ionic conductivity</u> (~ 50 mS/cm) compared to pure PVA hydrogel and PEO hydrogel. Although the liquid electrolyte induces the corrosion of biodegradable electrode (Mg, W, Mo etc.) surface leading to poor electrochemical performance, the prepared gel electrolyte can increase the anodic reaction up to 3.7 V, which reduce the corrosion and hydrogen evolution reaction (HER) of biodegradable anode and cathode. In addition, the PEG:PVA blended hydrogel is degraded by 14 days at 37 °C, which can be applied to biodegradable bioelectric devices. We anticipated that the biodegradable gel electrolyte can be applied for the biodegradable self-powered electroceuticals and biodegradable supercapacitor for implantable biomedical applications.