Bioelectronic Energy Storage: A Pseudocapacitive Hydrogel Composed of Endogenous Biomolecules

Advances in bioelectronics have produced implantable devices for in vivo biosensing and therapeutics, but batteries for implantable devices currently require bulky metal cases to sequester toxic electrolytes and immunogenic active materials; therefore, development of new materials is paramount for safety and miniaturization. Implantable batteries could be fully biocompatible if they exclusively comprised endogenous materials. Accordingly, we present an energy-storage material fabricated entirely from endogenous biomolecules via one-step carbodiimide conjugation of dopamine (DA) to hyaluronic acid (HA). The DAHA composite can be electropolymerized to create a pseudocapacitive biopolymer, p(DAHA), that exhibits catechol–quinone interconversion, stability, long-term electroactivity for 400 cycles, and high pseudocapacitance (up to ∼900 F g –1 ) and discharge capacity (∼130 mAh g –1 at ∼10 A g –1 ). These characteristics predispose it for bioelectronic energy storage, i.e., as a supercapacitor or, when coupled with an implantable Ag/AgCl electrode, a biobattery with an operating voltage of ∼0.85 V.