A hydrogel that combines conductive additives with the strength of dynamic bonds to create a naturally flexible and adhesive electrode.  

Biocompatible sensors offer immense opportunities in neurological and cardiac testing, health and fitness tracking, medical robotics, and prosthetics. Unfortunately, modern sensors use hard materials like silicon and metal which break after strains of just 3% and require adhesives for medical applications. These materials also require electrolytic gels to reduce impedance, leading to long-term breakdown and skin irritation. In addition, hard materials are difficult to miniaturize for next-generation implantable technologies, such as deep brain stimulators, which can treat neurological disorders like Parkinson’s Disease.  

The research team combined the biocompatibility and flexibility of hydrogels with the high conductivity found in two-dimensional MXenes and other conductors to create a naturally flexible and adhesive electrode. This device easily contours and adheres to the human form while maintaining high conductivity and low impedance.  

First, a base hydrogel comprising polyvinyl alcohol, boronic acid and chitosan is created. It is then mixed in a conductive filler made of carbon nanotubes, reduced graphene oxide, PEDOT:PSS, or two-dimensional MXenes with up to 5 wt%.  The conductive hydrogel mix can achieve DC conductivities ranging over three orders of magnitude depending simply on the loading percentage and conductive filler type. Preliminary tests on skin also show lower impedance than commercial 3M 2360 adhesive electrodes.

• DC conductivity up to 500 mS/cm at 5 wt% MXene loading, more than two orders of magnitude larger than the conductivity of water.
• Fine-tunable conductivity between 10 and 1000 mS/cm achievable with varying composition of reduced graphene oxide, PEDOT:PSS, MXene, carbon nanotube, salts, and antioxidants.