The PPES was designed in two main parts. First, the nanoengineered flexible electrochemical patch contains a biofuel cell array and a biosensor array for energy harvesting and molecular analysis in human sweat, all on serpentine-connected electrode arrays. The second piece is a flexible electronic patch that consolidates the rigid electronics on an ultrathin polyimide substrate through flexible interconnects for power management, signal processing, and wireless transmission.
The researchers also integrated a skin-interfaced microfluidic module with independent inlet-outlet design into the PPES, to achieve efficient fresh sweat sampling for stable BFC operation and accurate sweat analysis. The electronic components and the interconnects of the PPES are then encapsulated with polydimethyl siloxane (PDMS) to avoid sweat/electronic contact.
As for the actual biofuel cell, it consists of lactate oxidase (LOx) immobilized bioanodes that catalyze the lactic acid to pyruvate and Pt alloy nanoparticle-decorated cathodes that reduce oxygen to water. These redox reactions on the BFC electrodes were proven to yield a stable current, up to 3.5 mW/cm2, to power the metabolite sensors for up to 60 hours of continuous operation. The researchers demonstrated the PPES could selectively monitor key metabolic analytes as well as the skin temperature during prolonged physical activities.