Intestinal Villi-Inspired Living Biobatteries via Habitat-Engineered Conductive Hydrogel Architectures

Microbial bioelectrocatalysis demands more than electron-conducting surfaces-it demands living microenvironments that hydrate, protect, and nourish whole-cell biocatalysts. This biological imperative remains unaddressed by conventional electrode design. Here, we fundamentally reframe microbial biobattery architecture through living habitat engineering, drawing inspiration from the human small intestine-a biological interface evolutionarily optimized to sustain dense, metabolically active microbial communities through high-surface-area villi, mucus-mediated hydration, and short-path nutrient exchange. We translate these principles into spore-programmed conductive hydrogel pillar arrays, in which dormant Bacillus subtilis endospores are embedded within poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)-poly(vinyl alcohol)/reduced graphene oxide hydrogel villi that simultaneously serve as microbial reservoirs, bioelectrochemical scaffolds, and electron-harvesting conduits. Upon nutrient contact, spores germinate on demand into electroactive cells. This villi topology delivers an 8.3-fold volumetric power density enhancement (8.04 to 66.45 µW cm^{- 3}) over planar controls under volume-matched conditions. A 24-device geometry matrix uncovers a coupled radius-height design rule, with peak single-villus power of 8.35 µW at optimal dimensions. Conformable villi patches demonstrate nutrient-triggered electricity generation in a simulated pipe environment using a wastewater-mimicking nutrient/electrolyte solution, while a separate self-powered array achieves spatially resolved bioelectrochemical sensing. This work establishes living habitat engineering as a transformative paradigm for activatable, architecture-programmed, and potentially shelf-stable microbial biobatteries.