Wrinkling Pickering Emulsions via Endospore Germination

Pickering emulsions are stabilized by coating droplet surfaces with solid particles that provide exceptional stability and suppress coalescence. However, these particles are typically inert and lock emulsions into fixed morphologies, limiting their functionality. Creating smart emulsions, which can change their morphology in response to triggers, remains a major challenge. This research introduces an oil-in-water Pickering emulsion stabilized by Bacillus subtilis endospores that combines long-term stability with germination-triggered responsiveness. Upon nutrient exposure, dormant endospores germinate and expand, generating compressive stress on the droplet's surface. In response to this, droplets develop interfacial wrinkles, which correlate with the initial spore surface coverage, with higher coverage producing more pronounced, finer wrinkles. Notably, not only does our emulsion retain stability at room temperature for months, but the endospores remain viable and can be germinated on demand. This work provides a simple route to producing robust, sustainable, and "bio‑actuated" emulsions that undergo controlled interfacial morphological changes.