Extracellular polymeric substances from psychrophiles regulate ice crystal growth and thermal hysteresis to enhance frost resistance

Freeze-thaw cycles pose a significant threat to geotechnical stability, causing frost heave and permafrost degradation. Traditional chemical and mechanical mitigation methods are often costly and environmentally unsustainable, prompting interest in nature-inspired solutions. In this study, we investigate the cryoprotective potential of extracellular polymeric substances (EPS) produced by the psychrophilic bacterium Polaromonas hydrogenivorans . Six distinct EPS variants (EPS 1-6) were synthesized at 4 °C and 30 °C to evaluate their influence on ice crystal morphology, freezing point depression, and thermal hysteresis within fine sand, silt, and kaolinite matrices. EPS treatment dynamically reshaped ice crystals, achieving a size reduction of up to 96% and suppressing freezing points by as much as 24.12 °C. Performance was highly sensitive to soil texture: EPS 4 exhibited the maximum thermal hysteresis activity in fine sand (245% increase), whereas EPS 2 was most effective in silt (136.4%) and kaolinite (88.9%) relative to untreated controls. Our results indicate that while nominal dosages of EPS offer a potent, sustainable alternative for frost mitigation, its efficacy is modulated by soil pore structure and dispersion limits in fine-grained materials. These findings establish a framework for site-specific, bio-based soil stabilization in cold regions.