Bioinspired solid-liquid biphasic structures with programmable and tunable impact resistance properties

The design of impact-resistant materials for protective gear remains a critical challenge, requiring materials that can efficiently absorb energy while maintaining flexibility, i.e., the ability to undergo reversible deformation and avoid catastrophic brittle failure rather than a loss of stiffness. Inspired by the intricate microstructure of ram horns, this work proposes a novel approach incorporating biomimetic solid-liquid biphasic structure. Through optical microscopy and synchrotron tomography, we characterize the tubular cell or perforated arrangement and moisture distribution within the horn, revealing how these features contribute to its mechanical resilience. The total porosity of the horn sheath was ∼2.84 %, with the tubules and perforated comprising ∼20 % of the whole area. The horn sheath maintained a total water content of about 20±5 wt%, composed of approximately of about 10 wt% bound water and 6–14 wt% free water. Compression tests demonstrate that the hydrated horn sheaths exhibit strain rate insensitivity, and the presence of free water reduces modulus and yield strength but delays densification, thereby enhancing overall toughness. Inspired by these natural features, we design a PDMS-Ga-based biphasic structure, which exhibits low quasi-static modulus (∼1 MPa) and high energy absorption per volume (∼10⁶ J/m³) attributed to the synergistic effects of the liquid phase. In addition, as the strain rate increases, the specific energy absorption of the solid-liquid biphasic structure rises from 2.32 J/g at low strain rates to 15.04 J/g at high strain rates, resulting in a sevenfold increase in its energy dissipation effect. Correspondingly, the ultimate strength is about 8.43 MPa at a strain rate of 350 s⁻¹, but subsequently increases to 26.05 MPa at 1000 s⁻¹. This work underscores the promise of bio-inspired materials in advancing the design of next-generation protective gear, such as flexible guard and wearable electronics.