Ultrastrong and Tough Three-Dimensional Large-Scale Hydrogels via the in Situ Mineralization Assisted Salting-Out Strategy

The salting-out effect has been used to improve the strength and toughness of poly(vinyl alcohol) (PVA) hydrogel by the soaking process. However, the soaking process usually compromises the uniformity and structural stability of PVA hydrogel due to its freedom to shrink during the soaking process, making it difficult to prepare three-dimensional large-size PVA gel with ultrahigh strength, toughness, and fine surface patterns. To address this, we present a facile and efficient strategy based on the synergistic combination of in situ biomineralization and salting-out treatments. Compared with single salting-out soaking modification, this synergistic dual-treatment strategy perfectly solves the key defects of serious shrinkage and poor shape fidelity existing in conventional soaked hydrogels. The in situ biomineralization was achieved by directly introducing sodium citrate (Na3Cit) into the PVA/CaCl2 aqueous solution to form calcium citrate (Ca3Cit2) nanoparticles. The salting-out effect was realized by immersing the hydrogel obtained by freezing and thawing in the saturated Na3Cit solution for 24 h. Through these steps ultratough PVA hydrogels with regular and uniform shape were successfully obtained. Tensile testing results showed that the prepared hydrogel exhibited exceptional mechanical properties, with tensile strength of 14.1 ± 0.17 MPa, Young’s modulus of 16.2 ± 0.69 MPa, and toughness of 42.6 ± 2.70 MJ/m3, respectively. These values are 28 times, 4050 times, and 71 times higher than those of pure PVA hydrogels in terms of tensile strength, Young’s modulus, and toughness, respectively. More importantly, this hydrogel also demonstrated excellent biocompatibility and resistance to swelling, with over 80% cell viability within 1–5 days, reaching swelling equilibrium of 40% in physiological media within 24 h. This study provides a solution to the long-standing problem of uncontrollable shrinkage troubling the preparation of high strength PVA in the soaking process and enlarges its application potential in the fields of biomedicine and engineering.