Biological tissues, such as muscle, can increase their mechanical strength after swelling due to the existence of many biological membrane barriers that can regulate the transmembrane transport of water molecules and ions. Oppositely, typical synthetic materials show a swelling-weakening behavior, which always suffers from a sharp decline in mechanical strength after swelling, because of the dilution of the network. Here, we describe a swelling-strengthening phenomenon of polymer materials achieved by a bioinspired strategy. Liposomal membrane nanobarriers are covalently embedded in a crosslinked network to regulate transmembrane transport. After swelling, the stretched network deforms the liposomes and subsequently initiates the transmembrane diffusion of the encapsulated molecules that can trigger the formation of a new network from the preloaded precursor. Thanks to the tough nature of the double-network structure, the swelling-strengthening phenomenon is achieved to polymer hydrogels successfully. Swelling-triggered self-strengthening enables the development of various dynamic materials.
Synthetic hydrogels usually exhibit swelling-induced weakening upon water uptake, which greatly hampers their applications in tissue engineering, soft robotics, and load-bearing devices. Inspired by swelling-strengthening feature of hyperaemic muscles in biological soft tissues, we designed a new type of swelling-strengthening nanocomposite hydrogel through the controlled additional cross-linking of ionic coordination in polymer network. More impressively, the swelling nanocomposite hydrogel exhibits a remarkable increment of mechanical properties including tensile stress by 78 %, Young’s modulus by 152 %, fracture energy by 33 % and compressive stress by 136 %. The unprecedented performance is attributed to the swelling-mediated additional cross-linking of ionic coordination originating from the decreased acidity in the resultant hydrogel. Furthermore, the self-strengthening hydrogel upon swelling can be designed into a strong turgor actuator, which could break a glass slide within 17 min and lift a 1 kg weight to twice the initial height within 80 min. This bioinspired strategy of using the additional cross-linking for swelling-strengthening of hydrogels may enable broad application potentials in artificial cartilage and soft machine in aquatic environment.
危险品化学品经营许可证（带存储）