4D printing of self-healing and shape-memory hydrogels sensitive to body temperature

The development of thermoresponsive shape-memory hydrogels (SMHs) that combine robust mechanical properties, self-healing capabilities, and 4D printing potential holds great promise for advanced biomedical and smart material applications. Such hydrogels with trigger temperatures close to but below 37 degrees C are ideal for biomedical use. Despite their potential, developing SMHs that meet the right trigger temperature along with sufficient mechanical strength remains a significant challenge. We present here a simple strategy to create 4Dprinted mechanically robust, self-healing and shape-memory supramolecular hydrogels with a Young's modulus and tensile strength of 51 f 1 MPa, and 6.0 f 0.3 MPa, respectively. They exhibit a trigger temperature between 32 degrees C and 40 degrees C that can be adjusted by the composition of the hydrogel network. The hydrogels are prepared by terpolymerizing hydrophobic, crystallizable hexadecyl acrylate (C16A), hydrophilic N,N-dimethyl acrylamide (DMAA), and methacrylic acid (MAAc) monomers in the presence of TPO photoinitiator using a commercial stereolithography (SLA) device without any solvent, or cross-linker. Strong hydrogen bonding interactions between DMAA and MAAc units contribute to the mechanical properties of the hydrogels by creating reversible cross-links while the hexadecyl side chains of C16A units further increase the mechanical strength by forming crystalline domains in the hydrogels with a melting temperature between 32 and 40 degrees C. All the hydrogels exhibit complete heat-induced self-healing and shape-memory functions due to their entropic elasticity. The successful 4D printing of shapes like a flower and a paper clip showcases the adaptability of these hydrogels for functional devices such as smart packaging and drug delivery systems.