A Novel 3D-Printable Hydrogel with High Mechanical Strength and Shape Memory Property
3D-printing hydrogels with excellent mechanical properties have attracted extensive attention for their potential application in many fields. By photoinitiated copolymerization of methacrylic acid (MAAc) and N-(pyridin-2-yl) acrylamide (NPAM) in DMSO, a copolymer solution was prepared, then 3D printed it at 70oC and followed by a solvent replacement of DMSO to water at 25oC, a novel 3D-printing tough hydrogel was prepared. In the presence of water, NPAM could form “multi-fold” hydrogen bonding with MAAc. Thus, the hydrogen bonding is strengthened and stabilized by the hydrophobic α-methyl of MAAc and pyridine N-heterocycle of NPAM, so that the modules of hydrogel can be up to 5 times the original organogels. The swelling or shrinkage of gel is negligible during the solvent replacement and the resultant hydrogel exhibits excellent mechanical properties, with elastic modulus of 1.8-66 MPa, tensile fracture stress of 2.2-6.3 MPa, fracture strain of 360−570% and fracture energy of 0.5-7.2 KJ/m2. In addition, due to the dynamic nature and temperature sensitivity of the hydrogen bonds, the hydrogel also exhibited a fast self-recovery ability and temperature activated shape memory properties. In particular, the hydrogen-bonding hydrogel could be quickly degraded and recovered by adjusting the pH, which made the recycling of the hydrogels convenient. Our experimental results indicated that the combination of 3D-printing technique and solvent replacement may provide a new and effective method to obtain 3D-printing hydrogels with high mechanical strength and shape recovery property, fostering their use in a number of fields such as soft robots, implant devices, tissue engineering and other environment friendly materials.