3D printing is a rapidly growing technology that has an enormous potential to impact a wide range of industries such as engineering, art, education, medicine, and aerospace. The flexibility in design provided by this technique offers many opportunities for manufacturing sophisticated 3D devices. The most widely utilized method is an extrusion‐based solid‐freeform fabrication approach, which is an extremely attractive additive manufacturing technology in both academic and industrial research communities. This method is versatile, with the ability to print a range of dimensions, multimaterial, and multifunctional 3D structures. It is also a very affordable technique in prototyping. However, the lack of variety in printable polymers with advanced material properties becomes the main bottleneck in further development of this technology. Herein, a comprehensive review is provided, focusing on material design strategies to achieve or enhance the 3D printability of a range of polymers including thermoplastics, thermosets, hydrogels, and other polymers by extrusion techniques. Moreover, diverse advanced properties exhibited by such printed polymers, such as mechanical strength, conductance, self‐healing, as well as other integrated properties are highlighted. Lastly, the stimuli responsiveness of the 3D printed polymeric materials including shape morphing, degradability, and color changing is also discussed.

Achieving multifunctional shape changing hydrogels with synergistic and engineered material properties is highly desirable for their expanding applications, yet remains an ongoing challenge. The synergistic design of multiple dynamic chemistries enables new directions for development of such materials. Herein, we propose a molecular design strategy based on hydrogel combining acid-ether hydrogen bonding and imine bonds. Our approach utilizes simple and scalable chemistries to produce a doubly dynamic hydrogel network, which features high water uptake, high strength and toughness, excellent fatigue-resistance, fast and efficient self-healing, as well as superfast, programmable shape changing. Furthermore, deformed shapes could be memorized due to a large thermal hysteresis. This new type of shape changing hydrogel is expected to be a key component in future biomedical, tissue and soft robotic device applications.

The most pressing challenges for light‐driven hydrogel actuators include reliance on UV light, slow response, poor mechanical properties, and limited functionalities. Now, a supramolecular design strategy is used to address these issues. Key is the use of a benzylimine‐functionalized anthracene group, which red‐shifts the absorption into the visible region and also stabilizes the supramolecular network through π–π interactions. Acid–ether hydrogen bonds are incorporated for energy dissipation under mechanical deformation and maintaining hydrophilicity of the network. This double‐crosslinked supramolecular hydrogel developed via a simple synthesis exhibits a unique combination of high strength, rapid self‐healing, and fast visible‐light‐driven shape morphing both in the wet and dry state. As all of the interactions are dynamic, the design enables the structures to be recycled and reprogrammed into different 3D objects.

The most pressing challenges for light-driven hydrogel actuators include reliance on UV light, slowresponse,poor mechanical properties,a nd limited functionalities.N ow, as upramolecular design strategy is used to address these issues.K ey is the use of ab enzylimine-functionalized anthracene group,w hich red-shifts the absorption into the visible region and also stabilizes the supramolecular network through p-p interactions.Acid-ether hydrogen bonds are incorporated for energy dissipation under mechanical deformation and maintaining hydrophilicity of the network. This double-crosslinked supramolecular hydrogel developed via as imple synthesis exhibits au nique combination of high strength, rapid self-healing,and fast visible-light-driven shape morphing both in the wet and dry state.Asall of the interactions are dynamic, the design enables the structures to be recycled and reprogrammed into different 3D objects.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

Nature has designed and optimized materials to possess a range of properties and functions. Here, we introduced a molecular design strategy to impart customizable functionality and varying mechanical properties into gels; mimicking nature’s range of tunable materials. We demonstrate a gel that is not only tough but also exhibits self-healing, is easily controllable, and the final materials have a broad range of mechanical properties. To develop these materials, we first prepared a methacrylic acid (MAAc) and poly­(ethylene glycol) methyl ether methacrylate (OEGMA) random copolymer: poly­(MAAc-co-OEGMA). The network’s deliberate inter- and intramolecular hydrogen bondings were modified through some of the acid sites being postfunctionalized with benzaldehyde (BA) and cross-linked with diamine-terminated poly­(dimethylsiloxane) (PDMS) to form dynamic imine bonds. Due to the low glass transition temperature of the PDMS cross-linker, the chain mobility can be enhanced, enabling rapid self-healing (>98% within seconds), in addition to improving the stretchability (tensile strain) from a few % to almost 500%. The prepared polymers and gels were well characterized through various techniques including Fourier transform infrared spectroscopy (FTIR), 1H NMR, and size-exclusion chromatography (SEC) analysis. Mechanical testing and dynamic mechanical analysis (DMA) revealed interesting insights into the broad-range (Young’s modulus: 100 kPa to >300 MPa) and tunable mechanical properties, including the tensile strength (from 12 to 0.1 MPa) and strain (up to 500%) as well as the storage (0.1 to 60 MPa) and loss (1 to 40 MPa) moduli of the dynamic self-healing gel. Interestingly, the tensile strength decreasing with increasing cross-link density. Lastly, the biocompatibility of the gels was investigated, with an initial study of both human bone and skin cells indicating increased biocompatibility with gels that had been cross-linked with PDMS.