Multimaterial 3D printing of self-assembling smart thermo-responsive polymers into 4D printed objects: A review

The three-dimensional (3D) printing and its extension four-dimensional (4D) printing technique show great promise for advanced additive manufacturing of functional and architected materials with engineered micro- and nanoscale features. The actual usage of additive manufacturing to produce 3D/4D structures is primarily dependent on the improvement of printable polymeric inks. Thermoresponsive polymers (TRPs) show broad application prospects in additive manufacturing since they enable changing the physicochemical properties of the system at a specific temperature. Continuing to progress in the understanding of TRP phenomena enable the design of new feedstocks and their compatibility with fabrication processes. Therefore, increasing the overlap between the fields of fundamental TRPs and application-based research efforts can be important to emerging the technology. In this review, we provide an overview of the functional design of the TRPs, the different classes of TRPs, and their application in 3D printing, ranging from biosensors via advanced self-assembly to a variety of biofabrication, biomedical, biotechnology, and food applications. Basic knowledge of imperative processes like gelation mechanisms of TRPs, bio-based adsorption on the surfaces and adhesion, and fabrication strategies using 3D printing is also provided. For diverse TRPs synthesis and the basic physical and chemical features are described and the mechanism of their TRPs behavior is highlighted. Fabrication methods of TRP surfaces have also been discussed describing several methods in detail.