Smart polyurethane composites for 3D or 4D printing: General-purpose use, sustainability and shape memory effect

Abstract

Excellent biocompatibility, flexibility and shape memory features of polyurethane (PU) have attracted great attention to produce various objects for particular applications in biomedical and electronic fields. The objects with complex geometry in possession of shape memory effect (SME) are arduous when being fabricated by conventional manufacturing methods such as extrusion and injection moulding so that 3D or 4D printing can be offered to overcome this drawback. Neat PU has several material demerits, especially its mechanical strength. The incorporation of the reinforcements, namely fibres, nanoparticles and other polymers, can be achieved to improve mechanical strength, shape memory capability, thermal and electrical conductivities of PU. The most interesting performance of printed structures from smart PU composites lies in a wide range of glass transition temperature allowing these innovative materials to recover to their initial shape after being deformed. Such an ability has improved the materials’ usefulness, particularly for tissue scaffolds, flexible sensors and wearable devices. This review provides a holistic investigation of the current states of PU composites for 3D printing and shape memory PU (SMPU) composites for 4D printing, respectively along with their use, sustainability and SME for enormous future potential.