Comprehensive review of 3D/4D printing of soft materials, methods and applications

This article extensively reviews the transforming landscape of 3D and 4D printing of soft materials, their printing methods, and their applications in wider engineering and technological sectors. Soft materials are known for their suppleness and plasticity and have a wider scope in rapidly growing additive manufacturing sector. The contents of this article are appropriately designed to provide detailed subject knowledge to young or new researchers and also critically analysing several enabling strategies on manufacturing process, material design and formulation, and multifunctional application for subject experts. This article reviews the high potential 3D/4D printing methods for materials such as extrusion-based printing, inkjet-based printing, stereolithography, selective laser sintering, direct ink writing, vat photopolymerization, and comparison of techniques and compares their scope and limitations by process and materials. Further, the article reviews the printability of emerging soft materials such as elastomers, hydrogels, biopolymers, conductive and flexible materials, and biomimetic materials. The application of 3D/4D printed soft materials in wider engineering sectors are discussed such as biomedical and healthcare applications, soft robotics, sensors, and actuators, wearable devices and smart textiles, food technology, and pharmaceutical products. The later sections describe design considerations, challenges, and limitations of 3D/4D printing of soft materials in terms of geometric complexity, support structures, printing resolution, accuracy, cost, and fabrication time, material compatibility, scalability, and safety issues. The article concludes by summarizing advancements in printing technologies, material innovations and developments and reflecting on future challenges such as integration of 3D/4D printing of soft materials with other technologies and compounds and their regulatory and ethical considerations.