A review of 4D printing – Technologies, shape shifting, smart polymer based materials, and biomedical applications

Additive Manufacturing (AM) has been a noticeable technology and made significant progress since the late 1980s. Despite the tremendous growth, this technology is still facing numerous manufacturing challenges. AM of structures and smart materials such as shape memory polymers and alloys is one of the most actively researched areas in which printed objects can alter their properties and shape when exposed to a stimulus e.g., light, temperature, magnetic fields, pH, and humidity. The AM-build parts which can take advantage of these shape-changing features, lead to the growth of 4D printing by introducing time as a fourth dimension in AM processes. This new field originated in 2013, and since then, it has generated great interest due to its potential to build innovative, multi-functional, self-assembling, and self-repairing components with modifiable properties, shapes, and functionalities. This review article intends to examine the major developments of 4D printing in the biomedical field. The study will provide an overview of various 4D printing technologies including vat photo-polymerization, extrusion-based methods, and material jetting and their uses in the biomedical field. It focuses on smart materials like SMPs, LCEs, SMPAs, etc., and their applications in various industries e.g., mechanical, biomedical, aerospace, etc., and explores external stimuli such as moisture, temperature, pH, magnetic fields, and light. The article delves into the promising applications of 4D printing in biomedical fields such as drug delivery, orthopedics, medical devices, tissue engineering, and dentistry and analyzes the challenges associated with 4D printing in the biomedical field, and suggests the future directions including optimization of printing parameters, and exploration of novel materials to broaden its applications.