Stimuli-responsive materials for 4D Printing: Mechanical, Manufacturing, and Biomedical Applications

Abstract

Four-dimensional printing (4DP) is an interesting field of study that integrates intelligent materials into three-dimensional printing (3DP). Using this method, objects that can gradually change form in response to environmental stimuli, such as moisture, electric or magnetic fields, UV light, temperature swings, pH variations, or alterations in the composition of ions, can be created. Intelligent materials, such as shape memory polymers, alloys, hydrogels, ceramics, and composites, which can react to external stimuli, are essential for 4DP. Unlike traditional 3D printing, the ability of 4D printed materials to undergo structural and/or property alterations expands their applications across industries such as aerospace, biomedical, soft robotics, engineering, and fashion, potentially revolutionizing manufacturing. This review provides an overview of current advancements in 4D printing and discusses both established and emerging smart materials with shape-changing capabilities and their responses to stimuli. It explores the differences between 4D and 3D printing technologies, traces the origins of 4D printing, and examines the materials involved, with emphasis on shape-memory polymers. This paper also highlights the applications of 4D printing in pharmaceuticals and biomedicine, particularly in dynamic polymers, and in the development of drugs for genetic diseases. In addition, it discusses progress in creating implantable biomedical devices and pharmaceutical medications. Despite being in its early stages, 4D printing technology has immense potential and promising exciting possibilities in the future.