4D printing for minimally invasive biomedical applications: programmable smart materials for deployable devices, drug delivery, and tissue regeneration

4D printing extends additive manufacturing beyond static form by enabling structures that change shape or function over time in response to programmed stimuli. This capability is accelerating biomedical innovation in tissue regeneration, on-demand drug delivery, and minimally invasive deployable devices. This review focuses on recent advances in 4D printing for biomedical purposes, emphasizing key developments, challenges, and opportunities that define this emerging field. The review is divided into five main sections. It begins by introducing the concept of 4D printing and its specific relevance to biomedical applications. The second section focuses on applications of 4D printing, categorized into three main areas: drug delivery systems, tissue engineering, and biomedical devices. Following, the materials used in 4D printing for biomedical purposes, such as shape-memory polymers, hydrogels, shape-memory alloys, shape-memory ceramics, and composites, are discussed in detail. The techniques enabling the fabrication of adaptive structures tailored for medical use are then reviewed. Finally, the challenges associated with 4D printing in biomedical applications are critically analyzed, with a focus on material limitations, scalability in manufacturing, mechanical and functional stability, as well as environmental impact. This integrated perspective provides design guidelines and priority directions to accelerate clinically relevant 4D-printed biomedical systems.