4D Printing in Biomedical Implants and Functional Healthcare Devices

This review explains how 4D printing combines additive manufacturing with stimuli-responsive materials so that biomedical devices can change shape or function over time in a programmed way. It describes clinically relevant triggers such as temperature, hydration, pH, light (including near-infrared), magnetic fields, and electrical inputs, and the actuation mechanisms they enable (e.g., thermomechanical shape-memory recovery, swelling-driven morphing, and magnetothermal activation). The paper surveys key material platforms used in biomedical 4D printing—shape-memory polymers and alloys, hydrogels, liquid-crystal elastomers, and responsive composites—and connects material choice to expected device behavior. It also discusses example applications (self-expanding stents, cardiac occluders, tissue-engineered constructs, implantable drug delivery systems, and adaptive wearables) and highlights translational challenges such as sterilization compatibility, manufacturing reproducibility/quality control, safe stimulus delivery, predictable biodegradation/biocompatibility, and regulatory pathway definition.