Exploring 4D printing for biomedical applications: Advancements, challenges, and future perspectives

4D printing is advanced additive manufacturing (AM) technology with transforming extension of traditional 3D printing that introduces the time dimension for material manufacturing to allow printed objects to change their shape, functionality, or properties with respect to specific external stimuli such as moisture, temperature, pH, or light. 4D printing relies on smart materials such as shape memory polymers (SMPs), hydrogels, liquid crystal elastomers (LCEs), etc. It possesses tremendous scope in biomedical applications, particularly tissue engineering, drug delivery systems, orthodontics, and diagnostic devices. By adopting smart materials and exquisite fabrication techniques, smart biomedical devices developed via 4D printing reply to changes in the physiological situation, increase therapeutic effectiveness, and promote favorable treatment outcomes. This review aims to study the state of the art on 4D printing in biomedical engineering covering fundamentals, materials, applications, challenges, and future perspectives. Nevertheless, many challenges remain such as material biocompatibility, printing resolution, and precise control over transformation kinetics. Future advancements, including AI-assisted design, machine learning optimization, new smart material developments, and high-resolution printing, promise to address these challenges, accelerating the shift toward precision medicine. Collectively, 4D printing demonstrated the ability to revolutionize biosciences for patient-specific, adaptive, and minimally invasive responses to healthcare.