4D-PRINTED SHAPE-MEMORY POLYMERS FOR ADVANCED DRUG DELIVERY: PROGRAMMING, STIMULI-RESPONSIVE MECHANISMS AND BIOMEDICAL APPLICATIONS

ABSTRACT Four-dimensional (4D) printing is an emerging additive manufacturing technology that integrates three-dimensional (3D) printing with smart materials capable of undergoing programmed changes in shape or function over time in response to specific stimuli. This technology has attracted increasing interest in pharmaceutical drug delivery because it offers the possibility of developing dynamic, programmable, and personalized drug-delivery systems. This review provides an overview of the fundamental principles of 4D printing, including stimulus-responsive mechanisms, smart materials, and major printing technologies relevant to pharmaceutical applications. Particular emphasis is placed on shape-memory polymers, hydrogels, and other responsive materials that can respond to temperature, moisture, pH, light, magnetic fields, and other environmental stimuli. Recent applications in gastroretentive, esophageal, intravesical, intestinal, transdermal, implantable, and localized drug-delivery systems are discussed, with emphasis on their potential to improve drug retention, controlled release, site-specific therapy, minimally invasive administration, and personalized treatment. The major advantages and challenges associated with pharmaceutical 4D printing are also critically evaluated, including biocompatibility, drug–material compatibility, drug stability, reproducibility, quality control, manufacturing cost, scalability, long-term material stability, regulatory requirements, and clinical translation. Finally, future perspectives involving biodegradable smart materials, multi-material printing, nanotechnology, artificial intelligence, and personalized medicine are highlighted. Overall, 4D printing represents a promising approach for transforming conventional static dosage forms into dynamic and adaptive drug-delivery systems; however, comprehensive in-vitro, in-vivo, manufacturing, regulatory, and clinical studies are required to establish its safety, reproducibility, and therapeutic effectiveness. Keywords: 4D Printing, Shape Memory Polymers, Smart Drug Delivery, Stimuli-Responsive Materials, Personalized Medicine.