4D Printing of Physical Stimuli-Responsive Hydrogels for Localized Drug Delivery and Tissue Engineering

The biomedical industry has witnessed a transformative evolution with the advent of 3D printing technology. However, inherent limitations, such as the inability to produce dynamic human tissues due to the absence of the temporal dimension, have persisted, resulting in static and inanimate printed products. To address this challenge and enable the creation of dynamic and living constructs, the concept of 4D printing has emerged, marking a paradigm shift in additive manufacturing. In 4D printing, time becomes the fourth dimension, breathing life into previously static creations. This review paper explores the journey from 3D to 4D printing and the pivotal role of time in the additive manufacturing process. Specifically, it highlights the integration of time-dependent responsive materials, focusing on stimuli-responsive hydrogels, as a cornerstone in 4D printing advancements. These materials exhibit a remarkable ability to adapt and respond to various stimuli, encompassing physical, chemical, and biological signals. The review delves into recent publications on the synergy between these stimuli and responsive materials, shedding light on their intricate interactions and potential applications. One of the primary areas of interest lies in medical applications, notably tissue engineering, where 4D printing holds immense promise. The paper explores the utilization of 4D printing in creating biomimetic scaffolds that can dynamically adapt to complex tissue environments. Furthermore, the review discusses the technical considerations and prospects of 4D printing technology, emphasizing its potential to revolutionize the biomedical landscape. The amalgamation of 4D printing and stimuli-responsive materials opens new avenues for personalized medicine, localized drug delivery, and regenerative therapies, bridging the gap between static 3D printing and the dynamic requirements of modern healthcare. The present review offers a complete examination of the evolution, challenges, and prospects of 4D printing in biomedical applications, paving the way for transformative innovations in the field.