A review of stimuli-responsive materials in 4D bioprinting for biomedical applications

Four-dimensional (4D) bioprinting has been increasingly explored owing to its potential to create dynamic, tunable structures that can respond to external stimuli. The fusion of dynamic stimuli-responsive materials with conventional three-dimensional printing technologies forms the foundation of 4D bioprinting and has the potential to revolutionize tissue engineering. 4D bioprinting involves the printing of structures whose shape, function, or properties can be altered as a function of time in response to environmental stimuli. Critical to 4D bioprinting is the development of smart biomaterials that respond to different stimuli, such as temperature, pH, light, and biochemical signals. This review explores various stimuli-responsive materials used in 4D bioprinting for biomedical applications. Furthermore, it provides an overview of material properties and categorizes them according to their responsiveness to external stimuli. Additionally, the current trends in stimuli-responsive materials for 4D bioprinting, and their applications and critical challenges in tissue regeneration, drug delivery, and personalized medicine are identified.