Revolutionizing the Future of Smart Materials: A Review of 4D Printing, Design, Optimization, and Machine Learning Integration

With technological advancement and development, there is a tremendous increase in demand for different smart materials because of their stimulation from external sources. Moreover, the time-dependent response of smart materials provides insight into the fabrication of these materials using 4D printing (4DP) techniques. Hence, this study presents a comprehensive review of the 4DP of smart materials. The review covers different aspects of smart material, from design and optimization to printing. Herein, smart materials have been discussed in detail based on the physical, biological, and chemical stimuli-responsive and their subtype's behavior. For designing smart materials, different usage of tools such as new designing software, finite element analysis, and machine learning are also discussed. The design of smart materials is challenging because of the different responsive natures and complexity of design and mechanisms. Hence, a detailed review of present 3D printing techniques, the use of 4DP, and how future applications can be incorporated with smart material and 4DP is presented. With the help of machine learning, the fabrication of smart materials using 4DP is also discussed. The review provides future directions for fabricating smart materials using 4DP. The design and printing challenges of smart materials for future utilization have also been comprehensively covered.