Review of progress in 4D printing of piezoelectric energy harvesters

The fabrication of piezoelectric energy harvesters (PEHs) has evolved significantly over the past three decades, transitioning from mechanization to automation and computerization. Additive manufacturing (AM), a forefront technology in advanced manufacturing, has been extensively used to design and produce complex components from piezoelectric materials. By integrating the fourth dimension, we can improve the fabrication of PEHs, allowing them to alter their shape while converting mechanical stress into electrical energy, thus adding dynamic functionality and broadening their application spectrum. Despite the extensive literature on 3D printing of piezoelectric materials and 4D printing technology, a notable research gap exists in merging these two fields. This review aims to bridge this gap by providing a comparative analysis of 3D-printed piezoelectric materials and shape memory materials, discussing the relevant AM technologies, stimuli, and smart materials, and highlighting innovative integration methods. Furthermore, we explore a novel approach termed '4D printing of piezoelectric energy harvesters.' This innovative method merges the principles of 4D printing with the advanced capabilities of 3D printing of piezoelectric materials, resulting in multifunctional devices that can adapt and respond to external stimuli over time. The article also addresses the challenges and opportunities in optimizing AM processes to enhance the performance and functionality of these advanced materials and devices.