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Abstract Over the past decade, three-dimensional (3D) bioprinting has made significant progress, transforming into a key innovation in tissue engineering. Despite the early strides, critical challenges remain in 3D bioprinting that must be addressed to accelerate clinical translation. In particular, there is still a long way to go before functionally-mature, clinically-relevant tissue equivalents are developed. Current limitations range from the sub-optimal bioink properties and degree of biomimicry of bioprintable architectures, to the lack of stem/progenitor cells for massive cell expansion, and fundamental knowledge regardingin vitroculturing conditions. In addition to these problems, the absence of guidelines and well-regulated international standards is creating uncertainty among the biofabrication community stakeholders regarding the reliable and scalable production processes. This review aims at exploring the latest developments in 3D bioprinting approaches, including various additive manufacturing techniques and their applications. A thorough discussion of common bioprinting techniques and recent progresses are compiled along with notable recent studies. Later we discuss the current challenges in clinical application of 3D bioprinting and the major bottlenecks in the commercialization of 3D bioprinted tissue equivalents, including the longevity of bioprinted organs, meeting biomechanical requirements, and the often underrated ethical and legal aspects. Amidst the progress of regulatory efforts for regenerative medicine, we also present an overview of the current regulatory concerns which should be taken into account to translate bioprinted tissues into clinical practice. At last, this review emphasizes future directions in 3D bioprinting that includes the transformative ideas such as bioprinting in microgravity and the integration of artificial intelligence. The study concludes with a discussion on the need for collaborative efforts in resolving the technical and regulatory constraints to improve the quality, reliability, and reproducibility of bioprinted tissue equivalents to ultimately accomplish their successful clinical implementation. 

Abstract 4D printing technology enables the fabrication of constructs capable of shape transformation when exposed to external stimuli. Epoxy‐based shape memory polymers (SMPs) have shown great potential for various 4D printing applications. However, due to their thermocurable nature, the fabrication of 4D constructs using epoxy‐based materials is often limited to a mold casting strategy, limiting design flexibility and often yielding flat structures. In this work, photocurable smart 4D inks are developed by integrating polyethylene glycol diacrylate (PD) into epoxy‐based materials. These inks undergo a two‐step crosslinking process: i) photocuring of the PD network, and ii) thermocuring of the SMP, resulting in an interpenetrating polymer network (IPN). The inclusion of PD in the 4D inks not only enables the formation of complex shapes via the restructuring step but also allows for fine‐tuning of mechanical properties and thermal responsiveness. Additionally, these inks offered greater versatility in employable fabrication techniques, including mold casting, photolithography, and stereolithography (SLA). 

A novel multi-responsive nanocomposite integrates polypyrrole-coated magnetic nanoparticles into a thermo-responsive shape memory polymer, enabling precise, remotely dynamic control for 4D-printed biorobotic applications. 

As an innovative technology, four‐dimentional (4D) printing is built upon the principles of three‐dimentional (3D) printing with an additional dimension: time. While traditional 3D printing creates static objects, 4D printing generates “responsive 3D printed structures”, enabling them to transform or self‐assemble in response to external stimuli. Due to the dynamic nature, 4D printing has demonstrated tremendous potential in a range of industries, encompassing aerospace, healthcare, and intelligent devices. Nanotechnology has gained considerable attention owing to the exceptional properties and functions of nanomaterials. Incorporating nanomaterials into an intelligent matrix enhances the physiochemical properties of 4D printed constructs, introducing novel functions. This review provides a comprehensive overview of current applications of nanomaterials in 4D printing, exploring their synergistic potential to create dynamic and responsive structures. Nanomaterials play diverse roles as rheology modifiers, mechanical enhancers, function introducers, and more. The overarching goal of this review is to inspire researchers to delve into the vast potential of nanomaterial‐enabled 4D printing, propelling advancements in this rapidly evolving field.