Emerging 4D Fabrication of Tubular Structures and Clinical Challenges: Critical Perspective.

The burgeoning field of 4D fabrication holds transformative potential in fabricating dynamic, tubular structures such as artificial vascular grafts, stents, and nerve conduits. These are critical for cardiovascular, respiratory, and neurological applications. Traditional 3D printing, despite its advances, remains constrained by the static nature of its structures, often resulting in challenges such as improper vascular integration, restricted endothelialisation in small-diameter grafts, and complex surgical deployment requirements. This perspective delves into the novel integration of stimuli-responsive smart materials that imbue printed structures with the ability to morph, repair, and adapt to specific environmental stimuli, facilitating a more biocompatible and physiologically relevant interface. Highlighting recent breakthroughs in vascular graft fabrication, we discuss the strategic use of multimaterial printing to achieve endothelial compatibility and structural fidelity. Moreover, advancements in bifurcated stents and multichannel nerve conduits underscore the role of self-assembling and self-folding mechanisms in addressing anatomical and biomechanical complexities inherent in regenerative medicine. However, the translational trajectory of 4D bioprinting is impeded by persistent issues like material scalability, stimulus precision control, mechanical stability, and stringent biocompatibility standards. Future research should prioritize the refinement of multifunctional biomaterials and the development of composite, stimuli-responsive scaffolds equipped with biosensor functionalities to better mimic the dynamic biomechanics of native tissues. This review provides an in-depth analysis of these challenges and explores pathways toward the clinical adoption of 4D-printed, biomimetic tubular structures, aiming to bridge the gap between experimental innovation and clinical application.