High Internal Phase Pickering Emulsions as Structurally Tunable Bioinks for Extrusion-Based Printing From 3D Fabrication to Adaptive Multiresponsive Architectures.

High internal phase Pickering emulsions (HIPPEs) have recently emerged as a versatile class of bioinks for extrusion-based printing, offering unique opportunities for structural tunability, hierarchical architecture, and functional responsiveness. Stabilized by solid particles at high internal phase fractions (typically ≥74%), HIPPEs exhibit yield stress, pronounced shear thinning, and rapid structural recovery, which are essential for printability and shape fidelity. Unlike conventional hydrogel-based bioinks that primarily rely on bulk polymer networks, HIPPEs derive their mechanical integrity from particle-stabilized interfaces and jammed droplet assemblies, enabling decoupled control over mechanics, porosity, and functional loading. This systematic review critically examines the application of HIPPEs as bioinks in extrusion-based printing, from 3D fabrication toward emerging adaptive multiresponsive architectures. Emphasis is placed on fundamental stabilization mechanisms, particle-interface interactions, formulation parameters governing internal architecture, and rheological properties underpinning extrusion behaviors. Representative case studies are analyzed to elucidate structure-function relationships, encapsulation performance, and functional outcomes in food, biomedical, and bioengineering contexts. Additionally, a further comparison of HIPPE-based bioinks with conventional hydrogel systems highlights distinct advantages in hierarchical porosity, hydrophobic cargo protection, and responsiveness, while also addressing key challenges related to formulation sensitivity, scalability, reproducibility, and translational validation. Finally, emerging trends in interface-driven design, multi-stimuli adaptability, and integration with artificial intelligence and digital fabrication are discussed as future directions for advancing HIPPE-based bioinks toward intelligent, multifunctional printing platforms.