3D Printing of Bioactive Gel-like Double Emulsion into a Biocompatible Hierarchical Macroporous Self-Lubricating Scaffold for 3D Cell Culture

Dispersion strategies of nanomaterials in polymeric inks for efficient 3D printing of soft and smart 3D structures: A systematic review

Nanoscience-often summarized as "the future is tiny"-highlights the work of researchers advancing nanotechnology through incremental innovations. The design and innovation of new nanomaterials are vital for the development of next-generation three-dimensional (3D) printed structures characterized by low cost, high speed, and versatile capabilities, delivering exceptional performance in advanced applications. The integration of nanofillers into polymeric-based inks for 3D printing heralds a new era in additive manufacturing, allowing for the creation of custom-designed 3D objects with enhanced multifunctionality. To optimize the use of nanomaterials in 3D printing, effective disaggregation techniques and strong interfacial adhesion between nanofillers and polymer matrices are essential. This review provides an overview of the application of various types of nanomaterials used in 3D printing, focusing on their functionalization principles, dispersion strategies, and colloidal stability, as well as the methodologies for aligning nanofillers within the 3D printing framework. It discusses dispersive methods, synergistic dispersion, and in-situ growth, which have yielded smart 3D-printed structures with unique functionality for specific applications. This review also focuses on nanomaterial alignment in 3D printing, detailing methods that enhance selective deposition and orientation of nanofillers within established and customized printing techniques. By emphasizing alignment strategies, we explore their impact on the performance of 3D-printed composites and highlight potential applications that benefit from ordered nanoparticles. Through these continuing efforts, this review shows that the design and development of the new class of nanomaterials are crucial to developing the next generation of smart 3D printed architectures with versatile abilities for advanced structures with exceptional performance.

Depletion Flocculation of High Internal Phase Pickering Emulsion Inks: A Colloidal Engineering Approach to Develop 3D Printed Porous Scaffolds with Tunable Bioactive Delivery

Flocculation is a type of aggregation where the surfaces of approaching droplets are still at distances no closer than a few nanometers while still remaining in close proximity. In a high internal-phase oil-in-water (O/W) emulsion, the state of flocculation affects the bulk flow behavior and viscoelasticity, which can consequently control the three-dimensional (3D)-printing process and printing performance. Herein, we present the assembly of O/W Pickering high-internal-phase emulsions (Pickering-HIPEs) as printing inks and demonstrate how depletion flocculation in such Pickering-HIPE inks can be used as a facile colloidal engineering approach to tailor a porous 3D structure suitable for drug delivery. Pickering-HIPEs were prepared using different levels of cellulose nanocrystals (CNCs), co-stabilized using "raw" submicrometer-sized sustainable particles from a biomass-processing byproduct. In the presence of this sustainable particle, the higher CNC contents facilitated particle-induced depletion flocculation, which led to the formation of a mechanically robust gel-like ink system. Nonetheless, the presence of adsorbed particles on the surface of droplets ensured their stability against coalescence, even in such a highly aggregated system. The gel structures resulting from the depletion phenomenon enabled the creation of high-performance printed objects with tunable porosity, which can be precisely controlled at two distinct levels: first, by introducing voids within the internal structure of filaments, and second, by generating cavities (pore structures) through the elimination of the water phase. In addition to printing efficacy, the HIPEs could be applied for curcumin delivery, and in vitro release kinetics demonstrated that the porous 3D scaffolds engineered for the first time using depletion-flocculated HIPE inks played an important role in 3D scaffold disintegration and curcumin release. Thus, this study offers a unique colloidal engineering approach of using depletion flocculation to template 3D printing of sustainable inks to generate next-generation porous scaffolds for personalized drug deliveries.

A smart thermoresponsive macroporous 4D structure by 4D printing of Pickering-high internal phase emulsions stabilized by plasma-functionalized starch nanomaterials for a possible delivery system

Hierarchically porous structures combine microporosity, mesoporosity, and microporosity to enhance pore accessibility and transport, which are crucial to develop high performance materials for biofabrication, food, and pharmaceutical applications. This work aimed to develop a 4D-printed smart hierarchical macroporous structure through 3D printing of Pickering-type high internal phase emulsions (Pickering-HIPEs). The key was the utilization of surface-active (hydroxybutylated) starch nanomaterials, including starch nanocrystals (SNCs) (from waxy maize starch through acid hydrolysis) or starch nanoparticles (SNPs) (obtained through an ultrasound treatment). An innovative procedure to fabricate the functionalized starch nanomaterials was accomplished by grafting 1,2-butene oxide using a cold plasma technique to enhance their surface hydrophobicity, improving their aggregation, and thus attaining a colloidally stabilized Pickering-HIPEs with a low concentration of each surface-active starch nanomaterial. A flocculation of droplets in Pickering-HIPEs was developed after the addition of modified SNCs or SNPs, leading to the formation of a gel-like structure. The 3D printing of these Pickering-HIPEs developed a highly interconnected large pore structure, possessing a self-assembly property with thermoresponsive behavior. As a potential drug delivery system, this thermoresponsive macroporous 3D structure offered a lower critical solution temperature (LCST)-type phase transition at body temperature, which can be used in the field of smart releasing of bioactive compounds.