Aquabots

Interfacial jamming of surface-alkylated synthetic nanocelluloses for structuring liquids

Nanocelluloses derived from natural cellulose sources are promising sustainable nanomaterials. Previous studies have reported that nanocelluloses are strongly adsorbed onto liquid-liquid interfaces with the concurrent use of ligands and allow for the structuring of liquids, that is, the kinetic trapping of nonequilibrium shapes of liquids. However, the structuring of liquids using nanocelluloses alone has yet to be demonstrated, despite its great potential in the development of sustainable liquid-based materials that are biocompatible and environmentally friendly. Herein, we demonstrated the structuring of liquids using rectangular sheet-shaped synthetic nanocelluloses with surface alkyl groups. Synthetic nanocelluloses with ethyl, butyl, and hexyl groups on their surfaces were readily prepared following our previous reports via the self-assembly of enzymatically synthesized cello-oligosaccharides having the corresponding alkyl groups. Among the alkylated synthetic nanocelluloses, the hexylated nanocellulose was adsorbed and jammed at water-n-undecane interfaces to form interfacial assemblies, which acted substantially as an integrated film for structuring liquids. These phenomena were attributed to the unique structural characteristics of the surface-hexylated synthetic nanocelluloses; their sheet shape offered a large area for adsorption onto interfaces, and their controlled surface hydrophilicity/hydrophobicity enhanced the affinity for both liquid phases. Our findings promote the development of all-liquid devices using nanocelluloses.

Reconfigurable aqueous 3D printing with adaptive dual locks

Using aqueous two-phase systems (ATPSs) for three-dimensional (3D) printed complex structures has attracted considerable attention in the field of biomedicine. In this study, we present an unusual approach to constructing reconfigurable 3D printed structures within an aqueous environment. Inspired by biological systems, we introduce both specific and nonspecific interactions to anchor functionalized nanoparticles to the water-water interface, thereby imparting adaptive dual locks of structural integrity and permeability to the 3D printed liquid structures. Using state-of-the-art in situ liquid-liquid interfacial atomic force microscopy imaging, we successfully demonstrate various morphologies of interfacial films formed at the ATPS interface. In addition, by incorporating d-glucose or sodium alginate into the systems, the dual locks can be easily manipulated. Our study paves a pathway for 3D printing multiresponsive all-aqueous systems with controllable structures and permeability, showing promising implications for the development of smart drug delivery systems and in vivo reactions.

Thermal Welding of Liquids

Welding of thermoplastics is a common practice in many industrial sectors, but it has yet to be realized with fluids. Here, the thermal welding of liquids by using the assembly and jamming of nanoparticle surfactants (NPSs) at liquid-liquid interfaces is reported. By fine-tuning the dynamic interaction strength within NPSs, the interfacial activity of NPSs, as well as the binding energy of NPSs to the interface can be precisely controlled, leading to a dynamic exchange of NPSs, maximizing the reduction in the interfacial energy. With NPSs jammed at the interface, the structures of liquids can be manipulated to complex geometries by applying an external force and, due to the temperature responsiveness of NPSs, when bringing liquids into contact and heating the system, welding of liquids can be achieved. This work provides a straightforward strategy for the construction of modular all-liquid fluidics, opening up numerous opportunities in fields like biotechnology, healthcare, and materials science.

Vascular network-inspired fluidic system (VasFluidics) with spatially functionalizable membranous walls

In vascular networks, the transport across different vessel walls regulates chemical compositions in blood over space and time. Replicating such trans-wall transport with spatial heterogeneity can empower synthetic fluidic systems to program fluid compositions spatiotemporally. However, it remains challenging as existing synthetic channel walls are typically impermeable or composed of homogeneous materials without functional heterogeneity. This work presents a vascular network-inspired fluidic system (VasFluidics), which is functionalizable for spatially different trans-wall transport. Facilitated by embedded three-dimensional (3D) printing, elastic, ultrathin, and semipermeable walls self-assemble electrostatically. Physicochemical reactions between fluids and walls are localized to vary the trans-wall molecules among separate regions, for instance, by confining solutions or locally immobilizing enzymes on the outside of channels. Therefore, fluid compositions can be regulated spatiotemporally, for example, to mimic blood changes during glucose absorption and metabolism. Our VasFluidics expands opportunities to replicate biofluid processing in nature, providing an alternative to traditional fluidics.

Functional Janus structured liquids and aerogels

Janus structures have unique properties due to their distinct functionalities on opposing faces, but have yet to be realized with flowing liquids. We demonstrate such Janus liquids with a customizable distribution of nanoparticles (NPs) throughout their structures by joining two aqueous streams of NP dispersions in an apolar liquid. Using this anisotropic integration platform, different magnetic, conductive, or non-responsive NPs can be spatially confined to opposite sides of the original interface using magnetic graphene oxide (mGO)/GO, Ti3C2Tx/GO, or GO suspensions. The resultant Janus liquids can be used as templates for versatile, responsive, and mechanically robust aerogels suitable for piezoresistive sensing, human motion monitoring, and electromagnetic interference (EMI) shielding with a tuned absorption mechanism. The EMI shields outperform their current counterparts in terms of wave absorption, i.e., SET ≈ 51 dB, SER ≈ 0.4 dB, and A = 0.91, due to their high porosity ranging from micro- to macro-scales along with non-interfering magnetic and conductive networks imparted by the Janus architecture.

Liquid-Templating Aerogels

Modern materials science has witnessed the era of advanced fabrication methods to engineer functionality from the nano- to macroscales. Versatile fabrication and additive manufacturing methods are developed, but the ability to design a material for a given application is still limited. Here, a novel strategy that enables target-oriented manufacturing of ultra-lightweight aerogels with on-demand characteristics is introduced. The process relies on controllable liquid templating through interfacial complexation to generate tunable, stimuli-responsive 3D-structured (multiphase) filamentous liquid templates. The methodology involves nanoscale chemistry and microscale assembly of nanoparticles (NPs) at liquid-liquid interfaces to produce hierarchical macroscopic aerogels featuring multiscale porosity, ultralow density (3.05-3.41 mg cm-3 ), and high compressibility (90%) combined with elastic resilience and instant shape recovery. The challenges are overcome facing ultra-lightweight aerogels, including poor mechanical integrity and the inability to form predefined 3D constructs with on-demand functionality, for a multitude of applications. The controllable nature of the coined methodology enables tunable electromagnetic interference shielding with high specific shielding effectiveness (39 893 dB cm2 g-1 ), and one of the highest-ever reported oil-absorption capacities (487 times the initial weight of aerogel for chloroform), to be obtained. These properties originate from the engineerable nature of liquid templating, pushing the boundaries of lightweight materials to systematic function design and applications.

Phase-separation facilitated one-step fabrication of multiscale heterogeneous two-aqueous-phase gel

Engineering heterogeneous hydrogels with distinct phases at various lengths, which resemble biological tissues with high complexity, remains challenging by existing fabricating techniques that require complicated procedures and are often only applicable at bulk scales. Here, inspired by ubiquitous phase separation phenomena in biology, we present a one-step fabrication method based on aqueous phase separation to construct two-aqueous-phase gels that comprise multiple phases with distinct physicochemical properties. The gels fabricated by this approach exhibit enhanced interfacial mechanics compared with their counterparts obtained from conventional layer-by-layer methods. Moreover, two-aqueous-phase gels with programmable structures and tunable physicochemical properties can be conveniently constructed by adjusting the polymer constituents, gelation conditions, and combining different fabrication techniques, such as 3D-printing. The versatility of our approach is demonstrated by mimicking the key features of several biological architectures at different lengths: macroscale muscle-tendon connections; mesoscale cell patterning; microscale molecular compartmentalization. The present work advances the fabrication approach for designing heterogeneous multifunctional materials for various technological and biomedical applications.

Associative Liquid-In-Liquid 3D Printing Techniques for Freeform Fabrication of Soft Matter

Shaping soft materials into prescribed 3D complex designs has been challenging yet feasible using various 3D printing technologies. For a broader range of soft matters to be printable, liquid-in-liquid 3D printing techniques have emerged in which an ink phase is printed into 3D constructs within a bath. Most of the attention in this field has been focused on using a support bath with favorable rheology (i.e., shear-thinning behavior) which limits the selection of materials, impeding the broad application of such techniques. However, a growing body of work has begun to leverage the interaction or association of the two involved phases (specifically at the liquid-liquid interface) to fabricate complex constructs from a myriad of soft materials with practical structural, mechanical, optical, magnetic, and communicative properties. This review article has provided an overview of the studies on such associative liquid-in-liquid 3D printing techniques along with their fundamentals, underlying mechanisms, various characterization techniques used for ensuring the structural stability, and practical properties of prints. Also, the future paths with the potential applications are discussed.