Bulk hierarchical porous ceramics with unprecedented strength-to-weight ratio and tunable pore sizes across three different length scales are printed by direct ink writing. Such an extrusion-based process relies on the formulation of inks in the form of particle-stabilized emulsions and foams that are sufficiently stable to resist coalescence during printing.

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3D printing via direct ink writing (DIW) is a versatile additive manufacturing approach applicable to a variety of materials ranging from ceramics over composites to hydrogels. Due to the mild processing conditions compared to other additive manufacturing methods, DIW enables the incorporation of sensitive compounds such as proteins or drugs into the printed structure. Although emulsified oil-in-water systems are commonly used vehicles for such compounds in biomedical, pharmaceutical, and cosmetic applications, printing of such emulsions into architectured soft materials has not been fully exploited and would open new possibilities for the controlled delivery of sensitive compounds. Here, we 3D print concentrated emulsions into soft materials, whose multiphase architecture allows for site-specific incorporation of both hydrophobic and hydrophilic compounds into the same structure. As a model ink, concentrated emulsions stabilized by chitosan-modified silica nanoparticles are studied, because they are sufficiently stable against coalescence during the centrifugation step needed to create a bridging network of droplets. The resulting ink is ideal for 3D printing as it displays high yield stress, storage modulus and elastic recovery, through the formation of networks of droplets as well as of gelled silica nanoparticles in the presence of chitosan. To demonstrate possible architectures, we print biocompatible soft materials with tunable hierarchical porosity containing an encapsulated hydrophobic compound positioned in specific locations of the structure. The proposed emulsion-based ink system offers great flexibility in terms of 3D shaping and local compositional control, and can potentially help address current challenges involving the delivery of incompatible compounds in biomedical applications.

Thermal insulators are crucial to reduce the high energy demands and greenhouse emissions in the construction sector. However, the fabrication of insulating materials that are cost-effective, fire resistant, and environmental-friendly remains a major challenge. In this work, we present a room-temperature processing route to fabricate porous insulators using foams made from recyclable clays that can be locally resourced at very low costs. Foams containing either pure Kaolin or a Kaolin-based clay mixture are produced through mechanical frothing or an in-situ gas-generating reaction. Surface modification of the clay particles using a cationic amphiphilic molecule leads to particle-stabilized foams that are sufficiently strong to withstand the high capillary stresses developed during water evaporation. Self-supporting insulators with up to 90% porosity and thermal conductivities as low as 0.13 W/mK can thus be obtained by simple casting and drying at ambient temperature in an ultralow energy process. Such materials can be recycled by crushing, redispersion in water, and subsequent foaming. Porous structures with higher compressive strength are optionally created by sintering the dried foams at 1000 °C. The obtained porous materials perform comparably well with existing fire-resistant insulators while offering the possibility of closed-loop processing and wide availability from local resources as well as ultralow cost and embodied energy.

Electrodes for metal-ion batteries should combine high specific capacity with fast cycling-rate capability. Although the use of mesoporous particles is an attractive approach to reconciling these contradicting performance parameters, synthetic protocols to create such particles are typically time-consuming, require environmentally unfriendly chemistries, and are limited to small batches. We present a simple and scalable processing route to synthesizing mesoporous TiO 2 particles through freezing, drying, and grinding of gelled aqueous suspensions of 5-nm-sized TiO 2 nanoparticles. Freezing enables partial densification of the nanoparticle network present in the initial gel, thus leading to mesoporous particles combining high density with easily accessible specific surface area for metal-ion insertion. The resulting mesoporous particles can be assembled into hierarchical porous anodes that exhibit superior volumetric capacity in comparison to xerogel and aerogel reference compositions. The aqueous-based nature and simplicity of the freezing process makes this synthetic approach a promising route for the fabrication of architectured electrodes for the next generation of metal-ion batteries.