Direct ink writing (DIW) is an additive manufacturing technique that has garnered notable interest due to its precise and consistent printing of a wide range of materials, such as viscoelastic hydrogels, pastes, and complex composites, by adjusting the ink's rheology. This material flexibility combined with the ability to print at room temperature makes DIW ideal for diverse applications and is scalable from small to industrial levels. In recent years, DIW of conductive hydrogels has gained significant attention across various fields, ranging from biomedical scaffolds to flexible electronics. Conductive hydrogels are a category of hydrogels which exhibit conductivity in their wet and/or dry state. Precursors like conductive polymers, metallic nanoparticles, and carbon‐based materials can be used to induce electronic and/or ionic conductivity in hydrogels. This review presents a comprehensive overview of conductive hydrogels demonstrating printability using the DIW technique. The fundamentals of DIW and conductive precursors are presented. Following, the different pathways for reaching optimal conductive hydrogel properties, including mechanical, conductive, and rheological, with a focus on ink synthesis and printability are introduced. Finally, emerging applications of DIW of conductive hydrogels in flexible electronics and medicine are highlighted, and the anticipated challenges for advancement of printable conductive hydrogels using DIW are discussed.

Direct Air Capture (DAC) is a promising technology to fight climate change by capturing carbon dioxide (CO₂) from the air. For DAC to be a negative emissions technology, the captured CO₂ must be removed permanently, but can also be used as a net-zero technology to produce sustainable chemicals, fuels or other materials. This review presents a comprehensive survey of recent advancements, challenges, and potential applications of DAC technology, with an emphasis on the recent rapid increase in the number of DAC developers, the majority of them being founded in the past 4 years. Through pilot projects and recent commercial deployments, several DAC companies have made significant advances and demonstrated their scalability. Cost and energy efficiency remain significant impediments to the wide deployment of DAC. Integration with emission-free energy sources and utilization of waste heat are being researched to boost the total energy efficiency of DAC systems. Further research of electrochemical technologies for regeneration or direct capture are needed, as well as the development of new, modified, or hybrid adsorbents for improved capture efficiencies. Moreover, favorable regulations and financial incentives are crucial for enhancing the viability of DAC projects and will need to substantially increase if Paris Agreement goals are to be achieved.

A careful balance between extrusion flowability and rapid viscoelastic recovery is essential for direct ink writing (DIW). The ink must flow easily under shear during extrusion and quickly recover a solid‐like structure after extrusion to maintain the printed architecture. Conventional ionic crosslinking methods to tune the rheological features often lead to inhomogeneity, nozzle clogging, and printing failure. To overcome these challenges, we introduce a two‐step ionic crosslinking strategy for weakly structured graphene oxide (GO)/sodium alginate (SA) inks. First, to stabilize each printed layer of weak hydrogels while preventing nozzle clogging, each extruded layer is immediately sprayed with an ionic solution upon deposition to induce partial crosslinking. Second, the fully printed partially crosslinked scaffold is submerged in an ionic bath to complete the crosslinking. Using this method, flowing hydrogels are turned into tough or brittle 3D‐printed structures by methodically fine‐tuning materials’ qualities, affected by GO content, SA concentration, and crosslinker valency. Moreover, the effect of salt type on the hydrogels’ shape retention and printing quality, as well as on the morphological features of the resulting cryogels, is investigated. All in all, this study introduces a two‐step ionic crosslinking technique that separates printability from high rheological requirements to overcome complications in the DIW process.