Near‐Infrared Light‐Sensitive Polyvinyl Alcohol Hydrogel Photoresist for Spatiotemporal Control of Cell‐Instructive 3D Microenvironments

Advanced hydrogel systems that allow precise control of cells and their 3D microenvironments are needed in tissue engineering, disease modeling, and drug screening. Multiphoton lithography (MPL) allows true 3D microfabrication of complex objects, but its biological application requires a cell‐compatible hydrogel resist that is sufficiently photosensitive, cell‐degradable, and permissive to support 3D cell growth. Here, an extremely photosensitive cell‐responsive hydrogel composed of peptide‐crosslinked polyvinyl alcohol (PVA) is designed to expand the biological applications of MPL. PVA hydrogels are formed rapidly by ultraviolet light within 1 min in the presence of cells, providing fully synthetic matrices that are instructive for cell‐matrix remodeling, multicellular morphogenesis, and protease‐mediated cell invasion. By focusing a multiphoton laser into a cell‐laden PVA hydrogel, cell‐instructive extracellular cues are site‐specifically attached to the PVA matrix. Cell invasion is thus precisely guided in 3D with micrometer‐scale spatial resolution. This robust hydrogel enables, for the first time, ultrafast MPL of cell‐responsive synthetic matrices at writing speeds up to 50 mm s^?1. This approach should enable facile photochemical construction and manipulation of 3D cellular microenvironments with unprecedented flexibility and precision.     

Strategic Advances in Formation of Cell‐in‐Shell Structures: From Syntheses to Applications

Single‐cell nanoencapsulation, forming cell‐in‐shell structures, provides chemical tools for endowing living cells, in a programmed fashion, with exogenous properties that are neither innate nor naturally achievable, such as cascade organic‐catalysis, UV filtration, immunogenic shielding, and enhanced tolerance in vitro against lethal factors in real‐life settings. Recent advances in the field make it possible to further fine‐tune the physicochemical properties of the artificial shells encasing individual living cells, including on‐demand degradability and reconfigurability. Many different materials, other than polyelectrolytes, have been utilized as a cell‐coating material with proper choice of synthetic strategies to broaden the potential applications of cell‐in‐shell structures to whole‐cell catalysis and sensors, cell therapy, tissue engineering, probiotics packaging, and others. In addition to the conventional “one‐time‐only” chemical formation of cytoprotective, durable shells, an approach of autonomous, dynamic shellation has also recently been attempted to mimic the naturally occurring sporulation process and to make the artificial shell actively responsive and dynamic. Here, the recent development of synthetic strategies for formation of cell‐in‐shell structures along with the advanced shell properties acquired is reviewed. Demonstrated applications, such as whole‐cell biocatalysis and cell therapy, are discussed, followed by perspectives on the field of single‐cell nanoencapsulation.     

Immunogold FIB‐SEM: Combining Volumetric Ultrastructure Visualization with 3D Biomolecular Analysis to Dissect Cell–Environment Interactions

Volumetric imaging techniques capable of correlating structural and functional information with nanoscale resolution are necessary to broaden the insight into cellular processes within complex biological systems. The recent emergence of focused ion beam scanning electron microscopy (FIB‐SEM) has provided unparalleled insight through the volumetric investigation of ultrastructure; however, it does not provide biomolecular information at equivalent resolution. Here, immunogold FIB‐SEM, which combines antigen labeling with in situ FIB‐SEM imaging, is developed in order to spatially map ultrastructural and biomolecular information simultaneously. This method is applied to investigate two different cell–material systems: the localization of histone epigenetic modifications in neural stem cells cultured on microstructured substrates and the distribution of nuclear pore complexes in myoblasts differentiated on a soft hydrogel surface. Immunogold FIB‐SEM offers the potential for broad applicability to correlate structure and function with nanoscale resolution when addressing questions across cell biology, biomaterials, and regenerative medicine.     

Engineered Fibrillar Fibronectin Networks as Three‐Dimensional Tissue Scaffolds

Extracellular matrix (ECM) proteins, and most prominently, fibronectin (Fn), are routinely used in the form of adsorbed pre‐coatings in an attempt to create a cell‐supporting environment in both two‐ and three‐dimensional cell culture systems. However, these protein coatings are typically deposited in a form which is structurally and functionally distinct from the ECM‐constituting fibrillar protein networks naturally deposited by cells. Here, the cell‐free and scalable synthesis of freely suspended and mechanically robust three‐dimensional (3D) networks of fibrillar fibronectin (fFn) supported by tessellated polymer scaffolds is reported. Hydrodynamically induced Fn fibrillogenesis at the three‐phase contact line between air, an Fn solution, and a tessellated scaffold microstructure yields extended protein networks. Importantly, engineered fFn networks promote cell invasion and proliferation, enable in vitro expansion of primary cancer cells, and induce an epithelial‐to‐mesenchymal transition in cancer cells. Engineered fFn networks support the formation of multicellular cancer structures cells from plural effusions of cancer patients. With further work, engineered fFn networks can have a transformative impact on fundamental cell studies, precision medicine, pharmaceutical testing, and pre‐clinical diagnostics.     

Direct Fabrication of Freestanding and Patterned Nanoporous Junctions in a 3D Micro‐Nanofluidic Device for Ion‐Selective Transport

In the field of micro‐nanofluidics, a freestanding configuration of a nanoporous junction is highly demanded to increase the design flexibility of the microscale device and the interfacial area between the nanoporous junction and microchannels, thereby improving the functionality and performance. This work first reports direct fabrication and incorporation of a freestanding nanoporous junction in a microfluidic device by performing an electrolyte‐assisted electrospinning process to fabricate a freestanding nanofiber membrane and subsequently impregnating the nanofiber membrane with a nanoporous precursor material followed by a solidification process. This process also enables to readily control the geometry of the nanoporous junction depending on its application. By these advantages, vertically stacked 3D micro‐nanofluidic devices with complex configurations are easily achieved. To demonstrate the broad applicability of this process in various research fields, a reverse electrodialysis‐based energy harvester and an ion concentration polarization‐based preconcentrator are produced. The freestanding Nafion‐polyvinylidene fluoride nanofiber membrane (F‐NPNM) energy harvester generates a high power (59.87 nW) owing to the enlarged interfacial area. Besides, 3D multiplexed and multi‐stacked F‐NPNM preconcentrators accumulate multiple preconcentrated plugs that can increase the operating sample volume and the degree of freedom of handling. Hence, the proposed process is expected to contribute to numerous research fields related to micro‐nanofluidics in the future.     

Shaping Giant Membrane Vesicles in 3D‐Printed Protein Hydrogel Cages

Giant unilamellar phospholipid vesicles are attractive starting points for constructing minimal living cells from the bottom‐up. Their membranes are compatible with many physiologically functional modules and act as selective barriers, while retaining a high morphological flexibility. However, their spherical shape renders them rather inappropriate to study phenomena that are based on distinct cell shape and polarity, such as cell division. Here, a microscale device based on 3D printed protein hydrogel is introduced to induce pH‐stimulated reversible shape changes in trapped vesicles without compromising their free‐standing membranes. Deformations of spheres to at least twice their aspect ratio, but also toward unusual quadratic or triangular shapes can be accomplished. Mechanical force induced by the cages to phase‐separated membrane vesicles can lead to spontaneous shape deformations, from the recurrent formation of dumbbells with curved necks between domains to full budding of membrane domains as separate vesicles. Moreover, shape‐tunable vesicles are particularly desirable when reconstituting geometry‐sensitive protein networks, such as reaction‐diffusion systems. In particular, vesicle shape changes allow to switch between different modes of self‐organized protein oscillations within, and thus, to influence reaction networks directly by external mechanical cues.     

Toward Tailorable Zn‐Ion Textile Batteries with High Energy Density and Ultrafast Capability: Building High‐Performance Textile Electrode in 3D Hierarchical Branched Design

Rechargeable Zn‐ion batteries are promising candidates for wearable energy storage devices. However, their performance is severely restricted by the low conductivity and inferior mass loading. Herein, a new type of the textile based electrodes with 3D hierarchical branched design is reported. Both Ni nanoparticles and carbon nanotubes are used to build conductive coatings on the textiles. The 3D hierarchical nanostructures, consisting of the vertical‐aligned nanosheets and the fluffy‐like small flakes, grow on the conductive textiles to form the self‐supported electrodes. It ensures fast electron/ion transport and high mass loading, and maintains the structure stability during cycling. Two textile electrodes with the NiCo hydroxide and MnO₂ self‐branched nanostructures are constructed. Their faster kinetics, higher capacity and better rate capability than the solitary nanosheets based counterpart demonstrate the superiority of the hierarchical architecture. Moreover, the solid‐state Zn‐MnO₂ and Zn‐NiCo batteries are fabricated based on the textile electrodes and the polymer electrolytes. The high energy density, superior power density and good long‐term cycling stability confirm their excellent energy storage ability and fast charge/discharge capability. Particularly, the high safety under various conditions enable them promising candidates for wearable electronics.