3D tissue models recapitulating human physiology are important for fundamental biomedical research, and they hold promise to become a new tool in drug development. An integrated and defined microvasculature in 3D tissue models is necessary for optimal cell functions. However, conventional bioprinting only allows the fabrication of hydrogel scaffolds containing vessel‐like structures with large diameters (>100 µm) and simple geometries. Recent developments in laser photoablation enable the generation of this type of structure with higher resolution and complexity, but the photo‐thermal process can compromise cell viability and hydrogel integrity. To address these limitations, the present work reports in situ 3D patterning of collagen hydrogels by femtosecond laser irradiation to create channels and cavities with diameters ranging from 20 to 60 µm. In this process, laser irradiation of the hydrogel generates cavitation gas bubbles that rearrange the collagen fibers, thereby creating stable microchannels. Such 3D channels can be formed in cell‐ and organoid‐laden hydrogel without affecting the viability outside the lumen and can enable the formation of artificial microvasculature by the culture of endothelial cells and cell media perfusion. Thus, this method enables organs‐on‐a‐chip and 3D tissue models featuring complex microvasculature.

Tunable dynamic networks of cellulose nanofibrils (CNFs) are utilized to prepare high‐performance polymer gel electrolytes. By swelling an anisotropically dewatered, but never dried, CNF gel in acidic salt solutions, a highly sparse network is constructed with a fraction of CNFs as low as 0.9%, taking advantage of the very high aspect ratio and the ultra‐thin thickness of the CNFs (micrometers long and 2–4 nm thick). These CNF networks expose high interfacial areas and can accommodate massive amounts of the ionic conductive liquid polyethylene glycol‐based electrolyte into strong homogeneous gel electrolytes. In addition to the reinforced mechanical properties, the presence of the CNFs simultaneously enhances the ionic conductivity due to their excellent strong water‐binding capacity according to computational simulations. This strategy renders the electrolyte a room‐temperature ionic conductivity of 0.61 ± 0.12 mS cm−1 which is one of the highest among polymer gel electrolytes. The electrolyte shows superior performances as a separator for lithium iron phosphate half‐cells in high specific capacity (161 mAh g−1 at 0.1C), excellent rate capability (5C), and cycling stability (94% capacity retention after 300 cycles at 1C) at 60 °C, as well as stable room temperature cycling performance and considerably improved safety compared with commercial liquid electrolyte systems.

Fibrillar hydrogels are remarkably stiff, low-density networks that can hold vast amounts of water. These hydrogels can easily be made anisotropic by orienting the fibrils using different methods. Unlike the...