Materials with microchannels have attracted increasing attention due to their promising perfusability and biomimetic geometry. However, the fabrication of microfibers with more geometrically complex channels in the micro- or nanoscale remains a big challenge. Here, a novel method for generating scalable microfibers with consecutive embedded helical channels is presented using an easily made coaxial microfluidic device. The characteristics of the helical channel can be accurately controlled by simply adjusting the flow rate ratio of the fluids. The mechanism of the helix formation process is theorized with newly proposed heterogenerated rope-coil effect, which enhances the tunability of helical patterns and promotes the comprehension of this abnormal phenomenon. Based on this effect, microfibers with embedded Janus channels and even double helical channels are generated in situ by changing the design of the device. The uniqueness and potential applications of these tubular microfibers are also demonstrated by biomimetic supercoiling structures as well as the perfusable and permeable spiral vessel.

Fiber materials with different structural features, which in many cases endow the fibers extraordinary functions, are drawing considerable attention from biomedical and material researchers. Here, perfusable necklace-like knotted microfibers are presented for the first time. Additionally, a novel microfluidic spinning method facilitates the production of variable knots and channels. Not only spindle-, but also hemisphere- and petal-knotted microfibers can be controllably fabricated. Generation and perfusion of both Janus channels and helical channel in the knotted microfibers are also shown. With no need of oil and surfactant, the spinning process is highly cytocompatible. The potential bioengineering and biomedical application of the knotted hollow microfiber is demonstrated by its cell-encapsulation feasibility and the unique liver acinus-like diffusion gradient in the knot. The merits of perfusability, cytocompatibility, and structural diversity of the microfibers may open more avenues for further material and biomedical investigation.

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Inspired by helical structures in nature, novel hydrogel microfibers with an embedded helical channel are fabricated with the guide of the heterogenerated rope‐coil effect, by Qionglin Liang and co‐workers in article number https://doi.org/10.1002/adma.201701664, using a microfluidic device. The perfusable microfibers allow the construction of more complex vessel structures in vitro, such as spiral arteries and tumor tissue.

Fabrication of cell-encapsulated fibers could greatly contribute to tissue engineering and regenerative medicine. However, existing methods suffered from not only unavoidability of cell damaging conditions and/or sophisticated equipment, but also unavailability of proper materials to satisfy both mechanical and biological expectations. In this work, a simple method is proposed to prepare cell-encapsulated fibers with tunable mechanical strength and stretching behavior as well as diameter and microstructure. The hydrogel fibers are made from optimal combination of alginate and poly(N-iso-propylacrylamide)-poly(ethylene glycol), characteristics of double-network hydrogel, with enough stiffness and flexibility to create a variety of three dimensional structures like parallel helical and different knots without crack. Furthermore, such hydrogel fibers exhibit better compatibility as indicated by the viability, proliferation and expression of pluripotency markers of embryonic stem cells encapsulated after 4-day culture. The double-network hydrogel possesses specific quick responses to either of alginate lyase, EDTA or lower environmental temperature which facilitate the optional degradation of fibers or fibrous assemblies to release the cells encapsulated for subsequent assay or treatment.