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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.

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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.

This paper describes a method of fabricating rounded bottom microwell arrays (MA) in poly(dimethylsiloxane) (PDMS) by molding a monolayer of ordered polystyrene (PS) microspheres. PS microspheres were self-assembled on a glass slide and partially melted mainly from the bottom at 240 °C to increase adhesive force with the substrate. The partially melted PS arrays were used as master to generate MA. Microwell sizes are tunable in the 10-20 μm range with rounded bottoms; such a 3D structure is not readily obtainable through conventional soft lithography. Both adherent and nonadherent cell types can be retained in the microwells with high efficiency. As a demonstration of the advantage of real-time cell screening with this MA, single cell enzyme kinetic analysis was also carried out on trapped single cells. The PDMS MA may find applications in high-throughput drug screening, guided formation of cell clusters, and multicellular communication.

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