High-Throughput and Controllable Fabrication of Helical Microfibers by Hydrodynamically Focusing Flow

Abstract

Due to the unique spiral geometry, different functional helical fibers are fabricated to perform vital tasks, including cargo transportation, medical treatment, cell manipulation, and so on. Although microfluidic techniques are widely used to fabricate helical fibers, the problems of channel blockage and spinning instability have not been well solved, which limits the mass preparation and practical application of spiral microfibers. In addition, the spinning mechanism is simply limited to liquid rope coiling, which has little impact on the design of microfluidic devices. Here, new types of microfluidic devices, which were easy to make and exhibited excellent spiral spinning performance, were designed. It was found that adding a sleeve layer outside the inner core needle in a coaxial microfluidic device could effectively promote the stable formation of helical microfibers. This novel microchannel could fabricate helical microfibers of more than 100 m in length continuously at one time with almost no blockage or deformation, and the key parameters of the fibers could be precisely adjusted. Combined with micro-particle image velocimetry (micro-PIV) measurements, it was confirmed that the improvement in the spinning performances was mainly attributed to the emergence of a focusing flow in the presence of the sleeve layer. After loading magnetic nanoparticles, the helical microfibers exhibited excellent motion manipulation capabilities, which showed great potential for drug delivery, cargo transportation, clogging removal, etc. This new design not only realized the high-throughput fabrication of helical microfibers but also provided deeper insights into the underlying mechanisms of spiral generation and new ideas for the design of microfluidic devices.

Microfluidic fabrication of calcium alginate helical microfibers for highly stretchable wound dressing

“…A square membrane with a side length of 10 cm needs helical fiber of at least 10 m long to fully cover the surface, which has a high requirement for the stability of spinning. In our previous study, a new type of microfluidic channel, which was made of stainless steel needles was designed, and the experimental results showed that this new design was more stable and clogged less frequently than the conventional microchannels, which were made of tapered glass capillaries 27 . Even with nanoparticles loaded in the internal phase, a helical microfiber of nearly 100 m was still successfully generated.…”

“…In our previous study, a new type of microfluidic channel, which was made of stainless steel needles was designed, and the experimental results showed that this new design was more stable and clogged less frequently than the conventional microchannels, which were made of tapered glass capillaries. 27 Even with nanoparticles loaded in the internal phase, a helical microfiber of nearly 100 m was still successfully generated. Therefore, here we choose this new type of channel for the preparation of spiral fibers.…”

“…The channel consisted of a connector made by 3D printing method, a needle, and a receiving tube. 27 The needle part was a 32G standardized stainless steel needle (inner diameter 100 μm, outer diameter 230 μm) covered with a 25G stainless steel sleeve (inner diameter 250 μm, outer diameter 510 μm), glued together. The receiving tube was a glass capillary with an inner diameter of 0.9 mm and an outer diameter of 1.2 mm.…”

“…The sodium alginate solution solidified to form fibers after contacting. At a suitable flow rate, the calcium alginate fibers could be folded into spiral shape and maintained this morphology in the whole process 27–31 . Compared with other helical fiber preparation methods, the microfluidic method is easy to operate, does not require expensive instruments, while achieving continuous preparation and precise adjustment of key parameters (pitch, diameter, etc.).…”

“…At a suitable flow rate, the calcium alginate fibers could be folded into spiral shape and maintained this morphology in the whole process. [27][28][29][30][31] Compared with other helical fiber preparation methods, the microfluidic method is easy to operate, does not require expensive instruments, while achieving continuous preparation and precise adjustment of key parameters (pitch, diameter, etc.). The helical fibers were collected in a mold, and a photocuring precursor solution of polyacrylamide was injected to fill the gap.…”