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

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.