  Scalable technologies for the production of bio-compatible complex
microfibers with controllable size and composition at competitively high
throughput are urgently needed in order to meet the growing demand for such
microstructures in pharmaceutical or biomedical applications. Here, we
introduce a new in-air microfluidic strategy with throughput of > 1400 ml/h
(corresponding to > 17000 m fiber per h). The microfibers of uniform diameter
have regular inclusions, which can potentially be used for encapsulating cells
into a protecting and nutrient environment, or for finely tuning the release of
various actives at individualized doses. With the help of a newly developed
prototype, we test seven different liquid combinations and obtain seven types
of fibers, whose "dry" diameter range between 73um and 141um. The principle of
our approach is to solidify the complex liquid structures generated by the
controlled collisions of a drop stream with a continuous liquid jet, in air,
via ionic crosslinking. After the stream of water-based droplets, which
constitute the inclusions, collides in-air with the alginate-based jet (jet 1),
the generated "drops-in-jet" compound is brought in contact with a second jet
(jet 2) containing divalent strontium or calcium cations to initiate the
solidification. Finally, the fibers are collected via a horizontal spinning
plate, let to dry, i.e. to fully equilibrate under controlled conditions, and
characterized by their elongation at break and Young's modulus.
