Currently, most drug delivery carriers are micro-/nanoparticles 
. These spherical dosage forms have been studied extensively for their drug release profiles, but some limitations still exist. For example, they are easily expelled from the target site and that they have a high initial burst release rate 
. The structure of the microfibers is a potentially alternative dosage form for obtaining a controlled zero-order release profile 
. By providing a continuous structural integrity, microfibers can be new carriers for delivering delicate compounds such as water soluble drugs that have low encapsulation efficiency and reduced bioactivity in conventional vehicles 
Melt spinning, wet spinning, and electrospinning are common methods to produce microfibers 
. However, melt spinning needs bulky and heavy equipment for its high temperature process, while wet spinning involves volatile organic solvents, rendering them unacceptable for protein encapsulation. The microfibers produced by electrospinning are difficult to align directionally, and too thin to have a high enough mechanical strength for three-dimensional (3D) scaffolds applications 
. In contrast, microfluidic technology is simple, cost-effective, is compatible with biological materials and thus an alternative method for producing uniform micro-/nanofibers 
Numerous studies have utilized magnetic nanoparticles for medical and biological applications, such as drug/gene delivery, bio-separation, and magnetic resonance imaging 
. Previous studies have demonstrated that magnetic nanoparticles can be controlled to facilitate drug release from spherical particles 
. This suggests that magnetic nanoparticles can be entrapped in microfibers. However, this kind of magnetically-controlled release strategy has not yet been applied on microfibers.
Therefore, the aim of this study was to develop a facile way to obtain polymer microfibers by utilizing microfluidic technology. In order to have good control over the fabrication of the microfibers, we used the design of multi-inlets and multi-junctions to achieve the dispersed and the continuous phases for solidifying and shielding the microfibers without them clogging the microchannels 
. The advantage of the microchannel design is that it is simple and efficient to fabricate microfibers using a one-step continuous process. The main novelties of this study are (i) a linear release behavior from the diclofenac-loaded microfibers; (ii) an active control over the drug release rate from the microfibers by exerting magnetic iron oxide (MIO) nanoparticles; and (iii) a one-step cell encapsulation system to culture cancer cells for screening potential anticancer agents.