Synthesis of Janus colloids: A comprehensive review with emphasis on microfluidic approaches and drug delivery applications

Janus colloids, distinguished by their structural anisotropy and contrasting physicochemical characteristics, have emerged as a robust and versatile platform in the realm of therapeutic sciences, particularly in the domain of targeted drug delivery. Their unique structural asymmetry enables directional interactions, compartmentalized loading, and programmable responsiveness, which are critical features for multifunctional therapeutic applications. This review presents an in-depth overview of Janus colloidal particle synthesis, with a particular emphasis on microfluidic fabrication techniques that offer exceptional control, scalability, and reproducibility. We begin by outlining the foundational principles underlying Janus particle design, followed by an in-depth discussion of key microfluidic strategies such as the co-flowing approach, electrokinetic co-jetting technique, etc. These methods are critically compared in terms of their ability to engineer particle morphology, spatial material distribution, and interfacial properties. In addition, modelling and simulation approaches for Janus particle fabrication are discussed to provide a theoretical perspective complementing experimental advances. The review then examines recent advances in drug delivery, highlighting the utility of Janus systems for controlled release, synergistic co-delivery, and site-specific targeting. By integrating multiple functionalities into a single carrier, Janus microparticles address longstanding challenges in therapeutic delivery. Finally, we discuss the current challenges and highlight future directions grounded in these, with the hope that this contribution will help inform researchers and further advance the fabrication strategies of Janus colloids-based drug delivery systems.