Abstract
Polyelectrolyte (PE) microcapsules for drug delivery are typically fabricated via layer-by-layer (LbL) deposition of PE layers of alternating charge on sacrificial template microparticles, which usually requires multiple incubation and washing steps that render the process repetitive and time-consuming. Here, ferrofluid droplets were explored for this purpose as an elegant alternative of templates that can be easily manipulated via an external magnetic field, and require only a simple microfluidic chip design and setup. Glass microfluidic devices featuring T-junctions or flow focusing junctions for the generation of oil-based ferrofluid droplets in an aqueous continuous phase were investigated. Droplet size was controlled by the microfluidic channel dimensions as well as the flow rates of the ferrofluid and aqueous phases. The generated droplets were stabilised by a surface active polymer, polyvinylpyrrolidone (PVP), and then guided into a chamber featuring alternating, co-laminar PE solutions and wash streams, and deflected across them by means of an external permanent magnet. The extent of droplet deflection was tailored by the flow rates, the concentration of magnetic nanoparticles in the droplets, and the magnetic field strength. PVP-coated ferrofluid droplets were deflected through solutions of polyelectrolyte and washing streams using several iterations of multilaminar flow designs. This culminated in an innovative "Snakes-and-Ladders" inspired microfluidic chip design that overcame various issues of the previous iterations for the deposition of layers of anionic poly(sodium-4-styrene sulfonate) (PSS) and cationic poly(fluorescein isothiocyanate allylamine hydrochloride) (PAH-FITC) onto the droplets. The presented method demonstrates a simple and rapid process for PE layer deposition in <30 seconds, and opens the way towards rapid layer-by-layer assembly of PE microcapsules for drug delivery applications.
Highlights
Polymer multilayer capsules (PMLCs) to swell or contract upon exposure to various stimuli, including pH, light, magnetism, salt, and glucose.[15]
The most popular method for manipulating particles, cells and droplets through multilaminar flow streams is via the use of magnetic forces, largely due to the ease with which such forces can be employed in microfluidic devices,[30,31,32,33] including the coating of magnetic particles fluids in an immiscible phase.[34,35,36]
We further show the various iterations of the microfluidic devices and techniques we employed in order to demonstrate how a number of different issues, which could be experienced by researchers developing similar systems, were addressed
Summary
PMLCs to swell or contract upon exposure to various stimuli, including pH, light, magnetism, salt, and glucose.[15]. We employ an oil-based ferrofluid for the generation of magnetic droplets as PMLC templates and their deflection across multilaminar flow streams of PE solutions (Fig. 1b) towards the rapid and automated fabrication of PMLCs. The layer of immiscible fluid between the droplets and the channel walls as well as the droplet PE coating were expected to reduce the extent to which the magnetic
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