Microfluidic Fabrication of Porous Polymer Microspheres: Dual Reactions in Single Droplets

Abstract

We report the microfluidic fabrication of macroporous polymer microspheres via the simultaneous reactions within single droplets, induced by UV irradiation. The aqueous phase of the reaction is the decomposition of H(2)O(2) to yield oxygen, whereas the organic phase is the polymerization of NOA 61, ethylene glycol dimethacrylate (EGDMA), and tri(propylene glycol) diacrylate (TPGDA) precursors. We first used a liquid polymer precursor to encapsulate a multiple number of magnetic Fe(3)O(4) colloidal suspension (MCS) droplets in a core-shell structure, for the purpose of studying the number of such encapsulated droplets that can be reliably controlled through the variation of flow rates. It was found that the formation of one shell with one, two, three, or more encapsulated droplets is possible. Subsequently, the H(2)O(2) solution was encapsulated in the same way, after which we investigated its decomposition under UV irradiation, which simultaneously induces the polymerization of the encapsulating shell. Because the H(2)O(2) decomposition leads to the release of oxygen, porous microspheres were obtained from a combined H(2)O(2) decomposition/polymer precursor polymerization reaction. The multiplicity of the initially encapsulated H(2)O(2) droplets ensures the homogeneous distribution of the pores. The pores inside the micrometer-sized spheres range from several micrometers to tens of micrometers, and the maximum internal void volume fraction can attain 70%, similar to that of high polymerized high internal phase emulsion (polyHIPE).

Porous polymer particles—A comprehensive guide to synthesis, characterization, functionalization and applications

“…Another unique approach made use of a gas forming reactive porogen. Small droplets containing H 2 O 2 molecules were captured in bigger oil phase monomer droplets flowing in a carrier aqueous phase [227]. UV exposure not only solidified the oil phase but also decomposed H 2 O 2 molecules exhausting gas species, similar to the blowing agent strategy discussed in section 2.2.…”

“…It is important to mention that the solidification was not only based on vinyl polymerization but also on a commercial photo-curable thiol-ene adhesive in the latter report [227]. The addition of thiyl radicals to alkene or alkyne bonds (thiol-ene and thiol-yne reactions, respectively) has recently gained considerable interest as novel metal-free 'click' reactions among polymer scientists [228][229][230].…”

Fabrication of porous polymer microspheres by tuning amphiphilicity of the polymer and emulsion–solvent evaporation processing

“…Weng et al prepared porous poly(lactic-co-glycolic acid) microspheres by solvent evaporation method, sodium oleate was employed as porogen [20]. Density and size of the pores played important roles in determining the properties of the porous polymer spheres, including drug encapsulation efficiency and release kinetics [21][22][23][24][25][26][27]. Although many porous microspheres have been prepared by using porogens, it is a great challenge to control the size of microspheres and pores independently when porogens were used [4,[28][29][30][31].…”

Preparation of Biodegradable Liquid Core PLLA Microcapsules and Hollow PLLA Microcapsules Using Microfluidics

“…For making monodisperse polymer particles, both spherical or non-spherical, usually Flow-Focusing devices are used for the preparation of solid particles, [5,[13][14][15][16] liquid filled particles, [17][18][19] hollow particles, [20][21][22] and several other morphologies. [23][24][25][26][27] By improving the control over the size of the capsules it is possible to have a more effective drug release as demonstrated by Xu et al [14] They showed that when comparing drug loaded poly(lactic acid-co-glycolic acid) (PLGA) solid spheres prepared by conventional techniques, as described above, and by microfluidics, the monodisperse particles prepared by microfluidics exhibited a significantly reduced burst release and a slower overall rate of release compared to the conventionally prepared polydisperse particles.…”