Microfluidic Emulsion Templating, Directional Solidification and Controlled Release

微胶囊和微粒提供了携带和传递活性成分的有效手段，包括药物和化妆品，具有精确的时空释放曲线。从机理上了解微胶囊的包埋、固化和释放过程是设计未来微胶囊的关键，它将热力学、传质和非平衡现象结合在一起，包括动力学停滞或相变。在微流控装置中产生的乳液滴可以在货物和外部环境之间形成屏障，可以用来通过定向固化过程来制作微胶囊的模板，目前正在研究如何应对这一挑战。由硫醇-烯类抗蚀剂正面光聚合而成的200-600微米尺寸的快速原型微流控器件，被用来从几种聚合物、两亲性和疏水性物种中产生单乳状液和双乳状液滴。利用定向凝固过程，如溶剂萃取和离子交联，从液滴中形成固体胶囊。通过光学显微镜初步观察了不同的工艺参数，如多价盐浓度或非溶剂质量，以及所用材料对固化过程和颗粒/胶囊形态的影响。水凝胶颗粒(100-500微米)由羧甲基纤维素钠(NaCMC)的单一乳滴形成，并在多价盐中固化。凝胶颗粒的形成被认为是聚合物链聚集的结果；由盐添加时发生的屏蔽、离子桥和电荷反转的相互作用所决定。固体聚合物颗粒也是通过溶剂萃取过程产生的；将聚乙烯醇的水滴从微流体单乳液发生器浸入非溶剂浴中。聚合物浓度和非溶剂质量影响产物颗粒的形态和定向凝固过程的动力学。这种方法的多功能性也通过将NaCMC水滴固化成固体颗粒来展示。进一步了解这些定向凝固过程，以及它们对分子结构、工艺参数和流动变化的响应，将使它们能够应用于封装。以疏水材料为内核的双乳液滴，可以通过这些方法固化成固体外壳。它们在从制药到个人护理的广泛行业中的潜在应用将通过研究它们的控制释放特性来展示。

Microcapsules and particles offer efficient means of carrying and delivering active ingredients, including medical drugs and cosmetics, with precise spatio-temporal release profiles. Mechanistic understanding of the encapsulation, solidification and release processes is crucial in designing future microcapsules, combining thermodynamics, mass transfer and non-equilibrium phenomena, including kinetic arrest or phase changes. Emulsion droplets, generated within microfluidic devices, which can form a barrier between the cargo and external environment can be used to template microcapsules from, by directional solidification processes, and are being investigated to tackle this challenge. Rapidly prototyped microfluidic devices, produced by frontal photopolymerization of thiol-ene resists, with flow-focussing geometries, and 200-600 micrometers dimensions, were used to generate single and double emulsion droplets from several polymeric, amphiphilic and hydrophobic species. Directional solidification processes, e.g. solvent extraction and ionic crosslinking, were exploited to form solid capsules from the droplets. The effects of varying process parameters, such as multivalent salt concentration or non-solvent quality, as well as the materials used on the solidification process and particle/capsule morphology was observed primarily by optical microscopy. Hydrogel particles (100-500 micrometers) were formed from single emulsion droplets of sodium carboxy methylcellulose (NaCMC) and solidified in multivalent salts. Gel particle formation was thought to be a result of aggregation of polymer chains; dictated by the interplay of shielding, ion bridging and charge inversion occurring upon salt addition. Solid polymer particles were also produced by a solvent extraction process; immersion of aqueous poly (vinyl alcohol) droplets, from a microfluidic single emulsion generator, into a non-solvent bath. Polymer concentration and non-solvent quality affected the morphology of the resultant particles and the kinetics of the directional solidification process. This versatility of this approach was shown by also solidifying aqueous NaCMC droplets into solid particles. Further understanding of these directional solidification processes, their response to changes in molecular structure, processing parameters and flow, will enable them to be applied to encapsulation. Double emulsion droplets with an inner core of hydrophobic material, can be solidified by these methods to produce solid shells. Their potential application in a wide range of industries, from pharmaceuticals to personal care, will be demonstrated by studying their controlled release properties.