Segmented flow microfluidic devices offer an attractive means of studying crystallization processes. However, while they are widely employed for protein crystallization, there are few examples of their use for sparingly soluble compounds due to problems with rapid device fouling and irreproducibility over longer run‐times. This article presents a microfluidic device which overcomes these issues, as this is constructed around a novel design of “picoinjector” that facilitates direct injection into flowing droplets. Exploiting a Venturi junction to reduce the pressure within the droplet, it is shown that passive injection of solution from a side‐capillary can be achieved in the absence of an applied electric field. The operation of this device is demonstrated for calcium carbonate, where highly reproducible results are obtained over long run‐times at high supersaturations. This compares with conventional devices that use a Y‐junction to achieve solution loading, where in‐channel precipitation of calcium carbonate occurs even at low supersaturations. This work not only opens the door to the use of microfluidics to study the crystallization of low solubility compounds, but the simple design of a passive picoinjector will find wide utility in areas including multistep reactions and investigation of reaction dynamics.

中文翻译：

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被动皮针注射可在液滴微流控设备中实现可控的结晶

分段流动微流体装置提供了一种研究结晶过程的有吸引力的手段。但是，尽管它们被广泛用于蛋白质结晶，但由于设备结垢迅速且在较长的运行时间内无法再现，因此很少将其用于难溶化合物的实例。本文介绍了一种克服了这些问题的微流体装置，因为该装置是围绕“皮针注射器”的新颖设计而构建的，该“皮针注射器”有助于直接注入流动的液滴。利用文丘里管接头降低液滴内的压力，结果表明，在没有施加电场的情况下，可以实现从侧毛细管的溶液被动注入。该设备的操作已针对碳酸钙进行了演示，在高饱和度下，长时间运行可获得高度可重复的结果。这与使用Y形结实现溶液加载的常规设备相比，在传统设备中，即使在过饱和度较低的情况下，碳酸钙也会发生通道内沉淀。这项工作不仅为使用微流控技术研究低溶解度化合物的结晶打开了大门，而且被动皮针注射器的简单设计将在包括多步反应和反应动力学研究在内的领域中找到广泛的用途。