The Crystal Hotel: A Microfluidic Approach to Biomimetic Crystallization.
The Crystal Hotel: A Microfluidic Approach to Biomimetic Crystallization.
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DOI：
10.1002/adma.201503931
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发表时间：
2015-12-02
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影响因子：
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通讯作者：
Meldrum FC
中科院分区：
文献类型：
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作者：
Gong X;Wang YW;Ihli J;Kim YY;Li S;Walshaw R;Chen L;Meldrum FC
然而，很少有研究将这些策略与生物体实现对生物矿化如此显着的控制的最基本机制之一——限制结合起来。通过定义发生结晶的局部环境，生物体可以获得在本体溶液中永远无法实现的一定程度的控制，定义形态，[8, 14]稳定亚稳态多晶型物，[15]并实现对过饱和度和添加剂浓度的暂时控制。在本文中，我们受益于微加工技术的进步，创造了独特的局部结晶环境，在其中我们可以采用多种策略来控制结晶。我们的“晶体酒店”微流体装置具有包括限制、流动和空间组织在内的功能，提供了生物矿化系统的出色模拟，由于其光学透明性，我们可以在其中观察单个晶体如何在有限的体积内生长。使用碳酸钙作为合适的模型系统，我们使用该设备同时应用多种策略来控制结晶，从而生成具有预定晶体取向、微观结构和形状的大晶体。因此，该系统与以前的实验完全不同，以前的实验使用连续流微流体装置来评估生物大分子对CaCO 3 沉淀的影响，[16]或其中CaCO 3 和磷酸钙分别在水/油（W/O）液滴中沉淀，[17]和W/O/W双乳液。[18]“水晶酒店”微流体装置设计用于提供一系列形状明确的受限反应体积，尺寸和内部图案，可以实现反应离子和添加剂的受控流动（图 1 和图 S1，支持信息）。它们是使用常见的光刻方法[19]由聚（二甲基硅氧烷）（PDMS）制备的，并通过等离子体处理粘合到载玻片上。每家酒店均由一系列八个房间 (R1–R8) 组成，房间直径为 120 µm，高度为 3 µm，单个房间体积为 23.3 pL。房间内部还采用一系列 PDMS 柱图案，这些柱的直径和高度为 3 µm，间距为 3 µm（图 1 a-c）。这种内部图案提供了监测具有复杂形态的晶体形成的机会，而单个设备内多个房间的存在使得可以同时进行多个实验。从 R1（最靠近入口）到 R8（图 1 d、e），气压下降了大约七倍，这是通过在施加恒定气压时测量进料结构中液体的弧长来计算的（图 S2，支持信息）。因此，过饱和度在 R1 中建立得最快，并且在 R8 之前在 R1 中观察到结晶。房间内的碳酸钙沉淀是通过输送 NH 3 和 CO 2 气体（由分解产生）来实现的。控制结晶以产生具有规定尺寸、形态、多晶型物和取向的颗粒是一个引起极大兴趣的主题，在药物和生物材料的生产以及陶瓷、纳米材料和光学元件的制造中找到了应用。虽然我们普遍期望晶体应该表现出规则的几何形状，以反映晶格的基础结构，但当然有很多例子与此相反，最好的材料之一是生物矿物，如骨骼、牙齿和贝壳，其复杂的形态、层次结构和卓越的机械性能远远超出了......
Few studies, however, have combined such strategies with one of the most fundamental mechanisms by which organisms achieve such remarkable control over biomineralization—confinement. By defining the local environment in which crystallization occurs, organisms can obtain a degree of control that could never be achieved in bulk solution, defining morphologies,[8, 14] stabilizing metastable polymorphs,[15] and achieving temporal control over the supersaturation and additive concentrations. In this article, we profit from advances in microfabrication techniques to create unique, localized crystallization environments in which we can employ multiple strategies to control crystallization. Exhibiting features including confinement, flow, and spatial organization, our “crystal hotel” microfluidic device provides an excellent mimic of biomineralizing systems, in which—thanks to its optical transparency—we can watch how individual crystals grow within confined volumes. Using calcium carbonate as a suitable model system, we use this device to simultaneously apply multiple strategies to control crystallization, thereby generating large crystals with predefined crystallographic orientations, microstructures, and shapes. This system is therefore quite distinct from previous experiments in which continuous-flow microfluidic devices were used to evaluate the effects of biomacromolecules on CaCO 3 precipitation,[16] or in which CaCO 3 and calcium phosphate were precipitated within water/oil (W/O) droplets,[17] and W/O/W double emulsions respectively.[18]“Crystal hotel” microfluidic devices were designed to provide a series of confined reaction volumes of well-defined shape, size, and internal patterning into which a controlled flow of reactant ions and additives could be achieved (Figure 1 and Figure S1, Supporting Information). These were prepared from poly (dimethylsiloxane)(PDMS) using common lithographic methods [19] and bonded to a glass slide by plasma treatment. Each hotel comprises a series of eight rooms (R1–R8), which are 120 µm in diameter and 3 µm in height, giving individual volumes of 23.3 pL. The rooms are also internally patterned with an array of PDMS pillars that are 3 µm in diameter and height and set 3 µm apart (Figure 1 a–c). This internal patterning provides the opportunity to monitor the formation of crystals with complex morphologies, while the presence of multiple rooms within a single device enables multiple experiments to be performed simultaneously. There is an approximately sevenfold drop in the gas pressure from R1 (closest to the inlet) to R8 (Figure 1 d, e), where this was calculated by measuring the arc length of a liquid in the feeding structure when applying a constant gas pressure (Figure S2, Supporting Information). The supersaturation therefore builds fastest in R1, and crystallization is observed in R1 before R8. Calcium carbonate precipitation in the rooms is achieved by delivering NH 3 and CO 2 gases (arising from the decompositionControl over crystallization to yield particles with defined sizes, morphologies, polymorphs, and orientations is a subject that attracts huge interest, finding applications in the production of pharmaceuticals and biomaterials, and the fabrication of ceramics, nanomaterials, and optical components. While our common expectation is that crystals should exhibit regular, geometric forms that reflect the underlying structure of the crystal lattice, there are of course numerous examples that contradict this picture. One of the best is provided by biominerals such as bones, teeth, and seashells, whose complex morphologies, hierarchical structures, and superior mechanical properties go far beyond …