Institute of Particle Science & Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom.
Langmuir. 2010 May 4;26(9):6281-6. doi: 10.1021/la904064d.
Using a layer-by-layer (LbL) approach, this work presents the preparation of hollow microcapsules with a membrane constructed entirely from a cationic/zwitterionic pair of pH-responsive block copolymer micelles. Our previous work with such systems highlighted that, in order to retain the responsive nature of the individual micelles contained within the multilayer membranes, it is important to optimize the conditions required for the selective dissolution of the sacrificial particulate templates. Consequently, here, calcium carbonate particles have been employed as colloidal templates as they can be easily dissolved in aqueous environments with the addition of chelating agents such as ethylenediaminetetraacetic acid (EDTA). Furthermore, the dissolution can be carried out in solutions buffered to a desirable pH so not to adversely affect the pH sensitive micelles forming the capsule membranes. First, we have deposited alternating layers of anionic poly[2-(dimethylamino)ethyl methacrylate-block-poly(2-(diethylamino)ethyl methacrylate)] (PDMA-PDEA) and cationic poly(2-(diethylamino)ethyl)methacrylate-block-poly(methacrylic acid) (PDEA-PMAA) copolymer micelles onto calcium carbonate colloidal templates. After deposition of five micelle bilayers, addition of dilute EDTA solution resulted in dissolution of the calcium carbonate and formation of hollow polymer capsules. The capsules were imaged using atomic force microscopy (AFM) and scanning electron microscopy (SEM), which shows that the micelle/micelle membrane is sufficiently robust to withstand dissolution of the supporting template. Quartz crystal microbalance studies were conducted and provide good evidence that the micelle multilayer structure is retained after EDTA treatment. In addition, a hydrophobic dye was incorporated into the micelle cores prior to adsorption. After dissolution of the particle template, the resulting hollow capsules retained a high concentration of dye, suggesting that the core/shell structure of the micelles remains intact. Finally, thermogravimetric analysis (TGA) of dried capsules confirmed complete removal of the sacrificial inorganic template. As far as we are aware, this is the first demonstration of LbL assembled capsules composed entirely from responsive block copolymer micelles. The results presented here when combined with our previous findings demonstrate that such systems have potential application in the encapsulation and triggered release of actives.
采用层层（LbL）方法，本工作制备了由完全由阳离子/两性离子 pH 响应嵌段共聚物胶束构成的中空微胶囊。我们之前对这种系统的研究表明，为了保持多层膜中包含的单个胶束的响应性质，重要的是优化用于选择性溶解牺牲颗粒模板所需的条件。因此，在这里，碳酸钙颗粒被用作胶体模板，因为它们可以在添加乙二胺四乙酸（EDTA）等螯合剂的水性环境中很容易溶解。此外，溶解可以在缓冲到所需 pH 的溶液中进行，以免对形成胶囊膜的 pH 敏感胶束产生不利影响。首先，我们将阴离子聚[2-（二甲氨基）乙基甲基丙烯酸酯嵌段-聚（2-（二乙基氨基）乙基甲基丙烯酸酯）]（PDMA-PDEA）和阳离子聚（2-（二乙基氨基）乙基）甲基丙烯酸酯嵌段-聚（甲基丙烯酸）（PDEA-PMAA）共聚物胶束交替沉积在碳酸钙胶体模板上。沉积五倍胶束双层后，加入稀 EDTA 溶液导致碳酸钙溶解并形成中空聚合物胶囊。使用原子力显微镜（AFM）和扫描电子显微镜（SEM）对胶囊进行成像，结果表明胶束/胶束膜足够坚固，可以承受支撑模板的溶解。石英晶体微天平研究提供了很好的证据，表明在 EDTA 处理后保留了胶束多层结构。此外，在吸附之前将疏水性染料掺入胶束核中。颗粒模板溶解后，所得中空胶囊保留了高浓度的染料，表明胶束的核/壳结构保持完整。最后，干燥胶囊的热重分析（TGA）证实完全去除了牺牲的无机模板。据我们所知，这是首次证明完全由响应性嵌段共聚物胶束组成的 LbL 组装胶囊。这里呈现的结果与我们之前的发现相结合，表明这些系统在活性物质的封装和触发释放方面具有潜在的应用。
