Abstract Extracted from natural pollen grains, sporopollenin exine capsules (SECs) are robust, chemically inert biopolymer shells that posess highly uniform size and shape characteristics and that can be utilized as hollow microcapsules for drug delivery applications. However, it is challenging to extract fully functional SECs from many pollen species because pollen grains often collapse, causing the loss of architectural features, loading volume, and bulk uniformity. Herein, we demonstrate that polyethylene glycol (PEG) osmolyte solutions can help preserve the native architectural features of extracted SECs, yielding inflated microcapsules of high uniformity that persist even after subsequent lyophilization. Optimal conditions were first identified to extract SECs from cattail (Typhae angustfolia) pollen via phosphoric acid processing after which successful protein removal was confirmed by elemental (CHN), mass spectrometry (MALDI-TOF), and confocal laser canning microscopy (CLSM) analyses. The shape of SECs was then assessed by scanning electron microscopy (SEM) and dynamic image particle analysis (DIPA). While acid-processed SECs experienced high degrees of structural collapse, incubation in 2.5% or higher PEG solutions significantly improved preservation of spherical SEC shape by inducing inflation within the microcapsules. A theoretical model of PEG-induced osmotic pressure effects was used to interpret the experimental data, and the results show excellent agreement with the known mechanical properties of pollen exine walls. Taken together, these findings demonstrate that PEG osmolyte is a useful additive for preserving particle shape in lyophilized SEC formulations, opening the door to broadly applicable strategies for stabilizing the structure of hollow microcapsules.

中文翻译：

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用聚乙二醇渗透物保存冻干孢粉素外壁胶囊的膨胀结构

摘要 从天然花粉粒中提取的孢粉质外壁胶囊 (SEC) 是坚固的、化学惰性的生物聚合物外壳，具有高度均匀的尺寸和形状特征，可用作药物递送应用的中空微胶囊。然而，从许多花粉物种中提取功能齐全的 SEC 具有挑战性，因为花粉粒经常塌陷，导致结构特征、装载量和体积均匀性的损失。在此，我们证明聚乙二醇 (PEG) 渗透剂溶液可以帮助保留提取的 SEC 的天然结构特征，产生高度均匀的膨胀微胶囊，即使在随后的冻干后也能持续存在。首先确定了通过磷酸处理从香蒲 (Typhae angusfolia) 花粉中提取 SEC 的最佳条件，然后通过元素 (CHN)、质谱 (MALDI-TOF) 和共聚焦激光罐头显微镜 (CLSM) 分析确认成功去除蛋白质。然后通过扫描电子显微镜 (SEM) 和动态图像粒子分析 (DIPA) 评估 SEC 的形状。虽然酸处理的 SEC 经历了高度的结构崩溃，但在 2.5% 或更高的 PEG 溶液中孵育通过诱导微胶囊内的膨胀显着改善了球形 SEC 形状的保存。PEG 诱导的渗透压效应的理论模型用于解释实验数据，结果显示与已知的花粉外壁机械特性非常吻合。综合起来，