Assembly, disassembly, and mechanics of porous colloidal vesicles

非技术描述从薄的皂状薄膜形成封闭的无边胶囊或囊泡是一个基本重要的过程，渗透到物理、生物、工程和材料科学等多个领域。例如，当它们感染细胞时，生物病毒穿过并被可变形的细胞膜包裹。然而，在细胞膜等常规材料中观察封闭胶囊的形成是非常具有挑战性的。原因是，这种高度动态的过程发生在非常快的时间尺度和纳米尺度上，即使是最强大的显微镜也不容易可视化。胶体膜提供了一个模型实验系统，它与细胞膜有许多共同的特征，但大约大一千倍，因此更容易研究。将胶体膜的独特特性与最先进的光学显微镜相结合，将允许以分子级别的分辨率实时可视化囊泡形成过程。此外，使用相同的技术将揭示一个封闭的胶体囊泡是如何通过瞬间毛孔的重复成核和随后的自我修复的级联过程而解体的。胶体囊泡的化学交联提供了一个独特的机会来创造一种可用于尺寸选择性过滤和各种纳米货物的定向递送的多孔膜。实验工作将与对研究生和本科生的跨学科生物材料科学的严格培训和指导相结合。该项目还将通过提供研究机会，鼓励代表性不足的群体从事与科学、技术和经济有关的领域的工作，并将提高广大社区对科学研究重要性的普遍认识。技术描述胶体膜是由长度一致的一微米长的丝状病毒自发组装而成的类液体单分子层。胶体单层和脂双层的连续变形可用Helfrich提出的同一类连续介质弹性模型来描述。因此，胶体膜提供了一个独特的机会来阐明所有基于膜的材料的普遍行为。超高速三维共聚焦显微镜和介电张量层析成像将揭示胶体膜在重力辅助下形成细长的系链以及随后的断裂导致闭合胶体囊泡形成的动力学过程。此外，同样的技术将以分子水平的细节可视化瞬时气孔在超压小泡中成核的动力学路径。一旦成核，这些测量将量化通过毛孔的流体动力流动，从而导致它们重新密封。在较低的临界尺寸以下，胶体膜变得不稳定，并经历了戏剧性的拓扑转变为扁平的盘状结构。胶体膜和囊泡的孔结构由渗透压和离子强度决定。因此，它提供了一个独特的机会，为依赖刺激和选择尺寸运送纳米货物创造一个强大的实验平台。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical description Forming an enclosed edgeless capsule or vesicle from thin soap-like membranes is a process of fundamental importance that permeates fields as diverse as physics, biology, engineering, and materials science. For example, as they infect a cell, biological viruses pass through and are enveloped by a deformable cellular membrane. However, observing the formation of closed capsules in conventional materials such as cellular membranes is highly challenging. The reason is that such highly dynamical processes occur on very fast time scales and nanometer length scales that are not easily visualized with even the most powerful microscopes. Colloidal membranes provide a model experimental system that shares many common characteristics with cellular membranes, yet are about a thousand times larger and thus easier to study. Combining the unique features of colloidal membranes with state-of-the-art optical microscopy will allow for visualizing the process of vesicle formation in real time with molecular-level resolution. Furthermore, using the same technique will reveal how a closed colloidal vesicle falls apart through a cascading process of repeating nucleation of transient pores and their subsequent self-healing. Chemical crosslinking of colloidal vesicles provides a unique opportunity to create a porous membrane that can be used for size-selective filtration and targeted delivery of various nanosized cargoes. The experimental efforts will be integrated with rigorous training and mentoring in interdisciplinary biomaterial sciences to graduate and undergraduate students. The project will also encourage underrepresented groups to pursue work in STEM-related fields by providing them with research opportunities and will raise general awareness of the importance of scientific research to broader communities. Technical description Colloidal membranes are liquid-like monolayers that spontaneously assemble from one-micron-long filamentous viruses of uniform length. The continuum deformations of both colloidal monolayer and lipid bilayers are described by the same class of continuum elastic models proposed by Helfrich. Thus, colloidal membranes provide a unique opportunity to elucidate the universal behaviors of all membrane-based materials. Ultra-fast three-dimensional confocal microscopy and dielectric tensor tomography will reveal the dynamical processes by which colloidal membranes undergo gravity-assisted formation of elongated tethers and their subsequent fracture that leads to the formation of closed colloidal vesicles. Furthermore, the same techniques will visualize with molecular-level detail the kinetic pathways by which transient pores nucleate in over-pressurized vesicles. Once nucleated the measurements will quantify the hydrodynamic flows through the pore that leads to their resealing. Below the lower critical size colloidal membranes become unstable and undergo a dramatic topological transition into flat disk-like structures. The porous structure of colloidal membranes and vesicles is determined by the osmotic pressure and the ionic strength. Thus, it provides a unique opportunity to create a powerful experimental platform for the stimuli-dependent and size-selective delivery of nanosized cargoes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.