Assembly, disassembly, and mechanics of porous colloidal vesicles

从肥皂状薄膜形成封闭的无边胶囊或囊泡是一个基本的重要过程，它渗透到物理学、生物学、工程学和材料科学等各个领域。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长度尺度上，即使是最强大的显微镜也不容易看到。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，但却比细胞膜大1000倍，因此更容易研究。将胶体膜的独特特征与最先进的光学显微镜相结合，将允许以分子水平分辨率实时可视化囊泡形成的过程。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一个重复瞬态孔隙成核及其随后的自我修复的级联过程而破裂的。胶体囊泡的化学交联提供了一个独特的机会，可以创建一个多孔膜，可用于尺寸选择过滤和各种纳米货物的靶向递送。实验工作将与研究生和本科生在跨学科生物材料科学方面的严格培训和指导相结合。该项目还将通过为代表性不足的群体提供研究机会，鼓励他们从事stem相关领域的工作，并将提高人们对科学研究对更广泛社区重要性的普遍认识。胶体膜是一种液体状的单层膜，由长度均匀的一微米长的丝状病毒自发组装而成。胶体单层和脂质双层的连续变形均用Helfrich提出的一类连续弹性模型来描述。因此，胶体膜提供了一个独特的机会来阐明所有膜基材料的普遍行为。超快速三维共聚焦显微镜和介电张量断层扫描将揭示胶膜在重力辅助下形成细长系带及其随后断裂导致封闭胶囊形成的动力学过程。此外，同样的技术将以分子水平的细节可视化过压囊泡中瞬态孔隙成核的动力学途径。一旦成核，测量将量化通过孔隙导致其重新密封的流体动力学流动。低于低临界尺寸的胶体膜变得不稳定，并经历戏剧性的拓扑转变成扁平的圆盘状结构。胶体膜和囊泡的多孔结构是由渗透压和离子强度决定的。因此，它提供了一个独特的机会，为纳米货物的刺激依赖性和尺寸选择性输送提供了一个强大的实验平台。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.