Assembly, disassembly, and mechanics of porous colloidal vesicles

从薄的肥皂状膜形成封闭的无边缘胶囊或囊泡是一种具有根本重要性的过程，其渗透到物理学、生物学、工程学和材料科学等不同领域。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，在常规材料如细胞膜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观察到。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，但比细胞膜大上千倍，因此更容易研究。将胶体膜的独特功能与最先进的光学显微镜相结合，将允许以分子水平的分辨率在真实的时间内可视化囊泡形成的过程。此外，使用相同的技术将揭示封闭的胶体囊泡福尔斯如何通过瞬时孔的重复成核及其随后的自我修复的级联过程而分开。胶体囊泡的化学交联提供了一个独特的机会，以创建一个多孔膜，可用于大小选择性过滤和各种纳米级货物的靶向输送。实验工作将与跨学科生物材料科学的严格培训和指导相结合，以研究生和本科生。该项目还将鼓励代表性不足的群体在STEM相关领域开展工作，为他们提供研究机会，并将提高公众对科学研究对更广泛社区重要性的认识。胶体膜是由一微米长的均匀长度的丝状病毒自发组装而成的液体状单层。胶体单层和脂质双层的连续变形都由Helfrich提出的同一类连续弹性模型描述。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。超快三维共聚焦显微镜和介电张量断层扫描将揭示胶体膜经历重力辅助形成细长系链及其随后断裂导致形成封闭胶体囊泡的动力学过程。此外，同样的技术将可视化与分子水平的细节的动力学途径，瞬时孔成核在过压囊泡。 一旦成核，测量将量化导致其重新密封的通过孔的流体动力学流动。低于较低的临界尺寸，胶体膜变得不稳定，并经历了一个戏剧性的拓扑结构转变成扁平的盘状结构。胶体膜和囊泡的多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，创造一个强大的实验平台，为刺激依赖性和大小选择性交付的纳米货物。这一奖项反映了NSF的法定使命，并已被认为是值得支持，通过评估使用基金会的智力价值和更广泛的影响审查标准。

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.