Assembly, disassembly, and mechanics of porous colloidal vesicles

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

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.