This Career Award from the Biomaterials Program in the Division of Materials Research to the University of Oregon will support studies that aim to quantify and control interactions among microparticles to enable the self-organization of structurally complex colloidal crystals. Such superstructures have long been of interest as models of phenomena such as crystallization and defect dynamics, and are technologically important due to intriguing optical properties. The proposed experiments adopt a biomimetic approach to self-assembly, creating colloidal particles functionalized with two-dimensionally fluid bio-membranes. These studies are expected to expand paradigms of colloidal assembly by co-opting tools of biological self-organization, using functionalization of microparticles with lipid and protein membranes to control colloidal crystal formation. Several attributes make bio-membranes appealing mediators of inter-particle interactions: the variety and specificity of protein linkages; the ease with which lipid composition can control electrostatic properties; and the two-dimensional fluidity of membranes, which confers on their constituents the ability to reorganize their distribution as the context demands. The project could define an experimental route to both creating and characterizing the interactions among membrane-derivatized microspheres.
Activity-coupled educational programs described in the project will use explorations of contemporary biophysical and biomaterial topics as tools to promote higher education in the sciences to middle-school students from socioeconomically disadvantaged backgrounds and to improve non-science-major college students' understanding of science and scientific thinking. To engage and educate non-science-major college undergraduates, the PI will create a unique course exploring the physical properties of biological materials through readings, discussions, and laboratory exercises. Exposure to diverse contemporary subjects can change students' perceptions of the nature of the sciences and the relevance of scientific concepts to the everyday world. A coupled educational agenda will use activities that spotlight current, cross-disciplinary science, including the sort exemplified by the proposed research program, to impact the education of a wide spectrum of students. To address the low rate of college enrollment by students from socioeconomically disadvantaged backgrounds, as part of this project, a Physics Day Camp will be developed that would provide disadvantaged secondary school students with information about access to higher education, an introduction to the culture of scientific inquiry, and activity-based science education.
Fluids as diverse as milk, paint, and blood are composed of microscopic particles suspended in liquid. Measuring and controlling interactions between microparticles is a major goal in both science and industry. The spacing between microscopic particles in ordered arrays, for example, determines their optical properties and their utility for a wide range of technological applications. Our work has aimed to provide both new ways of quantifying forces between microscopic particles, and new ways to control inter-particle interactions. We built upon prior advances using light to "trap" and manipulate microscopic objects to invent a new sort of optical trap that enables straightforward measurement of the interactions between pairs of particles. We also invented new computational methods for extracting particle positions from microscope images that have a combination of accuracy and speed that transcends previous methods. To control particle behaviors, motivated by the membranes that surround biological cells, we used lipid and protein membranes to coat microparticles. This allowed us to easily modify properties such as electrical charge, exploiting the naturally occurring variety of charge in different lipids, for example, to modulate the charge of composite inorganic-plus-membrane particles. Combining these advances in biologically inspired particle construction and optical tool development, we showed that membrane-functionalization of particles does in fact provide a tunable "toolbox" of different interaction types. Different lipid compositions led, for example, to attractive particles with different attraction strengths, whose magnitude was correlated with the degree of electrical charge. In addition to demonstrating the utility of membrane-functionalization, the data provide insights into the electrical forces that underlie these interactions. We created a set of educational and outreach activities that intersect with our research aims. These involved creating and implementing a Physics and Human Physiology "day camp" for socioeconomically disadvantaged students, and designing and creating a new course on biophysics and biomaterials for non-science-major undergraduates. The camp has been help annually since 2008, co-organized and run by the PI, and is part of a sustained and growing set of such outreach activities at the University of Oregon. Students learned directly from college financial aid and admissions staff about university requirements and procedures, and directly from hands-on activities about topics in materials science and microscopy. These activities have included, among other things, a tour of research labs that involved hands-on exposure to optical traps, in which every student was able to directly manipulate microparticles using focused laser beams. This also meshed with discussions of self-assembled systems and complex fluids (including microscopy of mayonnaise, toothpaste, and other "familiar" items). We have also integrated this research into a new course for non-science-major undergraduates, with the aim of improving the scientific literacy of the general public. Biophysics and biomaterials provide an accessible route to these ends, as they involve concepts of both fundamental and practical importance related, for example, to the design of biomimetic materials, the mechanical actions of organisms and their constituent molecules, and the tools and techniques by which insights into nature are gained.
