Control of Molecular Fiber Bundle Mechanics and Dynamics by Bundle Architecture

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Biological fiber bundles are widely spread in nature. They are necessary for our senses of hearing and balance, facilitate wound healing, and enable cells to divide and migrate, to name just a few examples. Nature utilizes fiber bundles for their fast assembly and disassembly and rapid control over mechanical properties through changes in molecular interactions. The understanding of biological fiber bundles and their rich mechanical and dynamical properties is crucial to biomechanics and mechanical biology. This understanding, however, has been hampered by a lack of suitable microscopic techniques for simultaneously observing bundle architecture and dynamics. The research addresses this problem by combining high-precision position measurements, optical response measurements and manipulation of a prototype fiber bundle structure that is widely used in nature. The overall goal of this research is to determine the link between the molecular architecture of biological fiber bundles and their macroscopic mechanical properties. This understanding is essential for biomedical research and for the design of novel smart materials that self-assemble and exhibit predictable properties. Students will be exposed to a rich interdisciplinary environment that includes theoretical physics, physical chemistry, molecular biology and material science, thereby training them to develop an interdisciplinary approach towards research. Students will participate in an international collaboration, and the development of state of the art instrumentation will enhance the intentional competitiveness of the research. Female high school students will also participate in the research as part of the Alice in Wonderland outreach project.The project will advance our fundamental understanding of the link between biological fiber bundle architecture and macroscopic mechanics and dynamics. The findings could potentially have wide spread applications to other biological fiber bundle systems and manmade systems. Microtubules will be used as a model system. These particular fiber bundles consist of parallel protofilaments that arrange themselves to form closed tubes and other bundle structures. They are ideal for comprehensive study of bundle mechanics and dynamics because the weak interactions between protofilaments allow them to easily adapt various structures. The mechanical and dynamical properties or microtubules will be measured using their naturally occurring thermal shape fluctuations with a novel high-bandwidth position detection scheme. The architecture will be determined from optical scattering signals. The experiments test the hypothesis that bundle mechanics and dynamics can be described by the recently developed wormlike bundle model over a wide range of parameters such as filament number, strength of crosslinking, and the molecular state of the subunits. The wormlike bundle model provides a direct link between molecular and macroscopic properties and, if confirmed, will aid the rational design and assembly of smart fiber bundle-based materials for technical applications and biomedical research.