== Mechanics of Collagen == We are investigating the mechanical properties of the extracellular matrix protein collagen, which serves a structural role as a supporting scaffold for cells and as the basis for connective tissues. Specifically, we are addressing the question of how mechanical response at the molecular level relates to mechanical response of higher-order assemblies, by studying proteins that form hierarchical structures and probing their mechanical response at different levels of assembly. We probe the single-molecule mechanical properties of collagen using optical tweezers, atomic force microscopy and centrifuge force microscopy; characterize the viscoelasticity of solutions and networks using optical tweezers based microrheology; and are developing holographic optical tweezers to measure the evolution of through-space mechanical coupling in collagen gels. Molecular-level information is obtained by changing experimental conditions and determining how our results depend on physiologically relevant variables such as pH, temperature, and protein sequence. Transmission electron microscopy and atomic force microscopy are used to image the proteins from the molecular to the fibrillar scales. We seek to answer questions such as: How do the sequence and local structure of a protein relate to its mechanical properties? How do these influence the viscoelastic properties of higher-order structures? What factors influence whether mechanical response is kinetically or thermodynamically determined? From an applied perspective, our experiments aim to improve our understanding of how mechanical properties of proteins contribute to development and structure of associated tissues, results that may someday be of use in the study of tissue growth, diseases and degeneration, and may have applications in the design of artificial biomaterials. == Novel Molecular Motors == We are investigating the mechanisms by which molecular motors operate. As part of an international collaboration, we are developing numerical and experimental models to design and construct synthetic protein-based molecular motors. Our philosophy is that operational principles of molecular motors are understood if they can be implemented to build motors ab initio.