Single-molecule studies of hyaluronic acid

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Non-technical: This award by the Biomaterials program in the Division of Materials Research to University of California-Santa Barbara is to study the size, shape and solution properties of hyaluronic acid (hyaluronan, HA) in the presence of salts and other molecules that binds with this polymer. Hyaluronan, or hyaluronic acid (HA), is a huge polymer molecule that defines the structure and mechanics of many spaces in the human body such as tissue hydration, wound healing, lubrication of certain biological interfaces, and helps to define the mechanics of joints and functionality. Further, HA is under active investigation for use in biomaterials applications, notably functionalized HA gels that act as cell/tissue engineering substrates. These functions of HA rely on its polymeric, random-walk structure, which is modulated by solution conditions, including salt concentration, crowding by other biological polymers, and the presence of HA-binding molecules. It is thus of basic importance, for both biological and chemical reasons, to have a detailed understanding of the microscopic basis of HA conformation and solution behavior. The proposed studies are expected to lead to a better understanding of HA's various biological roles, as well as to permit rational engineering of HA-based biomaterials. Further, carrying out this project would have a variety of important broader impacts, including strengthening university/national lab partnerships, and training young scientists, at both undergraduate and graduate levels in an interdisciplinary scientific area with excellent long-term potential. International dissemination and scientific exchanges are parts of this project, and these unique activities are important in achieving scientific broader impacts. Technical: Hyaluronic acid (HA) is a polysaccharide present in nearly all mammalian tissues. HA is characterized by a large anionic charge density, conformational flexibility, and polymorphism due to a variety of hydrogen-bonding interactions. These features, along with its association with certain ligands, lead it to define the mechanical and viscoelastic properties of extracellular spaces, such as the pericellular matrix, eye vitreous, and synovial fluid. HA is of further interest for clinical applications, and as a biomaterial used to create gel substrates for cell and tissue growth. In all these biological and biomaterials applications, there is a common need for a thorough understanding of HA's microscopic structure and functions, particularly including mechanical properties and their relation to the ionic effects that dominate osmotic and viscoelastic properties. With the prior NSF project, this researcher has established that low-force single-molecule elasticity measurements are powerful tools to understand polyelectrolyte structure in complex solutions. Here, 'low force' means tensions small enough to permit looped, random-walk structure in the chain; such forces are inaccessible to standard force spectroscopy approaches that only access nearly-straight chain configurations. Low forces permit sensitivity to weak, long range interactions, and thus quantification of the effects that are key to HA's biological and biomaterials functions, such as electrostatic repulsion, direct and water-mediated hydrogen bonding, and self-avoidance. Here, the proposed studies are to apply the low-force approach to a rigorous examination of HA's solution-mediated conformational and mechanical properties. This research will proceed through the following two goals. In goal 1, HA conformation will be studied as modulated by electrostatic screening, water structure (using chao/kosmotropic salts), and in the presence of crowders. In goal 2, the effects of specific biological ligands on HA conformation will be studied, with emphasis on proteogylcans that cause swelling and crosslinking effects. International dissemination and scientific exchange that are unique and important in the context of achieving broader impact of the sciences are part of this awards.