This subproject is one of many research subprojects utilizing theresources provided by a Center grant funded by NIH/NCRR. The subproject andinvestigator (PI) may have received primary funding from another NIH source,and thus could be represented in other CRISP entries. The institution listed isfor the Center, which is not necessarily the institution for the investigator.Temporomandibular joint disorders (TMDs) are an important national health problem in the Unite States. Although the exact cause of TMDs is unclear, the temporomandibular joint (TMJ) disc pathophysiology (i.e., disc derangement and degeneration) is central to many TMDs. Poor nutritional supply as well as failure of mechanical function caused by pathological mechanical loading is believed to be one of the mechanisms for the biomechanical etiology of disc derangement and degeneration. The long-term goal of this project is to elucidate the roles of fluid and solute transport in tissue mechanical function and cell nutrition of the human TMJ disc for delineating the biomechanical etiology of TMDs and to develop new strategies for restoring tissue function. Due to the unique composition and structure of the materials as well as the complexity of the mechano-electrochemical coupling phenomena, there is a lack of knowledge about transport properties of the human TMJ disc and appropriate theoretical models for investigating fluid and nutrient transport in the TMJ disc systematically. Therefore, the specific aims of this proposal are to: 1) evaluate the effect of mechanical strain on the transport properties of the human TMJ disc and develop constitutive relationships between transport properties and tissue biochemical composition; 2) establish fluid flow dependent mechanisms for disc loading support and lubrication. To accomplish aim 1, we will: a) determine hydraulic permeability, fixed charge density, and electrical conductivity of the normal human TMJ disc under various mechanical strains; b) obtain ion diffusivities from electrical conductivity data and develop new constitutive relationships between transport properties (hydraulic permeability and solute diffusivity) and tissue hydration to establish strain-dependent transport properties. To accomplish aim 2, we will determine time-dependent fluid pressure, fluid load support, and friction coefficient of the normal human TMJ disc under sustained mechanical loading, and correlate fluid load support and friction coefficient to interstitial fluid pressure. These studies will provide new insights into a bio-transport related mechanism for disc degeneration. To achieve our long-term goal, we will further develop a new multiphasic mechano-electrochemical finite element model of the human TMJ disc which will provide details of mechanical stress, strain, fluid pressure, nutrient concentrations, electrical potential, fluid flow, and transport of nutrients within the TMJ disc under physiological or pathological loading conditions. Studies will also be conducted to understand the biological response of disc cells to these physicochemical signals for fully elucidating biomechanical etiology of TMJ disc degeneration.
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