Lecture+29-Mechanical+factors+_+bioreactor

Lecture+29-Mechanical+factors+_+bioreactor - Bioreactors:...

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Unformatted text preview: Bioreactors: Mechanical Regulation of Tissue Remodeling and rtificial Blood Vessels Artificial Blood Vessels Mechanical Loading Regulates Mechanical Loading Regulates Bone Remodeling Bone Remodeling External remodeling: Surface shape change Internal remodeling: Changes of bone porosity, mineral content, and density Culmanns Crane (1867) Wolffs Law (1869) The structure (distribution of bone mass) must correspond to the quantitative distribution of mechanical stress (e.g., principal stress) Questions hy should the bone be molded according Why should the bone be molded according to the stress trajectories of one particular loading? What happens to other loading conditions? Why is it sufficient to consider a curved eam of homogenous isotropic elastic beam of homogenous, isotropic, elastic material, when the bone is not? The problems in the mathematical model. Rouxs Functional Adaptation Concept (1880) Adaptation to a function by making use of it A quantitative self-regulating mechanism controlled by a functional stimulus Hypothesis on the roles of stresses in healing: Tensile and shear stress connective tissue Friction or shearing cartilage Compression bone Pauwels Hypothesis (1980) Elongation and hydrostatic pressure are the two specific stimuli for the differentiation of mesenchymal tissue. Hypothesis on the roles of stresses in healing: ensile (Elongation) connective tissue Tensile (Elongation) connective tissue Compression cartilage ? bone Frosts Mechanostat Theory (1987) Under physiologically normal loading, bone formation and resorption p y g y g, p are in equilibrium. Low strains experienced during disuse/microgravity result in bone loss. Mechanical loading resulting in high strains increases bone formation. Excessive strains result in an increased production of woven bone formation, similar to that observed during fracture repair. 10,000 =1% strain Mechanical Loading and Cell Function During adaptation to increased or decreased loading, bone tissue adjusts through a feedback system in which changes in the local mechanical environment signal bone cells to modify bone structure to the new requirements. This occurs through the processes of bone formation and resorption, with the ultimate result depending upon the balance between osteoblast and osteoclast activity and the anatomical...
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Lecture+29-Mechanical+factors+_+bioreactor - Bioreactors:...

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