The stress analysis of the porcine aortic valve leaflets in diastole at 80 mm Hg pressure in-vitro is presented. Incorporation of local geometrical asymmetry, material inhomogeneity, anistropy and non-linearity are applied. The stress theory used is a modified form of the thin membrane stress theory for a homogeneous linearly elastic and orthotropic lamina. Modifications are made so that the Hooke's law constitutive equations of stress may be applied to the inhomogeneous, non-lineary elastic and orthotropic thin (membrane) aortic valve leaflets. Stress calculations are made on the premise that the valve is in pre-transition (i.e. low elastic modulus) in the circumferential direction and post-transition (i.e. high elastic modulus) in the radial direction. It is shown that sigmaCIR less than 1 gm/mm2, and for most of the noncoronary leaflet, 0 less than sigmaRAD less than 30 gm/mm2. The areas of highest stress concentrations are in the areas of mutual leaflet coaptation near the Node of Arantii. A progressive increase of radial stresses from the sinus-annulus edge toward the node is observed.
A new method based on the measurement of the relative dye-binding capacity of Alcian Blue to carboxymethylchitin (CMC) at various molecular weights (MW) has been developed to facilitate the standardization of the initial polyelectrolyte concentration. In the absence of standardization, non-reproducible adsorption patterns are encountered during the adsorption of the MW CMC on neutral and positively charged liposomes. This method is sensitive down to a concentration of 5 mu g/ml of polymer in water. Static Light Scattering (SLS) measurements are used to obtain the weight average molecular weight (Mw) and the size of the polyelectrolyte (Rg) and overlap concentrations (c*). The Mws are then used to determine the constants K and a of the Mark-Houwink equation which are 1.65 x 10(-2) dl/g and 0.4701, respectively, evaluated at kappa = 0.154 M, pH = 7.4 and T = 25 degrees C. The critical electrolyte concentration decreases with molecular weight for Mws ranging from 5.0 x 10(4)-1.2 x 10(6). The dye-binding capacity changes with the molecular weight distribution of the polyelectrolyte demonstrating the sensitivity of this technique to polydispersity.
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