The physiological function of many cells is dependent on their ability to adhere via receptors to ligand-coated surfaces under fluid flow. We have developed a model experimental system to measure cell adhesion as a function of cell and surface chemistry and fluid flow. Using a parallel-plate flow chamber, we measured the binding of rat basophilic leukemia cells preincubated with anti-dinitrophenol IgE antibody to polyacrylamide gels covalently derivatized with 2,4-dinitrophenol. The rat basophilic leukemia cells' binding behavior is binary: cells are either adherent or continue to travel at their hydrodynamic velocity, and the transition between these two states is abrupt. The spatial location of adherent cells shows cells can adhere many cell diameters down the length of the gel, suggesting that adhesion is a probabilistic process. The majority of experiments were performed in the excess ligand limit in which adhesion depends strongly on the number of receptors but weakly on ligand density. Only 5-fold changes in IgE surface density or in shear rate were necessary to change adhesion from complete to indistinguishable from negative control. Adhesion showed a hyperbolic dependence on shear rate. By performing experiments with two IgE-antigen configurations in which the kinetic rates of receptor-ligand binding are different, we demonstrate that the forward rate of reaction of the receptor-ligand pair is more important than its thermodynamic affinity in the regulation of binding under hydrodynamic flow. In fact, adhesion increases with increasing receptor-ligand reaction rate or decreasing shear rate, and scales with a single dimensionless parameter which compares the relative rates of reaction to fluid shear.

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Biosensor measurement of transdermal alcohol oncentration in perspiration exhibits significant variance from subject to subject and device to device. Short duration data collected in a controlled clinical setting is used to calibrate a forward model for ethanol transport from the blood to the sensor. The calibrated model is then used to invert transdermal signals collected in the field (short or long duration) to obtain an estimate for breath measured blood alcohol concentration. A distributed parameter model for the forward transport of ethanol from the blood through the skin and its processing by the sensor is developed. Model calibration is formulated as a nonlinear least squares fit to data. The fit model is then used as part of a spline based scheme in the form of a regularized, non-negatively constrained linear deconvolution. Fully discrete, steepest descent based schemes for solving the resulting optimization problems are developed. The adjoint method is used to accurately and efficiently compute requisite gradients. Efficacy is demonstrated on subject field data.

Background-Islet transplantation is a promising treatment for type 1 diabetes. Due to a shortage of suitable human pancreata, high cost, and the large dose of islets presently required for long-term diabetes reversal; it is important to maximize viable islet yield. Traditional methods of pancreas preservation have been identified as suboptimal due to insufficient oxygenation. Enhanced oxygen delivery is a key area of improvement. In this paper, we explored improved oxygen delivery by persufflation (PSF), ie, vascular gas perfusion.