Santosh Yadav

University of Cincinnati, Cincinnati, OH, United States

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Publications (4)9.15 Total impact

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    ABSTRACT: The water content of skin has a significant impact on skin properties; sufficient hydration is necessary to keep the skin supple, flexible, and smooth. To understand more completely the water retention properties of the human skin barrier, physical macroscopic properties must be related to the structural organization of the stratum corneum (SC). Water, lipids, and natural moisturizing factor (NMF) influence the molecular structures that affect the properties of SC, including water sorption and binding enthalpy. In the research reported here, isothermal microcalorimetry was used to study the interaction of water vapor with isolated human SC in intact, delipidized, and water-washed delipidized forms to identify the influences of the principal components of SC on water sorption. The calorimetric data are interpreted in conjunction with spectroscopic results to identify the conformational changes in keratins induced by lipid and NMF removal and to assess the influence of these changes on water binding in SC. Isothermal calorimetry was used to measure the integral heat of water vapor sorption on intact, delipidized, and water-washed delipidized human SC at 32 degrees C as a function of relative humidity using back and thigh skin from three donors. Calorimetric measurements were combined with water vapor sorption measurements to determine the differential thermodynamic properties of these systems. Attenuated total reflection-Fourier transform infrared spectroscopy was used to investigate effects of extraction on protein secondary structure. The magnitudes of the differential enthalpy, entropy, and free energy were greatest for intact SC and least for water-washed delipidized SC. Water sorption followed a similar trend. Delipidization led to a significantly reduced binding enthalpy at low water content; water washing the delipidized SC had only a small additional effect on binding enthalpy. Delipidization converts a fraction of keratin alpha-helixes to turns and random coils, while water sorption converts a fraction of keratin alpha-helixes to beta-sheets, turns, and random coils. The results of this study are consistent with a water sorption model in which keratin-keratin hydrogen bonds are replaced by keratin-water hydrogen bonds. Delipidization reduces the fraction of dry keratin that is in the alpha-helix conformation, suggesting that lipids hold the keratins in a conformation conducive to optimal hydration.
    Skin Research and Technology 06/2009; 15(2):172-9. · 1.41 Impact Factor
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    ABSTRACT: Studies of adsorption on biologically derived materials typically include direct measurement of either the adsorption isotherm or the heat of adsorption, but not both. Simultaneous measurement of adsorption and heat of adsorption should provide a more reliable description of the material under study. In this context, an analysis of the thermodynamics of water sorption is presented and a multilayer heat of sorption equation is derived within the framework of the Guggenheim–Anderson–deBoer (GAB) model. This model is applied to the previously published data for water vapor sorption and heat of water vapor sorption on stratum corneum (SC) over a range of relative humidities. The GAB models effectively characterize both heat evolution and equilibrium mass uptake over a broad water activity range. The thermodynamic results suggest significant restructuring of the SC during the sorption process; the sorption data alone are not sufficient to identify this effect. The results of this study emphasize first, the importance of incorporating a multilayer approach with variable energies of interaction in modeling of water uptake by SC and second, the utility of correlating sorption and calorimetric data simultaneously.
    Chemical Engineering Science. 04/2009; 64(7):1480–1487.
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    ABSTRACT: A thermodynamic study of water interaction with human stratum corneum (SC) is presented. The procedure consisted of conjoint water vapor sorption and heat flow measurements. Heat of sorption of water in excised human SC at various relative humidities was measured in an isothermal calorimeter at 32 degrees C using back and thigh skin from three different donors. These measurements, combined with the gravimetric sorption isotherm, were used to calculate the integral and differential enthalpies and entropies associated with binding of water to SC. Differential enthalpy values suggest hydrogen-bonding interactions similar to those for water in wool keratin. The changes in differential enthalpy and entropy with increasing water content followed a pattern similar to that seen in wool and other hydrophilic polymers. The results are partially interpreted in terms of a BET isotherm with monolayer volume v(m) = 0.022 g H(2)O/g dry SC and binding parameter C = 6.5 x 10(8).
    Journal of Pharmaceutical Sciences 07/2007; 96(6):1585-97. · 3.13 Impact Factor
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    ABSTRACT: The synthesis of spherical particles of mesoporous silicates (SBA-15) with mesopore diameter upto 127A, and particle diameter of 4-10 microm has been achieved. The SBA-15 spheres were obtained using pluronics P123 (EO20PO70EO20) as a surfactant coupled with cetyltrimethylammonium bromide (CTAB) as a co-surfactant. Ethanol played a very important role in the formation of silica spheres, as it delays the reaction rate of the SBA-15 synthesis. A wide range of pore diameters (28-127 A) of these spherical SBA-15 materials with large surface area >700 m2/g has been synthesized. The effects of temperature, ethanol, CTAB and swelling agent have also been studied. The SBA-15 samples were characterized using small angle X-ray scattering (SAXS), N2 adsorption-desorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The spherical SBA-15 after mechanical grinding was used for protein adsorption, and adsorption capacity was compared with that of conventional fibrous SBA-15. The spherical SBA-15 particles with pore diameter of 127 A have a very high capacity of 700 mg/g for lysozyme at pH 7.
    Journal of Chromatography A 07/2006; 1122(1-2):13-20. · 4.61 Impact Factor