Effect of geometric modification of fumed nanoscale silica for medical applications on adsorption of human serum albumin: Physicochemical and surface properties.

The influence of the geometric modification (GM) of fumed nanoscale silica A300 (NS) on the adsorption capacity of human serum albumin (HSA) as well as the physicochemical and textural properties of the protein/nanosilica system was analyzed. An effective medical enterosorbent based on fumed nanosilica was designed and produced in the Chuiko Institute of Surface Chemistry, National Academy of Sciences of Ukraine. To design an effective nanomaterial for biomedical applications as a wound-healing material, the adsorption, physicochemical and surface properties of the initial nanosilica (NS), nanosilica after geometric modification (GM-nanosilica), and HSA/nanosilica biocomposites were characterized. The differences in sorption capacities, acid-base, textural, and surface properties of the obtained materials were monitored using the diffuse UV-vis reflectance spectroscopy, the potentiometric titration of suspension, the nitrogen adsorption/desorption isotherms, the scanning electron microscopy with the energy dispersive X-ray microanalysis and the digital optical microscope. For a deeper understanding of the nature of immobilized HSA molecules on the nanosilica and GM-nanosilica, the surface functional groups were characterized by the FTIR spectroscopy. It was found that the adsorption properties, physicochemical and textural characteristics of fumed nanoscale silica depend on the mechanical treatment time (tMT) and bulk density (db). In fact, as the tMT increases, the db of initial fumed nanosilica increases, and the protein adsorption capacity decreases, however, it remains at an acceptable level: 0.075 g/g, 0.056 g/g, 0.032 g/g for GM-nanosilica after 1, 4, and 7 h of mechanical treatment, respectively. HSA adsorption significantly changes the surface morphology, acid-base character, and structure of both unmodified and modified nanosilica.

Nanosilica modified by polydimethylsiloxane depolymerized and chemically bound to nanoparticles or physically bound to unmodified or modified surfaces: Structure and interfacial phenomena.

Three polydimethylsiloxanes (PDMS200, PDMS1000, and PDMS12500 with numbers showing the viscosity values dependent on the molecular weight) were used for adsorption (14-95 wt% PDMS) onto unmodified and PDMS-modified (16.7 wt% PDMS using dimethyl carbonate (DMC) as a siloxane bond breaking reagent) nanosilica A-300. The materials were studied using microscopy, infrared spectroscopy, thermodesorption, calorimetry, ethanol and water/ethanol evaporation, nitrogen adsorption-desorption, and quantum chemical methods. The interfacial and temperature behaviors of a PDMS layer at a silica surface depend strongly on the type of bonding to silica particles, molecular weight and content of PDMS. Upon chemical bonding, shorter PDMS200 forms a denser coverage of the silica surface since SBET diminution is larger and residual free silanols are practically absent (the degree of free silanol substitution Θ > 0.95) in contrast to the reactions with PDMS1000/DMC or PDMS12500/DMC providing Θ = 0.60-0.63 at larger SBET values. Upon thermal decomposition of the PDMS layer, oxidation/depolymerization desorption gives a greater contribution than pure depolymerization destruction. An increase in the PDMS adsorption layer thickness leads to enhancement of the depolymerization contribution because the oxidation mainly occurs at the top of the layer, but the depolymerization can occur in the total PDMS layer. The adsorption, desorption, and evaporation processes of low-molecular weight probes at a surface of PDMS-modified nanosilica depend strongly on the type of bonding and content of PDMS. Thus, the most effective hydrophobization of nanosilica by PDMS/DMC could be carried out using the shortest polymer giving the shortest PDMS fragments upon the interaction with DMC that is of interest from a practical point of view.

Study of Adsorption Equilibria in the Systems Ternary Liquid Mixtures-Modified Activated Carbons.

The adsorption abilities of commercial activated carbon after thermal and chemical treatment were investigated. The chemical character of carbon surfaces was determined by applying the thermogravimetric method, measurement of adsorption isotherms of water vapor, and the process of neutralization of surface functional groups. Total amounts of oxygen and nitrogen in all carbon samples were estimated by elemental analysis. Adsorption-desorption isotherms of benzene vapor were used to determine the parameters of the Dubinin-Radushkevich equation characterizing the porous structure of investigated carbons. These analyses show that chemical modification of carbon samples leads to strong differentiation of the chemical character of adsorbent surfaces; however, the porous structures show distinct similarity. In order to study the adsorption equilibria from liquid phase, the adsorption isotherms were measured for ternary mixtures of benzene, diethyl ketone, and n-heptane on all carbons. A strong effect of the chemical character of the carbon surface on liquid adsorption was found and discussed for all systems. Copyright 1999 Academic Press.