Namita Deo

Adsorption and dissolution behavior of human plasma fibronectin on thermally and chemically modified titanium dioxide particles.

Titanium is known for its biocompatibility and is widely used in dental and orthopedic reconstructive surgery. There are reports that osteointegration of these implants is not optimal. The objective of this study was to modify titanium dioxide particles and examine the resultant effects on protein adsorption to these altered surfaces using a model cell binding protein, human plasma fibronectin (HPF). HPF is an important matrix glycoprotein that plays a major role in cell and protein attachment, Titanium dioxide surfaces were modified by heating the titanium dioxide powder at 800 degrees C for 1 h or treating with an oxidizing agent: peroxide in ammonium hydroxide followed by peroxide in hydrochloric acid. Oxidized and control samples were further treated with 9:1 butanol:water for 30 min. Brunauer-Emmett-Teller showed no change in particle surface area as a result of thermal or chemical treatment. Hydrophobicity increased with butanol treatment of titanium dioxide. Diffuse reflectance Fourier transform infrared spectroscopy showed the presence of -CH2 and -CH3 vibrations in the region of 2850-3000 cm(-1) for both the heated, butanol and peroxide/butanol-treated samples. The absence of increased C-O and O-C=O features as determined by electron spectroscopy for chemical analysis indicates that butanol adsorption is not occurring via an esterification mechanism. The interaction between butanol and pre-heated or peroxide-treated titanium dioxide may be one of association (weak electrostatic and/or Van der Waals forces) rather than direct ionic bonding. Maximum HPF adsorption on modified or unmodified titanium dioxide occurred within 30 min, with greater protein adsorption occurring on butanol-treated samples. Desorption was minimal with all modifications. Zeta potential measurements showed that HPF adsorption caused an increase in the negative zeta potential with the greatest change noted for the butanol-treated samples. These findings suggest that wettability and surface charge both play an important role in protein adsorption to titanium dioxide. Thus, by modifying the physico-chemical properties of titanium dioxide surfaces, it may be possible to alter protein adsorption and hence optimize cell attachment.

Mechanisms of adhesion of Paenibacillus polymyxa onto hematite, corundum and quartz

Adhesion of bacteria onto solid surfaces is a necessary event in nature for the utilization of inorganic and organic values and for the enhanced growth of bacteria. Interactions between Paenibacillus polymyxa, with different minerals such as hematite, corundum and quartz are examined in this work in the light of Derjaguin, Landau, Verwey and Overbeek theory, popularly known as DLVO theory and possible chemical interactions. The adhesion process is normally controlled initially by physicochemical interactions between cells and mineral substrates and subsequently by the production of extra cellular polymers to make the attachment stronger, From this study, it is clear that maximum adsorption of cells on hematite and corundum occurs at a pH below the isoelectric point, whereas in the case of quartz the adsorption of cells remained almost constant in the entire pH range studied. From adhesion tests, it is also clear that the above bacteria adsorb preferentially on hematite and corundum than on quartz. It is obvious from the interaction energy calculations that the columbic forces play a major role in the interaction of P. polymyxa with hematite, corundum and quartz. Although the columbic forces do play such a role, it is evident from the Fourier Transform Infrared Spectroscopy (FTIR) results that other forces such as chemical forces are also involved simultaneously.

Mechanism of mixed liposome solubilization in the presence of sodium dodecyl sulfate

Abstract Structural transformations of vesicles to micelles that take place during the interaction of sodium dodecyl sulfate (SDS) with individual and mixed vesicles of phosphatidyl choline (PC) and phosphatidic acid (PA), have been studied by monitoring changes in optical density and in the concentration of free SDS monomer in the respective systems. Incorporation of the surfactant monomers (SDS) in the bilayers was found to result in an initial increase in concentration of the mixed vesicles up to its saturation. Subsequently a progressive relaxation of these structures together with a simultaneous formation of mixed micelles was found to occur. The breakup of bilayer and the formation of mixed micelles were completely dependent on the structure of the individual phospholipid. The solubilization of the anionic phosphatidic acid vesicle was very fast in the presence of SDS, due to its simple structure and its compatibility with the SDS molecule. But solubilization of the zwitter ionic phosphatidyl choline vesicle was very complicated in the presence of SDS, possibly due to its complex structure and the zwitterionic nature. On the other hand, solubilization of the mixed vesicle (mixed liposome) and formation of mixed micelle was found to be relatively easier. This may be attributed to one of the phospholipid component preferentially coming out first through interaction with SDS, thereby making the overall system unstable and enhancing the micellization processes.

Electron spin resonance study of phosphatidyl choline vesicles using 5-doxyl stearic acid

Abstract Harshness and skin irritation are related to surfactant–skin lipid interactions. Delipidization of the stratum corneum is caused by surfactant penetration into extracellualar lipid bilayers; disrupting the lipid microstructure and thereby impairing skin barrier properties. The mechanisms of interactions of sodium dodecyl sulfate (SDS) with lipid as a model membrane are investigated in this work by studying the vesicle to micelle structural transition, which occurs during such interactions of the membrane. The optical density of the phosphatidyl choline liposome was found to increase upon the addition of up to 2 mM SDS and then to decrease gradually on further increase in SDS concentration. Electron spin resonance (ESR) spectrum of 5-doxyl stearic acid (5-DSA) in liposome before and after interaction with SDS solutions at different concentrations showed the rotational correlation time of 5-DSA to increase markedly, possibly due to the penetration of 5-DSA into the lipid bilayers. SDS addition decreased the rotational correlation time of 5-DSA until it attained a constant value above a certain SDS concentration suggesting complete solubilization of liposome and formation of mixed micelles. The ESR spectrum of 5-DSA inside SDS micelle was also seen to be quite different from that obtained after complete solubilization of liposome and, this also indicates the formation of mixed micelles.

Ultracentrifugal Study of Liposome Solubilization by Sodium Dodecylsulfate

ABSTRACT Viscoelastic properties of mixed micelles formed upon interaction of liposomes (89% phosphatidylcholine and 11% phosphatidic acid) with sodium dodecylsulfate (SDS) were investigated using analytical ultracentrifugation, viscometry and light scattering to elucidate the mechanisms of liposome solubilization. The peak in viscosity observed at certain SDS concentrations was correlated with sedimentation coefficient and dynamic light scattering results. The effective size of mixed micelles showed a maximum at peak viscosity. The undissolved liposomes were the dominant factor in determining the sedimentation coefficient but had little effect on the viscosity itself. In the case of completely solubilized systems, results suggest the shape of mixed micelles transform from sphere to rod and such transformation is the governing process determining the viscosity and sedimentation coefficient of the system.