We characterized the size dependence of anatase TiO2 lattice parameters using Rietveld analysis of angle-dispersive synchrotron x-ray diffraction data obtained on a suite of nanocrystalline samples. The refined crystal structure and microstructure data suggest that for crystallites with size less than ∼10nm, the lattice parameters vary nonlinearly. Small lattice expansion, associated with possible increased Ti vacancy and lattice strain, at reduced crystallite size observed in our samples is in contrast to the lattice contraction behavior reported for “pure” anatase nanocrystals. The nonlinear, composition-dependent variation of anatase unit cell volume contrasts with the linear expansion behavior of rutile lattice at finite sizes.
Low-protein-fouling poly(ethylene glycol) (PEG-like) plasma polymer films were prepared using radio frequency glow discharge polymerization of diethylene glycol dimethyl ether (DGpp) on top of a heptylamine plasma polymer primer layer. By varying the plasma deposition conditions, the chemistry of the DGpp film was influenced, especially in regard to the level of ether content, which in turn influenced the relative levels of bovine serum albumin and lysozyme protein fouling. Surface potential measurements indicated that these surfaces carried a net negative charge. While protein fouling remained low ( approximately 10 ng/cm2), there was a slightly higher level of the positively charged protein adsorbed on these films than the negative protein. The interaction forces measured between a silica spherical surface on both "high"- and "low"-protein-fouling DGpp films were all repulsive and short ranged (2-3 nm). There was no correlation between the surface forces measured for high- and low-protein-fouling DGpp films. Thus, it appears that enthalpic effects are very important in reducing protein adsorption. We therefore conclude that it is the concentration of residual, ethylene glycol containing species that are the crucial parameter determining protein resistance due to a combination of both entropic and enthalpic effects.
The application of a thin, compact layer of TiO 2 on the conductive glass substrate in a dye-sensitized solar cell can prevent short-circuits in the solar cell and, therefore, prevent the back transfer of electrons by blocking direct contact between the electrolyte and the conductive substrate. In this work, it has been found that compact films of TiO 2 , produced by a sol-gel method and applied by dip-coating, increased the short-circuit current and efficiency of the solar cells. As the number of TiO 2 coatings increased, the solar cell efficiency increased, due to the film becoming thicker and more smooth and uniform.
As stem-cell-based therapies rapidly advance toward clinical applications, there is a need for cheap, easily manufactured, injectable gels that can be tailored to carry stem cells and impart function to such cells. Herein we describe a process for making hydrogels composed of hydroxyphenyl propionic acid (HPA) conjugated, branched poly(ethylene glycol) (PEG) via an enzyme mediated, oxidative cross-linking method. Functionalization of the branched PEG with HPA at varying degrees of substitution was confirmed via attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and (1)H NMR. The versatility of this hydrogel system was exemplified through variations in the degree of HPA substitution, polymer concentration, and the concentration of cross-linking reagents (horseradish peroxidase and H(2)O(2)), which resulted in a range of mechanical properties and gelation kinetics for these gels. Cross-linking of the PEG-HPA conjugate with a recombinantly produced Fibronectin fragment (Type III domains 7-10) encouraged attachment and spreading of human mesenchymal stem cells (hMSCs) when assessed in both two-dimensional and three-dimensional formats. Interestingly, when encapsulated in both nonfunctionalized and functionalized cross-linked PEG-HPA gels, MSCs showed good viability over all time periods assessed. With tunable gelation kinetics and mechanical properties, these hydrogels provide a flexible in vitro cell culture platform that will likely have significant utility in tissue engineering as an injectable delivery platform for cells to sites of tissue damage.
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