Gel

Hydrogels represent a class of high water content polymers with physical or chemical crosslinks. Their physical properties are similar to soft tissues. Cross linking is a stabilization process in polymer chemistry which leads to multidimensional extension of polymeric chain resulting in network structure. Cross-link is a bond which links one polymer chain to other. It can be ionic or covalent. Cross linking changes a liquid polymer into 'solid' or 'gel' by restricting the ability of movement. When polymer chains are linked together by cross-links, they lose some of their ability to move as individual polymer chains. A liquid polymer (where the chains are freely flowing) can be turned into a 'solid' or 'gel' by cross-linking the chains together. Cross linking increases the molecular mass of a polymer. Cross-linked polymers are important because they are mechanically strong and resistant to heat, wear and attack by solvents. However, the drawback associ...

Wet spinning and radial self-assembly of a carbohydrate low molecular weight gelator into well organized hydrogel fi laments A single biocompatible small molecule, the N-heptyl-D-galactonamide can be spun into well-defi ned hydrogel fi laments. A solution of this molecule in dimethylsulfoxide is injected in water, resulting in the formation of a continuous fi lament. The counter-diff usion of water and dimethylsulfoxide triggers the self-assembly of the molecule into supramolecular nanofi bers. A radial organization of the fi bers was observed in the gel fi laments. This method could be used for making well-defi ned cell culture scaff olds. As featured in: rsc.li/nanoscale

Oxygen vacancies at the SnO2(110) and (101) surface and subsurface sites have been studied in the framework of density functional theory by using both all-electron Gaussian and pseudopotential plane-wave methods. The all-electron calculations have been performed using the B3LYP exchange-correlation functional with accurate estimations of energy gaps and density of states. We show that bulk oxygen vacancies are responsible for the appearance of a fully occupied flat energy level lying at about 1 eV above the top valence band, and an empty level resonant with the conduction band. Surface oxygen vacancies strongly modify the surface band structures with the appearance of intragap states covering most of the forbidden energy window, or only a small part of it, depending on the vacancy depth from the surface. Oxygen vacancies can account for electron affinity variations with respect to the stoichiometric surfaces as well. A significant support to the present results is found by comparing them to the available experimental data.

The rheological properties and fractal dimensions of flaxseed gum gels were analyzed in various ionic strength values ranging between 0 and 1000 mM. The rheological properties of flaxseed gum were significantly influenced by the ionic strength. The gel strength first increased then decreased with the increasing of ionic strength and the strongest gel was obtained when the ionic strength was 400 mM. The calculated fractal dimensions of the flaxseed gum gels were 2.06–2.49 or 1.42–2.18, based on the model selected and the ionic strength applied. These results would help to understand the microstructure of the flaxseed gum gels and the influence of ionic strength on that. However, the difference in results between the two models implied that further study is needed to find suitable model for flaxseed gum gels.► The fractal structure of flaxseed gum was analyzed using two Rheological model. ► The fractal dimension of flaxseed gum was calculated to be 2.06–2.49 or 1.42–2.18. ► Ionic strength has significant effect on the fractal dimension of flaxseed gum.

Proniosomal gels or solutions of flurbiprofen were developed based on span 20 (Sp 20), span 40 (Sp 40), span 60 (Sp 60), and span 80 (Sp 80) without and with cholesterol. Nonionic surfactant vesicles (niosomes) formed immediately upon hydrating proniosomal formulae. The entrapment efficiency (EE%) of flurbiprofen (a poorly soluble drug) was either determined by exhaustive dialysis of freshly prepared niosomes or centrifugation of freeze-thawed vesicles. The influence of different processing and formulation variables such as surfactant chain length, cholesterol content, drug concentration, total lipid concentration, negatively or positively charging lipids, and the pH of the dispersion medium on flurbiprofen EE% was demonstrated. Also, the release of the prepared niosomes in phosphate buffer (pH 7.4) was illustrated. Results indicated that the EE% followed the trend Sp 60 (C18) > Sp 40 (C16) > Sp 20 (C12) > Sp 80 (C18). Cholesterol increased or decreased the EE% depending on either the type of the surfactant or its concentration within the formulae. The maximum loading efficiency was 94.61% when the hydrating medium was adjusted to pH 5.5. Increasing total lipid or drug concentration also increased the EE% of flurbiprofen into niosomes. However, incorporation of either dicetyl phosphate (DCP) which induces negative charge or stearyl amine (SA) which induces positive charge decreased the EE% of flurbiprofen into niosomal vesicles. Finally, in vitro release data for niosomes of Sp 40 and Sp 60 showed that the release profiles of flurbiprofen from niosomes of different cholesterol contents is an apparently biphasic release process. As a result, this study suggested the potential of proniosomes as stable precursors for the immediate preparation of niosomal carrier systems.

This work aims to predict the evolution in freezing processes due to climate change during the 21st century and the potential damage to historic structures and archaeological remains in Europe. We have developed a range of techniques to convert climate data into parameters related to the freeze-thaw processes and study their progression within the A2 scenario using the Hadley HadCM3 Model , from 1961 to 2099. Freezing and thawing is important because it represents a process where a phase change occurs at an exact temperature. A few degrees change in temperature or small percentages change in precipitation amount do not initially seem to present a threat to materials. However, freeze-thaw events occur at fixed temperature, so the effects of small temperature changes can be amplified. Our results suggest that much of temperate Europe will see a significantly reduced incidence of freezing in the future. This should mean that porous stone typically used in the monuments of temperate areas may be less vulnerable to frost damage in the future. Warmer temperatures in the far north look set to affect archaeological sites that have been preserved in the permafrost. These changes may also affect the foundations of structures and induce landslides. Exploring the range of possible changes allows us to contemplate appropriate contingencies and support strategic decision making by heritage managers.

In this work, we illustrate the usefulness of cyclodextrins, namely, methyl-β-cyclodextrin (MβCD), an amorphous, methylated derivative of the natural β-cyclodextrin (βCD), as a tool to form an inclusion complex with omeprazole (OME), a poorly water soluble drug. Solid binary systems between OME and MβCD were prepared experimentally in a stoichiometry 1:1 by different techniques (physical mixing, kneading, spray-drying and freeze-drying).

A solid state synthesis of calcium manganite (CaMnO3) is described where equimolecular mixtures CaCO3:MnCO3 have been subjected to mechanical stress (high energy milling) so yielding CaCO3-MnCO3 solid solutions of nanometric particle size. TG measurements have shown that a link exists between milling time, the extent of non-stoichiometry and the milling-induced decomposition of MnCO3 to Mn3O4. A short (2 h) annealing at 850 °C performed on a sample mixture milled for 25 h leads to non-stoichiometric CaMnO3−x. No sure conclusion could be drawn for the stoichiometry of CaMnO3 obtained, under the same annealing conditions, from a mixture milled for longer time (150 h). No synthesis of CaMnO3 could be effected by long (48 h) annealing at 1200 °C of mixtures that had not been subjected to mechanical stress.