University of Bremen

About: University of Bremen is a education organization based out in Bremen, Germany. It is known for research contribution in the topics: Population & Context (language use). The organization has 14563 authors who have published 37279 publications receiving 970381 citations. The organization is also known as: Universität Bremen.

Biomedical Activity of Chitin/Chitosan Based Materials—Influence of Physicochemical Properties Apart from Molecular Weight and Degree of N-Acetylation

Abstract: The physicochemical nature of chitin and chitosan, which influences the biomedical activity of these compounds, is strongly related to the source of chitin and the conditions of the chitin/chitosan production process. Apart from widely described key factors such as weight-averaged molecular weight (MW) and degree of N-acetylation (DA), other physicochemical parameters like polydispersity (MW/MN), crystallinity or the pattern of acetylation (PA) have to be taken into consideration. From the biological point of view, these parameters affect a very important factor—the solubility of chitin and chitosan in water and organic solvents. The physicochemical properties of chitosan solutions can be controlled by manipulating solution conditions (temperature, pH, ionic strength, concentration, solvent). The degree of substitution of the hydroxyl and the amino groups or the degree of quaternization of the amino groups also influence the mechanical and biological properties of chitosan samples. Finally, a considerable research effort has been directed towards developing safe and efficient chitin/chitosan-based products because many factors, like the size of nanoparticles, can determine the biomedical characteristics of medicinal products. The influence of these factors on the biomedical activity of chitin/chitosan-based products is presented in this report in more detail.

New Discovery in the Properties of Composites Reinforced with Natural Fibers

Abstract: Composite materials with thermoplastic matrices and a reinforcement of natural fibers are increasingly regarded as an alternative to glass fiber-reinforced composites. The substitution of the traditionally used reinforcing glass fibers by natural fibers such as flax, kenaf, or cotton can lead to a reduction of the component's weight and furthermore to a significant improvement of specific properties like impact strength, crash behaviour, or sound absorption. One of the major fields of application for such materials can be found in structural components for the automotive industry. Product examples are door trim panels, headliners, or back panels. At present the processing of such materials into structural parts usually takes place by thermal compression molding. Semiproducts (so-called hybrid fleeces) are employed, which are generated by carding or air-laid processes and subsequent mechanical bonding. This paper presents a survey and latest developments on the material, processing technologies, and fields...

Cadmium-induced apoptosis in C6 glioma cells: influence of oxidative stress.

Abstract: Cadmium has recently been shown to induce apoptosis in C6 glioma cells via disruption of the mitochondrial membrane potential and subsequent caspase 9-activation Here we show that both H2O2 and CdCl2 induced apoptotic DNA fragmentation in C6 cells The employment of glutathione as an antioxidant prevented the induction of apoptotic DNA fragmentation by cadmium completely and catalase strongly reduced cadmium-induced DNA fragmentation suggesting that cadmium exerts its apoptotic effects at least partly via the production of H2O2 Apoptosis may be induced by cadmium indirectly through formation of oxidative stress, eg, by inhibition of antioxidant enzymes After incubation of C6 cells with cadmium for short times (up to 4 h), we analyzed the formation of intracellular reactive oxygen species and cellular lipid peroxidation After 1 h of incubation with inreasing concentrations of CdCl2 (1-500 microM), no increase in dichlorofluorescein fluorescence was found At variance, lipid peroxidation was slightly elevated after 2 h incubation with cadmium (50-100 microM) Furthermore, we analyzed the modulation of markers for oxidative stress after prolonged (24 h) exposure to cadmium The intracellular glutathione content as measured using the fluorescent probe monobromobimane was decreased after incubation with CdCl2 (05-10 microM) for 24 h Furthermore, we measured the effect of cadmium on the level of oxidized DNA lesions (predominantly 8-hydroxyguanine) using the bacterial Fpg-DNA-repair protein After 24 h of incubation with 5 microM CdCl2 we found a sixfold increase in Fpg-sensitive DNA-lesions We conclude that short time incubations with cadmium (up to 4 h) caused only slight or insignificant effects on the generation of reactive oxygen species (formation of thiobarbituric acid reactive substances, fluorescence of dichlorofluorescein), whereas incubation with this heavy metal for 24 h lead to a decrease in intracellular glutathione concentration and an increase in oxidative DNA-lesions Our data demonstrate that cadmium as similar to H2O2 is a potent inducer of apoptosis in C6 cells Even if cadmium unlike Fenton-type metals can not produce reactive oxygen species directly, the apoptotic effects of cadmium at least in part are mediated via induction of oxidative stress Because both apoptosis and oxidative stress are thought to play important roles in neurodegenerative diseases, low concentrations of cadmium that initiate programmed cell death may lead to a selective cell death in distinct brain regions via generation of oxidative stress

Linear Theory of Elasticity

Abstract: The linear theory of elasticity, thanks to its relative simplicity and wide applicability, constitutes the principal model of continuum mechanics which will be employed in this text.