In situ forming stereocomplexed and post-photocrosslinked acrylated star poly(ethylene glycol)-poly(lactide) hydrogels

Biodegradable acrylate end-group functionalized poly(ethylene glycol)-poly(lactide) (PEG-PLA) star block copolymer hydrogels were formed by the consecutive physical gelation through stereocomplexation of star shaped PEG-(PLLA)8 and PEG-(PDLA)8 enantiomers and UV photopolymerization. The 8-armed PEG-PLA star block copolymers were prepared by ring opening polymerization of lactide onto an amine end-group functionalized PEG with a molecular weight of 20 kg/mol using stannous octoate as a catalyst. The degree of polymerization of the PLA blocks was 12 lactyl units and the end hydroxyl groups were reacted with acryloyl chloride to give the required acrylate end groups. Aqueous solutions of enantiomeric mixtures of the PEG-(PLA)8 macromonomers formed physically crosslinked hydrogels above a critical gel concentration of 4 w/v%. Subsequent photopolymerization at 365 nm in the presence of Irgacure 2959 resulted in gels with improved mechanical properties and hydrolytic stability. With 40% polymer mass loss after 45 d in vitro, these hydrogels show excellent resistance against hydrolytic degradation and dissolution, which is believed to result from the combination of stable amide linkages between the PEG and PLA blocks and the high physical and chemical crosslink density owing to the star architecture

Solid-state NMR study of stereocomplexes formed by enantiomeric star-shaped PEG-PLA copolymers in water

Solid-state NMR was applied to samples obtained by freeze-drying hydrogels of 1:1 (PEG65-NHCO-PLLA13)8/(PEG65-NHCO-PDLA13)8 or (PEG65-NHCO-PDLA13)8 only star block copolymers (where PEG, PLLA, and PDLA stand for poly(ethylene glycol), poly(l-lactide), and poly(d-lactide), respectively) in order to get insight into the different structural and dynamic properties of stereocomplexed poly(lactide) (PLA) aggregates with respect to single enantiomer ones responsible for the improved mechanical and degradation properties of the corresponding hydrogels. 13C MAS NMR experiments together with 13C relaxation time measurements indicated that the PLA domains in (PEG65-NHCO-PLLA13)8/(PEG65-NHCO-PDLA13)8 were highly crystalline, whereas those in (PEG65-NHCO-PDLA13)8 were mainly amorphous. On the basis of 1H relaxation and spin-diffusion experiments, similar average dimensions were determined for the PLA aggregates in the two samples. PLA stereocomplexation was found to strongly affect the conformational behavior of PEG chains. Under the assumption that freeze-drying preserves the structure of at least the PLA aggregates, the results obtained are of value for understanding self-aggregation of PEG–PLA star block copolymers in water

Rodent models of social stress and neuronal plasticity:Relevance to depressive-like disorders

Exposure to severe or persistent social stress may lead to the development of psychiatric disorders such as anxiety and depression. These mood disorders are associated with structural alterations of neural architecture in limbic brain regions that control emotion, mood and cognition. Structural remodeling may either be a sign of successful adaptation, or of failure to do so. In neuropsychiatric disorders like depression structural remodeling involves apoptosis, reduced neurogenesis, and structural remodeling of neuronal dendrites which most likely reflects the latter. Here we review key findings from animal models of psychosocial stress that have been used to gain insights into the relation between stress-related behavioral disorders like depression and structural plasticity. Specifically, we focus on models having a high face validity like social defeat stress in the resident-intruder paradigm and chronic stress of social subordination in social housing conditions. Moderate to severe social stress appears to stimulate plasticity and neuronal growth in regions of the amygdala, whereas the effects in the hippocampus and prefrontal cortex tend to be opposite. A major focus of the current review is to characterize social stress induced structural changes in these brain regions, aiming to provide insight in pathways and factors that underlie behavioral effects of stress and depression.</p

Enhanced sensitivity of postsynaptic serotonin-1A receptors in rats and mice with high trait aggression

Individual differences in aggressive behaviour have been linked to variability in central serotonergic activity, both in humans and animals. A previous experiment in mice, selectively bred for high or low levels of aggression, showed an up-regulation of postsynaptic serotonin-1A (5-HT1A) receptors, both in receptor binding and in mRNA levels, in the aggressive line. The aim of this experiment was to study whether similar differences in 5-HT1A receptors exist in individuals from a random-bred rat strain, varying in aggressiveness. In addition, because little is known about the functional consequences of these receptor differences, a response mediated via postsynaptic 5-HT1A receptors (i.e., hypothermia) was studied both in the selection lines of mice and in the randomly bred rats. The difference in receptor binding, as demonstrated in mice previously, could not be shown in rats. However, both in rats and mice, the hypothermic response to the 5-HT1A agonist alnespirone was larger in aggressive individuals. So, in the rat strain as well as in the mouse lines, there is, to a greater or lesser extent, an enhanced sensitivity of postsynaptic 5-HT1A receptors in aggressive individuals. This could be a compensatory up-regulation induced by a lower basal 5-HT neurotransmission, which is in agreement with the serotonin deficiency hypothesis of aggression.

Source localization in underwater sound fields

We investigated the acoustical information present in the field of arbitrary sound sources which may provide direction and distance to the source from a local reading of the sound field parameters. If the effects of reflections are negligible, the particle acceleration is directed radially at the instant of sound pressure nulls. The spectral relation between the radial component of the particle aceleration and the sound pressure is characterized by a critical frequency where a sharp transition occurs in the amplitude ratio and the phase relation of these variables. The critical frequency depends on the distance to the source and depends little on the source type (mono-, di- or quadrupole). Thus, a local reading of the particle acceleration and the sound pressure is in principle sufficient to localize the sound source in three dimensions. Fish might use this kind of information for acoustic orientation

Концепція сталого розвитку туризму в сучасних умовах

Мета статті – розробка основних положень концепції сталого розвитку туризму в регіоні

Energiezuinige teeltplanning voor de potplanten : een systeemontwerp

Het gaat in dit project om te onderzoeken wat er voor nodig is om in de potplantenteelt het planmatig telen te kunnen combineren met energiebesparing, om zo de energie-efficiëntie van het teeltproces te kunnen verhogen. Op grond van eerdere ervaring en vanwege de complexe wisselwerking van de klimaatregeling met weer, kasklimaat en de gewasfysiologie werd vooraf verondersteld dat hiervoor een model-ondersteund adviessysteem voor nodig is. Wil de ontwikkeling van een dergelijk systeem kans van slagen hebben dan zal het goed moeten aansluiten bij de informatiebehoefte van de telers

Psychoeducation for hypochondriasis:A comparison of a cognitive-behavioural approach and a problem-solving approach

In this study, two 6-week psychoeducational courses for hypochondriasis are compared, one based on the cognitive-behavioural approach, and the other on the problem-solving approach. Effects of both courses on hypochondriacal complaints, depression, trait anxiety, and number of problems encountered in daily life, are measured pre-treatment, posttreatment, and at 1- and 6-month follow-up. Participants (N = 48, of whom 4 dropped out), suffering from DSM-IV hypochondriasis, were randomized into one of the two course conditions. Results showed beneficial effects of both courses. Few differential treatment effects were found: in both conditions all effect measures decreased significantly over time (p <0.01). However, between- and inter-individual variability in decrease-patterns was of considerable size, leading to large deviations from the mean pattern. Acceptability and feasibility of both courses were rated highly by their respective participants. It is concluded that both courses can be considered equally beneficial and effective over time, with the effects evident immediately after treatment and maintained over the follow-up period. (c) 2006 Elsevier Ltd. All rights reserved

Effect of Shear Work Input on Steady Shear Rheology and Melt Functionality of Model Mozzarella Cheeses

Model Mozzarella cheeses with varied amounts of shear work input were prepared by working molten cheese mass at 70 °C in a twin screw cooker. Rheology and melt functionality were found to be strongly dependent on total shear work input. A non-linear increase in consistency coefficient (K from power law model) and apparent viscosity and decrease in flow behaviour index (n from power law model) were observed with increasing amounts of accumulated shear work, indicating work thickening behaviour. An exponential work thickening equation is proposed to describe this behaviour. Excessively worked cheese samples exhibited liquid exudation, poor melting and poor stretch. Nonfat cheese exhibited similar but smaller changes after excessive shear work input. We concluded that the dominant contributor to the changes in properties with increased shear work was shear induced structural changes to the protein matrix. A good correlation was found between the steady shear rheological properties and the melting properties of the cheeses