Phase behavior, crystallization, and morphology in thermosetting blends of a biodegradable poly(ethylene glycol)-type epoxy resin and poly(ε-caprolactone)

Thermosetting blends of a biodegradable poly(ethylene glycol)-type epoxy resin (PEG-ER) and poly(epsilon-caprolactone) (PCL) were prepared via an in situ curing reaction of poly(ethylene glycol) diglycidyl ether (PEGDGE) and maleic anhydride (MAH) in the presence of PCL. The miscibility, phase behavior, crystallization, and morphology of these blends were investigated. The uncured PCL/PEGDGE blends were miscible, mainly because of the entropic contribution, as the molecular weight of PEGDGE was very low. The crystallization and melting behavior of both PCL and the poly(ethylene glycol) (PEG) segment of PEGDGE were less affected in the uncured PCL/PEGDGE blends because of the very close glass-transition temperatures of PCL and PEGDGE. However, the cured PCL/PEG-ER blends were immiscible and exhibited two separate glass transitions, as revealed by differential scanning calorimetry and dynamic mechanical analysis. There existed two phases in the cured PCL/PEG-ER blends, that is, a PCL-rich phase and a PEG-ER crosslinked phase composed of an MAH-cured PEGDGE network. The crystallization of PCL was slightly enhanced in the cured blends because of the phase-separated nature; meanwhile, the PEG segment was highly restricted in the crosslinked network and was noncrystallizable in the cured blends. The phase structure and morphology of the cured PCL/PEG-ER blends were examined with scanning electron microscopy; a variety of phase morphologies were observed that depended on the blend composition. (C) 2004 Wiley Periodicals, Inc.

Characterization of neogenin-expressing neural progenitor populations and migrating neuroblasts in the embryonic mouse forebrain

Many studies have demonstrated a role for netrin-1-deleted in colorectal cancer (DCC) interactions in both axon guidance and neuronal migration. Neogenin, a member of the DCC receptor family, has recently been shown to be a chemorepulsive axon guidance receptor for the repulsive guidance molecule (RGM) family of guidance cues [Rajagopalan S, Deitinghoff L, Davis D, Conrad S, Skutella T, Chedotal A, Mueller B, Strittmatter S (2004) Neogenin mediates the action of repulsive guidance molecule. Nat Cell Biol 6:755-762]. Here we show that neogenin is present on neural progenitors, including neurogenic radial glia, in the embryonic mouse forebrain suggesting that neogenin expression is a hallmark of neural progenitor populations. Neogenin-positive progenitors were isolated from embryonic day 14.5 forebrain using flow cytometry and cultured as neurospheres. Neogenin-positive progenitors gave rise to neurospheres displaying a high proliferative and neurogenic potential. In contrast, neogenin-negative forebrain cells did not produce long-term neurosphere cultures and did not possess a significant neurogenic potential. These observations argue strongly for a role for neogenin in neural progenitor biology. In addition, we also observed neogenin on parvalbumin- and calbindin-positive interneuron neuroblasts that were migrating through the medial and lateral ganglionic eminences, suggesting a role for neogenin in tangential migration. Therefore, neogenin may be a multi-functional receptor regulating both progenitor activity and neuroblast migration in the embryonic forebrain. (c) 2006 IBRO. Published by Elsevier Ltd. All rights reserved.

Phase behavior, crystallization, and nanostructures in thermoset blends of epoxy resin and amphiphilic star-shaped block copolymers

This article reports thermoset blends of bisphenol A-type epoxy resin (ER) and two amphiphilic four-arm star-shaped diblock copolymers based on hydrophilic poly(ethylene oxide) (PEO) and hydrophobic poly(propylene oxide) (PPO). 4,4'-Methylenedianiline (MDA) was used as a curing agent. The first star-shaped diblock copolymer with 70 wt% ethylene oxide (EO), denoted as (PPO-PEO)(4), consists of four PPO-PEO diblock arms with PPO blocks attached on an ethylenediamine core; the second one with 40 wt% EO, denoted as (PEO-PPO)(4), contains four PEO-PPO diblock arms with PEO blocks attached on an ethylenediamine core. The phase behavior, crystallization, and nanoscale structures were investigated by differential scanning calorimetry, transmission electron microscopy, and small-angle X-ray scattering. It was found that the MDA-cured ER/(PPO-PEO)(4) blends are not macroscopically phase-separated over the entire blend composition range. There exist, however, two microphases in the ER/(PPO-PEO)(4) blends. The PPO blocks form a separated microphase, whereas the ER and the PEO blocks, which are miscible, form another microphase. The ER/(PPO-PEO)(4) blends show composition-dependent nanostructures on the order of 10-30 nm. The 80/20 ER/(PPO-PEO)(4) blend displays spherical PPO micelles uniformly dispersed in a continuous ER-rich matrix. The 60/40 ER/(PPO-PEO)(4) blend displays a combined morphology of worm-like micelles and spherical micelles with characteristic of a bicontinuous microphase structure. Macroscopic phase separation took place in the MDA-cured ER/(PEO-PPO)(4) blends. The MDA-cured ER/(PEO-PPO)(4) blends with (PEO-PPO)(4) content up to 50 wt% exhibit phase-separated structures on the order of 0.5-1 mu m. This can be considered to be due to the different EO content and block sequence of the (PEO-PPO)(4) copolymer. (c) 2006 Wiley Periodicals, Inc.

Building partnerships with families and communities to support children's numeracy learning

The importance of building home, school and community partnerships is increasingly acknowledged since family and community involvement in education is thought to be associated with children’s success at school. This paper reports on aspects of an Australian Government commissioned research project that analysed educational partnerships aiming to enhance children’s numeracy education. Snapshots of two school case studies are presented to highlight features of effective partnerships and the kinds of numeracy learning they supported.

Classification of Chenopodium Genus Populations and Species Based on Continuous and Categorical Variables

2000 Mathematics Subject Classification: 62P10, 62H30

Distribution and ecology of amphibians and reptiles in a fragmented landscape, northeastern Bolivia

Habitat loss and fragmentation have been implicated as driving forces behind recent waves of extinction. The regional landscape where this study occurred is a mosaic of forest and grassland, and therefore provides an ideal system with which to investigate the implications of habitat patchiness for the distribution and ecology of organisms. Here I describe patterns of amphibian and reptile distribution among and within habitats at the study site, investigate associations between habitat and community structure, describe nested subset patterns on forest islands, and quantify the relationship between body size and density across ecological scales and taxonomic groups. ^ Species richness did not vary across habitats, between forest island isolation classes or between island edges and cores. In contrast, species composition varied at all three ecological scales, reflecting differences in the distribution of both forest and open-habitat affiliated species. Species composition was associated with multivariate habitat profiles, with differences occurring along the isolation gradient of forest islands rather than the area gradient. The relationship between species composition and habitat was stronger for amphibians than for reptiles, a pattern that may be ascribed to physiological differences between the two groups. Analysis of nested subset pattern of community structure indicated that species composition of islands is nested as a function of isolation. Four species whose distribution on forest islands seems to be dispersal-limited drive the relationship between nestedness and isolation. Although there were several examples of shifts in body size across spatial scales and taxonomic groups, body size was not associated with density as predicted by theory, which may reflect differences between real and habitat islands, or differential responses of poikilothermic vertebrates to changes in density relative to homeotherms. ^ Taken together, the strongest result to emerge from this research is the importance of isolation, rather than area, on community structure in this system. Much evidence suggested that different ecological groups of species show distinct patterns of distribution both within and among habitat types. This suggests that species distributions at this site are not the result of 'neutral' processes at the community level, but rather reflect fundamental differences in the ecology of component species. ^

Impact of Genetic Testing and Family Health History Based Risk Counseling on Behavior Change and Cognitive Precursors for Type 2 Diabetes.

Family health history (FHH) in the context of risk assessment has been shown to positively impact risk perception and behavior change. The added value of genetic risk testing is less certain. The aim of this study was to determine the impact of Type 2 Diabetes (T2D) FHH and genetic risk counseling on behavior and its cognitive precursors. Subjects were non-diabetic patients randomized to counseling that included FHH +/- T2D genetic testing. Measurements included weight, BMI, fasting glucose at baseline and 12 months and behavioral and cognitive precursor (T2D risk perception and control over disease development) surveys at baseline, 3, and 12 months. 391 subjects enrolled of which 312 completed the study. Behavioral and clinical outcomes did not differ across FHH or genetic risk but cognitive precursors did. Higher FHH risk was associated with a stronger perceived T2D risk (pKendall < 0.001) and with a perception of "serious" risk (pKendall < 0.001). Genetic risk did not influence risk perception, but was correlated with an increase in perception of "serious" risk for moderate (pKendall = 0.04) and average FHH risk subjects (pKendall = 0.01), though not for the high FHH risk group. Perceived control over T2D risk was high and not affected by FHH or genetic risk. FHH appears to have a strong impact on cognitive precursors of behavior change, suggesting it could be leveraged to enhance risk counseling, particularly when lifestyle change is desirable. Genetic risk was able to alter perceptions about the seriousness of T2D risk in those with moderate and average FHH risk, suggesting that FHH could be used to selectively identify individuals who may benefit from genetic risk testing.