3D strain map of axially loaded mouse tibia: a numerical analysis validated by experimental measurements

A combined experimental/numerical study was performed to calculate the 3D octahedral shear strain map in a mouse tibia loaded axially. This study is motivated by the fact that the bone remodelling analysis, in this in vivo mouse model should be performed at the zone of highest mechanical stimulus to maximise the measured effects. Accordingly, it is proposed that quantification of bone remodelling should be performed at the tibial crest and at the distal diaphysis. The numerical model could also be used to furnish a more subtle analysis as a precise correlation between local strain and local biological response can be obtained with the experimentally validated numerical model.     

Zooplankton assembly in mountain lentic waters is primarily driven by local processes

The influence of local (i.e. physico-chemical constraints) and regional (i.e. dispersal) processes in determining the structure of zooplankton communities in lentic waters was analysed in a mountain district of 4500 km² (northern Apennines, Italy). In the 47 lakes and ponds considered in this study, a total of 139 taxa were found. Surface area (SA) and maximum depth (Z_max) significantly influenced species richness and nestedness, stressing the importance of habitat availability for zooplankton diversity and composition. Species richness and nestedness did not correlate with site isolation, indicating low influence of dispersal for these community properties. A negative relationship between the similarity in species composition among sites and their mutual geographic distance was also found. The relative importance of different sources of compositional variation was quantified by direct ordination. Local environmental conditions (i.e. Z_max, altitude, pH and conductivity) accounted for 65.9 % of the variation in rotifer assemblages. The importance of environmental constraints in structuring zooplankton communities was best documented by the microcrustacean distribution in the study area, which was mainly correlated (73.4 % of the variation in the species data) with water ionic content, surface area and hydroperiod of the habitats.Although previous studies on processes shaping zooplankton assemblages that operate at different scales have yielded contrasting results, our data provide clear evidence for a major role of local constraints.     

A constitutive model for vascular tissue that integrates fibril, fiber and continuum levels with application to the isotropic and passive properties of the infrarenal aorta

A fundamental understanding of the mechanical properties of the extracellular matrix (ECM) is critically important to quantify the amount of macroscopic stress and/or strain transmitted to the cellular level of vascular tissue. Structural constitutive models integrate histological and mechanical information, and hence, allocate stress and strain to the different microstructural components of the vascular wall. The present work proposes a novel multi-scale structural constitutive model of passive vascular tissue, where collagen fibers are assembled by proteoglycan (PG) cross-linked collagen fibrils and reinforce an otherwise isotropic matrix material. Multiplicative kinematics account for the straightening and stretching of collagen fibrils, and an orientation density function captures the spatial organization of collagen fibers in the tissue. Mechanical and structural assumptions at the collagen fibril level define a piece-wise analytical stress-stretch response of collagen fibers, which in turn is integrated over the unit sphere to constitute the tissue's macroscopic mechanical properties. The proposed model displays the salient macroscopic features of vascular tissue, and employs the material and structural parameters of clear physical meaning. Likewise, the constitutive concept renders a highly efficient multi-scale structural approach that allows for the numerical analysis at the organ level. Model parameters were estimated from isotropic mean-population data of the normal and aneurysmatic aortic wall and used to predict in-vivo stress states of patient-specific vascular geometries, thought to demonstrate the robustness of the particular Finite Element (FE) implementation. The collagen fibril level of the multi-scale constitutive formulation provided an interface to integrate vascular wall biology and to account for collagen turnover.     

Effect of thermal cycling on microleakage between hard chairside relines and denture base acrylic resins

doi:10.1111/j.1741‐2358.2009.00332.x
Effect of thermal cycling on microleakage between hard chairside relines and denture base acrylic resins Objectives: Microleakage is a pre‐stage of debonding between hard chairside relines and denture base acrylic resins. Therefore, it is important to assess them with regard to the longevity of the relined denture. This study investigated the effect of thermal cycling on the microleakage at the interface of three hard chairside reline resins and three denture base resins. Material and methods: Rectangular bars (12 mm × 3 mm × 3 mm) of Lucitone 550, Acron MC and QC 20 were made and relined with Kooliner, Tokuyama Rebase Fast II and Ufi Gel Hard, Lucitone 550, Acron MC and QC 20 resins. Specimens were divided into one control and two test groups (n = 10). In specimens of the control group, the microleakage was performed after the reline procedure. In Test Group 1, the specimens were stored for 24 h in distilled water at room temperature and in Test Group 2; the specimens were thermal cycled from 5 to 55°C for 5000 cycles with a 30‐s dwell time. Subsequently, all specimens were immersed in 50% silver nitrate solutions for 24 h. All specimens were sectioned longitudinally into three fractions and the lateral sections were examined (n = 20). Silver nitrate stain penetration was examined under a stereoscopic lens with ×30 magnification, and the images were captured. Leica Qwin image analysis software was used to determine microleakage at the interface of the materials. Data were analysed using the Kruskal–Wallis test at a 95% level of significance. Results: For all cycles, there were no statistically significant differences between thermal cycled and non‐thermal cycled groups (p > 0.05). Conclusion: It can be concluded that thermal cycling had no effect on the microleakage.     

Spirohydantoin derivatives of thiopyrano[2,3-b]pyridin-4(4H)-one as potent in vitro and in vivo aldose reductase inhibitors

The 2,3-dihydrospiro[4H-thiopyrano[2,3-b]pyridin-4,4'-imidazolidine]-2',5'-dione 3 and its 7-methyl analogue 4 were synthesized and tested for their ability to inhibit aldose reductase (ALR2). To expand the structure-activity relationships, the sulfone 5 and the acetic acid derivative 7 were also prepared and tested. Compounds 3 and 4 proved to be potent ALR2 inhibitors, with IC50 values in the submicromolar range (0.96 and 0.94 microM, respectively) similar to that of sorbinil (0.65 microM). Moreover, compound 3 was found to be highly potent in preventing cataract development in severely galactosemic rats, like tolrestat, when administered as an eyedrop solution. Docking simulations of both R- and S-isomers of 3 into the ALR2 crystal structure were carried out to guide, prospectively, the design of new analogues.     

A General and Concise Enantioselective Divergent Approach to 13‐Alkyl‐Substituted Ionones

A novel enantioselective divergent route to 13‐alkyl derivatives of α‐ and γ‐ionone, important components of perfumes and fragrances, is reported. This relatively short and convenient methodology takes advantage of the use of a common intermediate, easily obtained from highly enantiomerically enriched (S)‐α‐ionone, which avoids the separate installation of the butenone side chain at C(6) for each analog. Olfactory evaluation of synthesized compounds reconfirmed the influence of the hydrophobic interactions of alkyl substituents at C(5) with olfactory receptors (ORs) in the chemoreception of ionones, and suggested that a synperiplanar orientation of C(13) and the lateral chain is the better geometry fitting OR's cavity.