Evaluation of elastic modulus and hardness of thin films by nanoindentation

Simple equations are proposed for determining elastic modulus and hardness properties of thin films on substrates from nanoindentation experiments. An empirical formulation relates the modulus E and hardness H of the film/substrate bilayer to corresponding material properties of the constituent materials via a power-law relation. Geometrical dependence of E and H is wholly contained in the power-law exponents, expressed here as sigmoidal functions of indenter penetration relative to film thickness. The formulation may be inverted to enable deconvolution of film properties from data on the film/substrate bilayers. Berkovich nanoindentation data for dense oxide and nitride films on silicon substrates are used to validate the equations and to demonstrate the film property deconvolution. Additional data for less dense nitride films are used to illustrate the extent to which film properties may depend on the method of fabrication.

Dibucaine effects on structural and elastic properties of lipid bilayers

In this work we report the interaction effects of the local anesthetic dibucaine (DBC) with lipid patches in model membranes by Atomic Force Microscopy (AFM). Supported lipid bilayers (egg phosphatidylcholine, EPC and dimyristoylphosphatidylcholine, DMPQ were prepared by fusion of unilamellar vesicles on mica and imaged in aqueous media. The AFM images show irregularly distributed and sized EPC patches on mica. On the other hand DMPC formation presents extensive bilayer regions on top of which multibilayer patches are formed. In the presence of DBC we observed a progressive disruption of these patches, but for DMPC bilayers this process occurred more slowly than for EPC. In both cases, phase images show the formation of small structures on the bilayer surface suggesting an effect on the elastic properties of the bilayers when DBC is present. Dynamic surface tension and dilatational surface elasticity measurements of EPC and DMPC monolayers in the presence of DBC by the pendant drop technique were also performed, in order to elucidate these results. The curve of lipid monolayer elasticity versus DBC concentration, for both EPC and DMPC cases, shows a maximum for the surface elasticity modulus at the same concentration where we observed the disruption of the bilayer by AFM. Our results suggest that changes in the local curvature of the bilayer induced by DBC could explain the anesthetic action in membranes. (C) 2008 Elsevier B.V. All rights reserved.

A numerical study of effect of grain boundaries on elastic and plastic properties in nanocomposite materials

Nanocomposite materials have received considerable attention in recent years due to their novel properties. Grain boundaries are considered to play an important role in nanostructured materials. This work focuses on the finite element analysis of the effect of grain boundaries on the overall mechanical properties of aluminium/alumina composites. A grain boundary is incorporated into the commonly used unit cell model to investigate its effect on material properties. By combining the unit cell model with an indentation model, coupled with experimental indentation measurements, the ''effective'' plastic property of the grain boundary is estimated. In addition, the strengthening mechanism is also discussed based on the Estrin-Mecking model.

Collagen and Elastic Content of Abdominal Skin After Surgical Weight Loss

Collapsed skin folds after bariatric weight loss are often managed by plastic procedures, but changes in dermal composition and architecture have rarely been documented. Given the potential consequences on surgical outcome, a prospective histochemical study was designed. The hypothesis was that a deranged dermal fiber pattern would accompany major changes in adipose tissue. Female surgical candidates undergoing postbariatric abdominoplasty (n = 40) and never obese women submitted to control procedures (n = 40) were submitted to double abdominal biopsy, respectively in the epigastrium and hypogastrium. Histomorphometric assessment of collagen and elastic fibers was executed by the Image Analyzer System (Kontron Electronic 300, Zeiss, Germany). Depletion of collagen, but not of elastic fibers, in cases with massive weight loss was confirmed. Changes were somewhat more severe in epigastrium (P = 0.001) than hypogastrium (P = 0.007). Correlation with age did not occur. (1) Patients displayed lax, soft skin lacking sufficient collagen fiber network. (2) Elastic fiber content was not damaged, and was even moderately increased in epigastrium; (3) Preoperative obesity negatively correlated with hypogastric collagen concentration; (4) Future studies should pinpoint the roles of obesity, and especially of massive weight loss, on dermal architecture and response to surgery.

Increased elastic microfibrils and thickening of fibroblastic nuclear lamina in canine cutaneous asthenia

Cutaneous asthenia is a hereditary connective tissue disease, primarily of dogs and cats, resembling Ehlers-Danlos syndrome in man. Collagen dysplasia results in skin hyperextensibility, skin and vessel fragility, and poor wound healing. The purpose of this study was to describe the histological findings in a dog with a collagenopathy consistent with cutaneous asthenia. An 8-month-old crossbreed female dog presented with lacerations and numerous atrophic and irregular scars. The skin was hyperextensible and easily torn by the slightest trauma. Ultrastructurally, the dermis was comprised of elaunin and oxytalan microfibrils. These are immature fibres in which the fibrillar component is increased but elastin is reduced. Collagen fibres were profoundly disorganized. The fibrils had a highly irregular outline and a corroded appearance when viewed in cross-section, and were spiralled and fragmented in a longitudinal view. Dermal fibroblasts displayed a conspicuous thickening of the nuclear lamina. Nuclear lamins form a fibrous nucleoskeletal network of intermediate-sized filaments underlying the inner nuclear membrane. Mutations in lamins or lamin-associated proteins cause a myriad of genetic diseases collectively called laminopathies. Disruption of the nuclear lamina seems to affect chromatin organization and transcriptional regulation of gene expression. A common link among all laminopathies may be a failure of stem cells to regenerate mesenchymal tissue. This could contribute to the connective tissue dysplasia seen in cutaneous asthenia.

Elastic Fibers in Reinke`s Edema

Objectives: We describe the distribution of elastic system fibers in the superficial layer of the lamina propria of Reinke`s edema, as compared with normal vocal folds. Methods: Weigert`s resorcin-fuchsin stain after oxidation with 10% oxone was used to study the arrangement of elastic fibers. The findings were categorized and afterward compared with the severity of Reinke`s edema. Results: Analysis of 20 specimens of vocal folds with Reinke`s edema showed that the network of thin elastic fibers in Reinke`s space lost their undulated appearance and had a tangled aspect. In addition, these fibers were no longer parallel to the epithelial basement membrane, but had a random distribution scattered throughout Reinke`s space. The elastic fiber network immediately below the epithelial basement membrane also appeared more fragmented in Reinke`s edema because of some alteration in organization combined with the 5-mu m-thick histologic sectioning plane. No significant difference in the degree of elastic system fiber disarrangement was observed between severity grades II and III (p = 0.382). Large areas of disarrangement were predominant (80% of cases). Conclusions: The disarrangement of elastic fibers in Reinke`s edema may cause insufficient tissue resistance and resilience, contributing to the hypermobility observed in Reinke`s edema.

Is the wearing of elastic stockings for half a day as effective as wearing them for the entire day?

P>Background There is good evidence for the use of compression for some clinical indications but little is known about dosimetry in compression. Objective The aim of this work was to evaluate whether or not the use of compression stockings during part of the day would help in the reduction of evening oedema in patients with clinical, epidemiological, anatomical and physiopathological (CEAP) classifications C0 and C1. Methods The effects of elastic compression stockings on volumetric variations during the working day were evaluated for the legs of two men and 18 women (40 legs). The inclusion criterion was classification as C0 (10 legs) or C1 (30 legs) according to the CEAP criteria. Participants used three-quarter-length elastic compression stockings (20-30 mmHg) on three consecutive days for the entire day or only for the morning or they did not use the stockings at all. Volumetry using the water displacement technique was performed in the morning and in the evening. When the patients wore the stockings only during the morning, volumetry was also performed at 13:00 h. Results Significant increases in volume were observed for both legs when stockings were not used compared with the use of stockings in the morning only. After removing the stockings, both legs had significant increases in volume in the afternoon. However, use for half the day was better than not using the stockings at all. Conclusions The use of elastic compression stockings can reduce volumetric variations during working hours, with the use of stockings for the entire day being better than for just half the day.

Blockade of NMDA or NO in the dorsal premammillary nucleus attenuates defensive behaviors

The dorsal premammillary nucleus (PMd) is a hypothalamic structure that plays a pivotal role in the processing of predatory threats. Lesions of this nucleus virtually eliminate the expression of defensive responses to predator exposure. However, little is known about the neurotransmitters responsible for these behavioral responses. Since PMd neurons express ionotropic glutamate receptors and exposure to predators have been shown to activate nitric oxide (NO) producing cells in this region, the aim of this study was to verify the involvement of glutamate and NO-mediated neurotransmission in defensive reactions modulated by the PMd. We tested in male Wistar rats the hypothesis that intra-PMd injection of the NMDA receptor antagonist, AP7, or the NO synthase inhibitor, N-propyl-L-arginine (NP), would attenuate behavioral responses induced by cat exposure. Our results showed that both AP7 and NP significantly attenuated the behavioral responses induced by the live cat. These results suggest that the NMDA/NO pathway plays an important role in the behavioral responses mediated by the PMd. (C) 2011 Elsevier Inc. All rights reserved.

Involvement of dorsal raphe nucleus and dorsal periaqueductal gray 5-HT receptors in the modulation of mouse defensive behaviors

Previous findings point to the involvement of the dorsal raphe nucleus (DRN) and dorsal periaqueductal gray (dPAG) serotonergic receptors in the mediation of defensive responses that are associated with specific subtypes of anxiety disorders. These studies have mostly been conducted with rats tested in the elevated T-maze, an experimental model of anxiety that was developed to allow the measurement, in the same animal, of two behaviors mentioned: inhibitory avoidance and one-way escape. Such behavioral responses have been respectively related to generalized anxiety disorder (GAD) and panic disorder (PD). In order to assess the generality of these findings, in the current study we investigated the effects of the injection of 5-HT-related drugs into the DRN and dPAG of another rodent species, mouse, on the mouse defense test battery (MDTB), a test of a range of defensive behaviors to an unconditioned threat, a predator. Male CD-1 mice were tested in the MDTB after intra-DRN administration of the 5-HT(1A) receptor antagonist WAY-100635 or after intra-dPAG injection of two serotonergic agonists, the 5-HT1A receptor agonist 8-OH-DPAT and the 5-HT(2A/2C) receptor agonist DOI. Intra-DRN injection of WAY-100635 did not change behavioral responses of mice confronted with a rat in the MDTB. In the dPAG, both 8-OH-DPAT and DOI consistently impaired mouse escape behavior assessed in the MDTB. Intra-dPAG infusion of 8-OH-DPAT also decreased measures of mouse risk assessment in the rat exposure test. In conclusion, the current findings are in partial agreement with previous results obtained with rats tested in the elevated T-maze. Although there is a high level of similarity between the behavioral effects obtained in rats (elevated T-maze) and mice (MDTB and RET) with the infusion of 5-HT agonists into the dPAG, the same is not true regarding the effects of blockade of DRN 5-HT(1A) receptors in these rodent species. These data suggest that there may be differences between mice and rats regarding the involvement of the DRN in the mediation of defensive behaviors. (C) 2010 Elsevier B.V. and ECNP. All rights reserved.

The lateral habenula regulates defensive behaviors through changes in 5-HT-mediated neurotransmission in the dorsal periaqueductal gray matter

Chemical stimulation of the lateral nucleus of the habenula (LHb), an area implicated in the regulation of serotonergic activity in raphe nuclei, affects the acquisition of inhibitory avoidance and escape expression of rats submitted to the elevated T-maze test of anxiety. Here, we investigated whether facilitation of 5-HT-mediated neurotransmission in the dorsal periaqueductal gray (dPAG) accounts for the behavioral consequences in the elevated T-maze induced by chemical stimulation of the LHb. The dPAG in the midbrain, which is innervated by 5-HT fibers originating from the dorsal raphe nucleus (DRN), has been consistently implicated in the genesis/regulation of anxiety- and fear-related defensive responses. The results showed that intra-dPAG injection of WAY-100635 or ketanserin, 5-HT(1A) and 5-HT(2A/2C) receptor antagonists, respectively, counteracted the anti-escape effect caused by bilateral intra-LHb injection of kainic acid (60 pmol/0.2 mu l). Ketanserin, but not WAY-100635, blocked kainic acid`s facilitatory effect on inhibitory avoidance acquisition. Overall, the results suggest that the pathway connecting the LHb to the DRN is involved in the control of 5-HT release in the dPAG, and facilitation of 5-HT-mediated neurotransmission in the latter area distinctively impacts upon the expression of anxiety- and fear-related defensive behaviors. While stimulation of 5-HT(1A) receptors selectively affects escape performance, 5-HT(2A/2C) receptors modulate both inhibitory avoidance and escape. (C) 2010 Elsevier Ireland Ltd. All rights reserved.

FACILITATION OF ENDOCANNABINOID EFFECTS IN THE VENTRAL HIPPOCAMPUS MODULATES ANXIETY-LIKE BEHAVIORS DEPENDING ON PREVIOUS STRESS EXPERIENCE

Although several pieces of evidence indicate that the endocannabinoid system modulates anxiety-like behaviors and stress adaptation, few studies have investigated the brain sites of these effects. The ventral hippocampus (VHC) has been related to anxiety behaviors and has a high expression of cannabinoid-1 (CBI) receptors. Moreover, endocannabinoid signaling in the hippocampus is proposed to regulate stress adaptation. In the present study we investigated the role of previous stressful experience on the effects of AM404, an anandamide uptake inhibitor, microinjected into the VHC of rats submitted to the elevated plus maze (EPM), a widely used animal model of anxiety. Stressed animals were forced restrained for two h 24 h before the test. AM404 (5-50 pmol) microinjection promoted an anxiogenic-like effect in non-stressed rats but decreased anxiety in stressed animals. AM251 (0.01 to 1000 pmol), a CBI receptor antagonist, failed to change behavior in the EPM over a wide dose range but prevented the effects of AM404. Anxiolytic-like effects of AM404 (5 pmol) intra-VHC injection were also observed in the Vogel conflict test (VCT), another model of anxiety that involves previous exposure to stressful situations (48 h of water deprivation). These results suggest that facilitation of endocannabinoid system neurotransmission in the ventral hippocampus modulates anxiety-like behaviors and that this effect depends on previous stress experience. (C) 2010 IBRO. Published by Elsevier Ltd. All rights reserved.

Polymerization stress, shrinkage and elastic modulus of current low-shrinkage restorative composites

Objective. To compare currently available low-shrinkage composites with others regarding polymerization stress, volumetric shrinkage (total and post-gel), shrinkage rate and elastic modulus. Methods. Seven BisGMA-based composites (Durafill/DU, Filtek Z250/FZ, Heliomolar/HM, Aelite LS Posterior/AP, Point 4/P4, Filtek Supreme/SU, ELS/EL), a silorane-based (Filtek LS, LS), a urethane-based (Venus Diamond, VD) and one based on a dimethacrylate-derivative of dimer acid (N`Durance, ND) were tested. Polymerization stress was determined in 1-mm high specimens inserted between two PMMA rods attached to a universal testing machine. Total volumetric shrinkage was measured using a mercury dilatometer. Maximum shrinkage rate was used as a parameter of the reaction speed. Post-gel shrinkage was measured using strain-gages. Elastic modulus was obtained by three-point bending. Data were submitted to one-way ANOVA/Tukey test (p = 0.05), except for elastic modulus (Kruskal-Wallis). Results. Composites ranked differently for total and post-gel shrinkage. Among the materials considered as ""low-shrinkage"" by the respective manufacturers, LS, EL and VD presented low post-gel shrinkage, while AP and ND presented relatively high values. Polymerization stress showed a strong correlation with post-gel shrinkage except for LS, which presented high stress. Elastic modulus and shrinkage rate showed weak relationships with polymerization stress. Significance. Not all low-shrinkage composites demonstrated reduced polymerization shrinkage. Also, in order to effectively reduce polymerization stress, a low post-gel shrinkage must be associated to a relatively low elastic modulus. (C) 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Elastic modulus of posts and the risk of root fracture

The definition of an optimal elastic modulus for a post is controversial. This work hypothesized that the influence of the posts` elastic modulus on dentin stress concentration is dependent on the load direction. The objective was to evaluate, using finite element analysis, the maximum principal stress (sigma(max)) on the root, using posts with different elastic modulus submitted to different loading directions. Nine 3D models were built, representing the dentin root, gutta-percha, a conical post and the cortical bone. The softwares used were: MSC.PATRAN2005r2 (preprocessing) and MSC.Marc2005r2 (processing). Load of 100 N was applied, varying the directions (0 degrees, 45 degrees and 90 degrees) in relation to the post`s long axis. The magnitude and direction of the sigma(max) were recorded. At the 45 degrees and 90 degrees loading, the highest values of sigma(max) were recorded for the lowest modulus posts, on the cervical region, with a direction that suggests debonding of the post. For the 0 degrees loading, the highest values of sigma(max) were recorded for higher modulus posts, on the apical region, and the circumferential direction suggests vertical root fracture. The hypothesis was accepted: the effect of the elastic modulus on the magnitude and direction of the sigma(max) generated on the root was dependent on the loading direction.

Elastic moduli of model random three-dimensional closed-cell cellular solids

Most cellular solids are random materials, while practically all theoretical structure-property results are for periodic models. To be able to generate theoretical results for random models, the finite element method (FEM) was used to study the elastic properties of solids with a closed-cell cellular structure. We have computed the density (rho) and microstructure dependence of the Young's modulus (E) and Poisson's ratio (PR) for several different isotropic random models based on Voronoi tessellations and level-cut Gaussian random fields. The effect of partially open cells is also considered. The results, which are best described by a power law E infinity rho (n) (1<n<2), show the influence of randomness and isotropy on the properties of closed-cell cellular materials, and are found to be in good agreement with experimental data. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.