196,114 research outputs found
Corrosion of fasteners in concrete: Literature review and discussion of current test methods
No full textCorrosion damage may impair functioning and capacity of fasteners, hence affecting structures durability. The aim of this paper is to present the existing knowledge on fasteners’ corrosion behavior in concrete. The paper investigates the available literature and discusses the most significant test methods currently in use for the evaluation of fastener’s corrosion performance in concrete (i.e., hydrogen embrittlement, salt spray and sulfur dioxide tests). In this context, design standards and product norms often provide inconsistent requirements, while assessment procedures of non-zinc coatings are left to case-by-case implementation. Moreover, the study of existing test methods revealed that, beside the hydrogen embrittlement test for concrete screws, none of the other considered test methods are specifically conceived to investigate the fastener’s corrosion behavior at the steel-to-concrete connection scale, nor they account for service conditions. Therefore, the significance for both designers and manufacturers of the remarks pointed out in this paper
Low-cycle behavior of wood screws under alternating bending
No full textEarthquake-resistant timber structures may be designed accounting either for the dissipative or low-dissipative structural behavior, depending on the relevant ductility class. A timber structure belonging to a given ductility class shall meet specific requirements especially in the type and rotational ductility capacity of connections, since the timber members themselves shall be regarded as behaving elastically. In addition, Eurocode 8 prescribes that only materials and mechanical fasteners providing appropriate low-cycle fatigue behavior may be used in joints regarded as dissipative zones. In this context, the properties of dissipative zones may be determined by tests either on single joints, or on whole structures in accordance with EN 12512. At the same time, the appropriate fastener’s low-cycle behavior is currently deemed to be satisfied if the connectors are sufficiently slender with respect to the thickness of the joined members. Nowadays, this assumption may not be sufficiently reliable because of the actual trends in fasteners technology, which consists in providing heavily hardened connectors in order to achieve higher resistances and ease of insertion into timber. The aim of this study is to investigate the low-cycle behavior of modern wood screws by means of three-point alternating bending tests. The paper describes a new testing apparatus, the related test procedure and assessment criteria specifically designed for this purpose. A preliminary investigation of the low-cycle behavior of different wood screws currently on the market is then carried out and the related test results are discussed
M. Bartolomeo Scappi Dell arte del cucinare .Con Il mastro di casa e Trinciante
No full textSign.: A-Z4, 2A-2Z4, 3A-3Z4, 4A-4I4, 4K4Port. grav. calcIlustracions calcIl trincante di Vicenzo Cervio. Il Mastro di Casa di Cesare Pandin
Impact performance of thin glass-polycarbonate composite panels
No full textSafety glass is usually the proper designer choice when glazing may be subjected to the impact of a person. In order to avoid people injuries, glass products must comply with appropriate safety practices. Existing technical standards classify safety glass products by mode of breakage and post-breakage behavior. Critical demanding applications in terms of self-weight saving, like high efficiency elevator cars in buildings or aircrafts and other means of transportation interiors in aerospatial and automotive industries, are currently driving the innovation in the development of safety glass. In this framework, glass-polycarbonate composite panels offer a lightweight alternative which is at once able to preserve the aesthetic and safety aspects of traditional laminated safety glass. The aim of this paper is to present an experimental investigation on the performance under impact of thin glass layer with a cellular polycarbonate backing joined together by an auto-adhesive interlayer film. Different coatings (mirror and paint) at the glass-adhesive interface are also taken into account
SEISMIC DESIGN AND EXPERIMENTAL INVESTIGATION OF A NEW TIMBER HOLD-DOWN CONNECTION
No full textTimber connections made with hold-down are usually adopted for timber wall to foundation connection at the edges of
the wall to restraint the possible overturning moment (due to rocking) which can occur by applying a horizontal force to
the panel (e.g. under seismic action). The main components of the connection are the steel plate fastened to the panel
via threaded screws or nails and the anchor system to the concrete foundation. As such, the connection behavior under
seismic loading is characterized by the contemporarily contribution of different resistant mechanisms, i.e. (i) laterally
loaded timber screws or nails; (ii) axially loaded steel plate; (iii) axially loaded anchor in concrete. The former has been
basically neglected in past investigations having anchored the hold-down with steel bolt directly to the strong floor.
However, the design of the anchor should be considered as crucial when it comes to capacity design, especially in case
of narrow foundations (edge failure) and post-installed anchors when the resistance is highly reduced with respect to
steel bolt capacity. Moreover, the overall dissipative performance might be affected by the anchor’s displacement. An
innovative hold-down connection has been designed to promote steel failure of the axially loaded plate. The plate’s
geometry has been optimized such that capacity design rules according to Eurocode 8 can be applied. Additionally, a
target displacement requirement is addressed, and the stretch length is defined accordingly. The whole connection is
tested against cyclic loading and results show enhanced performances with respect to standard configuration. In
particular, brittle mechanism such as concrete-cone failure of the anchors and splitting of timber are prevented. The
paper discusses the experimental results for different type and size of the anchor, also the size of the optimized steel
plate is considered as a parameter
Cord blood derived endothelial progenitor cells: time dependent in vitro generation capacity.
No full textOBJECTIVES. To test in vitro endothelial progenitor cells (EPCs) generation from fresh cord blood (CBs) cultured at different time after collection.
MATERIALS AND METHODS. Mononuclear cells (MNCs) were isolated by density gradient centrifugation using Lympholyte Cell Separation Media (Cedarlane) from CBs collected for banking and discharged either for low TNC count or volume. 20 * 106 MNCs from CBs aged from 6 to 12 hours (group 1) and from 13 to 36 hours (group 2) were cultured in endothelial cell culture medium (EGM-2 Bulletkit, Lonza) on fibronectin-coated cell culture plates (Becton Dickinson) for maximum 20 days monitoring the appearance of EPC cobblestone-shaped colonies. The colony-derived cells (CDCs) were enumerated and studied by immunofluorescence and flow cytometry for typical endothelial markers as well as for capillary-like structures formation using the Matrigel assay (Becton Dickinson).
RESULTS. MNCs from group 1 CBs gave rise to EPC colonies with a mean generation rate (ratio of CDCs / CD34+ seeded cells) of 29.3% (range, 12.1 – 38.9), while MNCs from group 2 CBs showed a 0% generation rate. Consistently with an EPC phenotype, CDCs were able to form vascular networks on extracellular matrix (Matrigel), showed Ac-LDL uptake and were positive for CD34, CD31, CD146, vWF, KDR and negative for CD45 markers. A positive correlation between EPCs generation rate and MNCs CD34+ cell content was observed; while the other parameters (including MNCs viability) seemed not to influence EPCs generation.
CONCLUSIONS. Even if our data need to be confirmed in a larger study, our preliminary experience indicates that CBs may be an attractive source of EPCs and shows that EPCs generation is highly influenced by CB age. These biological features should be considered in planning regenerative medicine protocols
The cardioprotective paracrine effects exerted by human mesenchymal stem cells are negatively influenced by donor age
No full textBackground: In experimental animal models mesenchymal stem cells (MSC) repair infarcted hearts mainly through paracrine mechanisms. In particular, MSC produce and release anti-apoptotic factors that lead to cytoprotection. For translational purposes, it would be important to verify if human MSC also mediate cardioprotection. In particular, since ischemic heart diseases occur mainly in elderly, it is essential to establish if donor age negatively influences the production of cytoprotective factors. Accordingly, we have compared the paracrine properties of fetal MSC with adult MSC from young and old patients.
Methods: MSC of fetal origin (F-MSC) were isolated from placental amniotic membranes processed immediately after delivery. Adult MSC were collected from bone marrow samples of young (yBM-MSC; donor age 65 years). Rat neonatal cardiomyocytes (H9c2 cells) were used to test cytoprotection. H9c2 cells were exposed to 6 hours of hypoxia followed by 18 hours of reoxygenation in the presence of control medium (CTRL-M) or conditioned medium (CM) from F-MSC (F-CM) or yBM-MSC (Y-CM) or oBM-MSC (O-CM). CM was obtained by growing MSC for 36 hours in the absence of serum. H9c2 viability was measured by MTS assay. The rate of apoptosis was quantified by TUNEL staining. We also evaluated cleaved Caspase 3 using both a colorimetric assay and Western blotting. Gene expression profile of several known cytoprotective factors was assessed by RT-PCR.
Results: The hypoxia/reoxygenation protocol reduced H9c2 viability by 55% compared with basal condition (p<0.001). Both F-CM and Y-CM prevented cell damage compared with CTRL-M resulting in a significant increase in cell viability by 45% (p<0.017) and 33% (p<0.017), respectively. At the contrary, O-CM had no significant effect on H9c2 viability (p=n.s. vs CTRL-M). After the induction of hypoxia/reoxygenation injury, 35 ± 8% of H9c2 cells tested positive for TUNEL staining. Compared with CTRL-M and O-CM, in the presence of F-CM we observed a relative reduction in the number of TUNEL positive nuclei of 91% (p<0.001) and 89% (p<0.001) respectively. The Y-CM also reduced H9c2 apoptotic nuclei (- 67,5% vs CTRL-M, p<0.01; - 64% vs O-CM, p<0.01). In contrast, O-CM did not prevent H9c2 apoptotic death (-11% vs CTRL-M, p=n.s.). The colorimetric assay documented that the F-CM significantly reduce the level of cleaved Caspase 3 by 50% vs CTRL-M (p< 0.017) and by 42% vs Y-CM (p< 0.017); furthermore, the Y-CM reduced the amount of cleaved Caspase 3 by 33% vs O-CM (p< 0.017). Finally, the oBM-MSC-CM did not reduce cleaved Caspase 3 compared with CTRL-M. In the presence of F-CM Western blot analysis confirmed a marked reduction in Caspase 3 activation, while no striking differences were present between CTRL-M, Y-CM and O-CM. The RT-PCR analysis documented that F-MSC express several known cytoprotective factors such as PDGF-β, BMP2, EPO, FGF2 and VEGF at significantly higher level compared with oBM-MSC (p<0.05) and that VEGF, FGF2 and HGF transcripts were significantly higher in yBM-MSC than in oBM-MSC (p<0.05).
Conclusions: We have shown that human MSC can mediate cardiomyocyte protection through the release of soluble anti-apoptotic factors. However, we documented that donor age negatively influences the paracrine cytoprotective properties of adult MSC. Our data suggest that autologous MSC theraphy for ischemic heart disease might be less effective in elderly patients
Human fetal mesenchymal stem cells protect cardiac myocytes against hypoxia/reoxygenation injury
No full textBackground: Myocardial reperfusion injury represents a major complication of the reperfusive therapies used to treat acute infarction. Consequently, the identification of new cytoprotective strategies able to prevent reperfusion injury is urgently needed. We and others have shown that adult mesenchymal stem cells (MSC) limit infarct size in rodents mainly through cytoprotective paracrine mechanisms. More recently, the existence of fetal MSC in the human placenta has been described but it is unknown whether these cells can mediate cardiomyocyte protection.
Methods: MSC were isolated from the placental amniotic membrane (A-MSC) of women delivering male newborns. We performed FACS analysis and FISH staining for the Y-chromosome to determine the immunophenotype and to confirm the fetal origin of the cells, respectively. The expression of several known cytoprotective factors was verified by RT-PCR. Rat neonatal cardiomyocytes (H9c2) were exposed to 6 hours of hypoxia followed by 18 hours of reoxygenation in the presence of control medium (CTRL-M) or conditioned medium (CM) from A-MSC. H9c2 viability was evaluated by MTS assay and cleaved Caspase 3 was quantified by colorimetric assay and Western blotting. The anti-apoptotic protein Bcl-2 was analyzed in H9c2 cells by Western blotting.
Results: A-MSC were successfully isolated from 15 amniotic membranes. At passage three, the A-MSC displayed the antigen profile typical of MSC and were positive for the Y chromosome. Furthermore, the A-MSC expressed several known cytoprotective factors, such as EPO, HGF, IGF-1, FGF2, VEGF, BMP2, PDGF-b, SFRP2, TGF-B, and thymosin B4. The hypoxia/reoxygenation protocol reduced by 68% the H9c2 viability (p<0.05 vs basal conditions). The A-MSC-CM remarkably increased cell viability by 62% compared with CTRL-M (p<0.05%). The colorimetric assay documented that in H9c2 fed with CRTL-M the amount of cleaved Caspase 3 was increased by 36% after hypoxia/reoxygenation (p<0.05) and that the A-MSC-CM significantly reduced the level of cleaved Caspase 3 (- 70% vs CTRL-M, p<0.05). Western blotting analysis confirmed the reduction of Caspase 3 in the presence of A-MSC-CM and showed an increase in Bcl-2 expression.
Conclusions: We documented that it is possible to consistently isolate MSC of fetal origin from human placenta. Furthermore, we showed that A-MSC express several cytoprotective factors and that A-MSC-CM remarkably protects cardiac myocytes against hypoxia/reoxygenation damage. The systematic analysis of A-MSC profile may lead to the identification of new powerful therapies to prevent myocardial reperfusion injury
Donor age negatively influences the cytoprotective paracrine effects exerted by human mesenchymal stem cells
No full textBackground: In animal models mesenchymal stem cells (MSC) repair infarcted hearts mainly through cytoprotective paracrine mechanisms. For translational purposes, it would be important to verify if human MSC also mediate cardioprotection. In particular, since ischemic heart diseases occur mainly in elderly, it is essential to establish if donor age influences the production of cytoprotective factors. Accordingly, we compared the paracrine properties of fetal MSC (F-MSC) with adult MSC. Furthermore, we aimed to elucidate through which signalling pathway MSC lead to cytoprotection.
Methods: F-MSC were isolated from human placenta and adult MSC from the bone marrow of young (yBM-MSC; age65) donors. Rat neonatal cardiomyocytes (H9c2) were exposed to hypoxia (6 hrs)/reoxygenation (18 hrs) (H/R) in the presence of control medium (CTRL-M) or conditioned medium from F-MSC (F-CM), yBM-MSC (y-CM) or oBM-MSC (o-CM). H9c2 viability was evaluated by MTS assay. Apoptosis was measured by TUNEL staining and by cleaved Caspase 3 (colorimetric assay and Western blot). We evaluated SAPK/JNK and p38 MAPK activation by Western blot and the expression of pro- and anti-apoptotic genes by RT-PCR.
Results: The H/R protocol reduced H9c2 viability by 55% (p<0.001 CTRL-M vs basal condition). Compared with CTRL-M, both F-CM and y-CM increased cell viability (+45% and +33% respectively; p<0.017) while o-CM had no effect. F-CM significantly reduced the number of TUNEL positive cells (-91% vs CTRL-M and -89% vs o-CM; p<0.001). The y-CM also reduced H9c2 apoptotic nuclei (-67,5% vs CTRL-M, p<0.01; -64% vs o-CM, p<0.01). In contrast, o-CM did not prevent apoptosis (-11% vs CTRL-M, p=ns). Both colorimetric assay and Western blot showed that Caspase-3 activation was prevented by F-CM and y-CM but not by o-CM. The H/R protocol strongly activated both SAPK/JNK and p38 MAPK. This activation was markedly reduced by F-CM while y-CM and o-CM had modest effect on both pathways. Furthermore, compared with CTRL-M and both y-CM and o-CM, F-CM up-regulated the anti-apoptotic genes Bcl-2 and Stat3 and down-regulated the pro-apoptotic genes TNF-α and FasL.
Conclusions: We showed that human MSC mediate cardiomyocyte protection by releasing soluble anti-apoptotic factors. However, donor age negatively influences the cytoprotective properties of adult MSC. We also demonstrated that MSC of fetal origin exerts powerful cytoprotective effects via inhibition of different pro-apoptotic signalling pathways. Our data suggest that autologous MSC therapy for ischemic heart diseases may be less effective in elderly patients
Concomitant overexpression of IGF1 and BMP2 in mesenchymal stem cells mediates cytoprotection through both autocrine and paracrine activation of Akt, Erk1/2 and SMAD1/5/8 pathways.
No full textBackground. Bone marrow mesenchymal stem cells (BM-MSC) are valuable tools for cardiac repair, acting mainly through release of paracrine factors. However, the effects of BM-MSC are limited by poor engraftment and low rate of differentiation events. To overcome these limitations, we genetically engineered BM-MSC with a novel bicistronic lentivirus co-expressing IGF1 and BMP2 (IB), two factors known to be involved in both cardiac differentiation and cytoprotection.
Methods. Rat BM-MSC were transduced with a control virus (GFP-MSC) or IB virus (IB-MSC). Autocrine and paracrine cytoprotection was evaluated in transduced MSC or in H9c2 cells treated with unconditioned (CTRL-M) or conditioned media (GFP-CM or IB-CM), after 24h of hypoxia. Cell viability was measured by MTS assay. Apoptosis was evaluated through caspase-3 activation. Transcriptional levels of pro and anti-apoptotic genes in H9c2 were measured by RT-PCR. Activation of IGF1 and BMP2 pro-survival pathways (Akt, ERK1/2, and SMAD1/5/8) in both MSC and H9c2 were assessed by western blot.
Results. IB-MSC showed a marked reduction of apoptosis (-50% p<0.001) vs GFP-MSC after 24h of hypoxia. IB-CM increased H9c2 viability (+32,1% p<0.001) compared with CTRL-M, while GFP-CM had no effect. Caspase-3 activation was reduced in the presence of IB-CM of 63,9% vs CTRL-M (p<0.001) and of 49,7 % vs GFP-MSC (p<0.05). H9c2 treated with IB-CM showed enhanced expression of Bcl-2 and Stat3 pro-survival genes, and inhibition of FasL and TNFalpha pro-apoptotic genes. Both IB-MSC or IB-CM treated-H9c2 showed a strong activation of Akt, ERK1/2 and SMAD1/5/8 pathways, confirming that IGF1 and BMP2 transgenes are acting both in autocrine and paracrine manner.
Conclusions. IGF1 and BMP2 transgene overexpression in MSC increases cell survival and cytoprotective paracrine properties. In particular, these effects are mediated by the activation of pathways known to be involved in cell survival
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