scholarly journals Melanocyte pigmentation stiffens murine cardiac tricuspid valve leaflet

2009 ◽  
Vol 6 (40) ◽  
pp. 1097-1102 ◽  
Author(s):  
Kantesh Balani ◽  
Flavia C. Brito ◽  
Lidia Kos ◽  
Arvind Agarwal
Keyword(s):  
Mechanical Properties ◽  
Storage Modulus ◽  
Tricuspid Valve ◽  
Viscoelastic Properties ◽  
Mechanical Analysis ◽  
Current Work ◽  
Valve Leaflet ◽  
Stiffness Measurement ◽  
Proper Functioning

Pigmentation of murine cardiac tricuspid valve leaflet is associated with melanocyte concentration, which affects its stiffness. Owing to its biological and viscoelastic nature, estimation of the in situ stiffness measurement becomes a challenging task. Therefore, quasi-static and nanodynamic mechanical analysis of the leaflets of the mouse tricuspid valve is performed in the current work. The mechanical properties along the leaflet vary with the degree of pigmentation. Pigmented regions of the valve leaflet that contain melanocytes displayed higher storage modulus (7–10 GPa) than non-pigmented areas (2.5–4 GPa). These results suggest that the presence of melanocytes affects the viscoelastic properties of the mouse atrioventricular valves and are important for their proper functioning in the organism.

Bioactivity and Viscoelastic Characterization in Physiological Simulated Conditions of Chitosan/Bioglass® Composite Membranes

2010 ◽  
Vol 636-637 ◽  
pp. 26-30 ◽  
Author(s):  
Sofia G. Caridade ◽  
Esther G. Merino ◽  
Gisela M. Luz ◽  
N.M. Alves ◽  
João F. Mano
Keyword(s):  
Mechanical Properties ◽  
Storage Modulus ◽  
Tissue Regeneration ◽  
Viscoelastic Properties ◽  
Mechanical Performance ◽  
Composite Membranes ◽  
Mechanical Analysis ◽  
Chitosan Membranes ◽  
Tan Δ

A number of combinations of biodegradable polymers and bioactive ceramics have been used for orthopaedic applications including in hard tissue regeneration. Ideally, composites aimed to be used in orthopaedic applications should combine adequate mechanical properties and bioactivity. Chitosan (CTS) has been widely used for biomedical applications, namely in tissue regeneration or drug delivery. In this sense, membranes of chitosan and chitosan with Bioglass® (BG) were prepared by solvent casting and characterised using Scanning Electron Microscopy. In vitro bioactivity tests were performed in the composite membranes, namely by monitoring their capability to induce the precipitation of apatite upon immersion in simulated body fluid (SBF). The results showed that the addition of BG promoted the deposition of an apatite-like layer. The deposition of apatite could influence the mechanical performance of the material. Therefore, in order to follow this biomineralization, the viscoelastic properties of these composite membranes (immersed in SBF) were evaluated. The change in the storage modulus (E’) and the loss factor (Tan δ) were measured as a function of immersion time using non-conventional dynamic mechanical analysis (DMA) tests, in which the samples were kept in wet conditions and at 37°C during the measurements. The mechanical properties of the chitosan membranes were improved by the addition of BG particles. An increase on the storage modulus was observed by the composite membranes while for the pure chitosan membranes the storage modulus was stable up to 7 days. Clear changes were detected in the composite membranes that contrasted with pure chitosan (CTS) membranes that exhibit stable viscoelastic properties up to 7 days. In addition, this work showed that sample characterization in the hydrated state can be useful to predict the mechanical performance of composites under meaningful physiological conditions.

Viscoelastic properties of woody hemp core

Holzforschung ◽  
2011 ◽  
Vol 65 (2) ◽  
Author(s):  
Rahime Bag ◽  
Johnny Beaugrand ◽  
Patrice Dole ◽  
Bernard Kurek
Keyword(s):  
Cell Wall ◽  
Viscoelastic Properties ◽  
Specific Effect ◽  
Mechanical Analysis ◽  
Low Molecular Weight ◽  
Dielectric Analysis ◽  
Technological Transformation ◽  
Chain Mobility ◽  
Cell Wall Polymers

Abstract The aim of this study was to determine the effect of removing extractives from the woody core of hemp (chènevotte) on the chain mobility of hemicelluloses and lignins, which can react during technological transformation such as de-fibering and/or composite materials production. Extractives are molecules with low molecular weight, which are present in the cell wall matrix and can be readily removed by solvents. In the present paper, the nature and amounts of extractives, removed under different conditions and with solvents of different polarities, were determined. The mobility and structural relaxations of lignins and hemicelluloses were stu-died in situ by dynamic mechanical analysis and dielectric analysis under controlled moisture content. Extractions at low temperature led to rigidification of lignins and plasticizing of hemicelluloses, probably due to local changes by the selective removal of molecules interacting with the polymers. Probably, the accessibility of hemicelluloses to plasticizing water was increased at controlled humidity. In contrast, hot extractions including water induced rigidification of the hemi-celluloses and plasticizing of lignins. This could be related to a combination of molecule extractions and chemical modi-fications of both polymers. This interpretation is supported by the variation of activation energy for relaxation of hemi-celluloses. It can be concluded that each type of extraction has a clear specific effect on the relaxation properties of the amorphous cell wall polymers.

scholarly journals In situ formation of PLA-grafted alkoxysilanes for toughening a biodegradable PLA stereocomplex thin film

RSC Advances ◽  
2019 ◽  
Vol 9 (38) ◽  
pp. 21748-21759 ◽  
Author(s):  
Jieun Jeong ◽  
Muhammad Ayyoob ◽  
Ji-Heung Kim ◽  
Sung Woo Nam ◽  
Young Jun Kim
Keyword(s):  
Thin Film ◽  
Mechanical Properties ◽  
Significant Loss ◽  
Current Work ◽  
Synergistic Approach ◽  
In Situ Formation

Current work provides a synergistic approach to prepare super tough PLA without any significant loss of its excellent intrinsic mechanical properties.

Synergistic effect of carbon nanotubes and nano-hydroxyapatite on mechanical properties of polyetheretherketone based hybrid nanocomposites

2020 ◽  
pp. 096739112096950
Author(s):  
Manjeet Kumar ◽  
Rajesh Kumar ◽  
Sandeep Kumar
Keyword(s):  
Mechanical Properties ◽  
Carbon Nanotubes ◽  
Elastic Modulus ◽  
Storage Modulus ◽  
Fracture Resistance ◽  
Compression Molding ◽  
Mechanical Analysis ◽  
Hybrid Nanocomposites ◽  
Hybrid Nanocomposite ◽  
And Storage

Hybrid nanocomposites utilize the benefits of properties of different fillers to enhance its desired properties. Polyetheretherketone (PEEK) based hybrid nanocomposites have immense potential applications in aerospace, automobile, high-temperature electrical applications, and medical and health care. The present work is an attempt to improve the elastic modulus, hardness, fracture resistance, and storage modulus simultaneously by reinforcing the PEEK matrix with multiwall carbon nanotubes (MWCNTs) filler and 30 wt.% nano hydroxyapatite (nHA)-MWCNT hybrid filler. The nanocomposites having 0,1,3,5 and 7 wt.% of MWCNTs were fabricated by the Ball Mixing and Compression Molding Method. Customized Die Heater setup was used to ensure uniform heating and cooling during compression molding. The morphology was examined by Field Emission Scanning Electron Microscopy (FESEM) and Energy-Dispersive X-ray Spectroscopy (EDS) and uniform distribution of nano-fillers was observed. The nanoindentation method was adopted to investigate the Static Mechanical Analysis (SMA) and Dynamic Mechanical Analysis (DMA) at varying frequencies of loading, of nanocomposites. At 5 wt.% of MWCNTs, the enhancements in elastic modulus, hardness, fracture resistance, and storage modulus were observed to be 80%, 36%, 32%, and 58% respectively in case of PEEK/(0–7%)MWCNT nanocomposite and 104%, 76%, 16%, and 80% respectively in case of PEEK/30%nHA-(0–7%)MWCNT hybrid nanocomposite. The decrements in loss factor indicated the improvement in elastic behavior of nanocomposites with increasing wt.% of MWCNTs. The elastic modulus of PEEK/30%nHA-5%MWCNT hybrid nanocomposite was observed to be 7.67 GPa, which falls within the range of elastic modulus of the human cortical bone. The results revealed that 5 wt.% of MWCNTs is optimum filler composition for improving the mechanical properties.

scholarly journals Viscoelastic Properties of Contemporary Bulk-fill Restoratives: A Dynamic-mechanical Analysis

2018 ◽  
Vol 43 (3) ◽  
pp. 307-314 ◽  
Author(s):  
JEX Ong ◽  
AU Yap ◽  
JY Hong ◽  
AH Eweis ◽  
NA Yahya
Keyword(s):  
Dynamic Mechanical Analysis ◽  
Storage Modulus ◽  
Loss Tangent ◽  
Viscoelastic Properties ◽  
Loss Modulus ◽  
Artificial Saliva ◽  
Mechanical Analysis ◽  
Distilled Water ◽  
Glass Ionomer ◽  
Dynamic Mechanical

SUMMARY This study investigated the viscoelastic properties of contemporary bulk-fill restoratives in distilled water and artificial saliva using dynamic mechanical analysis. The materials evaluated included a conventional composite (Filtek Z350), two bulk-fill composites (Filtek Bulk-fill and Tetric N Ceram), a bulk-fill giomer (Beautifil-Bulk Restorative), and two novel reinforced glass ionomer cements (Zirconomer [ZR] and Equia Forte [EQ]). The glass ionomer materials were also assessed with and without resin coating (Equia Forte Coat). Test specimens 12 × 2 × 2 mm of the various materials were fabricated using customized stainless-steel molds. After light polymerization/initial set, the specimens were removed from the molds, finished, measured, and conditioned in distilled water or artificial saliva at 37°C for seven days. The materials (n=10) were then subjected to dynamic mechanical testing in flexure mode at 37°C and a frequency of 0.1 to 10 Hz. Storage modulus, loss modulus, and loss tangent data were subjected to normality testing and statistical analysis using one-way analysis of variance/Dunnett's test and t-test at a significance level of p < 0.05. Mean storage modulus ranged from 3.16 ± 0.25 to 8.98 ± 0.44 GPa, while mean loss modulus ranged from 0.24 ± 0.03 to 0.65 ± 0.12 GPa for distilled water and artificial saliva. Values for loss tangent ranged from 45.7 ± 7.33 to 134.2 ± 12.36 (10−3). Significant differences in storage/loss modulus and loss tangent were observed between the various bulk-fill restoratives and two conditioning mediums. Storage modulus was significantly improved when EQ and ZR was not coated with resin.

Rheology, morphology and mechanical properties of LLDPE/PS blends catalyzed by combined Lewis acids

e-Polymers ◽  
2009 ◽  
Vol 9 (1) ◽  
Author(s):  
Yan-Long Liu ◽  
Li-Gang Yin ◽  
Zhuo Ke ◽  
Qiang Shi ◽  
Jing-Hua Yin
Keyword(s):  
Mechanical Properties ◽  
Storage Modulus ◽  
Lewis Acids ◽  
Low Frequency ◽  
Complex Viscosity ◽  
Reactive Blending ◽  
Izod Impact ◽  
Rheological Experiments ◽  
And Storage

AbstractThe rheological, morphological and mechanical properties of LLDPE/PS blends with a combined catalyst, Me3SiCl and InCl3·4H2O, were studied in this work. The higher complex viscosity and storage modulus at low frequency were ascribed to the presence of graft copolymers, which were in situ formed during the mixing process. From the rheological experiments, the complex viscosity and storage modulus of reactive blends were higher than the physical blends. The dispersion of LLDPE particles of reactive blending becomes finer than that of physical blends, consistent with the rheological results. As a result of increased compatibility between LLDPE/PS, the mechanical properties of reactive blends show much higher tensile and Izod impact strength than those of physical blends.

Dynamic Mechanical Losses in Filled Poly(Dimethylsiloxane) Networks

1995 ◽  
Vol 68 (4) ◽  
pp. 601-608 ◽  
Author(s):  
M. A. Sharaf ◽  
A. Kloczkowski ◽  
J. E. Mark
Keyword(s):  
Mechanical Properties ◽  
Glass Transition ◽  
Viscoelastic Properties ◽  
Network Formation ◽  
Dynamic Testing ◽  
Glass Transition Temperatures ◽  
Dynamic Mechanical ◽  
Novel Method ◽  
Particulate Silica

Abstract This investigation focused on the study of dynamic mechanical losses in silica-filled networks of poly(dimethylsiloxane) (PDMS). Some of the samples were filled using a novel method, specifically the in situ precipitation of particulate silica either after or during network formation. Others were filled using the customary method of mechanically blending already-prepared silica into the elastomer prior to its crosslinking, and some were prepared without any filler at all. The resulting materials exhibited a variety of relaxation behaviors over the temperature range 120–260 K. The glass transition temperatures Tg showed only a slight dependence on the presence of the filler particles and crosslinks, but the filler was found to reduce both the degree and rate of crystallization for the in situ filled networks. The results obtained document how the techniques employed for incorporating particulate fillers change the viscoelastic properties of an elastomeric network, and how dynamic testing can yield a great deal of insight and useful information on the mechanical properties of polymers in general.

Study of Microstructure and Dynamic Mechanical Analysis of Biodegradable Tableware Produced with Corn Straw

2011 ◽  
Vol 380 ◽  
pp. 160-163 ◽  
Author(s):  
Alun ◽  
Zhi Hui Sun ◽  
Quan Rong Jing ◽  
Ri Dun Hu ◽  
Chun Li Yang
Keyword(s):  
Mechanical Properties ◽  
Mechanical Property ◽  
Storage Modulus ◽  
Dynamic Mechanical Properties ◽  
Mechanical Analysis ◽  
Dynamic Mechanical Property ◽  
Corn Straw ◽  
Dynamic Mechanical ◽  
Scan Electronic Microscope ◽  
Electronic Microscope

This paper focused on biodegradable tableware processed with plant fiber, which were obtained by mechanical processing corn straw, abundant in Heilongjiang Province of China. Firstly, the microstructure characteristics of tableware were described by Scan Electronic Microscope (SEM). Secondly, the dynamic mechanical property of biodegradable tableware was analyzed by DMA, which will provide a reference to optimize the biodegradable tableware design in future. And the dynamic mechanical property of biodegradable tableware also was compared with the dynamic mechanical properties of the plastic snack box. The results showed that biodegradable tableware had a highly storage modulus (E′) originally, it was 3216MPa,while the maximum storage modulus (E′) of plastic snack box was 852MPa. And the results also indicated that the treat temperature has a significant effect on the dynamic mechanical properties of biodegradable tableware, as the treat temperature increased closely to 95°C, the biodegradable tableware appeared glassy transition, but the storage modulus (1650MPa) was still much higher than that of the plastic snack box.

scholarly journals Mechanical testing of glutaraldehyde cross-linked mitral valves. Part two: Elastic and viscoelastic properties of chordae tendineae

2020 ◽  
pp. 095441192097593
Author(s):  
Matthew Constable ◽  
Rhiannon Northeast ◽  
Bernard M Lawless ◽  
Hanna E Burton ◽  
Vera Gramigna ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Material Properties ◽  
Viscoelastic Properties ◽  
Loss Modulus ◽  
Mechanical Analysis ◽  
Cross Linking ◽  
Chordae Tendineae ◽  
Mitral Valves ◽  
Lower Strain ◽  
The Mean

The aim of this study was to assess whether the mechanical properties of mitral valve chordae tendineae are sensitive to being cross-linked under load. A total 64 chordae were extracted from eight porcine hearts. Two chordae (posterior basal) from each heart were subjected to uniaxial ramp testing and six chordae (two strut, two anterior basal and two posterior basal) were subjected to dynamic mechanical analysis over frequencies between 0.5 and 10 Hz. Chordae were either cross-linked in tension or cross-linked in the absence of loading. Chordae cross-linked under load transitioned from high to low extension at a lower strain than cross-linked unloaded chordae (0.07 cf. 0.22), with greater pre-transitional (30.8 MPa cf. 5.78 MPa) and post-transitional (139 MPa cf. 74.1 MPa) moduli. The mean storage modulus of anterior strut chordae ranged from 48 to 54 MPa for cross-linked unloaded chordae, as compared to 53–61 MPa cross-linked loaded chordae. The mean loss modulus of anterior strut chordae ranged from 2.3 to 2.9 MPa for cross-linked unloaded chordae, as compared to 3.8–4.8 MPa cross-linked loaded chordae. The elastic and viscoelastic properties of chordae following glutaraldehyde cross-linking are dependent on the inclusion/exclusion of loading during the cross-linking process; with loading increasing the magnitude of the material properties measured.

Reinforcing MWCNTs to enhance viscoelastic properties of polyurethane nanocomposites by using nano DMA techniques

2020 ◽  
pp. 089270572093074 ◽  
Author(s):  
Dinesh Kumar ◽  
Navin Kumar ◽  
Prashant Jindal
Keyword(s):  
Composite Material ◽  
Storage Modulus ◽  
Viscoelastic Properties ◽  
High Strength ◽  
Mechanical Analysis ◽  
Elastic Behavior ◽  
Loading Frequency ◽  
Uniform Dispersion ◽  
Tan Δ ◽  
A Minor

Multi-walled carbon nanotubes (MWCNTs)-reinforced polyurethane (PU) composites were fabricated by using solution mixing technique followed by compression molding. Nano dynamic mechanical analysis was carried out to investigate the viscoelastic properties of PU/MWCNTs composites within a frequency range of 5–250 Hz. At higher frequencies (250 Hz), the storage modulus of PU/MWCNTs composites with 10 wt% loading of MWCNTs was enhanced by 148% in equivalence to pristine PU. An improvement of 13.3% in storage modulus was observed at a loading frequency of 250 Hz in comparison to that of a loading frequency of 75 Hz, which indicates that the effect of MWCNTs on storage modulus was more pronounced at higher frequencies. At 75 Hz, a minor composition of MWCNTs (3 wt%) was sufficient to reduce the value of tan δ from 0.20 to 0.15, indicating that the material becomes more elastic after reinforcing MWCNTs. This significant improvement in the mechanical behavior of composite material has been attributed to the uniform dispersion of MWCNTs, and their adhesion with PU molecules. Reported enhancement in the elastic behavior of PU composite will boost the applicability of PU-based composite material for the fabrication of high-strength boots, gloves, and jackets required to absorb high vibration frequencies experienced during conditions such as rock drilling.

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