Apparent Elastic Modulus Research Articles

Acoustic and Strength Characterization of Particleboard and Micronized Rubber Powder Composites

Abstract Waste rubber is abundant worldwide and threatens to be an environmental hazard for decades to come. This has led to an interest in the use of recycled rubber materials in value-added products. One such possible use is in the wood products industry. The research analyzed the strength and acoustic properties of composite pine particleboard that contained 10, 20, 30, and 40 percent micronized rubber powder, a dry powdered elastomeric crumb rubber, by weight. Methylene diphenyl diisocyanate was used as the bonding adhesive to produce five particleboard samples, including a control board. Test samples were cut from the five parent boards for use in strength and acoustic testing. Measured displacement values for a simply loaded and simply supported load scenario were used to calculate the modulus of rupture and apparent modulus of elasticity for each composite particleboard. Acoustic measurement by impedance tube provided comparisons of the sound absorption coefficient for frequencies ranging from 60 to 6,300 Hz. Results revealed that the addition of micronized rubber powder led to a decrease in modulus of elasticity and no significant difference in modulus of rupture values as compared with the control. Statistical analysis indicated a decrease in sound absorption in particleboard that contained micronized rubber powder when compared with the control.

Changes to dentin extracellular matrix following treatment with plant-based polyphenols

This study investigated whether treatment with plant-based polyphenols (PB–P) affected the biochemical and/or biomechanical properties of dentin extracellular matrix (ECM). Three PB-Ps were evaluated: luteolin (LT), galangin (GL), and proanthocyanidin (PAC). Because dentin ECM requires demineralization before treatment, this study also assessed the effect of these PB-Ps on dentin demineralized by two different chemicals. Dentin samples from extracted third molars were obtained, sectioned, and randomly assigned for demineralization with either phosphoric acid (PA) or ethylenediaminetetraacetic acid (EDTA). Following demineralization, baseline infrared (IR) spectra and apparent elastic modulus (AE) of each specimen were independently acquired. Based upon these initial tests, samples were randomly assigned to one of the PB-P treatments to ensure that distribution of baseline AE was similar across treatment groups. IR and AE specimens were individually immersed in either 0.2% LT, 0.4% GL or 1% PAC for 2 min. IR spectra of treated samples were compared to baseline IR spectra, looking for any interaction of PB-Ps with the demineralized dentin. The IR spectrum and AE of each PB-P-treated specimen were compared with their own correspondent baseline measurement. The ability of PB-Ps to inhibit proteolytic activity of dentin ECM was assessed by the hydroxyproline assay. Finally, the effect of PB-Ps on immediate bond strength of a dental adhesive to PA- or EDTA-etched dentin was also evaluated. PB-Ps exhibited distinctively binding affinity to dentin ECM and promoted significant increase in AE. PB-P treatment reduced the degradation rate of dentin ECM without causing detrimental effect on immediate bond strength to dentin. Our work represents the first-time that LT and GL have been assessed as dentin ECM biomodifiers.

Extraction of microstructural parameters from sculptured thin films nanoindentation

This work deals with the indentation analysis of nanocolumnar thin films and the difficulties encountered to deduce relevant mechanical parameters by this methodology. SiO 2 thin films prepared by physical vapour oblique angle deposition with different nanocolumnar microstructures have been subjected to indentation analysis. Despite the fact that the films had been made of the same material, deposited on the same substrate and had similar thickness, their indentation responses were different and depended on their particular microstructure. It has been also reali s ed that the measured hardness and elastic modulus variation with the indentation depth were length scale dependent and that there is not a unique analytical thin-film nanoindentation model to extract the mechanical properties from the experimental nanoindentation curves. To overcome these limitations a numerical finite element model (FEM) of the nanocolumnar coatings has been built to figure out the contributions of the different physical phenomena intervening in the indentation process. This FEM simulation relies on a description of the elasto-plastic microstructural units of the coatings and the contact friction interactions between them. Based on this simulation a parametrical representation, incorporating two length scales and the contributions of densification and/or the buckling of nanocolumnar units, has been developed to account for the evolution of the apparent elastic modulus deduced from numerical indentation tests . A Hall-Petch modification of this description considering two length scales instead of the common approximation considering a single length scale has rendered the best agreement with the elastic values determined experimentally. Although, at the present stage, the particular microstructure of the films can not be deduced from the evolution of their elastic moduli with the indentation depth, the obtained results and their interpretation constitute a first though essential step for the elaboration of an inverse analysis methodology capable of correlating microstructure and elastic response of nanocolumnar coatings. • The indentation response of multi-layered PVOAD columnar coatings greatly depends on their microstructure. • Buckling but also densification drive the evolution of indentation elastic modulus and hardness with indentation depth. • FEM of a columnar structure under indentation allow s to reproduce the experimental response of multi-layered PVOAD coatings. • Size dependent model allows to extract length scale parameters from elastic response of PVOAD coatings.

Modulus characterization of cells with submicron colloidal probes by atomic force microscope.

Colloidal probes have been increasingly demanded for the characterization of cellular modulus in atomic force microscope because of their well-defined geometry and large contact area with cell. In this work, submicron colloidal probes are prepared by scanning electron microscope/focused ion beam and compared with sharp tip and micron colloidal probe, in conjunction with loading velocity and indentation depth on the apparent elastic modulus. NIM and cartilage cells are used as specimens. The results show that modulus value measured by sharp tip changes significantly with loading velocity while remains almost stable by colloidal probes. Also, submicron colloidal probe is superior in characterizing the modulus with increasing indentation depth, which could help reveal the mechanical details of cellular membrane and the modulus of the whole cell. To test the submicron colloidal probe further, the modulus distribution map of cell is scanned with submicron colloidal probe of 50 nm radius during small and large indentation depths with high spatial resolution. The outcome of this work will provide the effective submicron colloidal probe according to the effect of loading velocity and indentation depth, characterizing the mechanical properties of the cells.

High temperature mechanical behavior of low stiffness Al2TiO5 and Al2TiO5–3Al2O3.2SiO2–ZrTiO4 composite materials

AbstractThe mechanical behavior of low (and negative) thermal expansion and low stiffness Al2TiO5 materials and Al2TiO5–3Al2O3.2SiO2–ZrTiO4 composite materials was studied by diametral compression test at room temperature 400 and 800°C. The effect of both temperature and composition was analyzed. Stress–strain curves were obtained and, from them, apparent elastic modulus (Eapp) and mechanical strength (σF) were determined. Fracture mechanisms and fracture patterns were also analyzed. All materials showed a brittle behavior up to 800°C. The thermal variation of σF, that was even higher as testing temperature increased, was interpreted based on the microcracks behavior. A double linear correlation of Eapp was found with temperature (T) and zircon content ([Z]), with a fitting coefficient > .9. The particular low stiffness and the mechanical and thermal behavior of the studied materials suggest that they would be able to withstand thermal stresses.

Impact of EO chain length of dodecanol ethoxylates (C12En) on the rheological properties and physical stability of pesticide suspension concentrate

Rheological measurement can provide not only the shear-induced but also strain-induced microstructural changes, as well as transient network formation and subsequent recovery with time. It has been explored as a useful tool for probing the interparticle interactions which govern the physical stability of concentrated suspension. However, its application in pesticide formulation is rarely investigated. Herein, the rheological properties of 25% mancozeb suspension concentrate stabilized with nonionic surfactants dodecanol ethoxylates (C12En, n = 3, 7, 9, 15, 20) were studied. The steady-state shear measurement showed that all the 25% mancozeb suspension concentrate displayed shear-thinning flow. The experimental flow behavior followed prediction of Herschel–Bulkley model with the correlation coefficients greater than 0.99. Oscillatory shear measurements showed the viscoelastic response of 25% mancozeb suspension concentrate transformed from solid-like to gel-like viscoelasticity with the addition of C12En. As the EO chain length of C12En increased, the apparent viscosity and elastic modulus decreased initially, followed by an increase behavior. The thixotropic response of mancozeb formulations was evaluated by applying a three-step test. It turned out that the addition of C12En changed the mancozeb suspension concentrate from normal viscoelastic fluid to inelastic thixotropic material, and the recovery of viscosity gradually decreased as the EO chain length increased. Besides, the influence of C12En on suspension rate and particle size of 25% mancozeb suspension concentrate was investigated. The results showed that C12E9 performed best in improving the physical stability of the formulations before and after thermal storage. From SEM imagines of mancozeb particles, it was found that the aggregation was inhibited by C12E9, which was also responsible for the best dispersibility, minimum apparent viscosity and elastic modulus of 25% mancozeb suspension concentrate with the addition of C12E9.

The effect of different spices on the moisture content, texture characterizations and consumer preferences of roasted sunflower seeds

Roasting is an important process in the industry of nuts and seeds production. The aim of this study was the effect of different spices (red pepper, paprika, hibiscus tea, curry powder, sistani wrench, black plum peel puree, caraway, fennel, vegetables) on the moisture content, texture characterizations and sensory properties of roasted sunflower seed. The roasting process was performed under similar industrial conditions. Sholi (coating agents with spices (4 and 6%)) was prepared and added to the samples during the roasting process. The results showed the sample containing 4% vegetables had the highest hardness and penetration work, while, the sample with 6% hibiscus tea had the highest moisture content and the lowest elasticity. Furthermore, the sample contained 6% and 4% paprika had the highest elasticity and the lowest moisture content, respectively. Sensory properties of roasted sunflower seeds indicated that samples had moderate consumers’ total acceptance, maybe, due to the new color and flavor of samples. The fracture force, hardness, penetration work and apparent modulus of elasticity of roasted sunflower seeds were in the range of 11.94–37.71 N, 28.31–55.83 N, 55.45–98.37 N.s and 12.53–24.06 N/s, respectively. PLS analysis showed the results of total acceptance, sensory hardness and instrumental properties were in agreement with each other. The use of new flavors and colors in this research can increase factory sales and respond to different consumer preferences.

Wide-range control of impulse transmission by cylindrical shell chains with varying aspect ratios

The ability to control wave propagation for impulse transmission in a wide range is desired. A novel structure, i.e. a cylindrical shell chain with varying aspect ratio, was proposed to design new waveform control systems. The chains can offer superior control of elastic wave propagation, including waveform attenuation and amplification. Nonlinear wave propagation in the chains was studied numerically, analytically and experimentally. The wave propagation in the chain with a positive/negative aspect ratio gradient (aspect ratio increasing/decreasing along the loading direction) was examined. It is found that the chain with a positive aspect ratio gradient amplifies the forces in wave propagation due to the dramatic increase in the apparent elastic modulus along the impact direction, whereas the chain with a negative aspect ratio gradient shows the opposite. The theoretical results are consistent with the data obtained from the corresponding numerical simulations and experimental tests. The transmitted peak force increases with the aspect ratio distribution parameters. Compared with density gradient chains, the aspect ratio gradient chains proposed in this study could control the transmitted impulse in a wider range. This study can be helpful to improve the design of waveform control systems for amplifying/attenuating impact impulses.

Dense VSiCN coatings deposited by filament-assisted reactive magnetron sputtering with varying amorphous phase precursor flow rates

Phase-modulated VSiCN coatings were deposited with hot filament assistance by magnetron sputtering of a vanadium target in a gas mixture of argon, nitrogen, and hexamethyldisilazane (HMDS). HMDS flow conditions and total working pressure were varied to influence coating amorphous phase content (0 at.% ≤ Si ≤ 9 at.%). Scanning electron microscopy revealed that deposition with HMDS vapor disrupted columnar growth and increased coating growth rate by as much as 27% relative to a VN 0.8 reference. Coating surface morphologies were characterized by atomic force microscopy . A transition from a nodular appearance ( R q = 8.9 nm) for the VN 0.8 coating to a pitted appearance ( R q = 2.7 nm) for the coating containing 9 at.% Si was observed. X-ray diffraction analysis and transmission electron microscopy indicated that the VSiCN coatings contained a nanocrystalline B1-VC x N y phase and an amorphous phase, whose phase fraction increased with HMDS flow. The crystallographic out-of-plane preferred orientation of the VN 0.8 coating was (220) while all VSiCN coatings were (111) textured. Coating hardness and apparent elastic modulus were measured by nanoindentation . The VSiCN coating with 3 at.% Si exhibited the highest hardness of 31.4 GPa, which was 8.8 GPa greater than the VN 0.8 coating. Coating apparent elastic modulus decreased with increasing HMDS flow from 288 GPa to 188 GPa. All coatings exhibited excellent adhesion to stainless steel substrates as evaluated by the Rockwell indentation test . The disruption of columnar growth and incorporation of Si in VSiCN coatings is a possible method of improving the high temperature wear resistance of VN-based coatings. • Deposition of dense, non-columnar VSiCN coatings is demonstrated. • Hexamethyldisilazane (HMDS) vapor is used as an amorphous phase precursor. • Granular and pitted surface topographies are obtained with R q < 3 nm. • Coating preferred orientation is (220) for the VN 0.8 reference and (111) for VSiCN. • Hardness decreases from 31 GPa to 19 GPa with increasing amorphous phase content.

Structure-function relationships of the human vertebral endplate.

BackgroundAlthough deformation and fracture of the vertebral endplate have been implicated in spinal conditions such as vertebral fracture and disc degeneration, few biomechanical studies of this structure are available. The goal of this study was to quantify the mechanical behavior of the vertebral endplate.MethodsEight‐five rectangular specimens were dissected from the superior and/or inferior central endplates of human lumbar spine segments L1 to L4. Micro‐computed tomography (μCT) imaging, four‐point‐bend testing, and ashing were performed to quantify the apparent elastic modulus and yield stress (modulus and yield stress, respectively, of the porous vertebral endplate), tissue yield stress (yield stress of the tissue of the vertebral endplate, excluding pores), ultimate strain, fracture strain, bone volume fraction (BV/TV), bone mineral density (BMD), and various measures of tissue density and composition (tissue mineral density, ash fraction, and ash density). Regression was used to assess the dependence of mechanical properties on density and composition.ResultsWide variations in elastic and failure properties, and in density and tissue composition, were observed. BMD and BV/TV were good predictors of many of the apparent‐level mechanical properties, including modulus, yield stress, and in the case of the inferior vertebral endplate, failure strains. Similar values of the mechanical properties were noted between superior and inferior vertebral endplates. In contrast to the dependence of apparent stiffness and strength on BMD and BV/TV, none of the mechanical properties depended on any of the tissue‐level density measurements.ConclusionThe dependence of many of the mechanical properties of the vertebral endplate on BV/TV and BMD suggests possibilities for noninvasive assessment of how this region of the spine behaves during habitual and injurious loading. Further study of the nonmineral components of the endplate tissue is required to understand how the composition of this tissue may influence the overall mechanical behavior of the vertebral endplate.

Biomechanics of the Femoral Head Cartilage and Subchondral Trabecular Bone in Osteoporotic and Osteopenic Fractures

This study aimed to investigate the relationship between the micro structural properties of the subchondral trabecular bone (STB) and the macro mechanical properties of the articular cartilage (AC) in patients with osteoporotic (OP) and osteopenic (OPE) fractures. Sixteen femoral head samples (OP;OPE, n = 8 each) were obtained from female patients who underwent hip hemiarthroplasty. STB and AC specimens were harvested from those heads. Bone specimens were scanned using µ-CT to determine the micro structural properties. In-situ nondestructive compressive tests were performed for the cartilages to obtain elastic properties. The finite element technique was implemented on STB models created from µ-CT data to compute apparent elastic modulus. In addition, dynamic cyclic destructive tests were performed on STB and AC specimens to assess failure cycles. The results demonstrated that STB specimens in OPE group have more interconnected structure and higher cyclic dynamic strength than those in OP group. Furthermore, bone mineral density, failure cycle, and trabecular number of STB were positively correlated with the cartilage failure cycle, which indicates that STB alteration may affect the macroscopic mechanical properties of AC. The findings suggest that STB loss correlates with a decrease in cartilage strength and that improving of bone quality may prevent cartilage weakness.

Influence Study of the Plastic Deformation Mode on the Micro-Indentation Mechanical Properties for the Pure Molybdenum

Four different plastic deformation modes of pure molybdenum in powder metallurgy were studied, including single tensile, single torsion, tensile-torsion and compressive-torsion. Then the influence of these four plastic deformation modes on the micro-mechanical properties of pure molybdenum in powder metallurgy was studied by the micro-indentation method. The results show that the accumulated strain before deformation instability or fracture of the studied material caused by different plastic deformation modes is different, while showing a regular variation. And the mean indentation hardness along the radial direction of the sample also change regularly, which results in different strengthening effects on the molybdenum material itself. The damage inside the deformed material will cause the apparent modulus of elasticity measured by micro-indentation to decrease significantly.

Structural performance of hybrid Poplar-Beech cross-laminated-timber (CLT)

The purpose of this research was to investigate the structural out-of-plane bending performance of three-layer hybrid cross-laminated-timber manufactured from outer layers of fast-growing Poplar (Populus alba) and a cross-layer of Iranian Beech species (Fagus orientalism) using polyurethane as a binder. The bending performance of the hybrid CLT was determined in both major and minor axis orientations in diverse span-to-thickness ratios by experimental and theoretical methods. It was compared to that of Poplar CLT reported in our previous research. The experimental and theoretical methods indicated that the bending performances comprising maximum shear force (Vmax), maximum bending moment (Mmax), apparent modulus of elasticity (MOEapp), modulus of rupture (MOR), shear strength (τmax), effective bending stiffness (EIeff), and effective shear stiffness (GAeff) of hybrid Poplar-Beech CLT in all span-to-thickness ratios at both major and orientations were greater than those of Poplar CLT. Moreover, in both orientations, the results of bending and shear stress distributions of the specimens showed that the hybrid Poplar-Beech CLT had greater load-carrying capacity than Poplar CLT. However, in both orientations, the failure modes of hybrid CLT were similar to those of Poplar CLT. The experimental dominant failure modes in the major axis orientation of CLTs were rolling shear and delamination, while tensile failure and crack were mainly observed in the minor axis orientation. In summary, in comparison with Poplar CLT, both experimental and theoretical results revealed that hybrid Poplar-Beech CLT had more tremendous potential for structural bending performance in the construction and building sector.

Acousto-elasticity of transversely isotropic incompressible soft tissues: characterization of skeletal striated muscle

Using shear wave elastography, we measure the changes in the wave speed with the stress produced by a striated muscle during isometric voluntary contraction. To isolate the behaviour of an individual muscle from complementary or antagonistic actions of adjacent muscles, we select the flexor digiti minimi muscle, whose sole function is to extend the little finger. To link the wave speed to the stiffness, we develop an acousto-elastic theory for shear waves in homogeneous, transversely isotropic, incompressible solids subject to an uniaxial stress. We then provide measurements of the apparent shear elastic modulus along, and transversely to, the fibre axis for six healthy human volunteers of different age and sex. The results display a great variety across the six subjects. We find that the slope of the apparent shear elastic modulus along the fibre direction changes inversely to the maximum voluntary contraction (MVC) produced by the volunteer. We propose an interpretation of our results by introducing the S (slow) or F (fast) nature of the fibres, which harden the muscle differently and accordingly, produce different MVCs. A natural follow-up on this study is to apply the method to patients with musculoskeletal disorders or neurodegenerative diseases.

A Damage Model to Trabecular Bone and Similar Materials: Residual Resource, Effective Elasticity Modulus, and Effective Stress under Uniaxial Compression

Experimental research of bone strength remains costly and limited for ethical and technical reasons. Therefore, to predict the mechanical state of bone tissue, as well as similar materials, it is desirable to use computer technology and mathematical modeling. Yet, bone tissue as a bio-mechanical object with a hierarchical structure is difficult to analyze for strength and rigidity; therefore, empirical models are often used, the disadvantage of which is their limited application scope. The use of new analytical solutions overcomes the limitations of empirical models and significantly improves the way engineering problems are solved. Aim of the paper: the development of analytical solutions for computer models of the mechanical state of bone and similar materials. Object of research: a model of trabecular bone tissue as a quasi-brittle material under uniaxial compression (or tension). The new ideas of the fracture mechanics, as well as the methods of mathematical modeling and the biomechanics of bone tissues were used in the work. Compression and tension are considered as asymmetric mechanical states of the material. Results: a new nonlinear function that simulates both tension and compression is justified, analytical solutions for determining the effective and apparent elastic modulus are developed, the residual resource function and the damage function are justified, and the dependences of the initial and effective stresses on strain are obtained. Using the energy criterion, it is proven that the effective stress continuously increases both before and after the extremum point on the load-displacement plot. It is noted that the destruction of bone material is more likely at the inflection point of the load-displacement curve. The model adequacy is explained by the use of the energy criterion of material degradation. The results are consistent with the experimental data available in the literature.

Design and Mechanical Properties Verification of Gradient Voronoi Scaffold for Bone Tissue Engineering.

In order to obtain scaffold that can meet the therapeutic effect, researchers have carried out research on irregular porous structures. However, there are deficiencies in the design method of accurately controlling the apparent elastic modulus of the structure at present. Natural bone has a gradient porous structure. However, there are few studies on the mechanical property advantages of gradient bionic bone scaffold. In this paper, an improved method based on Voronoi-tessellation is proposed. The method can get controllable gradient scaffolds to fit the modulus of natural bone, and accurately control the apparent elastic modulus of porous structure, which is conducive to improving the stress shielding. To verify the designed structure can be fabricated by additive manufacturing, several designed models are obtained by SLM and EBM. Through finite element analysis (FEA), it is verified that the irregular porous structure based on Voronoi-tessellation is more stable than the traditional regular porous structure of the same structure volume, the same pore number and the same material. Furthermore, it is verified that the gradient irregular structure has a better stability than the non-gradient structure. An experiment is conducted successfully to verify the stability performance got by FEA. In addition, a dynamic impact FEA is also performed to simulate impact resistance. The result shows that the impact resistance of the regular porous structure, the irregular porous structure and the gradient irregular porous structure becomes better in turn. The mechanical property verification provides a theoretical basis for the structural design of gradient irregular porous bone tissue engineering scaffolds.

Evaluating a theoretical and an empirical model of “side effects” in cancellous bone

Accurate measurement of cancellous bone’s apparent elastic modulus, E, is confounded by the experimental artefacts created when trabeculae are severed during specimen preparation. Although standardized axial testing protocols have been developed to deal with the so-called “end effects” caused by severed trabeculae at the loading surfaces, much less attention has been given to the “side effects” around the periphery and the specimen size dependence they create. Two models (one theoretical, one empirical) have been proposed in the literature to predict the reduction in E with decreasing specimen diameter. The current study used finite element method (FEM) modelling to analyze bovine cancellous bone from five different anatomic sites and quantify the changes in E that occurred with specimen diameter. The two models were adapted so that they could predict E based on diameter and architectural parameters (BV/TV, DA, Tb.Sp) alone, without requiring that a “true” modulus be known a priori. Both models fit the data equally well; however, the empirical model gives simpler estimations as a function of trabecular separation (Tb.Sp). A minimum diameter of 5–8 Tb.Sp is recommended.

Effect of hydrophobic association on the flow resistance of polymer solutions

Comprehending the percolation law of polymer solutions in porous media is the basis of effective application of polymer flooding. The solution properties of partially hydrolyzed polyacrylamide (HPAM) and the hydrophobically associating polymer AP-P4 were compared, and the seepage characteristics in porous media were studied. The results showed that HPAM is a viscoelastic fluid dominated by a viscosity modulus. The smaller hydrodynamic size (≥3 µm) and low adsorption capacity (200 µg/g) caused an increase in the resistance factor of HPAM in porous media with the increase in injection velocity. Hydrophobic association greatly improved the solution properties of the polymer, with a stronger apparent viscosity, elastic modulus, hydrodynamic size (≥10 µm), and adsorption capacity (780 µg/g), showing that the viscoelastic fluid properties were dominated by the elastic modulus. The resistance factor of the polymer solution in porous media decreased with the increase in injection velocity.

Unveiling a Hidden Event in Fluorescence Correlative Microscopy by AFM Nanomechanical Analysis.

Fluorescent imaging combined with atomic force microscopy (AFM), namely AFM-fluorescence correlative microscopy, is a popular technology in life science. However, the influence of involved fluorophores on obtained mechanical information is normally underestimated, and such subtle changes are still challenging to detect. Herein, we combined AFM with laser light excitation to perform a mechanical quantitative analysis of a model membrane system labeled with a commonly used fluorophore. Mechanical quantification was additionally validated by finite element simulations. Upon staining, we noticed fluorophores forming a diffuse weakly organized overlayer on phospholipid supported membrane, easily detected by AFM mechanics. The laser was found to cause a degradation of mechanical stability of the membrane synergically with presence of fluorophore. In particular, a 30 min laser irradiation, with intensity similar to that in typical confocal scanning microscopy experiment, was found to result in a ∼40% decrease in the breakthrough force of the stained phospholipid bilayer along with a ∼30% reduction in its apparent elastic modulus. The findings highlight the significance of analytical power provided by AFM, which will allow us to “see” the “unseen” in correlative microscopy, as well as the necessity to consider photothermal effects when using fluorescent dyes to investigate, for example, the deformability and permeability of phospholipid membranes.

The pursuit of resin-dentin bond durability: Simultaneous enhancement of collagen structure and polymer network formation in hybrid layers

ObjectiveImperfect polymer formation as well as collagen’s susceptibility to enzymatic degradation increase the vulnerability of hybrid layers over time. This study investigated the effect of new dimethyl sulfoxide (DMSO)-containing pretreatments on long-term bond strength, hybrid layer quality, monomer conversion and collagen structure. MethodsH3PO4-etched mid-coronal dentin surfaces from extracted human molars (n = 8) were randomly treated with aqueous and ethanolic DMSO solutions or following the ethanol-wet bonding technique. Dentin bonding was performed with a three-step etch-and-rinse adhesive. Resin-dentin beams (0.8 mm2) were stored in artificial saliva at 37 °C for 24 h and 2.5 years, submitted to microtensile bond strength testing at 0.5 mm/min and semi-quantitative SEM nanoleakage analysis (n = 8). Micro-Raman spectroscopy was used to determine the degree of conversion at different depths in the hybrid layer (n = 6). Changes in the apparent modulus of elasticity of demineralized collagen beams measuring 0.5 × 1.7 × 7 mm (n = 10) and loss of dry mass (n = 10) after 30 days were calculated via three-point bending and precision weighing, respectively. ResultsDMSO-containing pretreatments produced higher bond strengths, which did not change significantly over time presenting lower incidence of water-filled zones. Higher uniformity in monomer conversion across the hybrid layer occurred for all pretreatments. DMSO-induced collagen stiffening was reversible in water, but with lower peptide solubilization. SignificanceImproved polymer formation and higher stability of the collagen-structure can be attributed to DMSO’s unique ability to simultaneously modify both biological and resin components within the hybrid layer. Pretreatments composed of DMSO/ethanol may be a viable-effective alternative to extend the longevity of resin-dentin bonds.