Range Of Elastic Moduli Research Articles

Structure, tensile properties and cytotoxicity assessment of sebacic acid based biodegradable polyesters with ricinoleic acid.

A new family of ricinoleic acid based polyesters was synthesized using catalyst free melt-condensation polymerization with sebacic acid, citric acid, mannitol and ricinoleic acid as precursors. The use of FT-IR and NMR characterisation techniques confirms the presence of ester linkages in the as-synthesized polymers. Depending on the precursor combination, their relative amount and the degree of curing, a broad range of elastic modulus (22-327 MPa) and tensile strength (0.7-12.7 MPa) can be obtained in the newly synthesized biopolymers. The polymers show rubbery behaviour at a physiological temperature (37 °C) and the contact angles of the synthesized polymers fall in the range of 42° to 71°, making them ideal substrates to study delivery of drugs through polymer scaffolds. The cytocompatibility assessment of the cured polymers confirmed good cell attachment and growth of smooth muscle cells (C2C12 myoblast cells). Importantly, oriented cell growth was observed after culturing myoblast cells for 3 days. The in vitro degradation in PBS indicates that the mild cured polymers follow a first order reaction kinetics and have degradation rate constants in the range of 0.009-0.038 h-1, depending on the relative proportions of monomers. Overall, the results of our study indicate that the physical properties can be tailored by varying the composition of the monomers and curing conditions in the newly developed polyesters. Hence, they may be used as potential substrates for tissue engineering scaffolds and for localized drug delivery.

On the Stress Singularities at Clamped Butt Joints

This note considers two elastic quarter-planes perfectly bonded together on their common boundary and clamped on their other boundaries. Asymptotic analysis of the stresses in the corners of the quarter-planes identifies the power singularities present for a full range of elastic moduli. Configurations with nonsingular stresses at this juncture are also identified. These last results offer some means for removing stress singularities from clamped butt joints by perturbing elastic moduli.

Gradient polymeric materials: Part 2. structure and properties

Data on the synthesis and study of gradient polymeric materials obtained over the last decade are summarized. The review begins with a short description of works that reported the first data on gradient materials. The following chapters deal with a detailed account of principle for preparing gradient materials of new type that provide extremely wide range of elastic modulus continuously varying in the prescribed direction. Gradient materials derived from poly(urethane-isocyanurate) net-works and their use to prepare films with elastic modulus gradient with depth are considered. A separate chapter is dedicated to composite gradient materials processed by hot molding. The one-step synthesis of poly(urethane-isocyanurate) networks and gradient materials based on poly(urethaneisocyanurate)s combined with polyurethane networks is described. Polyurethane networks and opportunities to control and vary elastic modulus in gradient materials are considered. Gradient polymers and composites constructed from poly(epoxy-isocyanurate) matrices reinforced with carbon cloth or aramid fabric are considered in detail.

Optimizing siRNA efficacy through alteration in the target cell-adhesion substrate interaction.

The clinical potential of short interfering RNA (siRNA) based therapeutics remains hindered by the challenge of delivering enough siRNA into the cytoplasm to yield a clinically relevant effect. Although much research has focused on optimizing delivery vehicles for this class of molecules, considerably less is known about the microenvironmental influences on the response of target cells to siRNA. The substrate to which cells adhere is one component of the microenvironment that can modulate cellular behavior. Here, we tested the hypothesis that modulating the properties of cellular adhesion substrates can alter siRNA efficacy. Specifically, cationic lipid complexed siRNA particles were applied to U251 cells seeded on alginate hydrogel surfaces with systematic variation in elastic modulus and integrin ligand arginine-glycine-aspartate (RGD) peptide density. These experiments revealed no change in siRNA-mediated eGFP knockdown over the elastic modulus range tested (53-133 kPa). However, an eightfold increase in RGD content of the alginate growth substrate resulted in an increase in siRNA knockdown efficacy from 25 ± 12% to 52 ± 10%, a more than twofold increase in silencing. Our results identify control of the cell-adhesion substrate interaction as a modulator of siRNA protein silencing efficacy.

The potential of magnesium alloy use in orthopaedic surgery

Magnesium alloy use for orthopaedic applications has been ongoing since the early 1900s. Magnesium is a lightweight metal; with a density of 1.74 g/cm3, it is less dense than aluminum and steel and has a greater fracture toughness than ceramics or hydroxyapatite. Initial problems with the use of magnesium included the undesirable development of hydrogen gases. Newer generation magnesium alloys with more optimal mechanical properties have made use of this metal attractive in orthopaedics. Magnesium alloys provide optimal stability while degrading with no reported inflammatory reactions. The mechanical stiffness and elastic modulus of steel, titanium, and cobalt-chrome are not well suited for placement in human bone, and can result in stress shielding and lack of bone formation. The range of elastic moduli for magnesium alloys is closer to that for human bone, making the stiffness of magnesium alloys more compatible with bone. Magnesium alloy use in animal models has demonstrated efficacy in degradation in vivo and new bone formation for bone implant application. Use of magnesium alloys has a decreased risk of patient morbidity and infection and a reduced cost because a second procedure is not necessary to remove the implant. These advantages give magnesium alloys promise for increased use in modern day orthopaedics. The future of magnesium alloys for use in orthopaedics will involve enhanced basic science studies that translate to clinical orthopaedic practice.

Total Internal Reflection Fluorescence Microscopy, Cell Adhesion, and Cell Traction Force Measurements on Soft Silicone Gels

Substrate rigidity impacts cellular behaviors such as migration, gene expression, and cell fate. Total Internal Reflection Fluorescence (TIRF) microscopy enables selective visualization of the dynamics of substrate adhesions, vesicle trafficking, and biochemical signaling at the cell-substrate interface. Here we apply high-refractive-index silicone gels to perform TIRF microscopy on substrates with a wide range of physiological elastic moduli, measure traction forces exerted by cells on the substrate, and perform analysis of the cell spreading and the biochemical signaling that drives this process. We successfully implemented TIRF on mouse endothelial cells plated on ∼30 micron thick layers of silicone gels with a refractive index of 1.49 and obtained high quality images. We also functionalized gel surfaces and covalently bound to them 40nm far-red fluorescent beads that were distributed nearly evenly with a high surface density. Measurements of displacements of the beads under cell traction forces made it possible to obtain high-resolution substrate deformation maps that were converted to traction force maps. We show mouse embryonic fibroblasts (MEFs) spreading over a significantly larger area on silicone gels of moderate physiological stiffness, 30 kPa, versus those grown on softer substrates of 0.5 and 3.5 kPa, in agreement with cells grown on polyacrylamide substrates of similar stiffness. We developed a novel microfluidic technique to measure the elastic moduli of thin gel layers and applied it to characterizing gels made using Sylgard 184 silicone with elastic moduli from 0.4 to 300 kPa. We prepared gel substrates with elastic moduli covering nearly the entire physiological range in different wells of a 6-well plate. Western-blot analysis of harvested cells revealed varying levels of phosphorylated Focal Adhesion Kinase (FAK) in MEFs grown on silicone gels with different elastic moduli.

Nonlinear Mechanical Behavior of The Human Common, External, and Internal Carotid Arteries In Vivo

The mechanical environment and properties of the carotid artery play an important role in the formation and progression of atherosclerosis in the carotid bifurcation. The purpose of this work was to measure and compare the range and variation of circumferential stress and tangent elastic moduli in the human common (CCA), external (ECA), and internal (ICA) carotid arteries over the cardiac cycle in vivo. Measurements were performed in the surgically exposed proximal cervical CCA, distal ECA, and distal ICA of normotensive patients (n = 16) undergoing carotid endarterectomy. All measurements were completed in vivo over the cardiac cycle in the repaired carotid bifurcation after the atherosclerotic plaque was successfully removed. B-mode Duplex ultrasonography was used for measurement of arterial diameter and wall thickness, and an angiocatheter placed in the CCA was used for concurrent measurement of blood pressure. A semiautomatic segmentation algorithm was used to track changes in arterial diameter and wall thickness in response to blood pressure. These measurements were then used to calculate the variation of circumferential (hoop) stresses, tangent elastic moduli (the slope of the stress-strain curve at specified stresses), and strain-induced stiffness of the arterial wall (stiffening in response to the increase of intraluminal blood pressure) for each patient. The diameter and wall thickness of the segments (CCA, ECA, and ICA) of the carotid bifurcation were found to decrease and strain-induced stiffness to increase from proximal CCA to distal ECA and ICA. The circumferential stress from end-diastole (minimum pressure) to peak-systole (maximum pressure) varied nonlinearly from 25 ± 7 to 63 ± 23 kPa (CCA), from 22 ± 7 to 57 ± 19 kPa (ECA), and from 28 ± 8 to 67 ± 23 kPa (ICA). Tangent elastic moduli also varied nonlinearly from end-diastole to peak-systole as follows: from 0.40 ± 0.25 to 1.50 ± 2.05 MPa (CCA), from 0.49 ± 0.34 to 1.14 ± 0.52 MPa (ECA), and from 0.68 ± 0.31 to 1.51 ± 0.69 MPa (ICA). The strain-induced stiffness of CCA and ECA increased more than 3-fold and the stiffness of ICA increased more than 2.5-fold at peak-systole compared with end-diastole. The in vivo mechanical behavior of the three segments of the carotid bifurcation was qualitatively similar, but quantitatively different. All three arteries--CCA, ECA and ICA--exhibited nonlinear variations of circumferential stress and tangent elastic moduli within the normal pressure range. The variability in the properties of the three segments of the carotid bifurcation indicates a need for development of carotid models that match the in vivo properties of the carotid segments. Finally, the observed nonlinear behavior of the artery points to the need for future vascular mechanical studies to evaluate the mechanical factors of the arterial wall over the entire cardiac cycle.

High Refractive Index Silicone Gels for Simultaneous Total Internal Reflection Fluorescence and Traction Force Microscopy of Adherent Cells

Substrate rigidity profoundly impacts cellular behaviors such as migration, gene expression, and cell fate. Total Internal Reflection Fluorescence (TIRF) microscopy enables selective visualization of the dynamics of substrate adhesions, vesicle trafficking, and biochemical signaling at the cell-substrate interface. Here we apply high-refractive-index silicone gels to perform TIRF microscopy on substrates with a wide range of physiological elastic moduli and simultaneously measure traction forces exerted by cells on the substrate.

Determining a Suitable Material to Simulate the Tympanic Membrane Based on Quantitative Linear Elasticity

Objective: Find a material to simulate the quantitative, as well as qualitative, qualities of the tension and compliance of a tympanic membrane based on published values of the elastic modulus for a tympanic membrane. Method: Prospective study that took place from August to December 2009. Using the Instron Testing Instrument, an elastic modulus was calculated for various materials. Based on these values, 3 materials were chosen. Seven physicians performed a myringotomy and completed a survey to rank subjective qualities of the materials. Results: Nitrile gloves, Kimwipes, and laboratory stretch film all had an elastic modulus that fell within the previously published range of the tympanic membrane elastic modulus and were chosen to undergo further evaluation. Kimwipes scored the highest in terms of compliance, tension, and texture compared with an actual TM during blunt palpation. Nitrile gloves scored the highest in terms of compliance, tension, and texture while making the myringotomy incision. Nitrile gloves scored best when comparing how the incision split open, responded to suction, and felt during introduction of the PE tube. Overall Nitrile gloves scored the highest. Conclusion: As competency-based teaching and evaluation becomes a bigger part of resident-training, the utility of training models will also likely become more widespread. Nitrile gloves represent a material that is inexpensive, is widely available, and displays a quantitative and qualitative linear elasticity similar to that of a true tympanic membrane.

Modulating Biofunctional starPEG Heparin Hydrogels by Varying Size and Ratio of the Constituents

Heparin and four-armed, end-functionalized polyethylene glycol (starPEG) were recently combined in sets of covalently linked biohybrid hydrogel networks capable of directing various therapeutically relevant cell types. To extend the variability and applicability of this novel biomaterials platform, the influence of size and molar ratio of the two building blocks on the hydrogel properties was investigated in the present study. Heparin and starPEG were converted in various molar ratios and in different molecular weights to tune swelling, stiffness and pore size of the obtained polymer networks. Hydrogels with a range of elastic moduli could be generated by controlling either the crosslinking density or the chain length of the starPEG, whereas altering the molecular mass of heparin did not significantly affect hydrogel strength. The concentration of heparin in the swollen gels was found to be nearly invariant at varying crosslinking degrees for any given set of building blocks but adjustable by the size of the building blocks. Since heparin is the base for all biofunctionalization schemes of the gels these findings lay the ground for an even more versatile customization of this powerful new class of biomaterials.

Fluid-structure interaction analysis on the effects of vessel material properties on blood flow characteristics in stenosed arteries under axial rotation

We conducted blood flow analysis, using the Fluid-Structure Interaction (FSI) method, to examine how changes in the material properties of blood vessels affect blood flow characteristics, using the carotid artery as the model vessel. The geometry of the blood vessel included 50% stenosis at the center, and blood was modeled as a non-Newtonian fluid. In order to investigate the effects of vessel material properties, linear elastic models with 0.21 MPa, 0.51 MPa, and 1.25 MPa, which are within the typical elastic modulus range of the carotid artery, were used to simulate the blood vessel, and these were compared with the rigid body model. The difference in blood vessel elasticity caused periodic and transient changes in blood flow. The more elastic the blood vessel becomes, the longer the periods of velocity, pressure, and Wall Shear Stress (WSS) change and the smaller the size of the Fluid Recirculation Zone (FRZ). Also, transient changes in blood flow occurred due to the accumulation of differences in flow caused by vessel wall deformation. This is because a change in the stiffness of the vessel wall causes the vessel’s vibration period to change, leading to changes in blood flow.

STUDY OF MECHANICAL BEHAVIOR OF A SEBS BLEND FOR INJECTION MOLDING

This study focuses on a blend from the provider's SEBS extreme hardness (50% Shore-A 5 and 50% Shore-A 90) in order to analyze the miscibility of mixed materials from the storage of 2 references only. It has been used the thermoplastic elastomer Megol TA® SEBS, whose characteristics make it special due to the wide range of hardness and transparency. First step is injection of the extreme hardness virgin materials from the provider and the blend in a relation 50%-50% Next step is mechanical characterization of the blend, analyzing hardness, elongation at break and tensile strength. Finally, results are compared with original values of the materials incorporated. 1. INTRODUCTION. Styrene - ethylene - butadiene - styrene (SEBS) is a thermoplastic material which combines successfully the properties of an elastomer (rubber) with low costs of processing thermoplastics. Excellent resistance to aging of all compounds based on SEBS and flexibility in the formulation of the polymer allow the production of wide ranges of hardness for different applications in industry. It is remarkable its range of hardness and elastic modulus, excellent resistance to aging, very good processability at low temperatures and resistant to high temperatures. Injection molding is one of the different manufacturing processes that use this type of material, which is of great importance for the quantity of products that are made daily. The main objective of this study is the mechanical characterization of a blend from the provider's SEBS extreme hardness (50% Shore-A 5 and 50% Shore-A 90) in order to analyze the miscibility of mixed materials from the storage of 2 references only.

Alteration of dentin–enamel mechanical properties due to dental whitening treatments

The mechanical properties of dentin and enamel affect the reliability and wear properties of a tooth. This study investigated the influence of clinical dental treatments and procedures, such as whitening treatments or etching prior to restorative procedures. Both autoclaved and non-autoclaved teeth were studied in order to allow for both comparison with published values and improved clinical relevance. Nanoindentation analysis with the Oliver–Pharr model provided elastic modulus and hardness across the dentin–enamel junction (DEJ). Large increases were observed in the elastic modulus of enamel in teeth that had been autoclaved (52.0 GPa versus 113.4 GPa), while smaller increases were observed in the dentin (17.9 GPa versus 27.9 GPa). Likewise, there was an increase in the hardness of enamel (2.0 GPa versus 4.3 GPa) and dentin (0.5 GPa versus 0.7 GPa) with autoclaving. These changes suggested that the range of elastic modulus and hardness values previously reported in the literature may be partially due to the sterilization procedures. Treatment of the exterior of non-autoclaved teeth with Crest Whitestrips™, Opalescence™ or UltraEtch™ caused changes in the mechanical properties of both the enamel and dentin. Those treated with Crest Whitestrips™ showed a reduction in the elastic modulus of enamel (55.3 GPa to 32.7 GPa) and increase in the elastic modulus of dentin (17.2 GPa to 24.3 GPa). Opalescence™ treatments did not significantly affect the enamel properties, but did result in a decrease in the modulus of dentin (18.5 GPa to 15.1 GPa). Additionally, as expected, UltraEtch™ treatment decreased the modulus and hardness of enamel (48.7 GPa to 38.0 GPa and 1.9 GPa to 1.5 GPa, respectively) and dentin (21.4 GPa to 15.0 GPa and 1.9 GPa to 1.5 GPa, respectively). Changes in the mechanical properties were linked to altered protein concentration within the tooth, as evidenced by fluorescence microscopy and Fourier transform infrared spectroscopy.

Elastic modulus of low-k dielectric thin films measured by load-dependent contact-resonance atomic force microscopy

Correlated force and contact resonance versus displacement responses have been resolved using load-dependent contact-resonance atomic force microscopy (AFM) to determine the elastic modulus of low-k dielectric thin films. The measurements consisted of recording simultaneously both the deflection and resonance frequency shift of an AFM cantilever probe as the probe was gradually brought in and out of contact. As the applied forces were restricted to the range of adhesive forces, low-k dielectric films of elastic modulus varying from GPa to hundreds of GPa were measurable in this investigation. Over this elastic modulus range, the reliability of load-dependent contact-resonance AFM measurements was confirmed by comparing these results with those from picosecond laser acoustic measurements.

A measurement of elastic moduli for tungsten films on polymer substrate using wrinkling analysis

The elastic moduli of ultra thin tungsten (W) films on polymers were assessed with wrinkling analysis. Thin W films with a range of thickness between 17 and 100 nm were deposited on compliant polymers and Si strips using DC magnetron sputtering method, causing the tensile stress in a few GPa scale with respect to the thickness of W films. By applying lateral compression on polymer, wrinkle patterns were developed in the W thin film with well-defined amplitude and wavelength. Using a simple equation on wrinkle analysis, the range of elastic moduli was estimated with increasing the thickness. It was found that the elastic modulus and the tensile stress decreased with increasing the film thickness.

Nanobiomechanics of Repair Bone Regenerated by Genetically Modified Mesenchymal Stem Cells

Genetically modified mesenchymal stem cells (MSCs), overexpressing a BMP gene, have been previously shown to be potent inducers of bone regeneration. However, little was known of the chemical and intrinsic nanomechanical properties of this engineered bone. A previous study utilizing microcomputed tomography, back-scattered electron microscopy, energy-dispersive X-ray, nanoindentation, and atomic force microscopy showed that engineered ectopic bone, although similar in chemical composition and topography, demonstrated an elastic modulus range (14.6-22.1 GPa) that was less than that of the native bone (16.6-38.5 GPa). We hypothesized that these results were obtained due to the specific conditions that exist in an intramuscular ectopic implantation site. Here, we implanted MSCs overexpressing BMP-2 gene in an orthotopic site, a nonunion radial bone defect, in mice. The regenerated bone tissue was analyzed using the same methods previously utilized. The samples revealed high similarity between the engineered and native radii in chemical structure and elemental composition. In contrast to the previous study, nanoindentation data showed that, in general, the native bone exhibited a statistically similar elastic modulus values compared to that of the engineered bone, while the hardness was found to be marginally statistically different at 1000 muN and statistically similar at 7000 muN. We hypothesize that external loading, osteogenic cytokines and osteoprogenitors that exist in a fracture site could enhance the maturation of engineered bone derived from BMP-modified MSCs. Further studies should determine whether longer duration periods postimplantation would lead to increased bone adaptation.

Elastic properties of amorphous boron suboxide based solids studied using ab initiomolecular dynamics

We have studied the correlation between chemical composition,structure, chemical bonding and elastic properties of amorphousB6O based solids using ab initio molecular dynamics. These solids are of different chemicalcompositions, but the elasticity data appear to be a function of density. This is inagreement with previous experimental observations. As the density increases from 1.64 to2.38 g cm−3, the elastic modulus increases from 74 to 253 GPa. This may be understood by analyzing thecohesive energy and the chemical bonding of these compounds. The cohesive energy decreases from−7.051 to−7.584 eV/atom in the elastic modulus range studied. On the basis of the electron density distributions,Mulliken analysis and radial distribution functions, icosahedral bonding is the dominatingbonding type. C and N promote cross-linking of icosahedra and thus increase the density,while H hinders the cross-linking by forming OH groups. The presence of icosahedralbonding is independent of the density.

Effect of material properties of the eyeball coat on optical image stability

The dynamics of the eyeball, most notably the changes in intraocular pressure, need to be stabilized optically to prevent noticeable changes in image quality. This control depends on the rheological properties of the eyeball coats and how the elasticity of the cornea, sclera, and limbus vary relative to one another. Nonlinear finite element modeling shows that image quality can be preserved over a range of elastic moduli. For intraocular pressure variations from 8 to 40 mm Hg, optical image stability is best for an elastic secant modulus of the cornea of 0.267 MPa. Optimal quality is achieved when the elastic moduli of the limbus and sclera are, respectively, 3.6 and 4 times that of the corneal modulus.

Self-Propagating High-Temperature Synthesis of Porous Nickel-Titanium

Porous equiatomic Nickel-Titanium (NiTi) is a strong candidate material for bone engineering applications because its mechanical properties are within the range of bone and its porosity allows for biologic interlock of the material to the surrounding tissue. Self-propagating high-temperature synthesis (SHS) is one method for producing porous NiTi. Nickel and titanium powders, -325 mesh, were mixed for 24 hours then pressed into cylindrical pellets (0.5 inch diameter, 0.5 inch height) to a theoretical green density of approximately 53%. The pellets were preheated in flowing argon for one hour then ignited using a tungsten coil. Scanning electron microscopy and electron dispersive spectroscopy (EDS) show localized differences of stoichiometry suggesting variations in the crystal structure where the Ni to Ti atomic ratio varied between 48.5:51.5 and 50.7:49.3. X-ray diffraction (XRD) (Philips X’Pert PRO) confirmed the presence crystalline equiatomic NiTi as well as other intermetallic compounds including NiTi2 and Ni4Ti3. Nanoindentation (MTS Nano Indenter XP) of this heterogeneous material indicates a mean range indentation modulus of 89.6 ± 9.4 GPa. This is on the same order of magnitude as bone, which has an elastic modulus range of 14-20 GPa.

An experimental research on the fluidity and mechanical properties of high-strength lightweight self-compacting concrete

This paper evaluates the high-strength lightweight self-compacting concrete (HLSCC) manufactured by Nan-Su, of which the main factor PF of its design mixing method has been modified and improved. The study analyzes HLSCC performance at its fresh condition as well as its mechanical properties at the hardened condition. The evaluation of HLSCC fluidity has been conducted per the standard of second class rating of JSCE, by three categories of flowability, segregation resistance ability and filling ability of fresh concrete. For the mechanical properties of HLSCC, the study has been conducted as follows: compressive strength with elapsed age, splitting tensile strength, elastic moduli and density, all at its cured after 28 days. As a result, HLSCC at its fresh condition has been rated as less than LC 75% and LF 50% for the mix ratio of lightweight aggregate, thus satisfying the second class standard of JSCE. The compressive strength of HLSCC at 28 days has come out to more than 40 MPa in all mix except the case with LC 100%, while the structural efficiency in relation to its density tended to increase proportionally as the mixing ratio of LF increases. The relationship between the splitting tensile and compressive strength has been calculated as f s=0.076 f ck+0.5582. The range of elastic moduli has come out as 24–33 GPa, comparably lower than the control concrete. Compressive strength and structural efficiency of HLSCC at 28 days from the multiple regression analysis resulted as f c=−0.07619LC A+0.08648LF B+46.714 and f se=−0.00436LC A+0.0627LF B+20.257, respectively.