Bulk Compression Modulus Research Articles

Bottom-Up Extrusion-Based Biofabrication of the Osteoid Niche.

Bone regeneration remains a clinical challenge given the transplantation incidence rate and the associated economic burden. Bottom-up osteoid tissue engineering has the potential to offer an alternative approach to current clinical solutions that suffer from various drawbacks. In this paper, deposition-based bioprinting is exploited while the effect is explored of both the crosslinking mechanism (gelatin methacryloyl (GelMA) versus gelatin norbornene (DS 91) crosslinked with thiolated gelatin (GelNBSH)) and the degree of substitution (GelNBSH versus norbornene-norbornene-modified gelatin (DS 169) crosslinked with thiolated gelatin (GelNBNBSH)) on the presented biophysical cues as well as on the osteogenic differentiation. The incorporation of tris(2-carboxyethyl)phosphine (TCEP) to the step-growth inks allows the production of reproducible and biocompatible scaffolds based on thiol-ene chemistry. Dental pulp stem cell encapsulation in GelNBNBSH biofabricated constructs shows a favorable response due to the combination of its stress relaxation and substrate rigidity (bulk compressive modulus of 11-30kPa) as reflected by a sevenfold increase in calcium production compared to the tissue engineering standard GelMA. This work is the first to exploit a controlled biocompatible and cell-interactive thiolated macromolecular crosslinker (GelSH + TCEP) allowing the extrusion-based biofabrication of low concentration (5 w/v%) modified osteogenic gelatin-based inks (GelNBNBSH + TCEP).

2D fibrillar osteoid niche mimicry through inclusion of visco-elastic and topographical cues in gelatin-based networks

Given the clinical need for osteoregenerative materials incorporating controlled biomimetic and biophysical cues, a novel highly-substituted norbornene-modified gelatin was developed enabling thiol-ene crosslinking exploiting thiolated gelatin as cell-interactive crosslinker. Comparing the number of physical crosslinks, the degree of hydrolytic degradation upon modification, the network density and the chemical crosslinking type, the osteogenic effect of visco-elastic and topographical properties was evaluated. This novel network outperformed conventional gelatin-based networks in terms of osteogenesis induction, as evidenced in 2D dental pulp stem cell seeding assays, resulting from the presentation of both a local (substrate elasticity, 25–40 kPa) and a bulk (compressive modulus, 25–45 kPa) osteogenic substrate modulus in combination with adequate fibrillar cell adhesion spacing to optimally transfer traction forces from the fibrillar ECM (as evidenced by mesh size determination with the rubber elasticity theory) and resulting in a 1.7-fold increase in calcium production (compared to the gold standard gelatin methacryloyl (GelMA)).

Thermodynamic Properties and Equation of State for Tungsten

A high-temperature equation of state for tungsten was constructed in this study using experimental data on its thermodynamic properties, thermal expansion, compressibility, and bulk compression modulus. The totality of experimental data were optimized by the temperature-dependent Tait equation over a pressure range from 0 up to 1000 kbar and over a temperature range from 20 K to the melting point. An extended Einstein model was used to describe the temperature dependence of thermodynamic and thermophysical parameters. A linear temperature dependence was embraced for the derivative of the isothermal bulk modulus. The resultant equation of state provides a good fit to the whole set of experimental data within measurement uncertainties associated with individual quantities.

Scaling to zero of compressive modulus in disordered isostatic cubic networks.

Networks with as many mechanical constraints as degrees of freedom and no redundant constraints are minimally rigid or isostatic. Isostatic networks are relevant in the study of network glasses, soft matter, and sphere packings. Because of being at the verge of mechanical collapse, they have anomalous elastic and dynamical properties not found in the more commonly occurring hyperstatic networks. In particular, while hyperstatic networks are only slightly affected by geometric disorder, the elastic properties of isostatic networks are dramatically altered by it. In this paper, we show how disorder and system size strongly affect the ability of isostatic networks to sustain a compressive load. We develop an analytic method to calculate the bulk compressive modulus B for various boundary conditions as a function of disorder strength and system size. For simplicity, we consider square and cubic lattices with L^{d} sites, each having d mechanical degrees of freedom, and dL^{d} rotatable springs in the presence of hot-solid disorder of magnitude ε. Additionally, ∼L^{θ} sites may be fixed, thus introducing a nonextensive number of redundancies, either in the bulk or on the boundaries of the system. In all cases, B is analytically and numerically shown to decay as L^{-μ} with μ_{large}=d-θ for large disorder and μ_{small}=max{(d-θ-1),0} for small disorder. Furthermore B(L,ε)L^{μ_{small}}=g(λ) with λ=L^{(μ_{large}-μ_{small})}ε^{2} a scaling variable such that λ<<1 is small disorder and λ>1 is large disorder. The faster decay to zero of B in the large disorder regime results from a broad distribution of spring tensions, including tensions of both signs in equal proportions, which is remarkable since the system is under a purely compressive load. Notably, the bulk modulus is discontinuous at ε=0, a consequence of the fact that the regular network sits at an unstable degenerate configuration.

Pluronic-based lamellar phases: influence of polymer architecture on bilayer bending elasticity

ABSTRACT In this study, we investigate the influence of the block copolymer architecture on the bending elasticity of polymer-rich lamellar phases. In detail, we study the polymer-rich system water/o-xylene/Pluronic triblock copolymer/CTAB and change the polymer while keeping the mass ratios constant. We use neutron spin echo measurements (NSE) to determine κ. With the measurements we determine the relaxation rate of the bilayer bending mode and subsequently calculate the bilayer bending modulus κ using the Zilman-Granek approach [Zilman et al., Phys. Rev. Lett. 77, 4788–4791 (1996)]. Moreover, we have investigated the lamellar phases via small-angle X-ray scattering (SAXS) and have analysed the data with the modified Caillé theory to obtain the Caillé parameter η. Based on κ the bulk compression modulus can be calculated. Increasing values of κ are found with increasing EO and PO block size in the range of 3.8 to 13.4 T. The computed values of are in the range of 10 to 10 Pa.

Compression and swelling of hydrogels in polymer solutions: A dominant-mode model.

The swelling and compression of hydrogels in polymer solutions can be understood by considering hydrogel-osmolyte-solvent interactions which determine the osmotic pressure difference between the inside and the outside of a hydrogel particle and the changes in effective solvent quality for the hydrogel network. Using the theory of poroelasticity, we find the exact solution to hydrogel dynamics in a dilute polymer solution, which quantifies the effect of diffusion and partitioning of osmolyte and the related solvent quality change to the volumetric changes of the hydrogel network. By making a dominant-mode assumption, we propose a model for the swelling and compression dynamics of (spherical) hydrogels in concentrated polymer solutions. Osmolyte diffusion induces a biexponential response in the size of the hydrogel radius, whereas osmolyte partitioning and solvent quality effects induce monoexponential responses. Comparison of the dominant-mode model to experiments provides reasonable values for the compressive bulk modulus of a hydrogel particle, the permeability of the hydrogel network, and the diffusion constant of osmolyte molecules inside the hydrogel network. Our model shows that hydrogel-osmolyte interactions can be described in a conceptually simple manner, while still capturing the rich (de)swelling behaviors observed in experiments. We expect our approach to provide a roadmap for further research into and applications of hydrogel dynamics induced by, for example, changes in the temperature and the pH.

Ultrahard nanomaterials: myths and reality

The last 25 years has witnessed a wealth of publications on the creation of carbon materials whose compression bulk modulus and hardness are much higher than those of diamond. This review presents a critical analysis of these studies. Three groups of myths that have emerged lately are discussed. The first is related to the possibility of creating materials whose bulk moduli are significantly higher than those of diamond. The second group is devoted to ‘experimentally measured’ values of hardness, much higher than that of diamond. The third includes alleged ‘theoretical’ grounds for a several-fold (!) increase in the hardness of covalent substances due to the effects of quantum confinement. It is shown that materials whose elastic moduli significantly exceed those of diamond cannot in principle be produced under normal conditions. Issues surrounding the quantitative measurement of hardness are discussed; it is noted that the creation of obstacles to the movement of dislocations in nanomaterials may allow a 20–40% increase in the effective measured hardness of ultrahard materials. It is emphasized that alternative hypothetical approaches to increase hardness, for example, due to quantum confinement, actually have no physical grounds whatsoever. The highest mechanical characteristics of diamond are associated with reliably established physical laws, and any assertions regarding possible obtainment of materials whose elastic characteristics or hardness are several times greater than those of diamond may not be regarded as reliable to any extent or even science-based.

Low-Parametric Equation of State of Aluminum

A low-parameter equation of state of aluminum is constructed based on the proposed dependence of the Gruneisen coefficient on the specific volume and temperature. The characteristics of the state of aluminum in the region of high pressures and temperatures are determined: zero and normal isotherms; heat capacity; isentropic bulk compression modulus; the family of shock adiabats corresponding to different initial densities; secondary compression and discharge curves; and the speed of sound. The calculated values are close to the available experimental data. This indicates the adequacy of the proposed approach to the construction of a thermodynamically consistent equation of state of aluminum before three- to fourfold compression.

Contribution to the modelling and homogenization of 3D structures in the presence of flaws by XFEM

The aim of this study is the development of software code based on the eXtended Finite Element Method (XFEM) to model the behavior of three-dimensional structures containing heterogeneity (inclusions, voids and cracks). The shape of flaws are presented using combinations of spatial level functions called Level-Set. Firstly, the obtained results for several validate tests are compared to those evaluated analytically and those obtained by using the free software “Caste3M2018” based on the Finite Element Method (FEM), where good correlations are observed. This shows the efficiency and the robustness of the proposed programmed approach. In homogenization context, several cases of Representative Volume Elementary (RVE) are then studied, to get the evolution of the bulk compressibility modulus according to the void flattening ratio and according to its size when the flaws became cracks.

Ultrasmall diamond nanoparticles with unusual incompressibility

Based on experimental and theoretical studies, the 607 GPa bulk modulus of nanodiamond 2–5 nm was determined, which significantly exceeds the bulk modulus of diamond crystal (443 GPa) and approaches the values typical of ultrahard fullerite (600–1000 GPa). Bulk modulus of nanodiamond 2–5 nm was experimentally measured by piezospectroscopy using a diamond anvil cell with anvils made of synthetic diamond with a high (~60%) 13C isotope content. The Raman frequency in such diamond is at 1306 cm−1 and does not interfere with the recording of a peak at 1325 cm−1 of nanodiamond 2–5 nm. The bulk compression modulus was calculated from the dependence of the displacement of two Raman bands at 1325 cm−1 and 1600 cm−1 (the latter does not apply to sp2 bonds) of nanodiamond 2–5 nm on pressure up to 68 GPa. Simulation of nanodiamond 1.2–5.9 nm confirms experimental results and also predicts the rise of bulk modulus with a decrease of nanoparticles size. Analysis of simulated structures suggests a possible explanation of observed effect due to increasing contribution of surficial compressed bonds when nanoparticles size reduces.

Analysis of red mud doped Bi2O3-B2O3-BaO glasses for application as glass solder in radiation shield repair using MCNPX simulation

Glasses in the range 50Bi2O3-30B2O3-(20-x)BaO-xRedmud, x = 0.1–0.5 wt%, were synthesized and characterized for use as low melting point radiation shield glass solder using a combination of spectroscopic, thermal analysis and MCNPX simulation. The MCNPX general purpose Monte Carlo code was used to determine the Gamma-ray half-value layer (HVL) for several photon energies. The results showed that the HVL and the mass neutron removal cross-section, for neutrons below 15 MeV, of the samples under investigation were comparable to that of the shields used in nuclear reactors as moderators and Gamma-ray shields. The thermal studies of the glass samples showed they remained amorphous over the heating range of 30–1000 °C while at the same time having low softening temperatures and large values of Tc-Tg, indicating high heating rate independent stability. The bulk modulus calculated using bond compression model suggest that the glass system would be ideal to repair currently existing construction material without compromising the structural integrity. Spectroscopic analysis of the glass system showed the presence of BO4 and BO3 units as the major network former while BiO6 acted as an intermediate. The Raman spectrum also showed overlapping bands of SiO4 and B-O vibrations. The Optical absorption showed the presence of various bismuth ions active in both the UV and NIR region. The structural analysis was also complimented by x-ray diffraction (XRD) which showed two halos consistent with the borate network and energy dispersive spectroscopy (EDS) and scanning electron microscope (SEM) analysis which showed no major nucleation or crystalline phases. The Fe3+ content of red mud showed the most impact on the molar volume and bond compression bulk modulus of the samples.

Anomalous Lattice Properties of Manganese Monosilicide: the Thermodynamic Approach

The temperature dependences of the thermal and elastic MnSi properties are analyzed within the limits of the self-consistent approach. The role of the anharmonicity of acoustic and optical lattice vibrations is analyzed. It is demonstrated that anomalously weak anharmonicity is characteristic for acoustic phonons. In particular, this explains the temperature dependence of the MnSi bulk compressive modulus. The one-electron contribution is estimated and the anomalous non-lattice contribution to the formation of the temperature dependences of heat capacity and volume thermal expansion coefficients.

Densification of Type I Collagen Matrices as a Model for Cardiac Fibrosis.

Cardiac fibrosis is a disease state characterized by excessive collagenous matrix accumulation within the myocardium that can lead to ventricular dilation and systolic failure. Current treatment options are severely lacking due in part to the poor understanding of the complexity of molecular pathways involved in cardiac fibrosis. To close this gap, in vitro model systems that recapitulate the defining features of the fibrotic cellular environment are in need. Type I collagen, a major cardiac extracellular matrix protein and the defining component of fibrotic depositions, is an attractive choice for a fibrosis model, but demonstrates poor mechanical strength due to solubility limits. However, plastic compression of collagen matrices is shown to significantly increase its mechanical properties. Here, confined compression of oligomeric, type I collagen matrices is utilized to resemble defining hallmarks seen in fibrotic tissue such as increased collagen content, fibril thickness, and bulk compressive modulus. Cardiomyocytes seeded on compressed matrices show a strong beating abrogation as observed in cardiac fibrosis. Gene expression analysis of selected fibrosis markers indicates fibrotic activation and cardiomyocyte maturation with regard to the existing literature. With these results, a promising first step toward a facile heart-on-chip model is presented to study cardiac fibrosis.

Effective Elastic Properties of Stochastic Granular Composites with Interfacial Defects

The problem of effective elastic properties of a matrix composite material with imperfect contact conditions between the matrix and quasi-spherical inclusions in the form of porous interfacial layers between the matrix and quasi-spherical inclusions, which are considered as the third component, is considered. It is based on the stochastic equations of elasticity for a multi-component material. An approach, where three-component material is reduced to two-component material by replacing the inclusions with interfacial layer by composite inclusions with equivalent or effective elastic properties is used. Composite inclusions are modeled using two-component matrix material, where inclusions and matrix have elastic moduli and volume fractions of corresponding real inclusions and interfacial layers. The dependence of bulk compression and shear efficient moduli on the volume fractions of inclusions and porosity of interfacial layers is investigated.

Modeling of the Equation of State for 0 &lt; ρ/ρ0 &lt; 1010

An approximation of the equation of state of matter in nonrelativistic and relativistic regions is considered. The cold component is determined in the limit v → 0 by the properties of an ideal homogeneous degenerate relativistic electron gas, and under normal conditions, by four experimental parameters: the specific volume, the binding energy, the bulk compression modulus, and the parameter –(∂lnB/∂lnv). Results are confirmed and illustrated by the experimental equation of state for iron in the region up to p ≈ 3 Mbar. A comparison of the model equation of state and the classical equation of state of an ideal homogeneous degenerate electron gas is given.

Thermodynamic simulation of the elastic and thermal properties of cobalt monosilicide

A self-consistent thermodynamic model is used to calculate the temperature dependences of the heat capacity, the thermal expansion coefficient, the bulk compression modulus, the density, Debye temperature, and the Gruneisen parameter of CoSi in the temperature range 0–1400 K. The calculation results agree well with the existing experimental data and can be used to predict the properties of CoSi in the temperature range that has not been experimentally studied. Cobalt monosilicide is shown to have a significant phonon anharmonicity, which can be caused by an electron–phonon interaction, and this anharmonicity should be taken into account in the simulation of its thermoelectric properties.

Plasma Surface Functionalized Polyetheretherketone for Enhanced Osseo-Integration at Bone-Implant Interface.

This study aims at improving osseo-integration at the bone-implant interface of polyetheretherketone (PEEK) by water (H2O) and ammonia (NH3) plasma immersion ion implantation (PIII). The pertinent surface characteristics including surface energy, roughness, morphology, and chemical composition are investigated systematically and the in vitro biological performance is evaluated by cell adhesion and proliferation, alkaline phosphatase (ALP) activity, real-time RT-PCR evaluation, and mineralization tests. In vivo osseo-integration is examined via implanting samples into the distal femur of the rats. The hydrophilicity, surface roughness, cell adhesion, and proliferation, ALP activity, and osteogenic differentiation after H2O PIII or NH3 PIII are improved significantly. Furthermore, substantially enhanced osseo-integration is achieved in vivo. Nonline-of-sight plasma surface functionalization, which is particularly suitable for biomedical implants with an irregular geometry, does not alter the bulk compressive yield strength and elastic modulus of the materials. Consequently, the favorable bulk attributes of PEEK are preserved while the surface biological properties are enhanced thus boding well for wider orthopedic application of the biopolymer.

Biological response of human articular chondrocytes to shear loading following changes to hydrogel surface properties

Event Abstract Back to Event Biological response of human articular chondrocytes to shear loading following changes to hydrogel surface properties Christoph Meinert1, Karsten Schrobback1 and Travis Klein1 1 Queensland University of Technology, Institute of Health and Biomedical Innovation, Australia Introduction: Articular cartilage provides a nearly frictionless surface with remarkable capacity to bear and distribute loads in a synovial joint. Alterations to the articular surface may however lead to pathological loads and unbalanced metabolism, ultimately leading to the development of osteoarthritis. Here, we established a hydrogel-based cartilage model with tailorable friction coefficients and evaluated the response of human chondrocytes in these models to dynamic shear loading imparted through custom bioreactor components. Materials and Methods: Bilayered hydrogels, with a thin cell free layer and a 2 mm alginate methacrylate (ALMA) layer containing 10^7 human articular chondrocytes (3 donors, with ethical approval, Passage 2) per mL, were photocrosslinked in the presence of Irgacure 2959. The cell-free layer consisted of either ALMA or PEG diacrylate with either 40 or 80 mol % 4-styrene sulfonic acid (PEG-40S, PEG-80S), resulting in different charge densities, as verified by EPIC-uCT. Friction coefficients were assessed over a range of velocities using custom components on an Instron Microtester. Bulk compressive modulus, swelling ratio, and water content were also measured. Further, microscopic images taken during dynamic shear loading in a custom device were used to generate strain maps using digital image correlation. Constructs were cultured in chondrogenic medium for 21 days free-swelling, followed by 11 days with 0 or 1 mm shear loading (1 h/d, 1 Hz) using custom bioreactor components. Chondrocyte response was assessed by quantitative real-time polymerase chain reaction (qRT-PCR), and matrix accumulation was assessed by immunofluorescence and biochemical assays. Results and Discussion: Constructs were able to effectively model the frictional properties of healthy, damaged, and osteoarthritic cartilage, while other physical characteristics such as compressive moduli, mass swelling ratio, and water content were not affected (Figure 1). Dynamic shear stimulation of constructs with low surface friction significantly promoted chondrogenesis and extracellular matrix synthesis as assessed by gene expression, immunofluorescence, and biochemical analysis (Figure 2). In contrast, shear stimulation of constructs with high surface friction inhibited chondrogenesis to a great extent, but induced transcription of matrix metalloproteinases involved in the degradation of cartilage extracellular matrix in osteoarthritis. Shear strains during dynamic loading were higher in the high-friction constructs than low-friction constructs, which likely explains the differences in chondrocyte response. Conclusion: This study demonstrates that surface friction may act as a key regulator of chondrocyte homeostasis by governing the magnitude of shear deformation during dynamic loading. Australian Research Council; Peter Levett, Cameron Lutton, Robert Sah, Carly Sutton Keywords: Biomimetic, biomaterial, surface property, stimuli-response Conference: 10th World Biomaterials Congress, Montréal, Canada, 17 May - 22 May, 2016. Presentation Type: New Frontier Oral Topic: Biomimetic materials Citation: Meinert C, Schrobback K and Klein T (2016). Biological response of human articular chondrocytes to shear loading following changes to hydrogel surface properties. Front. Bioeng. Biotechnol. Conference Abstract: 10th World Biomaterials Congress. doi: 10.3389/conf.FBIOE.2016.01.00873 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 27 Mar 2016; Published Online: 30 Mar 2016. Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Christoph Meinert Karsten Schrobback Travis Klein Google Christoph Meinert Karsten Schrobback Travis Klein Google Scholar Christoph Meinert Karsten Schrobback Travis Klein PubMed Christoph Meinert Karsten Schrobback Travis Klein Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Dispersion of hydroxyapatite nanoparticles in solution and in polycaprolactone composite scaffolds.

The dispersion behaviour of hydroxyapatite nanoparticles (HAP) and surface-modified HAP was studied in 1,4-dioxane (DO), water and poly(ε-caprolactone) (PCL) solutions and the relationship between these and the dispersion in composite PCL scaffolds prepared by thermally induced phase separation (TIPS) was examined. Investigation of the change in particle sizes by dynamic light scattering, showed that the modification of HAP by adsorption or covalent attachment of heparin via a 3-aminopropyltriethoxysilane (APTES) layer improved the dispersion stability of the particles in water/DO mixtures, while no improvement was observed in DO. The distribution of the particles within the composite scaffolds was determined using a combination of transmission electron microscopy and a calcium quantification method which was used to determine distribution of the particles in the vertical direction. While the scaffolds fabricated in DO had particles embedded within the walls of the scaffold, the scaffolds fabricated in a DO/water mixed solvent showed the particles partitioned to the surface of the scaffold walls, which is likely because the particles acted as interface stabilisers and were not miscible with the PCL rich phase. Therefore, it can be concluded that the polymer-solvent system used, as well as the phase separation mechanism that occurs, significantly influences the distribution of the particles in the scaffolds and thus the particle behaviour in solution is not necessarily a good predictor for the ability to fabricate scaffolds with a high degree of particle dispersion and hence for overall materials performance. Bulk crystallinity and compressive modulus were examined and it was determined that no significant changes occurred compared with the pristine PCL, while the surface bioactivity of the scaffolds had improved significantly, indicating that the particles were present at the polymer-solution interface.

Elastic Moduli and Poisson’s Coefficient of Optical Glasses

Product of the hardness of a solid body and the squared RMS velocity of strain waves having the characteristics typical of the elastic modulus is referred to as the effective elastic modulus. The ratio of the bulk compression modulus to the effective elastic modulus of optical glasses is an unambiguous function of Poisson’s coefficient. The nature of Poisson’s coefficient of the glasses is discussed.