bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Role of Type I Collagen Molecular Structure in Tendon Elastic Energy Storage
Authors: Freeman Joseph W. , Silver Frederick H. , Woods Mia D. , Laurencin Cato T. 
Published: June 2019

AbstractIn order to facilitate locomotion and limb movement many animals store energy elastically in their tendons. The formation of crosslinked collagen fibers in tendons results in the conversion of weak, liquid-like embryonic tissues into tough elastic solids that can store energy and perform work. Collagen fibers in the form of fascicles are the major structural units found in tendons. The purpose of this paper is to review the literature on collagen self-assembly and tendon development and to relate this information to the development of elastic energy storage in nonmineralizing and mineralizing tendons. Of particular interest is the mechanism by which energy is stored in tendons during locomotion. In the turkey, much of the force generated by the gastrocnemius muscle is stored as elastic energy during tendon deformation and not within the muscle. As limbs move, the tendons are strained, causing the collagen fibers in the extracellular matrices to stretch. Through the analysis of turkey tendons, collagen fibers, and a molecular model, it is hypothesized that elastic energy is stored in the flexible regions of the collagen molecule. Data from the molecular model, mineralized fibers, and turkey tendons show that the presence of calcium and phosphate ions causes an increase in elastic energy stored per unit strain. Based on the theoretical modeling studies, the increase in stress with strain is a result of the initiation of stretching of the rigid regions of collagen molecules.
Architectural changes of trabecular bone caused by the remodeling process
Authors: Weinkamer Richard , Hartmann Markus A. , Brechet Yves , Fratzl Peter 
Published: June 2019

AbstractUsing a stochastic lattice model we have studied the architectural changes of trabecular bone occurring while the structure is remodeled. Our model considers the mechanical feedback loop, which control the remodeling process. A fast algorithm was employed to solve approximately the mechanical problem. A general feature of the model is that a networklike structure emerges, which further coarsens while the bone volume fraction remains unchanged. Decreasing the mechanical response of the system by either lowering the external load or the internal mechano-sensitivity leads not only to a reduction of the bone volume fraction, but results in topological changes of the trabecular bone architecture, where the loss of horizontal trabeculae is the most obvious effect.
Atomic Force Microscopy Contact Mode Study on Ultra High Molecular Weight Polyethylene
Authors: Cao Yifang , Zhou Jikou , Popoola Oludele , Swarts Dal F. , Soboyejo Wole 
Published: June 2019

AbstractThis paper presents the results of contact mode atomic force microscopy (AFM) study on the nanoscale Young's modulus and work of adhesion of ultra high molecular weight polyethylene (UHMWPE). Cryoultramicrotomed surfaces of UHMWPE were scanned using the contact mode of AFM. Fibril regions are commonly found on the sample, however, a non-fibril particulate region was also found. AFM force displacement curves were obtained for the sample. The JKR theory and Maugis Dugdale model were used for the analysis. A good fitting between the theories and experimental data was found. The nanoscale Young's modulus and work of adhesion of UHMWPE extracted from the experimental data were in reasonably good agreement with the values reported in other literatures.
Relating Local Bone Stiffness and Calcium Content by Combined Nanoindentation and Backscattered Electron Imaging
Authors: Weber M. , Schoeberl T. , Roschger P. , Klaushofer K. , Fratzl P. 
Published: June 2019

AbstractBone is a hierarchically structured mineral-organic composite material that has to bear static and dynamic mechanical loads applied by body weight and locomotion. Bone mechanical properties are influenced by a number of factors, depending on the particular hierarchical levels. The high stiffness of bone material is mainly achieved by reinforcement with calcium phosphate mineral platelets. A model for this elementary structure level consists of an arrangement of staggered mineral bricks, embedded in collagen matrix, which provides both stiffness and toughness. The mechanical properties depend on the amount, shape and arrangement of the mineral particles but also on the properties of the collagen-rich matrix.One of the difficulties in assessing the properties of hierarchical structures is the inherent inhomogeneity of the tissue: Parameters such as stiffness or calcium content vary throughout a bone section. Such type of investigations becomes more meaningful by a combination of two complementary methods e.g. quantitative backscattered electron imaging (qBEI) and nanoindentation. The local Ca-content, representing the degree of the mineralization, is extracted from the qBEI measurements, whereas the local mechanical properties, elastic modulus and hardness, are measured by nanoindentation, a miniaturized hardness testing using a small diamond tip. The measured correlations between local Ca-content and mechanical strength help, for example, to verify biomechanical models based on the nanocomposite structure of bone. They may also shed new light on bone diseases such as osteoporosis or osteogenesis imperfecta.
Elastic Modulus and Mineral Density of Dentine and Enamel in Natural Caries Lesions
Authors: Bembey Amanpreet K. , Oyen Michelle L. , Ko Ching-Chang , Bushby Andrew J. , Boyde Alan 
Published: June 2019

AbstractDental tissues have been reported to show a considerable decrease in both their mineral content and mechanical properties in carious lesions. The changed properties of dentine and enamel have been shown to be dependent on crystal size and not only mineral content [1], although the connectivity between the mineral crystals has been overlooked. Teeth with carious lesions were sectioned, embedded in polymethylmethacrylate (PMMA) and diamond polished. Nanoindentation and quantitative backscattered electron imaging were used to determine relationships between the elastic modulus and mineral density of sound and carious regions within dentine and enamel. The changes in elastic modulus with decreased mineralization for dentine and enamel could not be explained by simple composite mechanics expressions relating elastic modulus and mineral volume fraction. Finite element modeling of dentine and enamel as a two-phase composite material at the ultrastructure level were used to demonstrate how changes in the mineral phase connectivity can produce changes in the elastic modulus. Tissue models for enamel, in which the mineral phase is both the major component of the structure (∼ 85% by volume) and highly interconnected, were consistent with the modulus of sound enamel. The drastic change in enamel modulus with a relatively small change in mineral volume fraction could be modeled as a decrease in mineral phase connectivity at nearly constant volume fraction. The more gradual trend in the dentine data was also consistent with a structure that is initially highly connected in the mineral phase, consistent with the known structure of dentine, and for which the change in modulus is more directly related to changes in mineral content than mineral connectivity.
Microstructure and Adhesive Properties of Copal Composite in Dental Incrustations
Authors: Orta-Amaro M. N. , Rodríguez-Chávez J. A. , Belío-Reyes I. A. , Bucio L. , Arenas-Alatorre J. , Espinoza J.L. , Flores-Grajeda M. C. 
Published: June 2019

AbstractThere are evidences that in ancient cultures in Mexico,copalwas probably used for gluing precious stones in teeth cavities and for dental restorations as well. This is an important reason for making experiments using copal and copal-based composites in order to have more information for the potential applications of this material in modern dentistry. In our experiments concerning with dental incrustations of turquoise, we have practiced round cavities (about 1 mm depth) in the middle of incisive teeth by using a low-speed air turbine. Turquoise was cut in such a way that fits exactly on the tooth cavity. Copal and powdered apatite were used to glue the stone into the cavity. With Scanning electron microscopy we have observed that the composite copal-powdered apatite, penetrates the dentin tubules in the tooth tissue (depth of penetration from 5.6 to 41 micrometers), suggesting the existence of a micromechanical adherence. Concerning to the characterization of the adhesive properties, we have applied the ASTM D2095-72 test considering the adhesion of two cylinders of bone, and the copal composite as the adhesive. A maximum cohesive tensile strength around 0.1 MPa for elastic response was measured for hydroxyapatite compositions of 0, 25 and 75 wt%. We will discuss these results considering the reports of dental incrustations in ancient Mexico.
Mechanical Properties of the Lobster Cuticle
Authors: Raabe D. , Sachs C. 
Published: June 2019

AbstractWe present experiments on the mechanical and structural gradients through the cuticle of homarus americanus (lobster). The exocuticle (outer layer) is characterized by a very fine woven structure of the chitin-protein matrix (Bouligand structure) and by a high stiffness (8.5–9.5 GPa). The hardness increases within the exocuticle between the surface region (130 MPa) and the region close to the interface to the endocuticle (270 MPa). In the endocuticle which is characterized by a much coarser twisted plywood (Bouligand) structure both, the stiffness (3–4.5 GPa) and hardness (30–55 MPa) are much smaller than in the exocuticle. The transition in mechanical properties and structure between the exo- and endocuticle is abrupt.
Elasticity and Viscoelasticity of Human Tibial Cortical Bone Measured by Nanoindentation
Authors: Silva Leandro de Macedo Soares , Ebacher Vincent , Liu Danmei , McKay Heather , Oxland Thomas R. , Wang Rizhi 
Published: June 2019

AbstractBone is a composite material composed of collagen, carbonated apatite mineral, water, and other non-collagenous proteins. The bone structure inside human body is under constant remodelling. The mechanical properties of bone and their dynamic changes during remodelling are crucial to the health and quality of life.In this study, the elastic and viscoelastic properties of a 73 year-old female cortical bone were investigated at the lamellar level. This was realized by a nanoindentation technique equipped with dynamic loading function. 325 indentations were made in individual Haversian systems and interstitial bone at both dry and wet condition, and under two different loading frequencies. The results showed no statistically significant differences in elastic modulus between Haversian systems and interstitial bone. There were no systematic differences in modulus across the cortex except for a slight drop at the periosteal site. The lamellar structure of both Haversian system and interstitial bone is viscoelastic with water playing a significant role to the properties. When dry bone is re-hydrated, elastic modulus decreases and loss tangent increases.
Constitutive Modeling of the Stress-Stretch Behavior of Membranes Possessing a Triangulated Network Microstructure
Authors: Arslan Melis , Boyce Mary C. 
Published: June 2019

AbstractThe mechanical behavior of the membrane of the red blood cell is governed by two primary microstructural features: the lipid bilayer and the underlying spectrin network. The lipid bilayer is analogous to a 2D fluid in that it resists changes to its planar area, yet poses little resistance to planar shear. A skeletal network of spectrin molecules is crosslinked to the lipid bilayer and provides the shear stiffness of the membrane. Here, a continuum level constitutive model of the large stretch behavior of the red blood cell membrane that directly incorporates the microstructure of the spectrin network is developed. The resemblance of the spectrin network to a triangulated network is used to identify a representative volume element (RVE) for the model. A strain energy density function in terms of an arbitrary planar deformation field is proposed using the RVE. Differentiation of the strain energy density function provides expressions for the general multiaxial stress-stretch behavior of the material. The stress-strain behavior of the membrane when subjected to uniaxial loading conditions in different directions is given, showing the capabilities of the proposed microstructurally-detailed constitutive modeling approach in capturing the evolving anisotropic nature of the mechanical behavior.
Elasto-Mammography: Elastic Property Reconstruction in Breast Tissues
Authors: Wang Z. , Liu Y. , Sun L.Z. , Wang G. 
Published: June 2019

AbstractMammography is the primary method for screening and detecting breast cancers. However, it frequently fails to detect small tumors and is not quite specific in terms of tumor benignity and malignancy. The objective of this paper is to develop a new imaging modality called elastomammography that generates the modulus elastograms based conventional mammographs. A new elastic reconstruction method is described based on elastography and mammography for breast tissues. Elastic distribution can be reconstructed through the measurement of displacement provided by mammographic projection. It is shown that the proposed elasto-mammography provides higher sensitivity and specificity than the conventional mammography on its own for breast cancer diagnosis.
Indentation Micromechanics of Fibroblast-Populated Fibrin Constructs
Authors: Mooney R.G. , Costales C.A. , Curtin J.M. , Tawil B. , Shaw M.C. 
Published: June 2019

AbstractDuring normal wound healing, a fibrin clot is formed within the first few minutes and is replaced, over several days, by collagen and other extracellular matrix components which are populated with fibroblasts [Clark, 1996]. This process leads to the rebuilding of dermal tissue on which the epidermal tissue is slowly rebuilt. In severe acute and chronic wounds dermal replacement materials that mimic these processes are needed. Current trends are to use scaffolds as structural substitutes as well as carriers for growth factors and cells for wound treatment. Fibrin-based sealants have been used over the last 30 years in hemostasis and tissue sealing applications and in the last 5 years as a scaffold. Fibrin sealant consists of two primary components, fibrinogen and thrombin which form a fibrin clot when mixed. However, a basic understanding of the microstructure/property relationships of fibrin/collagen constructs is not yet fully established. Furthermore, while previous studies showed that cells proliferate and differentiate within 3D fibrin clots, their effect on structural mechanics of the fibrin clot has not been examined.Here, an indentation protocol was established to determine the effects of fibrin/collagen biochemistry and time-dependent cellular response on the elastic parameters of the constructs. Specifically, 4 ml fibrin/collagen constructs were prepared with varying compositions of human-derived fibrinogen (5 - 33 mg/ml), thrombin (1 or 2 U/ml) and bovine collagen (0, 25, 50, 75, 100 weight % of 2.4 mg/ml collagen). Constructs were prepared with/without the presence of human foreskin fibroblasts (ATCC NIH3T3) seeded at a density of 100K cells/ml. Using a 3-mm diameter punch indenter, the indentation load-displacement response was measured after 1, 5 and 10 days of incubation at 37°C in a humidified air/5% CO2 atmosphere. Four replicates per experimental condition were prepared, and three indentations per replicate were performed.For the unpopulated fibrin, there was a linear (R=0.983) relationship between the indentation stiffness and fibrinogen concentration. Also, there was a nonlinear relationship between indentation stiffness and concentration of collagen in the fibrin/collagen constructs. Finally, although in most cases there was no measurable change in the stiffness of the cell-populated tissue constructs with incubation time, in one of the cell-populated formulations, however, the indentation stiffness decreased steadily with increasing incubation time. These results are analyzed within the context of existing analytical micromechanics models for the relationships between scaffold structure, e.g., porosity / fibril diameter, and stiffness.
The Influence of the Thermal Treatment of Hydroxylapatite Scaffolds on the Physical Properties and the Bone Cell Ingrowth Behaviour
Authors: Woesz Alexander , Rumpler Monika , Manjubala Inderchand , Pilz Christine , Varga Franz , Stampfl Juergen , Fratzl Peter 
Published: June 2019

AbstractThe material bone consists of a biopolymer matrix (collagen) reinforced with mineral nanoparticles (carbonated hydroxylapatite), forming a natural composite which builds up a dense shell on the exterior and a network of struts with a mean diameter of 200μm in the core of many bones. The architecture of the foamy inner part of bones (spongiosa) is determined by loading conditions. The architecture strongly influences the mechanical properties of cellular solids together with the apparent density and the material it consists of. In addition, the ingrowth of bone cells into porous implants depends on pore size, size distribution and interconnectivity. From this it is clear that the possibility to design the architecture of a bone replacement material is beneficial from a biological as well as a mechanical point of view. Our approach uses rapid prototyping methods, ceramic gelcasting and sintering to produce cellular structures with designed architecture from hydroxylapatite and other bioceramics.The influence of sintering temperature and atmosphere on the physical properties of these scaffolds was investigated with x-ray diffraction and scanning electron microscopy. Furthermore, the cell ingrowth behaviour was determined in cell culture experiments, using the praeosteoblastic cell line MC3T3-E1, derived from mouse calvariae. The cell ingrowth behaviour was evaluated during a culture period of two and three weeks, by light microscopy and afterwards by histology after embedding and Giemsa-staining.The phase composition of the material was found to change with increasing sintering temperature and its surface characteristics was influenced by the sintering atmosphere. These changes also affected the cell ingrowth behaviour. In some experiments, the osteoblasts-like cells were found to cover the whole external and internal surface of the scaffold. The cells produced extracellular matrix consisting of collagen, which eventually filled nearly all the pores. In particular, the cells had the tendency to fill any crack or opening in the scaffolds, and to generally smooth the surfaces.In conclusion, rapid prototyping and ceramic gelcasting allows the freeform fabrication of porous bioceramics with controlled architecture. Such structures made of hydroxylapatit were found to support the growth of mouse osteoblasts.
Domain Switch Toughening in Polycrystalline Ferroelectrics
Authors: Landis Chad M. , Wang Jianxin 
Published: June 2019

AbstractMode I steady crack growth is analyzed to determine the toughening due to domain switching in poled ferroelectric ceramics. A multi-axial, electromechanically coupled, incremental constitutive theory is applied to model the material behavior of the ferroelectric ceramic. The constitutive law is then implemented within the finite element method to study steady crack growth. The effects of mechanical and electrical poling on the fracture toughness are investigated. Results for the predicted fracture toughness, remanent strain and remanent polarization distributions, and domain switching zone shapes and sizes are presented. Finally, the model predictions are discussed in comparison to experimental observations.
Simulation of a Ferromagnetic Shape Memory Actuator in a Magnetic Field
Authors: Krevet B. , Kohl M. 
Published: June 2019

AbstractIn this work, we present simulations of the thermo-magneto-mechanical performance of a ferromagnetic SMA microactuator in the inhomogeneous field of a CoSm permanent magnet and compare it with experimental results. For the simulations, a combination of different finite element (FEM) programs is used allowing the coupling of electrical, thermal, magnetic and mechanical properties. The field of a permanent magnet is calculated along the trajectory of the microactuator, from which the magnetic forces Fmag and their gradients are derived. Shape memory forces FSME are calculated based on a two-phase macromodel. Both forces, Fmag and FSME, determine the quasi-static behavior of a NiMnGa microscanner, which has been proposed recently.
Internal Stress Generation During Switching of Ferroelectrics
Authors: Haug Anja , Onck Patrick R. , Giessen Erik Van der 
Published: June 2019

AbstractProgressive switching of grains in ferroelectric materials leads to internal stresses, which may give rise to degradation of the material or even fracture. Here we propose a two-dimensional multigrain model for ferroelectric polycrystal. The numerical computations employ the nonlinear micromechanics model of Huber et al. [1] for each grain. Results for the macroscopic response, butterfly and hysteresis loops, as well as internal stress and electric field distributions are presented.
Finite Element Modeling of Piezoelectric Actuators and Sensors: Local Analysis of the Ferroelectric and Ferroelastic Effects
Authors: Elhadrouz M. , Zineb T. Ben , Patoor E. 
Published: June 2019

AbstractA new electromechanical finite element is implemented in the Abaqus F.E. code. It takes into account the ferroelectric and ferroelastic behavior. It is represented by a developed phenomenological constitutive law using two internal variables (remnant ferroelastic strain and remnant polarization) and two loading surfaces (electrical and mechanical ones). Saturation phenomena and depolarization under compression mechanical loading are taken into account.In order to lead to a more accurate description of the domain switching mechanisms, a micromechanical single-crystal ferroelectric and ferroelastic constitutive law was also developed.The self consistent scale transition technique will be adopted to derive the polycristalline behavior. The results that were obtained by the micromechanical and phenomenological approaches will be compared in order to identify material parameters that will be introduced in the F.E. modeling.
Fully Coupled 3-D Modelling of Ferroelectric Polycrystalline Material Behavior
Authors: Mehling V. , Tsakmakis Ch. , Gross D. 
Published: June 2019

AbstractA thermodynamically consistent phenomenological model for the material behavior of polycrystalline ferroelectric ceramics is presented. The internal state of the material is described by two internal state variables. The first one is a second-order texture tensor, determining a simple orientation distribution function (ODF) for the axes of the crystal unit cells. The second is the vector of relative irreversible polarization. The irreversible strains are derived from the ODF by volume averaging. The polarization saturation states are calculated by summing up the possible contributions of all cells to the overall polarization. An invariant formulation of the piezoelectric law is applied. Analogous to the thermodynamical framework of rate-independent plasticity, driving forces and evolution laws for the internal state variables are established. Saturation and coupling of the switching behavior are governed by energy barrier functions introduced in the electric enthalpy function. Numerical examples illustrate the models capabilities.