Understanding the behaviour and material properties of bone is critical in predicting the failure and fracture of bones in humans. To address this, mechanical tests have traditionally been conducted ...to characterize bone material and this has resulted in large body of literature. However, there appears to be a lack of complete information regarding the storage protocols used for bone specimens prior to conducting mechanical tests. For example, while storage methods are well described, parameters such as the time between donor death and bone retrieval, as well as time between specimen machining and testing, are seldom reported. As biological materials undergo degradation in storage after being removed from the donor, a clear understanding of this degradation behaviour would identify critical time frames in which previously stored cortical bone specimens should be tested such that they can still be considered representative of an in-vivo condition. In this paper, the results of an investigation to determine the effects of long duration storage on the measured mechanical properties of bovine cortical bone are reported. Three different storage protocols are compared; namely machined-refrigerated, machined-frozen and frozen-machined-frozen. Degradation effects are evident for both refrigerated and frozen specimens and the results demonstrate that testing bone specimens after more than one week in storage may not provide representative in-vivo properties. In addition, specimens exhibit severe degradation after six months in storage regardless of the storage protocol.
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Hepatitis C virus-like particles (VLPs) are being developed as a quadrivalent vaccine candidate, eliciting both humoral and cellular immune responses in animal trials. Biophysical, ...biomechanical and biochemical properties are important for virus and VLP interactions with host cells and recognition by the immune system. Atomic force microscopy (AFM) is a powerful tool for visualizing surface topographies of cells, bionanoparticles and biomolecules, and for determining biophysical and biomechanical attributes such as size and elasticity. In this work, AFM was used to define morphological and nanomechanical properties of VLPs representing four common genotypes of hepatitis C virus. Significant differences in size of the VLPs were observed, and particles demonstrated a wide range of elasticity. Ordered packing of the core and potentially envelope glycoproteins was observed on the surfaces of the VLPs, but detailed structural characterization was hindered due to intrinsic dynamic fluctuations or AFM probe-induced damage of the VLPs. All VLPs were shown to be glycosylated in a manner similar to native viral particles. Together, the results presented in this study further our understanding of the nanostructure of hepatitis C VLPs, and should influence their uptake as viable vaccine candidates.
Flexible organic single crystals capable of plastic or elastic deformations have a variety of potential applications. Although the integration of plasticity and elasticity in a crystal is ...theoretically possible and it may cause rich and complex deformations which are highly demanded for potential applications, the integration is hard to realize in practice. Here, we show that through utilizing different modes of external forces for influencing molecular packing in different crystallographic directions, plastic helical twisting and elastic bending can both be achieved for a crystal, and they can even be realized simultaneously. Detailed crystallographic analyses and contrast experiments disclose the mechanisms behind these two kinds of distinct deformations and their mutual compatibility. Based on the plastically twistable nature of the crystal, a new application field of flexible organic single crystals, namely polarization rotators, is successfully opened up.
Twist and shout: The integration of plastic twisting and elastic bending in an organic single crystal is achieved. By controlling the twisting degree of the crystal, the polarization direction of light can also be controlled quantitatively and easily. Thus, a new application field of flexible organic single crystals, that is, polarization rotators, is opened up.
Abstract Background Quantifying passive stretching responses of individual muscles helps the diagnosis of muscle disorders and aids the evaluation of surgical/rehabilitation treatments. Utilizing an ...animal model, we demonstrated that shear elastic modulus measured by supersonic shear wave elastography increases linearly with passive muscle force. This study aimed to use this state-of-the-art technology to study the relationship between shear elastic modulus and ankle dorsi–plantarflexion angle of resting tibialis anterior muscles and extract physiologically meaningful parameters from the elasticity–angle curve to better quantify passive stretching responses. Methods Elasticity measurements were made at resting tibialis anterior of 20 healthy subjects with the ankle positioned from 50° plantarflexion to up to 15° dorsiflexion at every 5° for two cycles. Elasticity–angle data was curve-fitted by optimizing slack angle, slack elasticity, and rate of increase in elasticity within a piecewise exponential model. Findings Elasticity–angle data of all subjects were well fitted by the piecewise exponential model with coefficients of determination ranging between 0.973 and 0.995. Mean (SD) of slack angle, slack elasticity, and rate of increase in elasticity were 10.9° (6.3°), 5.8 (1.9) kPa, and 0.0347 (0.0082) respectively. Intraclass correlation coefficients of each parameter were 0.852, 0.942, and 0.936 respectively, indicating excellent test–retest reliability. Interpretation This study demonstrated the feasibility of using supersonic shear wave elastography to quantify passive stretching characteristics of individual muscle and provided preliminary normative values of slack angle, slack elasticity, and rate of increase in elasticity for human tibialis anterior muscles. Future studies will investigate diagnostic values of these parameters in clinical applications.
•A new equivalent temperature-dependent cohesive energy is defined.•Develop a physics-based elastic modulus model without any fitting parameter.•The interrelationships between certain physical ...quantities are uncovered.•Provide a new method to predict temperature-dependent elastic modulus.
Elastic modulus is one of the key elemental material parameters. Its variation with temperature has long been concerned by researchers. In this study, a new temperature-dependent elastic modulus model without phenomenological fitting parameters for metallic bulk materials is developed. The model is capable of predicting the Young's modulus, elastic constant, and shear modulus at different temperatures. Good agreement is obtained between values predicted by the model and available experimental data of body-centered-cubic metals, faced-centered-cubic metals, wrought superalloys, and cast superalloys. The inherent relationships between temperature-dependent elastic modulus, coefficient of expansion, heat capacity (or Debye temperature), and melting point of metallic materials are uncovered by the model. Additionally, the model also provides a new method to predict elastic moduli: the elastic moduli at extremely high and low temperatures, which are difficult to obtain through experiments, can be predicted by the model with reference of an easy-to-access elastic modulus.
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In this article, design and finite element simulation of porous Ti-6Al-4V alloy structures was presented. Typically, titanium and titanium alloy implants can be manufactured with required ...pore size and porosity volume by using powder bed fusion techniques due to advancement in additive manufacturing technologies. However, the mismatch of elastic modulus between human cortical bone and the dense Ti-6Al-4V alloy implant resulted in stress shielding which accelerate the implant failure. The porous implant structures help in reduce the mismatch of elastic modulus between the cortical bone and implant structure and also improve the bone ingrowth. Hence, the present work focuses on design of Ti-6Al-4V alloy porous structures with various porosities ranging from 10% to 70% and simulated to determine the elastic modulus suitable for human cortical bone. The sample with 45% porosity is found to be best suited for replacement of cortical bone with elastic modulus of 74Gpa, preventing stress shielding effect and enhanced chances of bone ingrowth.
Conductive and stretchable materials that match the elastic moduli of biological tissue (0.5-500 kPa) are desired for enhanced interfacial and mechanical stability. Compared with inorganic and dry ...polymeric conductors, hydrogels made with conducting polymers are promising soft electrode materials due to their high water content. Nevertheless, most conducting polymer-based hydrogels sacrifice electronic performance to obtain useful mechanical properties. Here we report a method that overcomes this limitation using two interpenetrating hydrogel networks, one of which is formed by the gelation of the conducting polymer PEDOT:PSS. Due to the connectivity of the PEDOT:PSS network, conductivities up to 23 S m
are achieved, a record for stretchable PEDOT:PSS-based hydrogels. Meanwhile, the low concentration of PEDOT:PSS enables orthogonal control over the composite mechanical properties using a secondary polymer network. We demonstrate tunability of the elastic modulus over three biologically relevant orders of magnitude without compromising stretchability ( > 100%) or conductivity ( > 10 S m
).
Additive manufacturing or, as also called, three-dimensional (3D) printing is considered as a game-changer in replacing traditional processing methods in numerous applications; yet, it has one ...intrinsic potential weakness related to bonding of layers formed during the printing process. Prior to finding solutions for improvement, a thorough quantitative understanding of the mechanical properties of the interface is needed. Here, a quantitative analysis of the nanomechanical properties in 3D printed photopolymers formed by digital light processing (DLP) stereolithography (SLA) is shown. Mapping of the contact Young’s modulus across the layered structure is performed by atomic force microscopy (AFM) with a submicrometer resolution. The peakforce quantitative nanomechanical mapping (PF-QNM) mode was employed in the AFM experiments. The layered specimens were obtained from an acrylate-based resin (PR48, Autodesk), containing also a light-absorbing dye. We observed local depressions with values up to 30% of the maximum stiffness at the interface between the consecutively deposited layers, indicating local depletion of molecular cross-link density. The thickness values of the interfacial layers were approximately 11 μm, which corresponds to ∼22% of the total layer thickness (50 μm). We attribute this to heterogeneities of the photopolymerization reaction, related to (1) atmospheric oxygen inhibition and (2) molecular diffusion across the interface. Additionally, a pronounced stiffness decay was observed across each individual layer with a skewed profile. This behavior was rationalized by a spatial variation of the polymer cross-link density related to the variations of light absorption within the layers. This is caused by the presence of light absorbers in the printed material, resulting in a spatial decay of light intensity during photopolymerization.
Functionally graded and multi-morphology lattices are gaining increased attention recently in the tissue engineering research community because of the ability to control their physical, mechanical ...and geometrical properties spatially. In this work, relative density grading, cell size grading, and multi-morphology (lattice type grading) are mechanically investigated for sheet-based lattices with topologies based on triply periodic minimal surfaces (TPMS), namely; the Schoen Gyroid, and Schwarz Diamond minimal surfaces. To investigate the role of loading direction on the exhibited deformation mechanism, tests were performed parallel and perpendicular to the grading direction. For relative density grading, testing parallel to grading direction exhibited a layer-by-layer deformation mechanism with a lower Young’s Modulus as compared to samples tested perpendicular to grading direction which exhibited a shear band deformation. Moreover, multi-morphology lattices exhibited a shift in deformation mechanism from layer-by-layer to the formation of a shear band at the interface between the different TPMS morphologies when tested parallel and perpendicular to hybridization direction, respectively. FE analysis revealed that sheet-networks multi-morphology lattices exhibit higher elastic properties as compared to solid-networks multi-morphology lattices.
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