Mechanical Stiffnesses Research Articles

Nanoindentation response of small-volume piezoelectric structures and multi-layered composites: modeling the effect of surrounding materials

With piezoelectric small-volume composites gaining importance in smart device applications and nanoindentation being recognized as a versatile method for assessing the properties of layer materials, the present study is focused on the indentation response of the small-volume piezoelectric structures multi-layered composites. In particular, the effects of the nature of the substrate and surrounding materials, on the indentation response of piezoelectric nanocomposites, such as nanoislands, nanowires, and multi-layered composites are investigated. By developing three-dimensional finite element modeling, the complex interaction between the fundamental elastic, piezoelectric and dielectric properties of the piezoelectric materials and the elastic, plastic and electrically conducting or insulating properties of the surrounding materials, on the indentation response of the layered composites is analyzed. It is found that: (i) a substrate material that is elastically stiffer enhances the mechanical indentation stiffness and the electric indentation stiffness while plastic deformation in the substrate causes a reduction in the mechanical and electrical indentation stiffness; (ii) the effective piezoelectric and mechanical indentation stiffnesses of piezoelectric multi-layered composites are bounded by the corresponding characteristics of the bulk material counterparts from which the individual layers are constructed; (iii) electrically conducting surrounding materials produce a softening effect while insulating materials enhance the electrical indentation stiffness resulting in more charges being accumulated during the indentation process.

Abstract P2111: Characterizing Human Cardiac Fibroblast Responsiveness To Hemodynamic Unloading In Heart Failure With Reduced Ejection Fraction

Background: Myocardial interstitial fibrosis is a common pathology in cardiomyopathies leading to ventricular dilation and increased hemodynamic load that result in heart failure with reduced ejection fraction (HFrEF). Previous research has shown that HFrEF patients treated with a left ventricular assist device (LVAD) undergo hemodynamic unloading resulting in at least partial cardiomyocyte recovery. However, evidence supports that these patients do not experience a regression of fibrosis and demonstrate, in some cases, a worsening of fibrosis after LVAD treatment. Purpose: We hypothesize that human cardiac fibroblasts (HCFs) are constitutively activated in HFrEF myocardium but remain unresponsive to hemodynamic unloading with LVAD placement. Methods and Results: Forty human subjects with HFrEF undergoing LVAD implantation were enrolled to provide a portion of myocardium routinely removed during LVAD placement. In addition, 7 biopsies previously collected from transplanted hearts with extended LVAD treatment were also evaluated (LVEX). Quantification of PSR stained sections revealed a significant increase in collagen content in the HFrEF tissue (Collagen volume fraction % (CVF) = 2.8±0.2) in comparison to control tissues (CVF = 0.9±0.2) that remained elevated in LVEX hearts (CVF = 3.1±0.3). HCFs derived from biopsies received at LVAD placement were isolated and grown to confluence. HCFs from HFrEF patients and control HCFs from healthy donors were then plated on substrates with mechanical stiffnesses reflective of either normal myocardium (2kPa) or failing myocardium (8kPa). Cells were collected at 4- and 7-day timepoints and levels of collagen I (Col I) and alpha-smooth muscle actin (α-SMA) were quantified through western blot analysis with β-actin as a loading control. Whereas control HCFs were responsive to changes in substrate stiffness producing more Col I and α-SMA on 8kPa versus 2kPa, HCFs from HFrEF patients were unresponsive to changes in stiffness exhibiting no significant difference in production on 2 vs. 8kPa. Conclusion: These data suggest that HCFs isolated from the failing myocardium do not respond to changes in mechanical load and hence, might contribute to persistent increases in fibrosis in failing and unloaded hearts.

Effects of infill orientation and percentage on the magnetoactive properties of 3D printed magnetic elastomer structures

This work investigates how the internal meso structure of fused filament fabrication parts influence the magnetoactive properties of printed magnetic elastomer structures. Elastomers were made by adding 40wt% magnetite (Fe3O4) to a thermoplastic polyurethane (TPU) matrix. Magnetoactive testing was used to investigate how varying the infill structure affected the mechanical response of the structures within an applied magnetic field. Different infill percentages (40%, 60%, and 100%) and infill orientations (0, 45, and 90 degrees) were tested to account for different mechanical stiffnesses and internal geometries. Each sample was magnetoactively tested with three transverse magnetic field orientations (front, back and top). The samples were placed between two electromagnets, and the angle of deflection was recorded as a function of applied field. The maximum angles of deflection for the testing setup were reached when using lower infill percentages and having infill oriented parallel to the long axis of the sample and transverse to the magnetic field. Transverse fields applied parallel to the print plane (front/back sample orientations) demonstrated the most magnetoaction due to easier alignment of the long side of the sample with the field. This coupled with the 0-degree infill orientation having less crosslinking constraining the bending stiffness led to greater deflection. The magnetic anisotropy of the infill structure likely also contributed to the large response from certain samples. It was concluded that for this fixed base material, it is more important to 3D print structures with lower stiffnesses than more net magnetic particulate (more infill) to achieve the most magnetoaction.

Human cancer cells generate spontaneous calcium transients and intercellular waves that modulate tumor growth

Electrically excitable cells such as neurons transmit long-distance calcium or electrical signals to regulate their physiological functions. While the molecular underpinnings and down-stream effects of these intercellular communications in excitable cells have been well appreciated, little is known about whether and how non-excitable cancer cells spontaneously initiate and transmit long-distance intercellular signals. Here we report that non-excitable human colon and prostate cancer cells spontaneously initiate and spread intercellular calcium waves, in vitro and ex vivo. Xenograft model studies suggest that these calcium signals promote the growth rate of tumors in mice. Pharmacological studies elucidated that the inositol-trisphosphate-receptor (IP3R)-regulated calcium release from endoplasmic reticulum (ER), which is activated by the Gq-PLC-IP3R pathway, is a major cause for the initiation of spontaneous calcium transients. Further, the spatial-temporal characteristics of calcium dynamics can be tuned by the culture substrates of different mechanical stiffnesses. Our results provide evidence that calcium dynamics enables long-distance functional communication in non-excitable cancer cells and offer the potential to modulate calcium signaling for new cancer therapies.

MECHANICAL AUGMENTATION OF PROGESTERONE ACTION IN UTERINE FIBROID CELLS REQUIRES PROGESTERONE RECEPTOR B (PRB) AND IS ASSOCIATED WITH PRB PHOSPHORYLATION

Progesterone responsive genes are implicated in fibroid growth, but the mechanisms that integrate mechanical signaling with progesterone receptor activation are not fully understood. We previously reported that a mechanically stiff substrate promoted progesterone-dependent, progesterone receptor-mediated gene activation in fibroid cells. Here we investigated whether altered mechanical stiffnesses directly influenced phosphorylation of progesterone receptor B (PRB), and used siRNA directed against PRB to test whether this isoform was required to transduce mechanical signals in fibroid cells.

Initial bacterial retention on polydimethylsiloxane of various stiffnesses: The relevance of modulus (mis)match

Initial retention of the bacterium Escherichia coli on model poly(dimethylsiloxane) (PDMS) surfaces was studied as a function of substrate bulk and surface mechanical stiffness values. Our reference PDMS system was designed such that out of the parameters that govern bacterial adhesion only the mechanical stiffness was systematically varied. This was achieved by varying the crosslinking density of PDMS. Following crosslinking, we performed Soxhlet extraction of non-crosslinked, free chains to rule out their effect on bacterial response. Bulk moduli were assessed by dynamic mechanical analysis at 1 rad sec−1 frequency and the values obtained ranged between 0.03 and 1.8 MPa. The increase in crosslink density resulted in increasing surface modulus, as measured by atomic force microscopy, with values ranging between 0.7 and 9 MPa. The number of bacteria retained was then assessed. We observed a decreasing trend with the increase of both bulk and surface mechanical stiffnesses down to a limit corresponding to the Young’s modulus of the bacterial cell surface. For higher values than this threshold, the number of retained bacteria remained constant. We tentatively explain this observation by considering conformal overlay of bacterial and material surfaces.

Finite element modeling of α-helices and tropocollagen molecules referring to spike of SARS-CoV-2

The newly developed finite element (FE) modeling at the atomic scale was used to predict the static and dynamic response of the α-helix (AH) and tropocollagen (TC) protein fragments, the main building blocks of the spike of the SARS-CoV-2. The geometry and morphology of the spike’s stalk and its connection to the viral envelope were determined from the combination of most recent molecular dynamics (MD) simulation and images of cryoelectron microscopy. The stiffness parameters of the covalent bonds in the main chain of the helix were taken from the literature. The AH and TC were modeled using both beam elements (wire model) and shell elements (ribbon model) in FE analysis to predict their mechanical properties under tension. The asymptotic stiffening features of AH and TC under tensile loading were revealed and compared with a new analytical solution. The mechanical stiffnesses under other loading conditions, including compression, torsion, and bending, were also predicted numerically and correlated with the results of the existing MD simulations and tests. The mode shapes and natural frequencies of the spike were predicted using the built FE model. The frequencies were shown to be within the safe range of 1–20 MHz routinely used for medical imaging and diagnosis by means of ultrasound. These results provide a solid theoretical basis for using ultrasound to study damaging coronavirus through transient and resonant vibration at large deformations.

Injectable three-dimensional tumor microenvironments to study mechanobiology in ovarian cancer

Epithelial ovarian cancers are among the most aggressive forms of gynecological malignancies. Despite the advent of poly adenosine diphosphate-ribose polymerase (PARP) and checkpoint inhibitors, improvement to patient survival has been modest. Limited in part by clinical translation, beneficial therapeutic strategies remain elusive in ovarian cancers. Although elevated levels of extracellular proteins, including collagens, proteoglycans, and glycoproteins, have been linked to chemoresistance, they are often missing from the processes of drug- development and screening. Biophysical and biochemical signaling from the extracellular matrix (ECM) determine cellular phenotype and affect both tumor progression and therapeutic response. However, many state-of-the-art tumor models fail to mimic the complexities of the tumor microenvironment (TME) and omit key signaling components. In this article, two interpenetrating network (IPN) hydrogel scaffold platforms, comprising of alginate-collagen or agarose-collagen, have been characterized for use as 3D in vitro models of epithelial ovarian cancer ECM. These highly tunable, injection mold compatible, and inexpensive IPNs replicate the critical governing physical and chemical signaling present within the ovarian TME. Additionally, an effective and cell-friendly live-cell retrieval method has been established to recover cells post-encapsulation. Lastly, functional mechanotransduction in ovarian cancers was demonstrated by increasing scaffold stiffness within the 3D in vitro ECM models. With these features, the agarose-collagen and alginate-collagen hydrogels provide a robust TME for the study of mechanobiology in epithelial cancers. Statement of significanceOvarian cancer is the most lethal gynecologic cancer afflicting women today. Here we present the development, characterization, and validation of 3D interpenetrating platforms to shift the paradigm in standard in vitro modeling. These models help elucidate the roles of biophysical and biochemical cues in ovarian cancer progression. The agarose-collagen and alginate-collagen interpenetrating network (IPN) hydrogels are simple to fabricate, inexpensive, and can be modified to create custom mechanical stiffnesses and concentrations of bio-adhesive motifs. Given that investigations into the roles of biophysical characteristics in ovarian cancers have provided incongruent results, we believe that the IPN platforms will be critically important to uncovering molecular drivers. We also expect these platforms to be broadly applicable to studies involving mechanobiology in solid tumors.

Monitoring the antibiotic darobactin modulating the β-barrel assembly factor BamA

The β-barrel assembly machinery (BAM) complex is an essential component of Escherichia coli that inserts and folds outer membrane proteins (OMPs). The natural antibiotic compound darobactin inhibits BamA, the central unit of BAM. Here, we employ dynamic single-molecule force spectroscopy (SMFS) to better understand the structure-function relationship of BamA and its inhibition by darobactin. The five N-terminal polypeptide transport (POTRA) domains show low mechanical, kinetic, and energetic stabilities. In contrast, the structural region linking the POTRA domains to the transmembrane β-barrel exposes the highest mechanical stiffness and lowest kinetic stability within BamA, thus indicating a mechano-functional role. Within the β-barrel, the four N-terminal β-hairpins H1-H4 expose the highest mechanical stabilities and stiffnesses, while the four C-terminal β-hairpins H5-H6 show lower stabilities and higher flexibilities. This asymmetry within the β-barrel suggests that substrates funneling into the lateral gate formed by β-hairpins H1 and H8 can force the flexible C-terminal β-hairpins to change conformations.

Additive Manufacturing of Microcantilevers of Varying Stiffness for Sensing Applications

Introduction Microcantilevers have numerous applications in physical, biological and chemical sensing. They have been employed for determination of the fluid viscosity and density [1], detection of biomolecular interaction [2], and part per billion (ppb) level of ammonia in ambient atmosphere [3]. The silicon-based microcantilevers are the most common type of these microdevices, however the biological and physical applications of the polymeric and polymer-composite microcantilevers have been reported in the literature [4], [5]. The polymeric cantilevers have lower Young’s modulus compared to the ones made of silicon and are more sensitive for static deflection measurement [6]. The polydimethylsiloxane (PDMS) and SU-8 are examples of polymers used for fabricating cantilevers through the soft-lithography process. Although the soft-lithography is a matured process for fabrication of the micro-electromechanical systems (MEMS), it is time consuming and costly in comparison with the additive manufacturing process. This may justify further investigations on employing Additive Manufacturing (AM) technologies in fabrication of the MEMS devices. In this study, we report additive manufacturing of the polymeric microcantilevers with different dimensions using SLA 3D printing technology for employing in micro-sensing applications. Method Four 300 μm width microcantilevers with different lengths and thicknesses, were 3D printed using the Form 2 SLA 3D printer. Table 1 presents the dimensions of the cantilevers. Figure 1 shows the images of the green parts on the building platform and the final parts after post processing. 50 μm was chosen as a thickness of each layer for printing. The building material was Flexible resin (Formlabs, USA). Table 2 presents the characteristics of the printing material. The printing process of all cantilevers took 2.5 hours. To investigate the mechanical property of printed cantilevers, the linear stiffness of each part was determined by the static load-deflection tests. The tests were performed by imposing the deflection to the tip of cantilever and recording the corresponding load. The maximum deflection applied to cantilevers was 300 μm. The FemtoTools FT-RS1002 Microrobotic Measurement System was employed to perform the measurements using the mounted sensing probe with the needle tip section size of (50 × 50 μm), force range of ±100000 μN, and resolution of 5 μN. Figure 2 illustrates the front and side views of the sensing probe in contact with the one of cantilevers at the beginning of the measurement test. Results and Conclusions The length and thickness of the microcantilever affect its sensitivity. Figure 3 displays the force-deflection graphs of microcantilevers with different length-thickness ratios obtained from the tests explained in methodology. Due to the small deflection imposed to all plastic microcantilevers with respect to their dimensions, the results show the bilinear response of the cantilevers. The linear relation between the force and the deflection can be observed when the samples deflects beyond the 80 μm. Despite various dimensions of the fabricated microcantilevers, the graph confirms that the length-thickness ratio affects the stiffness of the beams which is determined by the slope of each graphs. Table 3 presents the stiffness of fabricated samples. The graphs show increasing the length-ratio of the microbeams results in increasing the stiffness of the beam. The mechanical stiffnesses of the low length-thickness ratio microcantilevers, samples 1 and 2, are comparable with the PDMS cantilever’s stiffness reported in reference [7] . This reveals the possibility of employing the SLA 3D printing method in fabrication of the operational microcantilevers. This manufacturing method offers the simplicity, time and cost reduction in fabrication of the microcantilevers. References Kim, Deokman, et. al. "Determination of fluid density and viscosity by analyzing flexural wave propagations on the vibrating micro-cantilever." Sensors 17, no. 11 (2017): 2466.Amritsar, Jeetender, et. al. "Conformational detection of heat shock protein through bio-interactions with microstructures." Research on Biomedical Engineering 36, no. 1 (2020): 89-98.Liu, Manyi, et. al. "Revealing humidity-enhanced NH3 sensing effect by using resonant microcantilever." Sensors and Actuators B: Chemical 257 (2018): 488-495.Seena, V., et. al. "Polymer microcantilever biochemical sensors with integrated polymer composites for electrical detection." Solid State Sciences 11, no. 9 (2009): 1606-1611.Sadabadi, Hamid, and Muthukumaran Packirisamy. "Nano-integrated suspended polymeric microfluidics (SPMF) platform for ultra-sensitive bio-molecular recognition of bovine growth hormones." Scientific reports 7, no. 1 (2017): 1-10.Chaudhary, Monika, and Amita Gupta. "Microcantilever-based sensors." Defence Science Journal 59, no. 6 (2009): 634-641.Nezhad, Amir Sanati, et. al. "PDMS microcantilever-based flow sensor integration for lab-on-a-chip." IEEE Sensors journal 13, no. 2 (2012): 601-609. Figure 1

Soft Topological Metamaterials with Pronounced Polar Elasticity in Mechanical and Dynamic Behaviors

We realize soft topological mechanical metamaterials with pronounced polar elastic responses (i.e., softer on one edge than the other) in both the quasistatic and dynamic regimes. Numerical simulations and experimental results confirm the presence of directional dependence in metamaterial response at low and high strain rates, despite the use of lossy elastomer as bulk media. The metamaterials exhibit means to tailor the location of topologically protected uniaxial mechanical stiffnesses by virtue of both loading orientation and geometric changes to the lattice architecture. High-speed video recordings show strong topologically protected asymmetric wave propagation for the soft metamaterials subjected to impact. The results indicate a class of metamaterial architectures possessing polar elastic behavior and confirm the persistence of the response in lossy media.

SMALLBug: A 30-mg Crawling Robot Driven by a High-Frequency Flexible SMA Microactuator

We present the design, fabrication and experimental testing of SMALLBug, a 30-mg crawling microrobot that is 13 mm in length and can locomote at actuation frequencies of up to 20 Hz. The robot is driven by an electrically-powered 6-mg bending actuator that is composed of a thin shape-memory alloy (SMA) wire and a carbon-fiber piece that acts as a loading leaf-spring. This configuration enables the generation of high-speed thermally-induced phase transformations of the SMA material to produce high-frequency periodic actuation. During development, several actuator prototypes with different mechanical stiffnesses were tested and characterized by measuring their bending motions when excited with pulse-width modulation (PWM) voltages with a variety of frequencies and duty cycles (DCs). In a similar manner, the displacement-force characteristic of the actuator chosen to drive SMALLBug was identified by measuring its bending displacements under a number of different loads ranging from 4.22 to 83.8 mN. The locomotion capabilities of SMALLBug were experimentally tested at three different input actuation frequencies, which were observed to produce three distinct gaits. At the low frequency of 2 Hz, the robot locomotes with a crawling gait similar to that of inchworms; at the moderate frequency of 10 Hz, the robot advances smoothly at an approximately constant speed using a shuffling gait; and at the high frequency of 20 Hz, the robot generates small and fast jumps in a galloping gait, reaching average speeds of up to 17 $\boldsymbol{\text {mm}} \cdot \boldsymbol{\text {s}}^{\boldsymbol{\text {--}}\boldsymbol{\text {1}}}$, equivalent to 1.3 body-lengths per second (BLPS).

Non-contact microfluidic mechanical property measurements of single apoptotic bodies

BackgroundCells exchange information by secreting micro­ and nanosized extracellular vesicles (EVs), ranging from exosomes (30–100 nm) to apoptotic bodies (ABs, 1–5 μm). There is still much to understand about fundamental EV biological, physical, and chemical properties before clinical applications can be developed. EV mechanical properties have only been measured with atomic force microscopy (AFM) with its problematic adhesion and hard substrate effects. To understand EV mechanical behavior in less extreme mechanical conditions relevant to blood flow and many soft tissue environments, a non-contact measurement technique is needed. MethodsWe measured the mechanical properties of single microscale ABs derived from human blood plasma using non-contact microfluidics. EVs were gently stretched in extensional flow, similar to a traditional tensile test, and a linear mechanical model was applied to estimate mechanical stiffnesses from the observed stretching. ResultsThe effective shear elastic modulus of ABs in non-contact flow conditions is approximately 5.6 ± 0.5 Pa, 7 orders of magnitude lower than previously reported AFM-measured biological exosome stiffnesses and 200 times smaller than suspended cells. ConclusionsApoptotic bodies are very soft in fluid environments and exhibit lower effective stiffnesses than suspended cells. By measuring ABs in a natural fluid environment and low-force regime without hard probes and surfaces, we achieved closer agreement with linear mechanical theory and therefore more accurate stiffness measurements. General significanceAFM manufacturers and users should consider implementing new mechanical models to interpret AFM force indentation curves so that accurate extracellular vesicle mechanical properties can be extracted.

Fabricating a Kidney Cortex Extracellular Matrix-Derived Hydrogel.

Extracellular matrix (ECM) provides important biophysical and biochemical cues to maintain tissue homeostasis. Current synthetic hydrogels offer robust mechanical support for in vitro cell culture but lack the necessary protein and ligand composition to elicit physiological behavior from cells. This manuscript describes a fabrication method for a kidney cortex ECM-derived hydrogel with proper mechanical robustness and supportive biochemical composition. The hydrogel is fabricated by mechanically homogenizing and solubilizing decellularized human kidney cortex ECM. The matrix preserves native kidney cortex ECM protein ratios while also enabling gelation to physiological mechanical stiffnesses. The hydrogel serves as a substrate upon which kidney cortex-derived cells can be maintained under physiological conditions. Furthermore, the hydrogel composition can be manipulated to model a diseased environment which enables the future study of kidney diseases.

Compliant Substratum Changes Osteocyte Functions: The Role of ITGB3/FAK/β-Catenin Signaling Matters.

Bone shows the potential to adapt its architecture to environmental rigidity via the bone remodeling process, which is governed by osteocytes. Once the remodeling process is disrupted, the mechanics of the bone architecture is impaired, and bone disease proceeds. During the process of pathogenesis, how the osteocytes start the process of sensing and transducing a weakened extracellular mechanical signal into a biochemical signal remains elusive. In the current study, using polydimethylsiloxane (PDMS) substrates with varied mechanical stiffnesses, we first showed that the osteocytes can sense the mechanical change and respond by showing different cell spreading areas and cytoskeleton distributions. Osteocytes sense ECM mechanics via integrin αvβ3, which interacts with focal adhesion kinase (FAK) to promote the transduction of extracellular mechanical stimuli into intracellular biochemical signals. FAK triggers cytoplasmic β-catenin signaling and the resultant nuclear translocation. This signaling results in changes in the gap junction and mineralization activity of the osteocytes. This study establishes the correlation between microenvironmental mechanics and osteocyte function by characterizing the interaction between integrin αvβ3/FAK signaling and β-catenin signaling, thus providing a deep understanding of mechanosensing and mechanotransduction in osteocytes and bone pathogenesis.

Biomechanical analysis using infrared thermography of a traditional metal plate versus a carbon fibre/epoxy plate for Vancouver B1 femur fractures

Traditional high-stiffness metal plates for Vancouver B1 femur shaft fractures below the tip of a hip implant can cause stress shielding, bone resorption, and implant loosening. This is the first study to compare the biomechanics of a traditional metal plate versus a low-stiffness carbon fibre/epoxy composite plate for this injury. A total hip replacement was implanted in two previously validated intact artificial femurs. Femurs were fitted with either a metal or composite plate and had a 5 mm fracture gap created to simulate a Vancouver B1 shaft fracture. Femurs were cyclically loaded using 5 Hz at 7° of adduction with an average axial load of 800 N (range = 400-1200 N). Overall mechanical stiffnesses and femur and plate thermographic stresses were obtained. Femur/metal plate stiffness (698 N/mm) was only 12% higher than femur/composite plate stiffness (625 N/mm). The femur with the composite plate had 22.7% higher combined average stress compared to the femur with the metal plate, having specific differences of 29.5% (anterior view), 33.9% (posterior view), 1.0% (medial view), and 26.4% (lateral view). The composite plate itself had an average 21.1% reduction in stress compared to the metal plate. The composite plate reduced stress shielding, yet provided adequate stiffness.

Dominant factors influencing the nanoindentation response of piezoelectric materials: a case study in relaxor ferroelectrics

The nanoindentation response of a piezoelectric material is, in general, influenced in a complex manner by its elastic, dielectric and piezoelectric properties. The present study is focused on obtaining a comprehensive understanding of the dominant material factors influencing the force–depth mechanical indentation response and the charge–depth electrical indentation response of piezoelectric materials. From a large number of three-dimensional finite element simulations of the indentation of simple and complex piezoelectric materials (such as PZT-5A and relaxor ferroelectrics), the following principal conclusions are obtained: (1) For indentations with both conducting and insulating indenters, the mechanical indentation stiffness is influenced more by the elastic properties, while the electrical indentation stiffness is influenced largely by the piezoelectric properties of the indented materials. (2) For longitudinal indentations using a conducting indenter, the elastic constants, C 33 and C 13, and piezoelectric constants, e33 and e15, are, respectively, the first and second most dominant material constants that influence the mechanical indentation stiffness and the electrical indentation stiffness. (3) For transverse indentations using a conducting indenter, the elastic constants, C 11 and C 12, are, respectively, the first and second most dominant material constants that influence the mechanical indentation stiffness. (4) In the indentation of relaxor ferroelectrics based on PMN-xPT and PZN-xPT, which exhibit a range of elastic, dielectric and piezoelectric properties, it is generally observed that materials with higher normal elastic and piezoelectric constants, i.e., C 33 and e33, respectively, exhibit higher mechanical and electrical indentation stiffnesses.

A Model of the Spatially Dependent Mechanical Properties of the Axon During Its Growth

Neuronal growth is a complex process involving many intra- and extracellular mechanisms which are collaborating conjointly to participate to the development of the nervous system. More particularly, the early neocortical development involves the creation of a multilayered structure constituted by neuronal growth (driven by axonal or dendritic guidance cues) as well as cell migration. The underlying mechanisms of such structural lamination not only implies important biochemical changes at the intracellular level through axonal microtubule (de)polymerization and growth cone advance, but also through the directly dependent stress/stretch coupling mechanisms driving them. Efforts have recently focused on modeling approaches aimed at accounting for the effect of mechanical tension or compression on the axonal growth and subsequent soma migration. However, the reciprocal influence of the biochemical structural evolution on the mechanical properties has been mostly disregarded. We thus propose a new model aimed at providing the spatially dependent mechanical properties of the axon during its growth. Our in-house finite difference solver Neurite is used to describe the guanosine triphosphate (GTP) transport through the axon, its dephosphorylation in guanosine diphosphate (GDP), and thus the microtubules polymerization. The model is calibrated against experimental results and the tensile and bending mechanical stiffnesses are ultimately inferred from the spatially dependent microtubule occupancy. Such additional information is believed to be of drastic relevance in the growth cone vicinity, where biomechanical mechanisms are driving axonal growth and pathfinding. More specifically, the confirmation of a lower stiffness in the distal axon ultimately participates in explaining the controversy associated to the tensile role of the growth cone.

Electric field–curvature relationships for small and large deformation of piezoelectric bi-layers

A simple analytical framework is developed to capture the characteristic features of the electric field–curvature response of piezoelectric bi-layers. For small deformations, the curvatures developed depend on the mismatch in the piezoelectric strengths and the mechanical stiffnesses in both the layers, and the relative thicknesses and the electric potentials applied across each of the layers. For large deformations, a bifurcation in curvature is generally observed at characteristic electric fields which depend strongly on the geometric asymmetry of the bi-layers.

기계적으로 다른 환경에서 예쁜 꼬마선충의 기는 파형 변화

The nematode Caenorhabditis elegans is a widely used model organism in biological research. Thanks to the availability of well-established knowledge about its neural connectivity, a wide range of studies have been attempted to uncover the relationship between behaviors and the responsible neurons. In our research, the adaptive behavior of C. elegans in solid environments with different surface rigidities is investigated, where the worm adapts to different mechanical stiffnesses by modulating its crawling waveform. The amplitude and wavelength of the crawling waveform decrease as the environment becomes more rigid. Interestingly, the mechanosensation-defective mutant shows different responses to the surface rigidity compared to those of the wild-type worm. To explain the adaptation process in mechanically different environments, we suggest a plausible neural circuit model.