Wide Range Of Stiffness Research Articles

Mechanical Characterization of Human Monocyte Derived Antigen Presenting Cells

T cells are at the root of the immune response protecting living organisms against pathogens and tumor cells, and have recently been shown to respond to mechanical changes. The activation of T cells triggering the immune response requires the formation of cell-cell interaction between T lymphocytes and various antigen presenting cells (APC) (tumor cells, dendritic cells, macrophages, B lymphocytes...). Yet, little is known about the rigidity of these different APCs. In the present study we use the single-cell microplates assay to measure the mechanical properties of human monocyte derived APCs. We show that APCs present a wide range of stiffnesses, that are affected during differentiation, maturation and in response to inflammatory signals.Noteworthily, dendritic cells, the most efficient APC for T cell activation, present the closest rigidity to T cell rigidity. These results suggest that cell stiffness could be an important factor in immune cell-cell interactions and T cell mediated responses. We will then show preliminary studies on the role of rigidity in T cell activation ; involving laying T cells on substrates mimicking APCs rigidities and monitoring T cell activation and T cell / substrate interface organization.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Flow observations in elastic stenosis biomodel with comparison to rigid-like model

Plaques in blood vessels exhibit a wide range of stiffness depending on disease conditions: stiffness is an important factor in plaque behavior. The geometrical change in plaque based on its behavior can affect blood flow patterns. Thus, it is important to study both blood flow and deformation of plaques and blood vessels. This study aims to identify the differences in flow conditions between in vitro models to discuss experimental materials for arterial wall and flow observation. In order to observe the blood flow pattern and plaque deformation simultaneously, a PVA-H stenosis model was used. In addition, a silicone model was also used as a rigid-like model for comparison with the PVA-H model. PIV was employed to measure the flow velocity distribution and determine the flow levels in the models. PVA-H model exhibits expansion with an increase in upstream pressure and silicone model maintains the diameter. The expansion depends on their mechanical properties and influences flow conditions such as velocity changes and RAP in the parent artery. The balance between the expansion and change in flow conditions determines the final geometries of PVA-H model and flow pattern. The results suggest that the stiffness measurement for blood vessels and plaques such as ultrasound measurements would be important for accurate treatments.

Pan-neuronal maturation but not neuronal subtype differentiation of adult neural stem cells is mechanosensitive

Most past studies of the biophysical regulation of stem cell differentiation have focused on initial lineage commitment or proximal differentiation events. It would be valuable to understand whether biophysical inputs also influence distal endpoints more closely associated with physiological function, such as subtype specification in neuronal differentiation. To explore this question, we cultured adult neural stem cells (NSCs) on variable stiffness ECMs under conditions that promote neuronal fate commitment for extended time periods to allow neuronal subtype differentiation. We find that ECM stiffness does not modulate the expression of NeuroD1 and TrkA/B/C or the percentages of pan-neuronal, GABAergic, or glutamatergic neuronal subtypes. Interestingly, however, an ECM stiffness of 700 Pa maximizes expression of pan-neuronal markers. These results suggest that a wide range of stiffnesses fully permit pan-neuronal NSC differentiation, that an intermediate stiffness optimizes expression of pan-neuronal genes, and that stiffness does not impact commitment to particular neuronal subtypes.

An all-purpose metric for the exterior of any kind of rotating neutron star

We have tested the appropriateness of two-soliton analytic metric to describe the exterior of all types of neutron stars, no matter what their equation of state or rotation rate is. The particular analytic solution of the vaccuum Einstein equations proved quite adjustable to mimic the metric functions of all numerically constructed neutron-star models that we used as a testbed. The neutron-star models covered a wide range of stiffness, with regard to the equation of state of their interior, and all rotation rates up to the maximum possible rotation rate allowed for each such star. Apart of the metric functions themselves, we have compared the radius of the innermost stable circular orbit $R_{\rm{ISCO}}$, the orbital frequency $\Omega\equiv\frac{d\phi}{dt}$ of circular geodesics, and their epicyclic frequencies $\Omega_{\rho}, \Omega_z$, as well as the change of the energy of circular orbits per logarithmic change of orbital frequency $\Delta\tilde{E}$. All these quantities, calculated by means of the two-soliton analytic metric, fitted with good accuracy the corresponding numerical ones as in previous analogous comparisons (although previous attempts were restricted to neutron star models with either high or low rotation rates). We believe that this particular analytic solution could be considered as an analytic faithful representation of the gravitation field of any rotating neutron star with such accuracy, that one could explore the interior structure of a neutron star by using this space-time to interpret observations of astrophysical processes that take place around it.

The Matrix Stiffness Regulates Morphology, Direction and Persistence of Motiles Cells

Cell motility is a fundamental process for embryonic development, wound healing, immune responses and for pathological processes such as cancer metastasis. During past few decades, the influence of the extracellular matrix stiffness, known as durotaxis, has been extensively studied on stationary cells. However, the impact of the matrix stiffness on the motion of motile cells is still unclear. By using a wide range of ECM stiffnesses with a contant cell-ligand density, we have investigated morphological and dynamical parameters of fish keratocytes in response to a wide range of matrix stiffnesses. We have found that modifying the matrix rigidity of the underlying substrate has a dramatic effect on keratocyte motility and directional persistence. To elucidate the mechanisms by which the matrix stiffness determines moving cell behavior, we examined the organization of adhesions, myosin II, and the actin network in keratocytes migrating on substrates with a wide range of stiffnesses and a constant surface chemistry. Our results are consistent with a quantitative physical model in which keratocyte shape and migratory behavior emerge from the self-organization of actin, cell-substrate adhesions and myosin II activity.

Synthesis and characterization of designed BMHP1-derived self-assembling peptides for tissue engineering applications

The importance of self-assembling peptides (SAPs) in regenerative medicine is becoming increasingly recognized. The propensity of SAPs to form nanostructured fibers is governed by multiple forces including hydrogen bonds, hydrophobic interactions and π-π aromatic interactions among side chains of the amino acids. Single residue modifications in SAP sequences can significantly affect these forces. BMHP1-derived SAPs is a class of biotinylated oligopeptides, which self-assemble in β-structured fibers to form a self-healing hydrogel. In the current study, selected modifications in previously described BMHP1-derived SAPs were designed in order to investigate the influence of modified residues on self-assembly kinetics and scaffold formation properties. The Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis demonstrated the secondary structure (β-sheet) formation in all modified SAP sequences, whereas atomic force microscopy (AFM) analysis further confirmed the presence of nanofibers. Furthermore, the fiber shape and dimension analysis by AFM showed flattened and twisted fiber morphology ranging from ∼8 nm to ∼70 nm. The mechanical properties of the pre-assembled and post assembled solution were investigated by rheometry. The shear-thinning behavior and rapid re-healing properties of the pre-assembled solutions make them a preferable choice for injectable scaffolds. The wide range of stiffnesses (G')--from ∼1000 to ∼27,000 Pa--exhibited by the post-assembled scaffolds demonstrated their potential for a variety of tissue engineering applications. The extra cellular matrix (ECM) mimicking (physically and chemically) properties of SAP scaffolds enhanced cell adhesion and proliferation. The capability of the scaffold to facilitate murine neural stem cell (mNSC) proliferation was evaluated in vitro: the increased mNSCs adhesion and proliferation demonstrated the potential of newly synthesized SAPs for regenerative medicine approaches.

Design and Control of a Variable Stiffness Actuator Based on Adjustable Moment Arm

For tasks that require robot-environment interaction, stiffness control is important to ensure stable contact motion and collision safety. The variable stiffness approach has been used to address this type of control. We propose a hybrid variable stiffness actuator (HVSA), which is a variable stiffness unit design. The proposed HVSA is composed of a hybrid control module based on an adjustable moment-arm mechanism, and a drive module with two motors. By controlling the relative motion of gears in the hybrid control module, position and stiffness of a joint can be simultaneously controlled. The HVSA provides a wide range of joint stiffness due to the nonlinearity provided by the adjustable moment arm. Furthermore, the rigid mode, which behaves as a conventional stiff joint, can be implemented to improve positioning accuracy when a robot handles a heavy object. In this paper, the mechanical design features and related analysis are explained. We show that the HVSA can provide a wide range of stiffness and rapid responses according to changes in the stiffness of a joint under varying loads by experiments. The effectiveness of the rigid mode is verified by some experiments on position tracking under high-load conditions.

High-Frequency Viscoelastic Shear Properties of Vocal Fold Tissues: Implications for Vocal Fold Tissue Engineering

The biomechanical function of the vocal folds (VFs) depends on their viscoelastic properties. Many conditions can lead to VF scarring that compromises voice function and quality. To identify candidate replacement materials, the structure, composition, and mechanical properties of native tissues need to be understood at phonation frequencies. Previously, the authors developed the torsional wave experiment (TWE), a stress-wave-based experiment to determine the linear viscoelastic shear properties of small, soft samples. Here, the viscoelastic properties of porcine and human VFs were measured over a frequency range of 10-200 Hz. The TWE utilizes resonance phenomena to determine viscoelastic properties; therefore, the specimen test frequency is determined by the sample size and material properties. Viscoelastic moduli are reported at resonance frequencies. Structure and composition of the tissues were determined by histology and immunochemistry. Porcine data from the TWE are separated into two groups: a young group, consisting of fetal and newborn pigs, and an adult group, consisting of 6-9-month olds and 2+-year olds. Adult tissues had an average storage modulus of 2309±1394 Pa and a loss tangent of 0.38±0.10 at frequencies of 36-200 Hz. The VFs of young pigs were significantly more compliant, with a storage modulus of 394±142 Pa and a loss tangent of 0.40±0.14 between 14 and 30 Hz. No gender dependence was observed. Histological staining showed that adult porcine tissues had a more organized, layered structure than the fetal tissues, with a thicker epithelium and a more structured lamina propria. Elastin fibers in fetal VF tissues were immature compared to those in adult tissues. Together, these structural changes in the tissues most likely contributed to the change in viscoelastic properties. Adult human VF tissues, recovered postmortem from adult patients with a history of smoking or disease, had an average storage modulus of 756±439 Pa and a loss tangent of 0.42±0.10. Contrary to the results of some other investigators, no significant frequency dependence was observed. This lack of observable frequency dependence may be due to the modest frequency range of the experiments and the wide range of stiffnesses observed within nominally similar sample types.

Vibrational characteristics of wood, aluminum, and composite hockey sticks

The stick used by ice hockey players consists of a long straight shaft attached to a curved blade. Composite materials have replaced wood and aluminum shafts for the vast majority of current professional and amateur players. The stiffness of the shaft plays a crucial role in the amount of potential energy that can be stored and released during a slap shot. Shafts are available in a wide range of stiffness and flex ratings in order to match player preference. Several wood, aluminum, and composite shafts were tested using a roving hammer experimental modal analysis with and without their blades. Mode shapes of the shaft tested alone were found to be those of a free-free beam. For shafts of similar lengths, aluminum shafts had the highest resonance frequencies and the lowest damping coefficients, while wood shafts had the lowest frequencies and the highest damping. Vibrational characteristics of whole sticks, including one-piece, two-piece sticks (shaft and blade from same material), and hybrid (shaft and blade of different materials) show that the presence of the blade significantly lowers the frequencies of the torsional modes of vibration. These results, especially damping coefficients, suggest reasons for the anecdotally preferred “feel” provided by composite sticks.

Do mechanical tests of glove stiffness provide relevant information relative to their effects on the musculoskeletal system? A comparison with surface electromyography and psychophysical methods

The main purpose of the present study was to test the construct validity of two mechanical tests of glove stiffness using a surface electromyography (SEMG) methodology that would allow estimating the effect of glove stiffness on forearm muscle activation during a standardized grip contraction. The mechanical tests [free-deforming multidirectional test (FDMT) and Kawabata Evaluation System for Fabrics (KESF)] were applied on 27 gloves covering a wide range of stiffness. In 30 human subjects, a psychophysical assessment of these gloves was also carried on in addition to the SEMG test. The results showed that the sensitivity of the different tests to glove stiffness differences was slightly better for the FDMT (75% sensitivity) than for the psychophysical assessment (72%), while the SEMG test showed much lower sensitivity (13–31%, depending on the muscle). The SEMG test was highly correlated to the psychophysical assessment (0.88–0.95, depending on the muscle tested), and the FDMT (0.88–0.94) and KESF (0.77–0.86) mechanical tests, showing the construct validity of mechanical tests, particularly for the FDMT. It was concluded that mechanical tests provide relevant information relative to the effect of glove stiffness on the musculoskeletal system of the forearm.

Copolymer-in-oil Phantom Materials for Elastography

Phantoms that mimic mechanical and acoustic properties of soft biological tissues are essential to elasticity imaging investigation and to elastography device characterization. Several materials including agar/gelatin, polyvinyl alcohol and polyacrylamide gels have been used successfully in the past to produce tissue phantoms, as reported in the literature. However, it is difficult to find a phantom material with a wide range of stiffness, good stability over time and high resistance to rupture. We aim at developing and testing a new copolymer-in-oil phantom material for elastography. The phantom is composed of a mixture of copolymer, mineral oil and additives for acoustic scattering. The mechanical properties of phantoms were evaluated with a mechanical test instrument and an ultrasound-based elastography technique. The acoustic properties were investigated using a through-transmission water-substituting method. We showed that copolymer-in-oil phantoms are stable over time. Their mechanical and acoustic properties mimic those of most soft tissues: the Young's modulus ranges from 2.2–150 kPa, the attenuation coefficient from 0.4–4.0 dB.cm –1 and the ultrasound speed from 1420–1464 m/s. Their density is equal to 0.90 ± 0.04 g/cm 3. The results suggest that copolymer-in-oil phantoms are attractive materials for elastography. (E-mail: jennifer.oudry@echosens.com)

Cricket balls: construction, non-linear visco-elastic properties, quality control and implications for the game

Compression and stress relaxation tests were applied to five different ball models (Kookaburra Special Test, Gray-Nicolls Super Cavalier, Regent Match red, Regent Match white, and Sanspareils-Greenlands Tournament). Of the five models tested, only the Kookaburra ball was manufactured consistently. All other balls proved to be produced inconsistently with a wide range of stiffness. Additionally, the other four balls revealed two different, yet externally indistinguishable constructions, which resulted in two clusters of different stiffness. The different constructions might be related to the tension of the woolen twine in Regent Match red and the lacquer surface finish and/or cork-rubber mixture in Regent Match white. Gray-Nicolls Super Cavalier was produced with two different core sizes (stiffer ball with smaller core), and Sanspareils-Greenlands Tournament exhibited two different core materials, namely cork or rubber core, with the latter being the softer one. The hard subtypes of Regent Match white, Regent Match red and Sanspareils-Greenlands Tournament turned out to be the hardest balls, the hard sub-type of Gray-Nicolls Super Cavalier and the soft sub-types of Regent Match red and Sanspareils-Greenland Tournament showed intermediate stiffness, and the soft sub-types of Gray-Nicolls Super Cavalier and Regent Match red as well as the Kookaburra Special Test ball proved to be the softest. The viscosity coefficient of all balls increased with the deflection and the stress relaxation followed a power law. The peak impact forces calculated from the power law model correlated well with the experimentally measured peak forces. The two different constructions (sub-types) of Regent Match white, Gray-Nicolls Super Cavalier and Sanspareils-Greenland Tournament behaved like two different balls of significantly different stiffness. The latter fact may have severe implications to the match, as softer balls are more forgiving by causing a smaller impact force, a longer contact with the bat, larger deflections, as well as larger contact areas during impact, and therefore allowing placing the ball preciser. A more stringent quality control and testing standard is required for cricket balls in order to avoid unequal chances for both teams. © 2008 John Wiley and Sons Asia Pte Ltd

Parametric study of single-degree-of-freedom systems with energy dissipating devices built on soft soil sites

Energy dissipating devices have been used in recent years to control structural response and reduce seismic damage. A study aimed at determining the possible benefits and providing some general design recommendation for structures with energy dissipating devices built on soft soil sites is presented. Results from a comprehensive parametric study of single-degree-of-freedom systems with metallic yielding devices are summarized. Response history analyses are conducted by considering a wide range of stiffness and strength parameters in the structure and energy dissipation devices. Special attention is devoted to determining behavior limit states, focusing on ductility demands on the frame and energy dissipation devices. It is shown that ductility demands are strongly influenced by the period of the frame relative to the predominant period of the ground motion as well as by the lateral strength of the frame and energy dissipation devices. Results presented in this study provide guidance for the preliminary selection of the mechanical and geometrical properties of structures with metallic yielding devices located at soft soil sites.

Calculating the Pressure and the Stiffness in Three Different Categories of Class II Medical Elastic Compression Stockings

Medical elastic compression stockings (MECSs) are currently classified according to the pressure they exert at the ankle at the point of its minimum girth (B level). Despite this classification, there are considerable differences between MECSs belonging to the same compression class from the same manufacturers and between different manufacturers. This makes it difficult for the clinician to choose the most suitable MECS for the patient. The stiffness may be used to distinguish between MECSs of different brands. To calculate the pressure and the stiffness at the B level in three categories of class II MECSs from nine different brands. Nine different brands of class II MECSs that were divided into three categories (flat-knitted custom-made, classic round-knitted ready-made, and modern (ultrathin) round-knitted ready-made) were tested. The tension of the textile of the MECSs was measured with the Instron tester (Instron International Ltd., Edegem, Belgium). The pressures and stiffness at the B level were calculated. The pressures exerted by flat-knitted custom-made MECSs were higher than those exerted by the ready-made round-knitted MECSs. Surprisingly, the former showed higher pressures than those published by the European Committee for Standardization. A wide range of stiffness was observed within the different brands and within the three different categories of MECS. Despite their assignment to compression class II, all nine brands of MECSs that were tested had widely ranging stiffness. This would indicate that the stiffness is an additional important characteristic for distinguishing between MECSs from different brands, which should be taken into account by the clinician in selecting the most suitable MECSs for the patient.

Calculating the Pressure and the Stiffness in Three Different Categories of Class II Medical Elastic Compression Stockings

BACKGROUND Medical elastic compression stockings (MECS) are currently classified according to the pressure they exert at the ankle at the point of its minimum girth (B level). Despite this classification, there are considerable differences between MECS belonging to the same compression class from the same manufacturers and between different manufacturers. This makes it difficult for the clinician to choose the most suitable MECS for the patient. The stiffness may be used to distinguish between MECS of different brands. OBJECTIVE To calculate the pressure and the stiffness at the B level in three categories of class II MECS from nine different brands. METHODS Nine different brands of class II MECS that were divided into three categories (flat-knitted custom-made, classic round-knitted ready-made, and modern (ultrathin) round-knitted ready-made) were tested. The tension of the textile of the MECS was measured with the Instron® tester. The pressures and stiffness at the B level were calculated. RESULTS The pressures exerted by flat-knitted custom-made MECS were higher than those exerted by the ready-made round-knitted MECS. Surprisingly, the former showed higher pressures than those published by the European Committee for Standardization. A wide range of stiffness was observed within the different brands and within the three different categories of MECS. CONCLUSION Despite their assignment to compression class II, all nine brands of MECS that were tested had widely ranging stiffness. This would indicate that the stiffness is an additional important characteristic for distinguishing between MECS from different brands, which should be taken into account by the clinician in selecting the most suitable MECS for the patient.

Polymer microcantilevers fabricated via multiphoton absorption polymerization

We have used multiphoton absorption polymerization to fabricate a series of microscale polymer cantilevers. Atomic force microscopy has been used to characterize the mechanical properties of microcantilevers with spring constants that were found to span more than four decades. From these data, we extracted a Young’s modulus of E=0.44GPa for these microscale cantilevers. The wide stiffness range and relatively low elastic modulus of the microstructures make them attractive candidates for a range of microcantilever applications, including measurements on soft matter.

Best stiffness for striation

A small change in substrate stiffness can deter striated muscle differentiation, as shown on page 877 by Engler et al. As stiffness changes of this magnitude are not uncommon in diseased tissues, injections of stem cells may be useless unless the target environment is also treated. Figure Striation (middle) is inefficient on too soft (left) or too hard (right) surfaces. Muscular dystrophy patients suffer from stiffened muscle tissue. Although muscle precursors are abundant in mdx mice, a muscular dystrophy model, they fail to regenerate injured muscle. The new article shows that this failure may be due to their overly stiff environment, which prevents skeletal muscle striation. Skeletal muscle precursors spread, assumed a spindle shape, and fused into multinucleated cells when grown on surfaces within a wide range of stiffness. However, striation—the alignment of actin and myosin into repeated units—was blocked if the substrates were either too soft (e.g., fibroblasts or weak gels) or too stiff (e.g., glass). Adhesions were strongest on the stiffest substrate. Differentiation therefore requires enough adhesion to sense the matrix stiffness, but not so much that cytoskeletal changes leading to striation are inhibited. What translates forces felt at adhesion sites into differentiation is unknown, but the membrane-bound scaffold protein N-RAP is one possibility, as it both nucleates actin filaments and regulates transcription. Striation was most prominent on substrates within just 25% of the stiffness of normal muscle. The authors found that mdx muscle is stiffer than this optimal range, and thus may inhibit differentiation of its own precursors. If cardiac muscles are similarly sensitive, careful application of antifibrotics may be needed before injections of precursor cells can regenerate tissue damaged by heart attacks. ▪

Connectors for Timber–Lightweight Concrete Composite Structures

In timberconcrete composite structures (TCCSs), a timber member is connected to a concrete slab so that the timber primarily resists tensile forces and the concrete resists compressive forces generated from flexure. In Europe, renovating historical timber floors to TCCS has become the most prevalent market for the usage of this technology. The addition of a concrete slab to a timber floor makes the system performance competitive to reinforced concrete floors. The horizontal timberconcrete interface is the challenge of the TCCS. Various connectors are on the market with a wide range of stiffnesses and load capacities which are crucial design parameters for TCCSs and empirically determined by tests. The results of push-out tests with five different connectors are presented. A lightweight concrete (LC) with a density of 1.6 kN/m3 (100 lb/ft3) was used as the concrete floor in the samples. The application of LC provides an interesting variation in TCCS technology to minimize the dead load on the timber floors. Results show that the combination of stiffness and capacity are crucial in choosing an economical connector.

Adaptive and Nonlinear Fuzzy Force Control Techniques Applied to Robots Operating in Uncertain Environments

AbstractFor robots to perform many complex tasks there is a need for robust and stable force control. Linear, fixed‐gain controllers can only provide adequate performance when they are tuned to specific task requirements, but if the environmental stiffness at the robot/task interface is unknown and varies significantly, performance is degraded. This paper describes the design of two nonlinear, fuzzy force controllers, developed primarily using analytical methods, which overcome the problems of conventional control. Using simulation and an experimental robot, they are shown to perform well over a wide range of stiffness and both a quantitative and qualitative assessment of their performance compared with conventional force control is presented. © 2003 Wiley Periodicals, Inc.

MR elastography of the breast:preliminary clinical results.

Imaging of breast tumors and various breast tissues using magnetic resonance (MR) elastography (MRE) to explore the potential of elasticity as a new parameter for the diagnosis of breast lesions. Low-frequency mechanical waves are transmitted into breast tissue by means of an oscillator. The local characteristics of the mechanical wave are determined by the underlying elastic properties of the tissue. Theses waves can be displayed by means of a motion-sensitive spin-echo MR sequence within the phase of the MR image. Elasticity reconstruction is performed on the basis of 8 "snapshots" of each wave within the three spatial directions. We performed in-vivo measurements in 15 female patients with malignant tumors of the breast, 5 patients with benign breast tumors, and 15 healthy volunteers. Malignant invasive breast tumors documented the highest values of elasticity with a median of 15.9 kPa and a wide range of stiffnesses between 8 and 28 kPa. In contrast, benign breast lesions represented low values of elasticity, which were significantly different from malignant breast tumors (median elasticity: 7.0 kPa; p = 0.0012). This was comparable to the stiffest tissue areas in healthy volunteers (median elasticity 7.0 kPa), whereas breast parenchyma (median: 2.5 kPa) and fatty breast tissue (median: 1.7 kPa) showed the lowest values of elasticity. Two invasive ductal carcinomas had elasticity values of 8 kPa and two stiff parenchyma areas in healthy volunteers had elasticities of 13 and 15 kPa. These lesions could not be differentiated by their elasticity. We conclude that MRE is a promising new imaging modality with the capability to assess the viscoelastic properties of breast tumors and the surrounding tissues. However, from our preliminary results in a small number of patients it is obvious that there is an overlap in the elasticity ranges of soft malignant tumors and stiff benign lesions.