bluuebunny/crossref_metadata_2025 huggingface dataset:
Cytoskeletal architecture and mechanical behavior of living cells
Authors: Volokh K.Yu.
Published: November 2024

Conventional continuum mechanics models considering living cells as viscous fluid balloons are unable to explain some recent experimental observations. In contrast, new microstructural models provide the desirable explanations. These models emphasize the role of the cell cytoskeleton built of struts‐microtubules and cables‐microfilaments. A specific architectural model of the cytoskeletal framework called “tensegrity” deserved wide attention recently. Tensegrity models particularly account for the phenomenon of linear stiffening of living cells. These models are discussed from the structural mechanics perspective. Classification of structural assemblies is given and the meaning of “tensegrity” is pinpointed. Possible sources of non‐linearity leading to cell stiffening are emphasized. The role of local buckling of microtubules and overall stability of the cytoskeleton is stressed. Computational studies play a central role in the development of the microstructural theoretical framework allowing for the prediction of the cell behavior from “first principles”. Algorithms of computer analysis of the cytoskeleton that consider unilateral response of microfilaments and deep postbuckling of microtubules are addressed.
Mechanical assessment by magnetocytometry of the cytosolic and cortical cytoskeletal compartments in adherent epithelial cells
Authors: Laurent Valérie M. , Planus Emmanuelle , Fodil Redouane , Isabey Daniel
Published: November 2024

This study aims at quantifying the cellular mechanical properties based on a partitioning of the cytoskeleton in a cortical and a cytosolic compartments. The mechanical response of epithelial cells obtained by magnetocytometry – a micromanipulation technique which uses twisted ferromagnetic beads specifically linked to integrin receptors – was purposely analysed using a series of two Voigt bodies. Results showed that the cortical cytoskeleton has a faster response (∼1 s) than the cytosolic compartment (∼30 s). Moreover, the two cytoskeletal compartments have specific mechanical properties, i.e., the cortical (resp. cytosolic) cytoskeleton has a rigidity in the range: 49–85 Pa (resp.: 74–159 Pa) and a viscosity in the range 5–14 Pa.s (resp.: 593–1534 Pa.s), depending on the level of applied stress. Depolymerising actin‐filaments strongly modified these values and especially those of the cytosolic compartment. The structural relevance of this two‐compartment partitioning was supported by images of F‐actin structure obtained on the same cells.
Comparative studies of LFA‐1/ICAM‐1 interaction by micropipette and flow chamber techniques
Authors: Zhao Hong , Zhuang Fengyuan , Stoltz Jean François , Wang Xiong
Published: November 2024

Interaction of lymphocyte function‐associated antigen‐1 (LFA‐1) with intercellular adhesive molecule‐1 (ICAM‐1) is important in a number of cellular events, including inflammation, adhesion, transendothelial migration. The aim of this work was to study comparatively the adhesive interaction between LFA‐1 and ICAM‐1 by a micropipette technique and a flow chamber method, and also to explore the effects of tumor necrosis factor (TNF‐α), phytohemagglutinin (PHA), and tetramethylpyrazine (TMP) on this interaction. The adhesion probability (Pa) between a lymphocyte cell line SKW‐3 expressing LFA‐1 and a red blood cell (RBC) coated with soluble ICAM‐1 was approached by the micropipette technique, while the flow chamber allowed to observe the firm adhesion of SKW‐3 on human umbilical vein endothelial cells (HUVECs). Experimental results show that PHA stimulation of lymphocytes resulted in significant increases in the adhesion probability (Pa) and in number of firmly adhered lymphocytes to HUVECs, but TMP treatment could significantly inhibit such increases.
CD34+ cells homing: Quantitative expression of adhesion molecules and adhesion of CD34+ cells to endothelial cells exposed to shear stress
Authors: Gigant C. , Latger‐Cannard V. , Bensoussan D. , Fawzi S. , Feugier P. , Bordigoni P. , Stoltz J.F.
Published: November 2024

To investigate the function of the main adhesion receptors (CD62L, CD49d, CD49e, CD11b and CD18) on CD34+ cells during homing, their expression was quantified by flow cytometry using calibration beads. CD34+ cells were isolated from bone‐marrow (BM), cord blood (CB) or peripheral blood (PB) from patients with myeloma. As this process might mimic the mature leukocyte migration, we also observed the effect of exposing endothelial cells to shear stress (7 dyn/cm2) on the adhesion of CB CD34+ cells.

The proportion of CD34+/CD62L+ cells was greater in PB than in BM (p<0.05). Likewise, we found a significantly greater expression of CD62L receptor on PB cells compared to BM cells (p<0.05) and on BM cells compared to CB cells (p<0.05). The proportions of CD34+/CD49d+ cells and CD34+/CD49e+ cells were significantly higher in the BM and CB than in PB. However, no significant difference in CD49d or CD49e antigen densities was observed. The β2 integrins (CD11b and CD18) receptors are also implicated in CD34+ cells homing to BM. No significant variation in CD34+/CD11b+ and CD34+/CD18+ cells frequency was noted. However quantitative analysis revealed that CD18 was more strongly expressed on BM cells than on PB and CB cells.

The adhesion assay showed that fluid flow may favour a firm adhesion of CB CD34+ cells to endothelial cells whereas static conditions just allowed CD34+ cells sedimentation.

In conclusion, quantitative expression of the main receptors on CD34+ cells indicates that the three main sources of CD34+ cells currently used for transplantation have neither the same phenotype nor the same number of antigenic sites for a receptor. So, we hypothesize that migrational capacity of these cells might be different. Moreover, it seems that shear stress could favor adhesion of CD34+ cells to endothelial cells.
Dermal fibroblasts respond to mechanical conditioning in a strain profile dependent manner
Authors: Berry C.C. , Cacou C. , Lee D.A. , Bader D.L. , Shelton J.C.
Published: November 2024

Fibroblasts within tissues are exposed to a dynamic mechanical environment, which influences the structural integrity of both healthy and healing soft tissues. Various systems have been proposed to subject such cells to mechanical stimulation in culture. However the diverse nature of the studies, in terms of the strain profiles and the cell types, makes direct comparisons almost impossible. The present study addresses this issue by examining the metabolic response of two cell types subjected to three well defined strain profiles.

A young fibroblast cell population, represented by HuFFs, showed both greater cell proliferation and collagen production than adult dermal fibroblasts under unstrained conditions. The three strain profiles produced differing effects on both cell types. Uniaxial strains enhanced [3H]‐thymidine incorporation for both cell types, whilst biaxial strains either inhibited or had no effect on its incorporation. In contrast, [3H]‐proline incorporation was inhibited under biaxial and uniaxial strains for the adult fibroblasts, whilst the HuFF cells showed a small increase in proline incorporation under non‐uniform and uniaxial strains.
Comparative analysis of diffusive and stress induced nutrient transport efficiency in the lacunar–canalicular system of osteons
Authors: Petrov Nikola , Pollack Solomon R.
Published: November 2024

Marker migration experiments suggest that cyclic mechanical loading of cortical bone in vivo increases marker penetration into bone. Is this a result of stress induced fluid flow or of stress stimulation of active transport processes? Active lacunar–canalicular transport of nutrients was suggested by Ham in 1979 on the basis of the presence of actin filaments in osteocyte processes and their suspected role in cell motility. In addition, Tanaka in 1984 observed active transport of microperoxidase in bone and Tanaka‐Kamioka et al. in 1998 observed experimentally that osteocyte processes are able to actively change their form.

In this study we performed parametric and comparative analyses of the transport efficiencies of diffusion and stress generated fluid flow of (glucose) nutrients in lacunar–canalicular systems in cortical bone. The result obtained is that neither diffusion nor stress induced fluid flow is capable of sustaining osteocyte viability. It is possible that cyclic stress stimulates an active nutrient transport mechanism to supplement stress flows.
Development of a technique to determine strains in tendons using the cell nuclei
Authors: Screen H.R.C. , Lee D.A. , Bader D.L. , Shelton J.C.
Published: November 2024

Tenocytes detect mechanical stimuli in vivo, and respond through mechanotransduction pathways to initiate matrix remodelling in tendons. Due to the crimped nature of tendon fascicles, the strain field throughout is non‐homogeneous. The present study has developed a means to quantify the local strain fields within a fascicle by monitoring the relative movement and deformation of fluorescently labelled tenocyte nuclei. A stage mounted test rig was designed to apply tensile strain to fascicles. Rat tail and bovine extensor tendons were harvested for analysis, and the cell nuclei stained and visualised using an inverted confocal microscope. As the fascicles were subjected to gross strains of up to 5%, the movement of selected tenocyte nuclei were recorded. Results from a series of cell nuclei from both tendon sources revealed that local strains were significantly less than the applied strain. The nuclei length to width ratio, an indicator of cell deformation, also increased with applied strain, most significantly between 2 and 3% applied strain.
Rheological properties of healthy and atherosclerotic human arteries
Authors: Blondel Walter C.P.M. , Lehalle Bertrand , Lercher Marie‐Noëlle , Dumas Dominique , Bensoussan Danielle , Stoltz Jean‐François
Published: November 2024

The aim of this study was to determine the comparative three‐dimensional mechanical properties of healthy and atherosclerotic muscular human arteries. Using a previously developed experimental system, in vitro inflation tests were performed on twelve segments of arteries, in static conditions. Two different initial states were used to carry the mechanical study through (large deformation, thick‐walled). Main significant differences between healthy and atherosclerotic tested segments are observed for axial traction force whatever the initial state and radial and circumferencial strains referenced to longitudinally pre‐stretched state. We showed that strain energy allows to differentiate between both types of arteries only when absolute values of transversal components were considered. Differential values of energy were not discriminating. Our results also show the potential interest of studying arteries in vivo at low transmural pressure.
Effect of angelica on the expressional changes of cytokines in endothelial cells induced by hyperlipidemic serum
Authors: Jing‐ping Ou‐yang , Baohua Wang , Yongming Liu , Lei Wei , Jingwei Yang
Published: November 2024

The aim of this article was to examine the protective effect of Chinese traditional medicine angelica on human umbilical vein endothelial cells (HUVECs, ECV304) from injury induced by hyperlipidemic serum (HLS) and to study the underlying mechanism. Spectrophotometer and immunocytochemical methods were used to detect the content of nitric oxide (NO) in suspension and expression of intercellular adhesion molecule‐1 (ICAM‐1), transforming growth factor β1 (TGFβ1), basic fibroblast growth factor (bFGF) on the cell surface, respectively. After incubated with 50 μl/ml HLS for 24 hours, expression of ICAM‐1 and bFGF in ECs was significantly increased, while expression of TGFβ1 and the release of NO from ECs were significantly decreased. All these effect of HLS on ECs can be reversed by angelica significantly. The above effect of angelica may be related to its anti‐atherosclerotic action. Our findings provided experimental basement for the clinical application of angelica to prevent the development of atherosclerosis.
The separate roles of calcium and mechanical forces in mediating cell death in mechanically injured neurons
Authors: Lusardi Theresa A. , Smith Douglas H. , Wolf John A. , Meaney David F.
Published: November 2024

In this study, we examine the response of cultured hippocampal neurons to mechanical stretch. To measure the immediate response, we measured the response of a calcium sensitive fluorescent dye (Fura‐2AM) prior to and for five minutes following stretch. In separate experiments, we measured the viability of the cells using propidium iodide labeling at 24 hours following a single stretch. Results show that cytosolic calcium increases immediately following stretch to levels much higher than those associated with maximal chemical agonist (NMDA) stimulation. Moreover, the calcium response data indicate a loss in calcium regulation in the neurons at the most severe level of stretch. Finally, at the highest levels of stretch, the cell survivability decreases at 24 hrs following the stretch injury. These data show the association between loss in calcium regulation and early signs of neuronal cell death.
Linear and nonlinear analyses of pulsatile blood flow in a cylindrical tube
Authors: El‐Khatib F.H. , Damiano E.R.
Published: November 2024

A non‐Newtonian shear‐thinning constitutive relation is proposed to study pulsatile flow of whole blood in a cylindrical tube. The constitutive relation, which satisfies the principle of material frame indifference, is derived from viscometric data obtained from whole blood over a range of hematocrits. Assuming axisymmetric flow in a rigid cylindrical tube of constant diameter, a second‐order, nonlinear partial differential equation governing the axial velocity component is obtained. Imposing a periodic pressure gradient, the governing equation was solved numerically using finite difference methods over a range of Stokes values and hematocrits. For a forcing frequency of 1 Hz, results are presented over tube diameters ranging between 0.1 and 2 cm and over hematocrits ranging between 10 and 80%. For a given hematocrit, velocity profiles predicted for the non‐Newtonian model under sinusoidal forcing reveal attenuated volume flow rate and enhanced vorticity transport over the tube cross‐section relative to a Newtonian fluid having a viscosity corresponding to the high shear‐rate limit. For moderate to high Stokes numbers, consistent with flow in large arteries, our results revealed a viscosity distribution that was nearly time invariant. An analytic solution was obtained for a fluid having arbitrarily prescribed radially varying, temporally invariant viscosity and density distributions under arbitrary periodic pressure forcing. Close agreement was observed between our numerical and analytical results when the imposed viscosity distribution was chosen to approximate the time‐averaged viscosity distribution predicted by the shear‐thinning non‐Newtonian model. For $\mathit{St}\gtrsim 100$ , the disparity between our results and those of a Newtonian fluid of constant viscosity grows with a decreasing ratio of the DC to AC components of the pressure‐gradient amplitude below 50%. In particular, for any purely oscillatory pressure‐gradient (vanishing DC component), the Womersley solution is a particularly poor predictor of the amplitude and phase of wall shear rate for over half of the flow cycle. Under such circumstances, the analytical models presented here provide a simple and accurate means of estimating instantaneous wall shear rate, knowing only the pressure gradient and hematocrit.
Rheological behavior and parameters of the in vitro model of lung surfactant systems: The role of the main phospholipid component
Authors: Antonova Nadia , Todorov Roumen , Exerowa Dotchi
Published: November 2024

The proposed in vitro model for studying the alveolar surface layer of the lungs enables one to investigate the surface intermolecular forces which influence the stability of the alveolus. The general role for the stability of the alveolus belongs to the phospholipids in the alveolar surfactant and predominantly to their main component dipalmitoylphosphatidylcholine (DPPC). The aim of the study was to investigate the rheological behavior of DPPC and exogenous surfactant preparations used in neonatal clinical practice. Data for the rheological behavior of the solutions of the commercially available surfactants, Infasurf, Exosurf and Survanta, as well as of DPPC (their main phospholipid component) at shear rates from 0.024 to 94.5 s−1 under steady and transient flow conditions at 23°C were obtained. Infasurf and Exosurf showed Newtonian rheological behavior, while Survanta revealed the shear‐thinning behavior of a non‐Newtonian pseudoplastic fluid. The rheological properties of aqueous solutions of DPPC containing 0.14 M NaCl at concentrations from 100 and 630 μg/ml of phospholipid (chosen from the dependence of the probability for bilayer film formation) were studied. Differences observed in the rheological properties of the exogenous surfactants were interpreted on the basis of their composition, the presence of other phospholipid components, certain additives and surfactant proteins, as well as the bulk structures formed from them. The relevance of the results for the delivery of exogenous surfactants and their spreading in replacement therapy is discussed.
Effects of diagnostic guidewire catheter presence on translesional hemodynamic measurements across significant coronary artery stenoses
Authors: Banerjee Rupak K. , Back Lloyd H. , Back Martin R.
Published: November 2024

This study gains insight on the nature of flow blockage effects of small guidewire catheter sensors in measuring mean trans‐stenotic pressure gradients $\Delta\tilde{p}$ across significant coronary artery stenoses. Detailed pulsatile hemodynamic computations were made in conjunction with previously reported clinical data in a group of patients with clinically significant coronary lesions before angioplasty. Results of this study ascertain changes in hemodynamic conditions due to the insertion of a guidewire catheter (di=0.46 mm) across the lesions used to directly determine the mean pressure gradient $(\Delta\tilde{p})$ and fall in distal mean coronary pressure ( $\tilde{p}_{r})$ . For the 32 patient group of Wilson et al. [1988] (minimal lesion diameter dm=0.95 mm; 90% mean area stenosis; proximal measured coronary flow reserve (CFR) of 2.3 in the abnormal range) the diameter ratio of guidewire catheter to minimal lesion was 0.48, causing a tighter “artifactual” mean area stenosis of 92.1%. The results of the computations indicated a significant shift in the $\Delta\tilde{p}$ – $\widetilde{Q}$ relation due to guidewire induced increases in flow resistances ( $\widetilde{R}=\Delta\tilde{p}/\widetilde{Q})$ of 110% for hyperemic flow, a 35% blockage in hyperemic flow $(\widetilde{Q}_{h})$ and a phase shift of the coronary flow waveform to systolic predominance. These alterations in flow resulted in a fall in distal mean coronary pressure (at lower mean flow rates) below the patho‐physiological range of $\tilde{p}_{rh}\sim 55$ mmHg, which is known to cause ischemia in the subendocardium (Brown et al. [1984]) and coincides with symptomatic angina. Transient wall shear stress levels in the narrow throat region (with flow blockage) were of the order of levels during hyperemic conditions for patho‐physiological flow. In the separated flow region along the distal vessel wall, vortical flow cells formed periodically during the systolic phase when instantaneous Reynolds numbers Ree(t) exceeded about 110. For patho‐physiological flow without the presence of the guidewire these vortical flow cells were much stronger than in the more viscous flow regime with the guidewire present. The non‐dimensional pressure data given in tabular form may be useful in interpretation of guidewire measurements done clinically for lesions of similar geometry and severity.
Turbulence detection in a stenosed artery bifurcation by numerical simulation of pulsatile blood flow using the low‐Reynolds number turbulence model
Authors: Ghalichi Farzan , Deng Xiaoyan
Published: November 2024

The pulsatile blood flow in a partially blocked artery is significantly altered as the flow regime changes through the cardiac cycle. This paper reports on the application of a low‐Reynolds turbulence model for computation of physiological pulsatile flow in a healthy and stenosed carotid artery bifurcation. The human carotid artery was chosen since it has received much attention because atherosclerotic lesions are frequently observed. The Wilcox low‐Re k–ω turbulence model was used for the simulation since it has proven to be more accurate in describing transition from laminar to turbulent flow. Using the FIDAP® finite element code a validation showed very good agreement between experimental and numerical results for a steady laminar to turbulent flow transition as reported in a previous publication by the same authors. Since no experimental or numerical results were available in the literature for a pulsatile and turbulent flow regime, a comparison between laminar and low‐Re turbulent calculations was made to further validate the turbulence model. The results of this study showed a very good agreement for velocity profiles and wall shear stress values for this imposed pulsatile laminar flow regime. To explore further the medical aspect, the calculations showed that even in a healthy or non‐stenosed artery, small instabilities could be found at least for a portion of the pulse cycle and in different sections. The 40% and 55% diameter reduction stenoses did not significantly change the turbulence characteristics. Further results showed that the presence of 75% stenoses changed the flow properties from laminar to turbulent flow for a good portion of the cardiac pulse. A full 3D simulation with this low‐Re‐turbulence model, coupled with Doppler ultrasound, can play a significant role in assessing the degree of stenosis for cardiac patients with mild conditions.
Growth‐related changes in the mechanical properties of collagen fascicles from rabbit patellar tendons
Authors: Yamamoto Ei , Iwanaga Wataru , Yamamoto Noritaka , Hayashi Kozaburo
Published: November 2024

Growth‐related changes in the mechanical properties of collagen fascicles (approximately 300 μm in diameter) were studied using patellar tendons obtained from skeletally immature 1 and 2 months old and matured 6 months old rabbits. Tensile properties were determined using a specially designed micro‐tensile tester. In each age group, there were no significant differences in the properties among cross‐sectional locations in the tendon. Tangent modulus and tensile strength significantly increased with age; the rates of their increases between 1 and 2 months were higher than those between 2 and 6 months. The tangent modulus and tensile strength were positively correlated with the body weight of animals. However, growth‐related changes in the mechanical properties were different between collagen fascicles and bulk patellar tendons, which may be attributable to such non‐collagenous components as ground substances and also to mechanical interactions between collagen fascicles.
Influence of cell‐specific factors on red blood cell aggregation
Authors: Rampling M.W. , Meiselman H.J. , Neu B. , Baskurt O.K.
Published: November 2024

The reversible aggregation of red blood cells (RBC) into linear and three‐dimensional structures continues to be of basic science and clinical interest: RBC aggregation affects low shear blood viscosity and microvascular flow dynamics, and can be markedly enhanced in several clinical states. Until fairly recently, most research efforts were focused on relations between suspending medium composition (i.e., protein levels, polymer type and concentration) and aggregate formation. However, there is now an increasing amount of experimental evidence indicating that RBC cellular properties can markedly affect aggregation, with the term “RBC aggregability” coined to describe the cell's intrinsic tendency to aggregate. Variations of aggregability can be large, with some changes of aggregation substantially greater than those resulting from pathologic states. The present review provides a brief overview of this topic, and includes such areas as donor‐to‐donor variations, polymer–plasma correlations, effects of RBC age, effects of enzymatic treatment, and current developments related to the mechanisms involved in RBC aggregation.
Validation and application of an automated rheoscope for measuring red blood cell deformability distributions in different species
Authors: Dobbe J.G.G. , Hardeman M.R. , Streekstra G.J. , Grimbergen C.A.
Published: November 2024

Background. The deformability of red blood cells (RBCs) is of great importance for the conservation of oxygen delivery in the microcirculation. Even a small fraction of rigid cells is considered to harm the exchange of respiratory gases. Techniques that measure RBC deformability often provide an indication of the mean deformability. It may not be possible, however, to assess whether this mean value is reduced by the presence of a small rigid cell fraction or by a slight overall reduction in RBC deformability. A technique that provides a deformability distribution would be of great value to study diseases that are marked by subpopulations with a reduced deformability.

Methods. This paper describes a rheoscope system that uses advanced image analysis techniques to quickly quantify the deformability of many individual cells in shear flow, in order to find the RBC‐deformability distribution. Since variations in the shear stress are responsible for variations in cell elongation, and hence introduce an additional spread in the cell deformability distribution, we first determined the spread caused by instrumental error. We then utilized the technique to investigate the relation between cell deformability and cell size of single blood samples of different species (human, pig, rat and rabbit).

Results. The spread caused by instrumental error was small compared to the actual RBC‐deformability spread in blood samples. The deformability distribution of human and pig cells are alike although their cell sizes are different. Rat and rabbit cells show comparable deformability and size distributions. With this technique no correlation was found between cell deformability and cell size in animal RBCs. In the human sample a minor correlation was found between cell deformability and cell size.

Conclusions. The automated rheoscope enables us to study the mechanical properties of RBCs more thoroughly by their deformability distribution. These deformability distributions are hardly influenced by the technique or by cell size.
Platelet near‐wall excess in porcine whole blood in artery‐sized tubes under steady and pulsatile flow conditions
Authors: Xu Chun , Wootton David M.
Published: November 2024

Platelet margination (enhanced platelet concentration in the near wall region of a blood vessel) has been well documented in small vessels. In artery‐sized vessels margination has only been demonstrated in one study, using ghost cell suspensions and under relatively non‐physiologic conditions of steady flow and 50 cm development length. Local sampling experiments were performed to confirm platelet margination in artery‐sized stainless steel tubes, for a typical anatomical length and under pulsatile flow, using fresh EDTA‐anticoagulated porcine whole blood (N=21). Experiments were designed using three‐dimensional Computational Fluid Dynamics (CFD) to model the sample region with greater fidelity. Steady flow experiments in 50 cm long tubes verify published laser Doppler measurements of platelet margination in 3 mm ID tubes at normal arterial shear rate (500 s−1). Margination persists under pulsatile flow conditions (63.8 pulses/min), but in steady flow at length of 10 cm, margination is reduced. Platelet margination ratio (the ratio of the platelet concentration near the wall to bulk average platelet count) ranges from 1.21 to 2.48. No significant effects of calculated sampling thickness (20 μm and 50 μm) or pulsatility were detected. Hematocrit margination ratio is 0.68 to 0.90. Two model platelet concentration profiles are fit to the experimental results.
Epidermal growth factor differentially affects integrin‐mediated adhesion and proliferation of ACL and MCL fibroblasts
Authors: McKean Jason M. , Hsieh Adam H. , Sung K.L. Paul
Published: November 2024

The anterior cruciate ligament (ACL) and the medial collateral ligament (MCL) are two commonly injured structures in the human knee. While the MCL heals post‐traumatically, the ACL does not. Since growth factors play a major role in the proliferation phase of wound healing, we compared the differential effects of epidermal growth factor (EGF) on adhesion and proliferation of ACL and MCL fibroblasts. Using a micropipette/micromanipulator system we found that cells subjected to shorter incubation periods (15 minutes) with EGF (5, 10, 50 ng/ml) showed a general increase in adhesion to the extracellular matrix fibronectin while cells subjected to longer incubation periods (4, 6, 10, and 24 hr) with EGF (5 ng/ml) showed decreases in adhesion. For both incubation durations, MCL fibroblasts displayed a greater change in adhesion than ACL fibroblasts, when compared to control. Investigation of integrin expression showed no fluctuation in cell surface expression of the α5 subunit of the FN‐binding integrin α5β1 for all EGF (5 ng/ml) incubation times. MCL cells showed a significant increase in proliferation upon stimulation with EGF compared to ACL cells when cultured in FN coated wells. The results found in this study help provide a better understanding of EGF's role in adhesion and proliferation, two events that may contribute to the differential healing response between ACL and MCL fibroblasts. Following exposure to EGF, ACL and MCL cells initially respond by increasing their adhesion strength. MCL cells respond to all concentrations of EGF while ACL cells appear to have a threshold concentration after which EGF effects plataeu. After this initial response period (<10 hr) cells exhibit lower adhesion strength and higher proliferation rate. It is possible that the release from FN serves to enhance the ability of the cells to proliferate. These results may aid in understanding the ligament healing process.
Tenocyte response to cyclical strain and transforming growth factor beta is dependent upon age and site of origin
Authors: Goodman S.A. , May S.A. , Heinegård D. , Smith R.K.W.
Published: November 2024

The effect of strain and transforming growth factor beta on equine tendon fibroblasts (tenocytes) was assessed in vitro. Tenocytes were isolated from flexor and extensor tendons of horses from foetal to 10 years of age. These cells were cultured until confluent on collagen‐coated silicone dishes. Cyclic biaxial strain of 9±1% was applied at 0.5 Hz for 24 hours with or without added TGFβ1 or 3 (10 ng/ml). Proliferation and synthetic responses were dependent on the tendon of origin. Neither strain nor TGFβ caused flexor tenocytes to proliferate significantly, while strain alone did proliferate extensor tenocytes. TGFβ, with or without strain, increased the incorporation of [3H]‐proline and the production of types I and III collagen and COMP in both cell types, although the effect on COMP production was more marked in flexor tenocytes, perhaps reflecting the higher levels found in this tendon in vivo. Immature flexor tenocytes synthesised more collagen and COMP than those from mature animals, while age had little effect in extensor tenocytes. Our results suggest that tenocytes become differentiated at an early age and present tendon‐specific responses.
Effect of steady and oscillatory shear stress on F‐actin content and distribution in neutrophils
Authors: Chen Huai‐Qing , Tian Wei , Chen Yun‐Shuang , Li Liang , Raum Jeffrey , Sung K.‐L. Paul
Published: November 2024

We investigated neutrophil activation, specifically F‐actin content and distribution, in situations mimicking the in vivo environment using steady and oscillatory shear. Under low steady shear (<150 s−1) F‐actin levels were decreased for both treated (n‐formyl‐L‐methioryl‐L‐leucyl‐L‐phenylalanine (fMLP)) and untreated neutrophils. The F‐actin content increased with a change to higher steady shear levels. Neutrophils show the same behavior of decreased F‐actin content for oscillatory shear (26.7 s−1) as they did for steady shear. In both situations, the low shear levels caused a decrease in F‐actin content. However, as the magnitude of the shear rate increased, cells showed a reversal to increasing F‐actin content. Shear caused a decrease in F‐actin in the cell cortex for both control and fMLP treated cells. Ctyochalasin B (CB), a common F‐actin assembly blocker, significantly decreased F‐actin content. The results indicate that neutrophils regulate their actin network based on the level and type of shear stress they encounter in the bloodstream.
Role of Toll‐like receptor 4/NF‐κB pathway in monocyte–endothelial adhesion induced by low shear stress and ox‐LDL
Authors: Yang Qing‐wu , Mou Lin , Lv Feng‐lin , Wang Jing‐zhou , Wang Lin , Zhou Hong‐jie , Gao Dong
Published: November 2024

TLR4 plays an important role in atherosclerosis, but little is known about the precise mechanism. Herein, we investigated the role of TLR4/NF‐κB signaling pathway in monocyte–endothelial adhesion induced by low shear stress and Ox‐LDL. We found that low shear stress up‐regulated TLR4 expression in endothelial cells, and that ox‐LDL exerted an obvious synergistic action as revealed by RT‐PCR and Western blotting analysis. Low shear stress also significantly up‐regulated IL‐8 expression in endothelial cells. Meanwhile, NF‐κB activity and the adhesion force of monocytes were increased, and there was a synergetic action of ox‐LDL. However, following transfection with a functional mutant of TLR4 (C3H/HeJ, TLR4 Dicd) or addition of anti‐human TLR4 mAb, IL‐8 expression was obviously decreased, NF‐κB activity in cells remarkably inhibited, and the adhesion force of monocyte significantly reduced. Nevertheless, anti‐human TLR2 mAb had no similar effects. These findings suggest that TLR4 may be involved in the early stages of atherosclerosis, associating ox‐LDL, inflammation/infection, and low shear stress. Therefore, TLR4 is expected to be a new target for preventing and treating atherosclerosis.
Coupled oxygen transport analysis in the avascular wall of a post-angioplasty coronary artery stenosis
Authors: Vaidya Vinayak S. , Back Lloyd H. , Banerjee Rupak K.
Published: November 2024

The coupled oxygen transport in the avascular wall of a coronary artery stenosis is studied by numerically solving the convection–diffusion equations. Geometry, replicating residual stenosis after percutaneous transluminal coronary angioplasty (PTCA), is used for the analysis. Important physiological aspects, such as oxygen consumption in the wall, oxygen carried by the hemoglobin, non-Newtonian viscosity of the blood, and supply of oxygen from the vasa vasorum are included. Mean blood flow rate in the lumen is varied from basal to hyperemic conditions. The results show that the PO2 in the medial region of the arterial wall is ∼10 mmHg. The oxygen flux to the wall increases in the flow acceleration region, whereas it decreases at the flow reattachment zone. Near the location of flow separation there is a small rise and a sharp fall in the oxygen flux. The minimum PO2 in the avascular wall, PO2, min , at the point of flow reattachment reduces to ∼6 mmHg for a 300 micron wall thickness. For a thinner wall of 200 micron, the PO2, min  at the location of flow reattachment increases to 6 times that of a 300 micron wall. The PO2, min  in the wall decreases by 60% when volumetric oxygen consumption is increased by 30% for the same avascular wall thickness.
Development of a rheological analogue to periprosthetic fluid
Authors: Fam H. , Kontopoulou M. , Bryant J.T.
Published: November 2024

The purpose of this work is to design a rheological analogue to periprosthetic fluid, for potential use in wear testing of orthopaedic implants. Polymer solutions of sodium carboxymethyl cellulose (CMC), xanthan and mixtures thereof were prepared, and the experimentally determined viscosity–shear rate dependence was analyzed using the three-parameter modified Cross model. A mixture containing 0.185 wt% CMC and 0.075 wt% xanthan was identified as being the closest rheological match for periprosthetic fluid in both steady shear and oscillatory modes of deformation.
Interaction of fluorescent molecular rotors with blood plasma proteins
Authors: Akers Walter J. , Cupps Jay M. , Haidekker Mark A.
Published: November 2024

Many disease states have associated blood viscosity changes. Molecular rotors, fluorescent molecules with viscosity sensitive quantum yields, have recently been investigated as a new method for biofluid viscosity measurement. Current viscometer measurements are complicated by proteins adhering to surfaces and forming air-surface layers. It is unknown at this time what effects proteins may have on biofluid viscosity measurements using molecular rotors. To answer this question, binding affinities to blood plasma proteins were investigated by equilibrium dialysis for four hydrophilic molecular rotors. Aqueous solutions of 9-[(2-cyano-2-hydroxy-carbonyl)vinyl]julolidine (CCVJ) and three derivatives were prepared and dialyzed against solutions of bovine source albumin, fibrinogen and immunoglobulin G approximating normal physiologic concentrations and fresh-frozen human plasma. After equilibration, dye concentration on each side of the dialysis membrane was assessed by spectrophotometry. The relative binding affinity of the four dyes to the proteins and to the plasma was compared. Affinity of all dyes was highest for albumin. The bound dye fraction showed little change in relation to protein concentration in the physiological concentration range. Diol, the most hydrophilic molecular rotor tested showed the lowest affinity for albumin. This study indicates that hydrophilic molecular rotors are well-suited for biofluid viscosity measurement.
Morphology of elastase-induced cerebral aneurysm model in rabbit and rapid prototyping of elastomeric transparent replicas
Authors: Seong Jaehoon , Sadasivan Chander , Onizuka Masanari , Gounis Matthew J. , Christian Fletcher , Miskolczi Laszlo , Wakhloo Ajay K. , Lieber Baruch B.
Published: November 2024

In this work, we describe a methodology to fabricate transparent elastomeric vascular replicas using rapid prototyping techniques. First, the three-dimensional morphology of an elastase-induced aneurysm model in rabbit is acquired. The morphology is reconstructed from in vivo rotational angiography and it is compared with three-dimensional reconstructions obtained by computerized tomography and magnetic resonance imaging of an intraluminal arterial cast that was obtained from the same animal at sacrifice. Results show that resolution of the imaging modality strongly influences the level of detail, such as small side branches, in the final reconstruction. We developed an average morphology model for elastase-induced aneurysms in rabbits including the surrounding vasculature and describe a method for rapid prototyping of vascular models from the three-dimensional morphology. Our replicas can be manufactured in a short period of time and the final product is optically clear. In addition, the elasticity of the models can be controlled to represent arterial elasticity, which makes them ideal for optical investigations of detailed flow dynamics using measurement tools such as particle image velocimetry.
Measuring cell viscoelastic properties using a force-spectrometer: Influence of protein–cytoplasm interactions
Authors: Canetta Elisabetta , Duperray Alain , Leyrat Anne , Verdier Claude
Published: November 2024

Cell adhesive and rheological properties play a very important role in cell transmigration through the endothelial barrier, in particular in the case of inflammation (leukocytes) or cancer metastasis (cancer cells). In order to characterize cell viscoelastic properties, we have designed a force spectrometer (AFM) which can stretch cells thereby allowing measurement of their rheological properties. This custom-made force spectrometer allows two different visualizations, one lateral and one from below. It allows investigation of the effects of rheology involved during cell stretching. To test the ability of our system to characterize such viscoelastic properties, ICAM-1 transfected CHO cells were analyzed. Two forms of ICAM-1 were tested; wild type ICAM-1, which can interact with the cytoskeleton, and a mutant form which lacks the cytoplasmic domain, and is unable to associate with the cytoskeleton. Stretching experiments carried out on these cells show the formation of long filaments. Using a previous model of filament elongation, we could determine the viscoelastic properties of a single cell. As expected, different viscoelastic components were found between the wild type and the mutant, which reveal that the presence of interactions between ICAM-1 and the cytoskeleton increases the stiffness of the cell.
Biorheological views of endothelial cell responses to mechanical stimuli
Authors: Sato Masaaki , Ohashi Toshiro
Published: November 2024

Vascular endothelial cells are located at the innermost layer of the blood vessel wall and are always exposed to three different mechanical forces: shear stress due to blood flow, hydrostatic pressure due to blood pressure and cyclic stretch due to vessel deformation. It is well known that endothelial cells respond to these mechanical forces and change their shapes, cytoskeletal structures and functions. In this review, we would like to mainly focus on the effects of shear stress and hydrostatic pressure on endothelial cell morphology. After applying fluid shear stress, cultured endothelial cells show marked elongation and orientation in the flow direction. In addition, thick stress fibers of actin filaments appear and align along the cell long axis. Thus, endothelial cell morphology is closely related to the cytoskeletal structure. Further, the dynamic course of the morphological changes is shown and the related events such as changes in mechanical stiffness and functions are also summarized. When endothelial cells were exposed to hydrostatic pressure, they exhibited a marked elongation and orientation in a random direction, together with development of centrally located, thick stress fibers. Pressured endothelial cells also exhibited a multilayered structure with less expression of VE-cadherin unlike under control conditions. Simultaneous loading of hydrostatic pressure and shear stress inhibited endothelial cell multilayering and induced elongation and orientation of endothelial cells with well-developed VE-cadherin in a monolayer, which suggests that for a better understanding of vascular endothelial cell responses one has to take into consideration the combination of the different mechanical forces such as exist under in vivo mechanical conditions.
Hemorheologic events in severe shock
Authors: Zhao Ke-Seng
Published: November 2024

Persistent low perfusion and low blood pressure are the two major events in the pathogenesis of irreversible shock. This review is focused on our recent study on the mechanism of, and a new therapeutic approach to the two events in IS. One of the main causes of persistent low perfusion are leukocyte adhesion on venule walls and plugging in capillaries which comes from the low wall shear stress or shear rate, and high leukocyte–endothelial adhesion force in IS. However, blockade of leukocyte adhesion by monoclonal antibodies against the adhesion molecules can only attenuate the number of sticking WBC in venules, but cannot make an appreciable improvement in capillary reflow and survival rate in IS, because it is difficult for the agents to flow into an obstructed capillary. We have shown that the administration of Polydatin, a crystalline product isolated from a traditional Chinese medicine, can restore the pulse pressure with high survival rate in irreversible shock. With an increase in pulse pressure, and the highly dispersive force resulting from pulsatile blood flow, the stationary blood cells can be pushed away from the obstructed capillary and thus promote capillary reflow. Therefore, enhancement of pulse pressure is a key factor for the treatment of low perfusion in irreversible shock. Hyperpolarization of arteriolar smooth muscle cells occurs in irreversible shock, which inhibits the potential-operated calcium channel and the influx of Ca2+ in arteriolar smooth muscle cells stimulated by norepinephrine, and finally leads to low vascular contractile responsiveness with refractory hypotension in irreversible shock. Activation of the potassium channels KATP and BKCa is involved in arteriolar smooth muscle cells hyperpolarization. In irreversible shock, ATP depletion, intracellular acidosis, ONOO− formation, and enhancement of a calcium spark results in activation of KATP and BKCa and consequent arteriolar smooth muscle cell hyperpolarization. Therefore, a new therapeutic strategy for refractory hypotension was suggested, including blockade of potassium channel activation to reconstitute vasoreactivity and the administration of vasopressors to elevate blood pressure in the treatment of irreversible shock.
Blood rheology of Weddell seals and bowhead whales
Authors: Castellini Michael , Elsner Robert , Baskurt Oguz K. , Wenby Rosalinda B. , Meiselman Herbert J.
Published: November 2024

Red blood cell (RBC) aggregation and blood viscosity are important determinants of in vivo blood flow dynamics and, in marine mammals, these parameters may impact diving physiology by altering blood oxygen delivery during the diving response. Weddell seals are superb divers and exhibit age-related patterns in blood oxygen chemistry and diving ability. By contrast, bowhead whales are not long duration divers, and little is known of their blood properties relative to diving. The present study was designed to compare rheological characteristics of blood from Weddell seal pups, Weddell seal adults, and from adult bowhead whales: blood viscosity and RBC aggregation in plasma and in polymer solutions (i.e., RBC “aggregability”) were measured. Salient findings included: (1) significant 4- to 8-fold greater aggregation in blood from adult seals compared with pups and human subjects; (2) 2-to 8-fold greater aggregation in bowhead whale blood compared with human blood; (3) compared to human red cells, enhanced RBC aggregability of RBC from adult seals and whales as determined by their greater aggregation in polymer solutions; (4) increasing RBC aggregation and aggregability of seal pup blood over a seven day period following birth; (5) significantly greater blood viscosity for adult seals compared with pups at both native and standardized hematocrits. These results indicate that, for both species, hemorheological parameters differ markedly from those of humans, and suggest progressive changes with seal age; the physiological implications of these differences have yet to be fully defined.