bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical signals for chondrocytes in cartilage
Authors: Lai W.M. , Sun D.D. , Ateshian G.A. , Guo X.E. , Mow V.C.
Published: November 2024

An important step toward understanding signal transduction mechanisms modulating cellular activities is the accurate predictions of the mechanical and electro‐chemical environment of the cells in well‐defined experimental configurations. Although electro‐kinetic phenomena in cartilage are well known, few studies have focused on the electric field inside the tissue. In this paper, we present some of our recent calculations of the electric field inside a layer of cartilage (with and without cells) in an open circuit one‐dimensional (1D) stress relaxation experiment. The electric field inside the tissue derives from the streaming effects (streaming potential) and the diffusion effect (diffusion potential). Our results show that, for realistic cartilage material parameters, due to deformation‐induced inhomogeneity of the fixed charge density, the two potentials compete against each other. For softer tissue, the diffusion potential may dominate over the streaming potential and vice versa for stiffer tissue. These results demonstrate that for proper interpretation of the mechano‐electrochemical signal transduction mechanisms, one must not ignore the diffusion potential.
Differential responses of chondrocytes from normal and osteoarthritic human articular cartilage to mechanical stimulation
Authors: Salter D.M. , Millward‐Sadler S.J. , Nuki G. , Wright M.O.
Published: November 2024

Mechanical stimulation is critically important for the maintenance of normal articular cartilage integrity. Molecular events regulating responses of chondrocytes to mechanical forces are beginning to be defined. Chondrocytes from normal human knee joint articular cartilage show increased levels of aggrecan mRNA following 0.33 Hz mechanical stimulation whilst at the same time relative levels of MMP3 mRNA are decreased. This anabolic response, associated with membrane hyperpolarisation, is activated via an integrin‐dependent interleukin (IL)‐4 autocrine/paracrine loop. Work in our laboratory suggests that this chondroprotective response may be aberrant in osteoarthritis (OA). Chondrocytes from OA cartilage show no changes in aggrecan or MMP3 mRNA following 0.33 Hz mechanical stimulation. α5β1 integrin is the mechanoreceptor in both normal and OA chondrocytes but downstream signalling pathways differ. OA chondrocytes show membrane depolarisation following 0.33 Hz mechanical stimulation consequent to activation of an IL1β autocrine/paracrine loop. IL4 signalling in OA chondrocytes is preferentially through the type I (IL4α/cγ) receptor rather than via the type II (IL4α/IL13R) receptor. Altered mechanotransduction and signalling in OA may contribute to changes in chondrocyte behaviour leading to increased cartilage breakdown and disease progression.
High pressure effects on cellular expression profile and mRNA stability. A cDNA array analysis
Authors: Sironen Reijo K. , Karjalainen Hannu M. , Törrönen Kari , Elo Mika A. , Kaarniranta Kai , Takigawa Masaharu , Helminen Heikki J. , Lammi Mikko J.
Published: November 2024

Hydrostatic pressure has a profound effect on cartilage tissue and chondrocyte metabolism. Depending on the type and magnitude of pressure various responses can occur in the cells. The mechanisms of mechanotransduction at cellular level and the events leading to specific changes in gene expression are still poorly understood. We have previously shown that induction of stress response in immortalized chondrocytes exposed to high static hydrostatic pressure increases the stability of heat shock protein 70 mRNA. In this study, our aim was to examine the effect of high pressure on gene expression profile and to study whether stabilization of mRNA molecules is a general phenomenon under this condition. For this purpose a cDNA array analysis was used to compare mRNA expression profile in pressurized vs. non‐pressurized human chondrosarcoma cells (HCS 2/8). mRNA stability was analyzed using actinomycin‐treated and nontreated samples collected after pressure treatment. A number of immediate‐early genes, and genes regulating cell cycle and growth were up‐regulated due to high pressure. Decrease in osteonectin, fibronectin, and collagen types VI and XVI mRNAs was observed. Also bikunin, cdc37 homologue and Tiam1, genes linked with hyaluronan metabolism, were down‐regulated. In general, stability of down‐regulated mRNA species appeared to increase. However, no increase in mRNA above control level due to stabilization was noticed in the genes available in the array. On the other hand, mRNAs of certain immediate‐early genes, like c‐jun, jun‐B and c‐myc, became destabilized under pressure treatment. Increased accumulation of mRNA on account of stabilization under high pressure conditions seems to be a tightly regulated, specific phenomenon.
Integrins and cell signaling in chondrocytes
Authors: Loeser Richard F.
Published: November 2024

Integrins are adhesion receptor heterodimers that transmit information from the extracellular matrix (ECM) to the cell through activation of cell signaling pathways. Chondrocytes express several members of the integrin family including α5β1 which is the primary chondrocyte receptor for fibronectin. Cell signaling mediated through integrins regulates several chondrocyte functions including differentiation, matrix remodeling, responses to mechanical stimulation and cell survival. Integrin‐mediated activation of members of the mitogen‐activated protein kinase family likely plays a key role in transmitting signals regulating chondrocyte gene expression. Upstream mediators of mitogen‐activated protein kinase (MAP kinase) activation include focal adhesion kinase (FAK) and proline‐rich tyrosine kinase 2 (pyk2) which are both expressed by chondrocytes. A better understanding of chondrocyte integrin signaling is needed to define the mechanisms by which the ECM regulates chondrocyte function.
The influence of exercise on the composition of developing equine joints
Authors: van de Lest Chris H.A. , Brama Pieter A.J. , van Weeren P. René
Published: November 2024

An overview is given of the direct and long‐term effects of exercise on the biochemical characteristics of cartilage and subchondral bone, and on the metabolic activity of chondrocytes in the juvenile horse. In the experimental setup 43 foals were reared until weaning at 5 months of age under similar conditions, except for the type and amount of exercise. Fifteen foals remained at pasture (Pasture group and also control group), 14 foals were kept in box stalls (Box group), and 14 foals were kept in the same box stalls but were subjected daily to an increasing number of gallop sprints (Training group). After weaning 8 foals from each group were euthanised. All remaining 19 animals were housed together in a loose box with access to a small paddock to study a possible reversibility of exercise‐induced effects. Post mortem subchondral bone and cartilage samples were collected and analysed for bone morphogenic enzymes, matrix composition, chondrocyte metabolic activity, and bone mineral density.

It resulted that lack of exercise leads to a retardation of the normal development of the joint. This is largely compensated for when afterwards a more normal exercise regimen is followed. Most parameters in the Training group approximated those of the pastured foals at age 5 months. However, at age 11 months there were indications for a reduced performance of the investigated tissues in this group.

It is concluded that regular, sub‐maximal loading, as occurred in the Pasture group, seems best for an optimal development of the musculoskeletal tissues. The combination of short bouts of heavy exercise superimposed on a basic box rest regimen appears to have adverse effects on long‐term viability of the tissues and may hence lead to an impaired resistance to injury.
Tensile fatigue behaviour of articular cartilage
Authors: Bellucci Giordano , Seedhom Bahaa B.
Published: November 2024

Although fatigue has been implicated in cartilage failure there are only two studies by the same author, and in both of which cartilage was tested in the direction parallel to the collagen orientation in the surface layer. In the present work articular cartilage was tested also along the perpendicular direction, being the direction in which cartilage possesses lower tensile strength.

Specimens were tested under cyclic tensile load. Number of cycles at failure was recorded as well as elongation of the specimen. To date 72 specimens have been tested all from one knee joint.

The number of cycles to failure ranged between two and 1.5 million. The surface and deep layers have better fatigue properties whether tested in the parallel or the perpendicular direction, while the middle layer was far weaker. Better fatigue behaviour was observed with specimens tested in parallel than in perpendicular direction to the fibres.
The convergence of haemodynamics, genomics, and endothelial structure in studies of the focal origin of atherosclerosis
Authors: Davies Peter F. , Polacek Denise C. , Shi Congzhu , Helmke Brian P.
Published: November 2024

The completion of the Human Genome Project and ongoing sequencing of mouse, rat and other genomes has led to an explosion of genetics‐related technologies that are finding their way into all areas of biological research; the field of biorheology is no exception. Here we outline how two disparate modern molecular techniques, microarray analyses of gene expression and real‐time spatial imaging of living cell structures, are being utilized in studies of endothelial mechanotransduction associated with controlled shear stress in vitro and haemodynamics in vivo. We emphasize the value of such techniques as components of an integrated understanding of vascular rheology. In mechanotransduction, a systems approach is recommended that encompasses fluid dynamics, cell biomechanics, live cell imaging, and the biochemical, cell biology and molecular biology methods that now encompass genomics. Microarrays are a useful and powerful tool for such integration by identifying simultaneous changes in the expression of many genes associated with interconnecting mechanoresponsive cellular pathways.
Arterial bends: The development and decay of helical flows
Authors: Blyth M.G. , Mestel A.J. , Zabielski L.
Published: November 2024

The macrocirculation is modelled by incompressible Newtonian flow through a rigid network of pipes for which possible simplifications are discussed. The common assumptions of two‐dimensionality or axisymmetry can be generalised to helical symmetry, and in the first part of the paper, the three‐dimensionality of arterial bends is considered by varying the curvature and torsion of a section of a helical pipe. The torsion is found to impart a preferential twist to the cross‐sectional flow. This loss of symmetry ensures that flow separation is less severe for a helical bend than for a toroidal bend. The effects of variations in body size are examined using allometric scaling laws.

In the second part of the paper, the approach to “fully developed” Dean or Womersley flow is considered in an attempt to quantify the regions of validity of idealised models. A perturbation approach, akin to hydrodynamic stability theory, is used. It is argued that often potential flows are more suitable for describing the rapid interactions between geometry and pulsatility rather than the eventual fully developed state so that, for example, the first 100° of the aortic arch may be considered irrotational. Helical potential flows are found to develop faster than the corresponding toroidal flows, but slower than those in a straight pipe. The presence of vorticity in the core also retards the development of symmetric flows. It is concluded that while idealised flows can occur at some points in the body, in general experimental observation is needed to justify their use. Particular caution is recommended when interpreting calculations with Poiseuille input.
Towards early diagnosis of atherosclerosis: The finite volume method for fluid–structure interaction
Authors: Ivankovic A. , Karac A. , Dendrinos E. , Parker K.
Published: November 2024

Blood flow through arteries represents a very complex, fluid–structure interaction (FSI) problem. Strong coupling between the blood and artery is due to the relatively low stiffness of the artery compared to that of blood. Hence, the pressure exerted by the flowing blood on the artery wall can result in considerable deformations of the artery, and vice‐versa, arterial deformations can in turn affect the blood flow. In the present work, the finite volume method is employed to solve the problem where compressible fluid, representing blood, flows in healthy arteries as well as in unhealthy, i.e., partly stiffened arteries. The stiffening of the arterial wall is assumed to be the first key stage in the development of atherosclerosis. The comparison between various deformation profiles of healthy and unhealthy arteries demonstrates significant and measurable differences, in particular in the radial direction. This is hoped to help toward establishing procedures for early diagnosis of the disease.
Adhesion of leukocytes under oscillating stagnation point conditions: A numerical study
Authors: Walker P.G. , Alshorman A.A. , Westwood S. , David T.
Published: November 2024

Leukocyte recruitment from blood to the endothelium plays an important role in atherosclerotic plaque formation. Cells show a primary and secondary adhesive process with primary bonds responsible for capture and rolling and secondary bonds for arrest. Our objective was to investigate the role played by this process on the adhesion of leukocytes in complex flow. Cells were modelled as rigid spheres with spring like adhesion molecules which formed bonds with endothelial receptors. Models of bond kinetics and Newton's laws of motion were solved numerically to determine cell motion. Fluid force was obtained from the local shear rate obtained from a CFD simulation of the flow over a backward facing step.

In stagnation point flow the shear rate near the stagnation point has a large gradient such that adherent cells in this region roll to a high shear region preventing permanent adhesion. This is enhanced if a small time dependent perturbation is imposed upon the stagnation point. For lower shear rates the cell rolling velocity may be such that secondary bonds have time to form. These bonds resist the lower fluid forces and consequently there is a relatively large permanent adhesion region.
Experimental assessment of wall shear flow in models
Authors: Affeld K. , Kertzscher U. , Goubergrits L.
Published: November 2024

The blood flow immediately adjacent to the wall of a blood vessel or an artificial surface is of great interest. This flow defines the shear stress at the wall and is known to have a great physiological importance. The use of models is a viable method to investigate this flow. However, even in models the shear stress at the wall is difficult to assess. A new optical method is based on transparent models and uses particles in the model fluid, which are only visible near the wall. This is achieved with a model fluid having a defined opacity. This fluid obscures particles in the center of the models, but permits the observation and recording of particles close to the wall. The method has been applied for Hagen–Poiseuille flow and for the likewise well researched flow in a tube with a sudden expansion.
Towards the treatment of saphenous vein bypass graft failure – a perspective of the Bristol Heart Institute
Authors: Angelini Gianni D. , Jeremy Jamie Y.
Published: November 2024

Coronary artery bypass graft surgery (CABG) is widely used for the treatment of atheromatous stenosis of coronary arteries. However, as many as 50% of grafts fail within 10 years after CABG due to neointima (NI) formation, a process involving the proliferation and migration of vascular smooth muscle cells (VSMCs). Superimposed on neointima formation is accelerated atherogenesis which ultimately results in late vein graft failure. To date no therapeutic intervention has proved successful in treating late vein graft failure and as such is a matter of some urgency. However, in recent years, several diverse approaches aimed at preventing neointimal formation have been devised which have yielded promising results. These include the use of external stents, gene therapy as well as conventional pharmacological interventions. The objective of this article, therefore, is to review these recent approaches and their potential clinical applications in the treatment of vein graft disease.
Atherosclerosis and flow in carotid arteries with authentic geometries
Authors: Goubergrits L. , Affeld K. , Fernandez‐Britto J. , Falcon L.
Published: November 2024

The influence of blood flow on the depositions and development of atherosclerotic lesions have been observed and described since the 19th century. Observations have shown that depositions correlate with regions of low wall shear stress. However, the exact correlations between depositions, vessel geometry and flow parameters are not yet known. The purpose of this study was the quantification of atherosclerosis risk factors in carotid bifurcation. This artery has attracted particular interest because lesions are often found in this bifurcation. Post mortem, the arteries are excised and vessel casts are produced. Afterwards, the arteries are analyzed morphometrically. The vessel casts are used for the assessment of some geometrical parameters. 31 carotid bifurcations were analyzed in this study. Eight vessel casts were digitized and rendered three‐dimensional mathematical models of the arteries. These data were imported by the computational fluid dynamics program FLUENT. Further, the blood flow was reconstructed in a computer model based on the individual vessel geometry. The flow parameters, such as velocity, pressure and wall shear stress were computed. At the same time the geometrical parameters and wall alterations are known. This permits the comparison of the anatomical shape and its flow with the distribution and level of the wall alterations.
Disease patterns at arterial branches and their relation to flow
Authors: Weinberg Peter D.
Published: November 2024

The distribution of lesions around arterial branch points is complex and changes with age. Four distinct patterns – here termed the arrowhead pattern, the lateral pattern, the upstream streak and the volcano – have been reported around the origins of intercostal arteries in the human aorta at different ages. The first two patterns also occur in young and old rabbits, the third in minipigs, and the fourth in apolipoprotein E/LDL receptor knockout mice. It is unclear how all four patterns can depend solely on flow; a particular problem is that the prevalence of lipid deposition remains highly nonuniform for several branch diameters upstream of the ostium. Variations in the prevalence of fatty streaks may originate near the branch and then spread by the migration of activated endothelial cells towards the heart. The pattern of raised lesions may reflect a different aetiology.
Peristaltic transport of a couple stress fluid in a uniform and non‐uniform channels
Authors: Mekheimer Kh.S.
Published: November 2024

The problem of peristaltic transport of a couple stress fluid in uniform and non‐uniform two‐dimensional channels has been investigated under zero Reynolds number with long wavelength approximation. Blood is represented by a couple stress fluid (a fluid which its particles size are taken into account, a special case of a non‐Newtonian fluid). It is found that the pressure rise decreases as the couple stress fluid parameter γ increases (i.e., small size fluid particle). So the pressure rise for a couple stress fluid (as a blood model) is greater than that for a Newtonian fluid. Also the pressure rise increases as the amplitude ratio ϕ increases for different values of γ. Further, the pressure rise in the case of non‐uniform geometry is found to be much smaller than the corresponding value in the case of uniform geometry. Finally, the maximum pressure rise when the mean flow rate over one period of the wave, $\bar{Q}$ =0, increases as ϕ increases and γ decreases.
Gene expression profiles in chondrosarcoma cells subjected to cyclic stretching and hydrostatic pressure. A cDNA array study
Authors: Karjalainen Hannu M. , Sironen Reijo K. , Elo Mika A. , Kaarniranta Kai , Takigawa Masaharu , Helminen Heikki J. , Lammi Mikko J.
Published: November 2024

Mechanical forces have a profound effect on cartilage tissue and chondrocyte metabolism. Strenuous loading inhibits the cellular metabolism, while optimal level of loading at correct frequency raises an anabolic response in chondrocytes. In this study, we used Atlas Human Cancer cDNA array to investigate mRNA expression profiles in human chondrosarcoma cells stretched 8% for 6 hours at a frequency of 0.5 Hz. In addition, cultures were exposed to continuous and cyclic (0.5 Hz) 5 MPa hydrostatic pressure. Cyclic stretch had a more profound effect on the gene expression profiles than 5 MPa hydrostatic pressure. Several genes involved with the regulation of cell cycle were increased in stretched cells, as well as mRNAs for PDGF‐B, glucose‐1‐phosphate uridylyltransferase, Tiam1, cdc37 homolog, Gem, integrin α6, and matrix metalloproteinase‐3. Among down‐regulated genes were plakoglobin, TGF‐α, retinoic acid receptor‐α and Wnt8b. A smaller number of changes was detected after pressure treatments. Plakoglobin was increased under cyclic and continuous 5 MPa hydrostatic pressure, while mitogen‐activated protein kinase‐9, proliferating cell nuclear antigen, Rad6, CD9 antigen, integrins αE and β8, and vimentin were decreased. Cyclic and continuous pressurization induces a number of specific changes. In conclusion, a different set of genes were affected by three different types of mechanical stimuli applied on chondrosarcoma cells.
Tensile properties of fibroblasts and vascular smooth muscle cells
Authors: Miyazaki Hiroshi , Hayashi Kozaburo , Hasegawa Yoshitaka
Published: November 2024

Tensile properties of fibroblasts (FBs) and vascular smooth muscle cells (VSMCs) of synthetic and contractile phenotypes were studied using a newly developed micro‐tensile tester. FBs were obtained from the rabbit patellar tendon. Synthetic and contractile VSMCs were isolated from the rabbit thoracic aorta with an explant and an enzymatic digestion method, respectively. Each cell was attached to the fine tips of a pair of micropipettes with a cell adhesive and, then, stretched at the speed of 6 μm/sec. Load and length were obtained using a cantilever‐type load cell and a VDA, respectively.

FBs were broken at the load of 0.9 μN and the elongation to failure of 86 μm, and had the stiffness of 0.02 N/m. VSMCs were not broken even at 2.4 μN. The stiffness of synthetic and contractile VSMCs were 0.09 and 0.17 N/m, respectively. Such large different tensile properties among the three cells are attributable to the differences in components and cytoskeletal structures.
Induced changes of leukocyte slow rolling in an in flow pharmacological model of adhesion to endothelial cells
Authors: Renard M. , Heutte F. , Boutherin‐Falson O. , Finet M. , Boisseau M.R.
Published: November 2024

Background: Rolling of leukocytes at the surface of the vascular endothelium is a prerequisite for a subsequent firm adhesion, particularly the slow rolling appearing on ELAM CD62E. Therefore, it may be considered that increasing the rolling velocities should be a precise therapeutic target in clinical situations where leukocytes accumulate, mainly venous and arterial ischaemia.

Methods: Human neutrophils were allowed to flow on endothelial HUVECs, with and without 4 hours interleukin‐1α activation, the cells having or not been incubated with INO5042 anti‐inflammatory drug. Under a mean shear‐stress of 2 dyn/cm2, rollers and stickers were identified and quantified, using a video‐camera and picture analysing software.

Results: When the drug had been added to endothelial cells a shift of velocities was observed towards fast speeds (from 3–5 to 7–11 μm/sec). The same results was significantly found when neutrophils, alone or along with endothelium, had been submitted to the drug, the number of stickers and rollers beeing reduced as well. Finally, such a precise pharmacological method proved efficient to detect the exact mechanism of INO5042 on white cell adhesion.
ET‐1 and NOS III gene expression regulation by plaque‐free and plaque‐prone hemodynamic conditions
Authors: Mattart Mélanie , Mazzolai Lucia , Chambaz Céline , Hayoz Daniel , Brunner Hans R. , Silacci Paolo
Published: November 2024

Both plaque‐free and plaque‐prone hemodynamic environments induce an increase in the oxidative state of endothelial cells (ECs), whereas differential gene expression regulation was described in cells exposed to these conditions. In order to investigate the role of the increased oxidative state in flow‐regulation of gene expression, we first exposed EC to non‐pulsed unidirectional shear stress. These conditions only slightly increases ECs oxidative state and endothelin‐1 (ET‐1) mRNA expression, whereas endothelial nitric oxide synthase (NOS III) mRNA level were significantly up‐regulated. On the contrary, both ET‐1 and NOS III gene expression were significantly induced in EC exposed to pulsed‐unidirectional flow (plaque‐free). Only ET‐1 gene expression was up‐regulated by oscillatory flow (plaque‐prone). Moreover, use of an antioxidant only partially inhibited NOS III gene up‐regulation by unidirectional flow, whereas it completely abrogated ET‐1 gene up‐regulation by unidirectional and oscillatory flows. Thus suggesting that mechanical forces regulate gene expression in ECs both via oxidative stress‐dependent and ‐independent mechanisms.
Human osteoblast‐like cells in three‐dimensional culture with fluid flow
Authors: Botchwey Edward A. , Pollack Solomon R. , El‐Amin Saadiq , Levine Elliot M. , Tuan Rocky S. , Laurencin Cato T.
Published: November 2024

In a previous study, we showed that the combination of appropriately designed three‐dimensional (3D) microcarrier scaffolds and fluid flow through and around the scaffolds during high aspect ratio vessel (HARV) rotation enhances the elaboration of mineralized bone matrix by osteoblast‐like cells. In this study, we describe the ongoing characterization of our 3D culture system, including the investigation of interior fluid flow within the scaffolds and early stage integrin expression during hydrodynamic culture. Using theoretical and experimental methods, we have estimated that cells cultured on the interior of microcarrier scaffolds experience an interior nutrient flow velocity between 1×10−3 and 1×10−2 cm/s and maximum shear stress of 0.03 N/m2. Under these conditions, osteoblast‐like cells grew extensively in the interior regions of the scaffold and retained their osteoblastic phenotype as measured by alkaline phosphatase. In addition, flow cytometric analysis of the overall cell population showed that cells constitutively expressed integrin α3β1 during 3D hydrodynamic culture.
Interactive role of tyrosine kinase, protein kinase C, and Rho/Rho kinase systems in the mechanotransduction of vascular smooth muscles
Authors: Nakayama Koichi , Obara Kazuo , Tanabe Yoshiyuki , Saito Maki , Ishikawa Tomohisa , Nishizawa Shigeru
Published: November 2024

Blood vessels are always subjected to hemodynamic stresses including blood pressure and blood flow. The cerebral artery is particularly sensitive to hemodynamic stresses such as pressure and stretch, and shows contractions that are myogenic in nature; i.e., the mechanical response is generated by the vascular smooth muscle itself. The artery constricts in response to an increase in intraluminal pressure, and dilates in response to a decrease in the intraluminal pressure. We provide herein some insights into the mechanotransduction of vascular tissue; i.e., we discuss how the tissue is receptive to mechanical force and how the latter induces the specific signals leading to myogenic contraction in terms of mechanosensor action and subsequent intracellular signaling. The interactive role of tyrosine kinase, protein kinase C, and Rho/Rho‐kinase systems in the mechanotransduction process is discussed, which systems also seem to play an important role in the development of experimental cerebral vasospasm. The study of the mechanotransduction in vascular tissue may aid in clarifying the mechanisms underlying vasospastic episodes and pathologic remodeling in cardiovascular diseases, and may potentially have therapeutic consequences.
Surface characterization of poly(ethylene glycol) coated human red blood cells by particle electrophoresis
Authors: Neu Björn , Armstrong Jonathan K. , Fisher Timothy C. , Meiselman Herbert J.
Published: November 2024

Recent studies have shown that the covalent attachment of poly(ethylene glycol), abbreviated as PEG, to the surface of human red blood cells (RBC) leads to masking of membrane antigenic sites and inhibition of RBC aggregation. The effects of PEG coating on the regions near the RBC glycocalyx were thus explored using cell micro‐electrophoresis. Both linear (3.35, 18.5, 35.0) and an 8‐arm 35.9 kDa reactive PEG were used; in one series, thick cross‐linked coats were obtained using a branched PEG amine as a cross‐linker. The results indicate marked decreases of RBC mobility (up to 90%) which were affected by polymer molecular mass and geometry. Since PEG is neutral and its covalent attachment is predominantly to primary amine groups, such decreases of mobility most likely reflect structural changes near and within the RBC glycocalyx rather than decreased surface charge density. Experimental data were analyzed using a theoretical approach which allows calculation of the thickness and friction of the polymer layers: (1) for linear PEGs, thickness increased and friction decreased with polymer mass; (2) compared to linear PEGs of similar molecular mass, thickness was less and friction was greater for the branched PEG; (3) cross‐linked PEG coatings were more than 50 nm thick and were insensitive to changes of ionic strength. These observations are consistent with the aggregation behavior of PEG‐coated RBC and indicate the usefulness of micro‐electrophoresis methods for studies of covalently‐attached polymers: the resulting calculated thickness and friction factors should be of value in achieving desired cellular surface characteristics or levels of cell–cell interaction.
Increased resistance of neutrophils to deformation upon cooling and rate of recovery on rewarming
Authors: Jetha Karim A. , Egginton Stuart , Nash Gerard B.
Published: November 2024

Increase in the resistance to deformation of neutrophils upon exposure to the cold may impair their passage through microvessels. However, the potential for such rheological changes to cause prolonged microvascular obstruction in cooled tissue will depend on whether and at what rate the neutrophils recover on rewarming. We tested the ability of neutrophils to pass through micropore filters, and found that neutrophils cooled to 10°C for 10–20 minutes could block either 5 μm or 8 μm pore filters. On return to 37°C, flow resistance remained impaired briefly but recovered over about 5 minutes. The kinetics of changes in flow resistance in the cold and on rewarming were linked to kinetics of actin polymerisation during these periods. However, they were not closely linked to distortion of cell shape in the cold, which recovered only slowly with rewarming. The results suggest that while rigid neutrophils might occlude capillaries in cold tissue, mechanical obstruction should not be long‐lived on rewarming. Moreover, rigid neutrophils washed out of cold tissue should experience only temporary mechanical trapping in remote tissues.
Lubricated squeezing flow: A useful method for measuring the viscoelastic properties of soft tissues
Authors: Nasseri Simin , Bilston Lynne , Tanner Roger
Published: November 2024

Conducting experiments on very soft biological tissues can be difficult. Traditionally, unconfined compression and shear have been used. Here, an improved method of compression testing, lubricated squeezing flow is described. This gives a uniform compression along the squeezing axis and almost uniform equi‐biaxial elongation at right angles to the squeezing axis, with minimal shear deformation due to the constant lubrication of the sample surfaces during testing. Sample results for porcine liver obtained using this method are described here.
Conductometric study of shear‐dependent processes in red cell suspensions. II. Transient cross‐stream hematocrit distribution
Authors: Pribush A. , Meyerstein D. , Meiselman H.J. , Meyerstein N.
Published: November 2024

A novel experimental approach based on electrical properties of red blood cell (RBC) suspensions was applied to study the effects of the size and morphology of RBC aggregates on the transient cross‐stream hematocrit distribution in suspensions flowing through a square cross‐section flow channel. The information about the effective size of RBC aggregates and their morphology is extracted from the capacitance (C) and conductance (G) recorded during RBC aggregation, whereas a slower process of particle migration is manifested by delayed long‐term changes in the conductance. Migration‐induced changes in the conductance measured at low shear rates (≤3.1 s−1) for suspensions of RBCs in a strongly aggregating medium reveal an increase to a maximum followed by a decrease to the stationary level. The ascending branch of G(t) curves reflects the aggregate migration in the direction of decreasing shear rate. A further RBC aggregation in the region of lower shear stresses leads to the formation of RBC networks and results in the transformation of the rheological behavior of suspensions from the thinning to the thickening. It is suggested that the descending branches of the G(t) curves recorded at low shear rates reflect an adjustment of the Hct distribution to a new state caused by a partial dispersion of RBC networks. For suspensions of non‐aggregating RBCs it is found that depending on whether the shear rate is higher or lower compared with the prior value, individual RBCs migrate either toward the centerline of the flow or in the opposite direction.
Quantitative analysis of the effects of hyaluronan and aggrecan concentration and hyaluronan size on the elasticity of hyaluronan–aggrecan solutions
Authors: Nishimura M. , Kawata M. , Yan W. , Okamato A. , Nishimura H. , Ozaki Y. , Hamada T. , Kato Y.
Published: November 2024

We determined elasticity (G′) and viscosity (G″) of various aggrecan–hyaluronan solutions using a controlled‐stress rheometer with high (10 Hz) to low (0.1 Hz) frequencies. Aggrecan solution (50 mg/ml) alone showed little elasticity at any frequency, but the addition of 3300 kDa hyaluronan at 0.001–0.1 mg/ml markedly increased the elasticity, but not the viscosity, at all frequencies. Increasing hyaluronan concentration at >0.1 mg/ml did not further increase the elasticity of the aggrecan solution, and the elasticity of the aggrecan–hyaluronan complex solution reached a plateau at a 500 :1 (w/w) ratio. In studies with increasing concentrations of aggrecan and a constant concentration (0.5 mg/ml) of 3300 kDa hyaluronan, aggrecan induced elasticity only at >20 mg/ml, indicating the presence of a critical concentration for elasticity. In the presence of 50 mg/ml aggrecan, 1000 kDa hyaluronan had far less effect on the elasticity of the aggrecan solution than did 3300 kDa hyaluronan. These findings suggest that only ∼50% reduction in aggrecan concentration (<20 mg/ml), or reduced hyaluronan size (<1000 kDa) – compared with their physiological levels in young cartilage – can abolish the elastic network of the aggrecan–hyaluronan complex.
Magnetic resonance microscopy determined velocity and hematocrit distributions in a Couette viscometer
Authors: Cokelet Giles R. , Brown Jennifer R. , Codd Sarah L. , Seymour Joseph D.
Published: November 2024

Magnetic resonance microscopy is used to non-invasively measure the radial velocity distribution in Couette flow of erythrocyte suspensions of varying aggregation behavior at a nominal shear rate of 2.20 s−1 in a 1 mm gap. Suspensions of red blood cells in albumin-saline, plasma and 1.48% Dextran added plasma at average hematocrits near 0.40 are studied, providing a range of aggregation ability. The spatial distribution of the red blood cell volume fraction, hematocrit, is calculated from the velocity distribution. The hematocrit profiles provide direct measure of the thickness of the aggregation and shear rate dependent red blood cell depletion at the Couette surfaces. At the nominal shear rate studied hematocrit distributions for the red blood cells in plasma show a depletion zone near the inner Couette wall but not the outer wall. The red blood cells in plasma with Dextran show cell depletion regions of approximately 100 μm at both the inner and outer Couette surfaces, with greater depletion at the inner wall, but approach the normal blood hematocrit distribution with a doubling of shear rate due to decreased aggregation. The material response of the blood is spatially dependent with the shear rate and the hematocrit distribution non-uniform across the gap.
Numerical study of the impact of non-Newtonian blood behavior on flow over a two-dimensional backward facing step
Authors: Choi Hyo Won , Barakat Abdul I.
Published: November 2024

Endothelial cell (EC) responsiveness to shear stress is essential for vasoregulation and plays a role in atherogenesis. Although blood is a non-Newtonian fluid, EC flow studies in vitro are typically performed using Newtonian fluids. The goal of the present study was to determine the impact of non-Newtonian behavior on the flow field within a model flow chamber capable of producing flow disturbance and whose dimensions permit Reynolds and Womersley numbers comparable to those present in vivo. We performed two-dimensional computational fluid dynamic simulations of steady and pulsatile laminar flow of Newtonian and non-Newtonian fluids over a backward facing step. In the non-Newtonian simulations, the fluid was modeled as a shear-thinning Carreau fluid. Steady flow results demonstrate that for Re in the range 50–400, the flow recirculation zone downstream of the step is 22–63% larger for the Newtonian fluid than for the non-Newtonian fluid, while spatial gradients of shear stress are larger for the non-Newtonian fluid. In pulsatile flow, the temporal gradients of shear stress within the flow recirculation zone are significantly larger for the Newtonian fluid than for the non-Newtonian fluid. These findings raise the possibility that in regions of flow disturbance, EC mechanotransduction pathways stimulated by Newtonian and non-Newtonian fluids may be different.
Volume flow estimation in the precapillary mesenteric microvasculature in vivo and the principle of constant pressure gradient
Authors: Koutsiaris Aristotle G.
Published: November 2024

Volume flow was estimated from axial erythrocyte velocity measurements in 30 mesenteric microvessels of 6 rabbits and was compared to Murray's law predictions. The diameters of capillaries and precapillary arterioles ranged between 5.6 and 12 μm. The significant pulsating flow component existing in these microvessels was taken into account by measuring instantaneous axial blood velocity throughout the course of a cardiac cycle and then averaging over the period. In addition, the effect of the velocity profile variation with diameter was taken into account, for the first time, by using a profile factor function. According to Murray's law, the relation between blood volume flow and diameter is governed by a ‘cube’ law. Curve fitting to volume flow and diameter data pairs for rabbits, showed a dependence of volume flow on diameter raised to the 4th power (with a correlation coefficient equal to 0.97). The above result supports the hypothesis that, in the precapillary part of microvasculature, the principle of constant longitudinal pressure gradient rather than the principle of minimum work may be valid.
Molecular basis of rheological modulation of endothelial functions: Importance of stress direction
Authors: Chien Shu
Published: November 2024

Vascular endothelial cells (EC) play significant roles in regulating circulatory functions. Shear stress and stretch can modulate EC functions by activating mechano-sensors, signaling pathways, and gene and protein expressions. Laminar shear stress with a significant forward direction causes transient activations of monocyte chemotactic protein-1 (MCP-1), sterol response element binding protein (SREBP), and proliferative genes. Sustained laminar shear stress down-regulates these genes and up-regulates genes that inhibit EC growth. In EC subjected to complex flow patterns with little forward direction, activations of MCP-1, SREBP, and proliferation genes become sustained, and mitosis and apoptosis are enhanced. Cyclic uniaxial stretch causes actin stress fibers to orient perpendicular to stretch direction, with a consequent reduction of intracellular stress, transient JNK activation, and protection of EC against apoptosis. Cyclic biaxial stretch without a preferred direction has opposite effects. In the straight part of arterial tree, laminar shear stress with a net forward direction and uniaxial strain in the circumferential direction have anti-atherogenic effects. At vascular branch points, the complex shear flow and mechanical strain with little net direction are atherogenic. Therefore, the direction of stress has important influences on the biorheological effects of flow and deformation on vascular endothelium in health and disease.
The effect of hydrodynamic shear on 3D engineered chondrocyte systems subject to direct perfusion
Authors: Raimondi Manuela T. , Moretti Matteo , Cioffi Margherita , Giordano Carmen , Boschetti Federica , Laganà Katia , Pietrabissa Riccardo
Published: November 2024

Bioreactors allowing direct-perfusion of culture medium through tissue-engineered constructs may overcome diffusion limitations associated with static culturing, and may provide flow-mediated mechanical stimuli. The hydrodynamic stress imposed on cells within scaffolds is directly dependent on scaffold microstructure and on bioreactor configuration. Aim of this study is to investigate optimal shear stress ranges and to quantitatively predict the levels of hydrodynamic shear imposed to cells during the experiments. Bovine articular chondrocytes were seeded on polyestherurethane foams and cultured for 2 weeks in a direct perfusion bioreactor designed to impose 4 different values of shear level at a single flow rate (0.5 ml/min). Computational fluid dynamics (CFD) simulations were carried out on reconstructions of the scaffold obtained from micro-computed tomography images. Biochemistry analyses for DNA and sGAG were performed, along with electron microscopy. The hydrodynamic shear induced on cells within constructs, as estimated by CFD simulations, ranged from 4.6 to 56 mPa. This 12-fold increase in the level of applied shear stress determined a 1.7-fold increase in the mean content in DNA and a 2.9-fold increase in the mean content in sGAG. In contrast, the mean sGAG/DNA ratio showed a tendency to decrease for increasing shear levels. Our results suggest that the optimal condition to favour sGAG synthesis in engineered constructs, at least at the beginning of culture, is direct perfusion at the lowest level of hydrodynamic shear. In conclusion, the presented results represent a first attempt to quantitatively correlate the imposed hydrodynamic shear level and the invoked biosynthetic response in 3D engineered chondrocyte systems.
Mesenchymal progenitor cells in adult human articular cartilage
Authors: Hiraoka Koji , Grogan Shawn , Olee Tsaiwei , Lotz Martin
Published: November 2024

The transmembrane receptor Notch-1 regulates cell fate and differentiation and was suggested to identify a cell type with progenitor characteristics in newborn bovine articular cartilage. We show that Notch-1 is expressed on >70% of BM-MSC in early passage monolayer culture. We also demonstrate that normal articular cartilage contains Notch-1+ cells and that the frequency is increased in OA. Most Notch-1+ cells in OA cartilage are located in the clusters of proliferating cells. These findings indicate that multipotential mesenchymal progenitor cells are present in articular cartilage from adult humans and that their frequency is increased in OA. This observation has implications for understanding the intrinsic repair capacity of articular cartilage and raises the possibility that these progenitor cells might be involved in the pathogenesis of arthritis.
Long-term mechanical loading of chondrocyte–chitosan biocomposites in vitro enhanced their proteoglycan and collagen content
Authors: Fehrenbacher Andreas , Steck Eric , Roth Wolfgang , Pahmeier Andrea , Richter Wiltrud
Published: November 2024

One major problem in cartilage tissue engineering is the insufficient biochemical composition of the generated biocomposites. The aim of this study was to improve the collagen and proteoglycan deposition in tissue engineering constructs by application of long-term mechanical loading in culture. Chondrocyte-seeded chitosan biocomposites revealed a homogenous cell distribution, high viability (>95%) and maintenance of a rounded cell shape typical for chondrocytes over 3 weeks of load-free culture. Cyclic compression of chitosan biocomposites (0.1 Hz, amplitude 5–15%, 45 min on and 315 min off) was applied after two different preculture times (3, 21 days) for 3 weeks. At day 42 this resulted in enhanced mRNA levels for aggrecan and a significantly higher specific proteoglycan (5-fold, p<0.0002) and collagen type II (2-fold, p<0.02) deposition compared to unloaded controls. In sum, the chitosan scaffold was highly attractive for cartilage tissue engineering approaches and mechanical loading allowed to further improve the biochemical composition of these biocomposites.
Hydrodynamic interaction between erythrocytes and leukocytes affects rheology of blood in microvessels
Authors: Pappu Vijay , Bagchi Prosenjit
Published: November 2024

Hydrodynamic interaction between erythrocytes (RBC) and leukocytes (WBC) in a microvessel of size 20–40 micron, typical of a postcapillary venule, is studied using a two-dimensional computational model. The model is based on immersed boundary method, and it takes into consideration the particulate nature of blood by explicitly modeling individual blood cell, and cell deformation. Due to their highly flexible nature, RBC drift away from the wall and toward the center of a vessel creating a cell-free layer. It is shown here that the lateral motion of RBC is strongly affected in presence of a WBC, and is dependent on whether the WBC is non-adherent or firmly adhered. When the WBC is non-adherent, some RBC, depending on their initial radial locations and vessel size, may be deflected closer toward the wall, resulting in a decrease in the cell-free layer. The apparent viscosity of the whole blood containing both RBC and WBC is computed, and shown to be much higher than that containing RBC only. The increased viscosity cannot be accounted for by the contribution due to WBC only. This observation is in agreement with a previous in vivo measurement. Here we show that the additional flow resistance is due to the decrease in the cell-free layer resulting from the WBC-RBC interaction. It can be accounted for by a two-layer model of blood when the reduced values of the cell-free layer thickness are used. When the WBC is firmly adhered, RBC easily move away from the wall, and the cell-free layer is not significantly changed. In such cases, the major contribution to whole blood viscosity comes from the WBC alone. The hydrodynamic interaction between WBC and RBC, though it exists, does not contribute significantly when WBC are adhered.