bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrophoretic mobility of human red blood cells coated with poly(ethylene glycol)
Authors: Neu Björn , Armstrong Jonathan K. , Fisher Timothy C. , Bäumler Hans , Meiselman Herbert J.
Published: November 2024

Poly(ethylene glycol), abbreviated as PEG, was covalently attached to the surface of human red blood cells (RBC) and the effects of such coating on the regions near the cell's glycocalyx were explored by means of cell electrophoresis. RBC electrophoretic mobilities were measured, in polymer‐free buffers of various ionic strengths, as functions of PEG molecular mass (3.35, 18.5, 35.0, 35.9 kDa), geometry, (linear or 8‐arm branched) and polymer/RBC ratio during attachment. The results indicate marked decreases of the mobility (up to 85%) which were affected by polymer molecular mass and geometry. Since PEG is neutral and its covalent attachment only removes positively‐charged amino groups on the cell membrane, such decreases of mobility likely reflect structural changes near and within the RBC glycocalyx. Experimental results were analyzed using an extended “hairy sphere” model to consider friction and thickness of the polymer layer. Calculated polymer layer thickness increased with molecular mass for linear PEGs and was less extended for a branched PEG of similar molecular mass. Friction within the polymer layer increased with polymer/RBC ratio and for the linear PEGs was inversely related to molecular mass; friction was greatest for the branched PEG. Our results are consistent with the effects of attached PEGs on RBC aggregation and surface antigenic site masking, and suggest the usefulness of electrophoretic mobility techniques for studies of bound neutral polymers.
Comparison of the effects of human erythrocyte ghosts and intact erythrocytes on platelet interactions with subendothelium in flowing blood
Authors: Bozzo Jordi , Tonda Raúl , Hernández María‐Rosa , Alemany Mònica , Galán Ana‐María , Ordinas Antonio , Escolar Ginés
Published: November 2024

We investigated whether ghosts behaved similarly to intact erythrocytes to maintain regular primary hemostasis under flow conditions. To this end we performed perfusion experiments with whole blood in which erythrocytes were replaced by pink ghosts, and platelet interaction with the subendothelial surface of a damaged vessel was morphometrically evaluated. The same objective was sought by means of studies with a platelet function analyzer (PFA‐100TM instrument). Perfusions performed with control blood reconstituted with intact erythrocytes gave rise to 0.4±0.2% contact but not spread platelets, 10.8±3.4% adhering and spread platelets, 16.3±4.6% platelets in thrombi, with 27.5±7.4% of the surface covered. Even though the average diameter of the ghosts was smaller than that of intact erythrocytes (5.3 μm vs. 7.7 μm), the values obtained in perfusions performed with ghosts were similar to those of the erythrocyte controls. Studies performed with the PFA‐100TM analyzer were consistent with those observed in perfusion studies. The viscosity of control blood was compared with that of blood reconstituted with ghosts. At shear rates lower than 450 s−1, the viscosity of the ghost samples was higher than that of the controls, but the difference progressively decreased as shear rate increased up to 750 s−1 (3.61±0.15 and 3.71±0.17 cP, respectively). In conclusion, the results of our study showed that ghosts behaved similarly to intact erythrocytes in maintaining a normal platelet interaction with digested subendothelium, under conditions of moderate shear rate and constant hematocrit (40%). The rheological activity of ghosts, bodies that are metabolically less active, was sufficient for them to satisfactorily act as substitutes for intact erythrocytes in our system.
Measuring principles of frictional coefficients in cartilaginous tissues and its substitutes
Authors: Huyghe J.M. , Janssen C.F. , van Donkelaar C.C. , Lanir Y.
Published: November 2024

The frictional properties of cartilaginous tissues, such as the hydraulic permeability, the electro‐osmotic permeability, the diffusion coefficients of various ions and solutes, and the electrical conductance, are vital data to characterise the extracellular environment in which chondrocytes reside. This paper analyses one‐dimensional measurement principles of these coefficients. Particular attention is given to the deformation dependence of them and the highly deformable nature of the tissues. A suggested strategy is the combination of a diffusion experiment using radiotracer methods, an electro‐osmotic flow experiment and an electro‐osmotic pressure experiment at low electric current.
Influence of ion channels on the proliferation of human chondrocytes
Authors: Wohlrab David , Lebek Susanne , Krüger Thomas , Reichel Heiko
Published: November 2024

The goal of the study was to examine connections between ion channel activity and the proliferation of human chondrocytes. Chondrocytes were isolated form human osteoarthritic knee joint cartilage. In this study the concentration‐dependent influence of the ion channel modulators tetraethylammonium (TEA), 4‐aminopyridine (4‐AP), 4′,4′ diisothiocyanato‐stilbene‐2,2′‐disulfonic acid (DIDS), 4‐acetamido‐4′‐isothiocyano‐2,2′‐disulfonic acid stilbene (SITS), verapamil (vp) and lidocaine (lido) on the membrane potential and the proliferation of human chondrocytes was investigated using flow cytometry and the measurement of 3H‐thymidine incorporation as measure for the cell proliferation. The results show an effect of the used ion channel modulators causing a change of the membrane potential of human chondrocytes. The maximal measurable effects of the membrane potential were listed with 0.25 mmol/l verapamil (−18%) and 0.1 mmol/l lidocaine (+20%). When measuring DNA distribution, it became apparent that the human chondrocytes are diploid cells with a very low proliferation tendency. After 12 days culture duration, lidocaine and 4‐AP cause an increase of the DNA synthesis rate being a limited effect. These results allow the conclusion of an influence of ion channel modulators on chondrocyte proliferation. To gain knowledge of the regulation of chondrocyte proliferation via ion channel modulators could serve the research of new osteoarthritis treatment concepts.
The effect of mechanical stress on cartilage energy metabolism
Authors: Lee R.B. , Wilkins R.J. , Razaq S. , Urban J.P.G.
Published: November 2024

Cartilage is routinely subjected to varying mechanical stresses which are known to affect matrix turnover by a variety of pathways. Here we show that mechanical loads which suppress sulphate incorporation or protein synthesis by articular chondrocytes, also inhibit rates of oxygen uptake and of lactate production. Although the mechanisms have not been definitively identified, it has been shown that high hydrostatic pressures reduce the activity of the glucose transporter GLUT. Furthermore, fluid expression consequent on static loading changes intracellular pH and ionic strength; intracellular changes which would reduce the activity of glycolytic enzymes. Both pathways would thus lead to a fall in rates of glycolysis and a reduction in intracellular ATP, and – since ATP concentrations directly affect sulphation of proteoglycans – a rapid fall in sulphate incorporation. Our results suggest that load‐induced changes in matrix synthesis in cartilage can occur by means other than changes in gene expression.
Ultrasonic characterization of articular cartilage
Authors: Töyräs J. , Nieminen H.J. , Laasanen M.S. , Nieminen M.T. , Korhonen R.K. , Rieppo J. , Hirvonen J. , Helminen H.J. , Jurvelin J.S.
Published: November 2024

Osteoarthrosis is the most important joint disease that threatens health of the musculoskeletal system of elderly people. Today, there is a need for sensitive, quantitative diagnostic methods for successful and early diagnosis of the disorder. In the present study, we aimed at evaluating the applicability of ultrasound for quantitative assessment of cartilage structure and properties. Bovine articular cartilage was investigated both in vitro and in situ using high frequency ultrasound. Cartilage samples were also tested mechanically in vitro to reveal relationships between acoustic and mechanical parameters of the tissue. The collagen organization and proteoglycan content of cartilage samples were mapped, using quantitative polarized light microscopy and digital densitometry, respectively, to reveal their effect on the acoustic properties of tissue. The high frequency pulse‐echo ultrasound (20–30 MHz) technique proved to be sensitive in detecting the degeneration of the superficial collagen‐rich cartilage zone. In addition, ultrasound was found to be a potential tool for measuring cartilage thickness. When the results from biomechanical indentation measurements and ultrasound measurements of normal and enzymatically degraded articular cartilage were combined, collagen or proteoglycan degradation in the tissue could be sensitively and specifically differentiated from each other. To conclude, high frequency ultrasound is a useful tool for evaluation of the quality of superficial articular cartilage as well as for the measurement of cartilage thickness. Therefore, ultrasound appears to be a valuable supplement to the mechanical measurements of articular cartilage stiffness.
On flow through bends and branchings
Authors: Smith F.T.
Published: November 2024

Theoretical modelling of bending and branching tube flows at medium‐to‐high flow rates is described for current industrial and biomedical projects. This mostly uses slender‐flow modelling. Much pressure loss occurs in bends, with increased swirl, large variations in velocity components and wall shear stress, skewing of the downstream motion and reduced flow rate, but the flow regime which is established shows sensitive dependence on the imposed pressure drop and entrance conditions. A small side‐branch off a mother tube produces most rapid variation in pressure and velocity near the daughter entrance, this variation now being quantifiable. A multiple branching yields large flow rates and nonunique flow patterns, depending on the form of the imposed pressure differences.
Morphodynamics of flow through sinuous curvatures of the heart
Authors: Kilner Philip J. , Yang Guang‐Zhong , Firmin David N.
Published: November 2024

Through cardiac looping during embryonic development, human and other vertebrate hearts adopt sinuous curvatures with marked changes in direction of flow at atrial, ventricular and arterial levels. We used magnetic resonance phase velocity mapping to study flow through the hearts of resting volunteers, and Doppler ultrasound to record changes with exercise. We found asymmetric recirculation of blood during filling phases of all four heart cavities, with blood redirected appropriately for onward passage to the next cavity. Doppler traces showed that biphasic ventricular filling became rapid and monophasic on strenuous exercise. We propose that looped curvatures of the heart have fluidic and dynamic advantages. Intra‐cavity flow appears to be asymmetric in a manner that preserves stability, and allows momentum of inflowing streams to be redirected towards rather than away from the next cavity. Direction‐change at ventricular level is such that recoil away from ejected blood is in a direction that can enhance rather than inhibit ventriculo‐atrial coupling. These factors may combine to allow a reciprocating, sling‐like, ‘morphodynamic’ mode of action become effective when heart rate and output increase with exercise. Dynamic efficiency of the looped heart may have favoured evolution of large, complex, active species characteristic of the vertebrate line.
Quantification of the non‐planarity of the human carotid bifurcation
Authors: King E. , Xu X.Y. , Hughes A.D. , Long Q. , Thom S.A. , Parker K.H.
Published: November 2024

The carotid bifurcation has been a region of particular interest due to its predilection for clinically significant atherosclerosis. It has been shown that the vessel geometry is a major determinant of the local haemodynamic properties which are believed to be associated with the location of atherosclerotic lesions. Current knowledge of the geometry of the carotid bifurcation is insufficient and restricted to basic geometric parameters. To provide some means of quantifying the degree of complexity of the 3D shape of the bifurcation, we made an initial attempt by evaluating the non‐planarity of an arterial bifurcation based upon the singular value decomposition theorem.

In this paper we present our results obtained on the right carotid bifurcations of six normal subjects, each of whom was scanned twice using the 2D time‐of‐flight MR sequence. The acquired 2D cross sectional images were processed by using our in‐house software which comprises 2D segmentation, 3D reconstruction and smoothing. The centroids of each transverse slices were determined and used as input data for the non‐planarity analysis. Our results using the singular value decomposition method have demonstrated discernible differences in non‐planarity among individuals. Comparisons with the planarity definition proposed by other investigators suggest that the singular value decomposition method offers more information about the linearity and planarity of the bifurcation. However, it is also realised that a single measure of non‐planarity can never fully characterise a bifurcation owing to the great variety of geometries.
Experimental evaluation of flow patterns in interposition vein cuff anastomosis. The influence of non‐planarity of the inflow
Authors: How T.V. , Fisher R.K. , Hoedt M.T.C. , Brennan J. , Harris P.L.
Published: November 2024

Clinical evidence suggests that the development of myointimal hyperplasia in prosthetic femorodistal bypass grafts may be reduced by the interposition of a cuff of autologous vein between the graft and the recipient artery. Previous experimental work has shown that some of the benefits may be attributed to the geometry of the cuffed anastomosis. Since the distal anastomosis in vivo is often non‐planar we have carried out a preliminary study in a model where the graft is at an angle of 45° to the anterior–posterior plane of the anastomosis. This out‐of‐plane angulation produces highly asymmetric flow patterns in the anastomosis with significant flow separation on the ipsilateral side of the cuff. In the proximal and distal outflow, however, the velocity vectors show significant helical motion with temporal instability in the distal outflow.
Effects of stents under asymmetric inflow conditions
Authors: Atherton M.A. , Tesch K. , Collins M.W.
Published: November 2024

Patient‐to‐patient variations in artery geometry may determine their susceptibility to stenosis formation. These geometrical variations can be linked to variations in flow characteristics such as wall shear stress through stents, which increases the risk of restenosis. This paper considers computer models of stents in non‐symmetric flows and their effects on flow characteristics at the wall. This is a fresh approach from the point of view of identifying a stent design whose performance is insensitive to asymmetric flow. Measures of dissipated energy and power are introduced in order to discriminate between competing designs of stents.
A covalently cross‐linked gel derived from the epidermis of the pilot whale Globicephala melas
Authors: Baum C. , Fleischer L.‐G. , Roessner D. , Meyer W. , Siebers D.
Published: November 2024

The rheological properties of the stratum corneum of the pilot whale (Globicephala melas) were investigated with emphasis on their significance to the self‐cleaning abilities of the skin surface smoothed by a jelly material enriched with various hydrolytic enzymes. The gel formation of the collected fluid was monitored by applying periodic‐harmonic oscillating loads using a stress‐controlled rheometer. In the mechanical spectrum of the gel, the plateau region of the storage modulus G′ (<1200 Pa) and the loss modulus G″ (>120 Pa) were independent of frequency (ω=43.98 to 0.13 rad·s−1,τ=15 Pa, T=20°C), indicating high elastic performance of a covalently cross‐linked viscoelastic solid. In addition, multi‐angle laser light scattering experiments (MALLS) were performed to analyse the potential time‐dependent changes in the weight‐average molar mass of the samples. The observed increase showed that the gel formation is based on the assembly of covalently cross‐linked aggregates. The viscoelastic properties and the shear resistence of the gel assure that the enzyme‐containing jelly material smoothing the skin surface is not removed from the stratum corneum by shear regimes during dolphin jumping. The even skin surface is considered to be most important for the self‐cleaning abilities of the dolphin skin against biofouling.
A mechanosensitive cation channel in endothelial cells and its role in vasoregulation
Authors: Yao X. , Kwan H.Y. , Dora K.A. , Garland C.J. , Huang Y.
Published: November 2024

Ca2+ is an important intracellular second messenger in signal transduction of endothelial cells. It has long been recognized that a mechanosensitive Ca2+‐permeable channel is present in vascular endothelial cells. The activity of this channel may increase intracellular Ca2+ level in endothelial cells. A recent finding is that the activity of this channel may be regulated by cGMP through a protein kinase G‐dependent pathway. Inhibition of the channel by cGMP abolishes the Ca2+ influx elicited by flow. Several inhibitors of the cation channel including Gd3+, Ni2+, and SK&F‐96365 also inhibit the Ca2+ influx due to flow stimulation. These data suggest that a mechanosensitive cation channel is the primary pathway mediating the flow‐induced Ca2+ entry in vascular endothelial cells. Another important finding is that the opening of this mechanosensitive channel by KT5823 leads to endothelium‐dependent vascular dilation. Therefore, it appears that this channel may play a crucial role in the regulation of vascular tone.
Shear stress modulates tumour cell adhesion to the endothelium
Authors: Gomes N. , Berard M. , Vassy J. , Peyri N. , Legrand C. , Fauvel‐Lafeve F.
Published: November 2024

The adhesion of breast adenocarcinoma cells (MDA‐MB‐231) to human umbilical vein endothelial cells (HUVEC) was studied in whole blood and under varying flow conditions. This study was done on HUVEC either kept under static conditions or pre‐conditioned in flow for 2 hours at a shear stress of 5 or 13 dyn/cm2. Coverslips coated by HUVEC were placed in a parallel plate perfusion chamber and perfused at a shear rate of 300 or 1500 sec−1 with heparin‐anticoagulated blood containing 111In labelled MDA‐MB‐231 cells. We report here the optimal conditions for studying the adhesion of MDA‐MB‐231 to endothelial cells under shear constraints corresponding to those observed into small and medium sized arteries.
Adaptation of articular chondrocytes to changes in osmolality
Authors: Hopewell Bethan , Urban Jill P.G.
Published: November 2024

Articular chondrocytes are exposed to a unique osmotic environment, which varies throughout the depth of cartilage, and in response to mechanical loading or pathological conditions. In light of such osmotic variations we investigated the response of chondrocytes cultured in alginate beads to long term hypo‐ and hyperosmotic challenge. Following pre‐incubation at 380 mOsmol, exposure to hyperosmotic conditions (550 mOsmol) initially decreased 35S‐sulphate incorporation, but after 24 hours of culture, rates had recovered and surpassed their original levels. MAP kinase inhibitors abrogated this response suggesting their involvement in the adaptation mechanism. Hypo‐osmotic challenge caused a decrease in 35S‐sulphate incorporation throughout the culture period. These results suggest that osmolality is a powerful regulator of macromolecular synthesis, and that perturbations in the osmotic environment may alter the set point for turnover.
Numerical simulation of deformations and electrical potentials in a cartilage substitute
Authors: Frijns A.J.H. , Huyghe J.M. , Kaasschieter E.F. , Wijlaars M.W.
Published: November 2024

Cartilage exhibits a swelling and shrinking behaviour that influences the function of the cells inside the tissue. This behaviour is caused by mechanical, chemical and electrical loads. It is described by the electrochemomechanical mixture theory, in which the tissue is represented by four components: a charged porous solid, a fluid, cations and anions. By distinguishing between the cations and anions, electrical phenomena can be modelled. This mixture theory is verified by fitting the deformations and the electrical potentials in a uniaxial confined swelling and compression experiment to a mixed finite element simulation. The fitted stiffness, permeability, diffusion coefficients, and osmotic coefficients are in the same range as reported in literature.
Investigation of mechanical behavior of articular cartilage by fibril reinforced poroelastic models
Authors: Li LePing , Shirazi‐Adl A. , Buschmann M.D.
Published: November 2024

The fibril reinforced poroelastic models have been found successful in describing some mechanical behaviors of articular cartilage in unconfined compression that were not understood previously, including the strong and nonlinear transient response, the strain‐magnitude and strain‐rate dependent cartilage stiffness and the depth‐varying stresses and strains. It has been demonstrated that a better description for the mechanical behavior of cartilage is obtained by introducing a fibrillar matrix into a poroelastic model, in addition to the nonfibrillar matrix and water. This paper reports the development of the nonlinear fibril reinforced homogeneous and nonhomogeneous models and further explores the potentials of the models for investigation of cartilage mechanical response. Some comments are made in regard to further applications of the models and improved accuracy of the material representation.
Coumarin‐like fluorescent molecular rotors for bioactive polymers probing
Authors: Even P. , Chaubet F. , Letourneur D. , Viriot M.L. , Carré M.C.
Published: November 2024

Polysaccharides are interesting and often essential macromolecules but are difficult to analyse due to their lack of convenient chromophores. We propose an efficient labelling procedure for polysaccharides such as functionalized dextrans with coumarin derivatives: the fluorescent tracers present inter alia properties of emission of fluorescence dependent on the molecular environment (polarity, viscosity, temperature, pH, etc.). Hence, with in mind the understanding of cell–polysaccharide interactions, the labelled polymers were studied by in vitro tests on a line of endothelial cells sensitive to the proliferative effect of these dextran polysaccharides. Using 3D fluorescence microscopy, the fixation and internalization of fluorescent functionalized dextrans were observed in endothelial cells.
The cooperative effect of L‐selectin clusters and velocity‐dependent bond formation that stabilizes leukocyte rolling
Authors: Riha P. , Dumas D. , Latger V. , Muller S. , Stoltz J.F.
Published: November 2024

The role of clustered of L‐selectin receptors on the leukocyte surface is discussed in connection with the postulated velocity‐dependent formation of selectin–ligand tether bonds to interpret the mechanism of leukocyte tethering to, and rolling along, the vascular endothelium. The distinct feature of this step‐wise process is a weak dependence of leukocyte rolling velocity on the hydrodynamic forces of ambient flow due to the increased number of selectin bonds with increasing flow shear rate and also their clustering. The contact zones on the leukocyte surface are separated by distances with distribution which corresponds to the distribution of distances of the observed L‐selectin clusters. It suggests that the localization of L‐selectin receptors to clusters and the way of their approach to the ligand molecules creates such conditions for binding of L‐selectin and ligand molecules that resulting number of bonds stabilizes rolling velocity.
Characterization of monoclonal antibodies against human red blood group cells antigens by laser backscattering
Authors: Rasia R.J. , de Isla N. , Altube L. , Muller S. , Valverde J. , Stoltz J.F.
Published: November 2024

A problem in immunohematology is to define the antibody quality which is related to its affinity expressed by the equilibrium constant. The activity of an antibody can be measured by the strength of its interaction, related to the adhesive energy exchanged during RBC agglutination which depends on the antigen–antibody liaison strength. To estimate this adhesive energy, two methods are used in this paper. Firstly, the dissociation behaviour of suspended RBC agglutinates was analysed by laser backscattering intensity (r) in a Couette flow. Backscattered intensity issued from shear‐induced mechanical dissociation is recorded and submitted to a numerical process to obtain the energy parameter (ED). Secondly, a modification of this technique is proposed for measuring specific binding energy. Samples were exposed to increasing shear stress, and backscattered intensity was recorded. A constant increase of this intensity with raising shear stress was observed, pointed to a progressive dissociation of RBC agglutinates into smaller ones. Considering that complete dissociation of agglutinates is only approached asymptotically it is assumed that the final break‐up of doublets (two‐cell agglutinates) is produced at a critical shear stress (τC) reflecting the work done to breaking‐up the molecular bridges between both adjacent cells. This shear stress is defined by the extrapolation of the linear part of the curves [r–log τ] to the backscattered signal (r0) corresponding to the complete dispersion of RBCs. These approaches permit to define the specific surface adhesive energy (Γ) by using the Derjaguin relation and to assess the functional characterization of specific immunoglobulins. In conclusion, two parameters characterizing monoclonal antibody agglutination properties, ED and Γ, were estimated by laser backscattering methods, which could be very useful for antibodies quality control.
A 3‐dimensional computer model to simulate trabecular bone metabolism
Authors: Ruimerman Ronald , van Rietbergen Bert , Hilbers Peter , Huiskes Rik
Published: November 2024

Mechanical loading of trabecular bone affects the bone architecture. Bone mass is correlated to the magnitude of the external load and trabeculae are aligned to the loading direction. Physical exercise increases bone mass while disuse or microgravity decreases it. In previous work we have presented a mathematical model of bone metabolism that could explain the emergence, maintenance and adaptation of trabecular bone under influence of the load imposed, using a 2‐dimensional computer model (Huiskes et al., Nature 404 (2000), 704–706). This model was based on hypothetical mathematical descriptions of bone formation by osteoblastic cells, and resorption by osteoclastic cells, both as governed by mechanical stimuli. In order to quantitatively compare the behavior of the proposed regulation mechanism to real trabecular bone metabolism we present a 3‐dimensional computer simulation model.

The first 3‐dimensional simulation results show that the regulatory rules proposed earlier mimic trabecular bone metabolism in a robust way.
Influence of Angelicae sinensis extract on lipid accumulation in rabbit aortic smooth muscle cells induced by oxidized LDL
Authors: Traoré Mariama , Jialing Hong , Chunling Xu
Published: November 2024

Objective: To further establish a definite basic of the application value of sodium ferulate (SF) for prevention and cure of acute coronary heart disease, we examined the effects of SF on LDL oxidation and lipid accumulation in rabbit aortic smooth muscle cells induced by modified‐LDL.

Methods: LDL oxidation was carried out in the presence and absence of SF. Cultured rabbit aortic smooth muscle cells were used as the model. To investigate the effects of SF on intracellular lipid accumulation, cells were incubated with Ox‐LDL and SF. The lipid content (cholesterol and triglycerides) of the cells were determined.

Results: Intracellular cholesterol and triglycerides were significantly increased in cell‐modified LDL group. The enhancements of above indexes were decreased after addition of SF (200 μg/ml). On the other hand, incubation of LDL with SF resulted in a significant decrease in TBARS activity and electrophoretic mobility.

Conclusion: The results indicated that SF assume significance both in the protection of LDL against oxidation and inhibition of cell‐modified LDL effects on intracellular lipid with the potential to prevent cell foamation.
Autologous cell transplantation and cardiac tissue engineering: Potential applications in heart failure
Authors: Tran Nguyen , Li Yan , Bertrand Sylvie , Bangratz Sébastien , Carteaux Jean‐Pierre , Stoltz Jean‐François , Villemot Jean‐Pierre
Published: November 2024

The promising concept of cell transplantation and cardiac tissue engineering has been developed in the last few years and focused on strategies attempting to replace dysfunctional, necrotic, and/or apoptotic cardiomyocytes with new cells of mesodermal origin. Transplantation of autologous cells minimizes the risk of neoplasia and avoids immune rejection associated with allogenic or xenogenic cells and recent data hold enormous hopes for short term clinical practices. Tissue engineering represents another promising approach that makes possible the creation of new functional tissues to replace the lost or failing one. Three‐dimensional polymeric scaffolds provide the mechanical support for the candidate cells until the formation of cardiac‐like tissue prior to surgical repair of the infarcted myocardium. For ultimate clinical applications, further investigations have to select the appropriate cell types, to determine the sufficient number of grafted cells and to provide the long term evaluation of these strategies in the global improvements of cardiac function (neoangiogenesis, synchronous contraction and extracellular matrix remodelling).
Physiological flow analysis in significant human coronary artery stenoses
Authors: Banerjee Rupak K. , Back Lloyd H. , Back Martin R. , Cho Young I.
Published: November 2024

To evaluate the local hemodynamics in flow limiting coronary lesions, computational hemodynamics was applied to a group of patients previously reported by Wilson et al. (1988) with representative pre‐angioplasty stenosis geometry (minimal lesion size dm=0.95 mm; 68% mean diameter stenosis) and with measured values of coronary flow reserve (CFR) in the abnormal range (2.3±0.1). The computations were at mean flow rates ( $\widetilde{Q}$ ) of 50, 75 and 100 ml/min (the limit of our converged calculations). Computed mean pressure drops Δ $\tilde{p}$ were ∼9 mmHg for basal flow (50 ml/min), ∼27 mmHg for elevated flow (100 ml/min) and increased to an extrapolated value of ∼34 mmHg for hyperemic flow (115 ml/min), which led to a distal mean coronary pressure $\tilde{p}$ rh of ∼55 mmHg, a level known to cause ischemia in the subendocardium (Brown et al., 1984), and consistent with the occurrence of angina in the patients. Relatively high levels of wall shear stress were computed in the narrow throat region and ranged from about 600 to 1500 dyn/cm2, with periodic (phase shifted) peak systolic values of about 3500 dyn/cm2. In the distal vessel, the interaction between the separated shear layer wave, convected downstream by the core flow, and the wall shear layer flow, led to the formation of vortical flow cells along the distal vessel wall during the systolic phase where Reynolds numbers Ree(t) were higher. During the phasic vortical mode observed at both basal and elevated mean flow rates, wide variations in distal wall shear stress occurred, distal transmural pressures were depressed below throat levels, and pressure recovery was larger farther along the distal vessel. Along the constriction (convergent) and throat segments of the lesion the pulsatile flow field was principally quasi‐steady before flow separation occurred. The flow regimes were complex in the narrow mean flow Reynolds number range $\widetilde{\mathrm{R}}$ ee=100–230 and a frequency parameter of αe=2.25. The shear layer flow disturbances diminished in strength due to viscous damping along the distal vessel at these relatively low values of $\widetilde{\mathrm{R}}$ ee, typical of flow through diseased epicardial coronary vessels. The distal hyperemic flow field was likely to be in an early stage of turbulent flow development during the peak systolic phase.
Noninvasive determination of perfused artery dimensions ex vivo using a pressure–diameter relationship
Authors: Lawrence A.R. , Gusic R.J. , Gooch K.J.
Published: November 2024

Based on the decisive effects of the hemodynamic and mechanical environments on the development and remodeling of arteries in vivo, several groups have cultured tissue‐engineered vessels and excised vessels in various mechanically active perfusion systems. To facilitate the interpretation and design of such studies, accurate estimates of the applied forces and resulting stresses are required, which in turn require an accurate estimate of vessel dimensions. The measured pressure drop along the length of the vessel could be used to calculate the average inner diameter, but practical considerations, including the modest accuracy of many pressure transducers, limit this approach. Using nine porcine arteries harvested from pigs weighing between 25 and 100 kg, we show that when real‐time measurements of the pressure drop and the outer diameter during a vasoactive event are fit to a theoretical model, offset errors in the pressure measurement can be compensated for and estimates of vessel wall transverse area with an average error of 4.1% (not exceeding 8.3%) are achieved.
Probing the tissue to subcellular level structure underlying bone's molecular sieving function
Authors: Tami A.E. , Schaffler M.B. , Knothe Tate M.L.
Published: November 2024

Transport of fluorescent probes between 300 and 2,000,000 Da was studied in mechanically loaded and unloaded ulnae of skeletally mature rats to characterize the permeability of the pericellular space of the lacunocanalicular system (LCS), and the microporosity of the bony matrix. The mineral matrix porosity allowed for penetration of the 300 Da probe but impeded transport of larger probes. The pericellular space of the LCS was permeable up to 10 kDa; above 10 kDa, diffusion was ineffective for transport through the pericellular space. Convective transport via load‐induced fluid flow increased penetration of all probes up to 70 kDa. Above this threshold, probes were excluded from bone, both with and without loading. This exploratory study suggests that bone acts as a molecular sieve and that mechanical loading modulates transport of solutes through the pericellular space that links osteocytes deep within the tissue to the blood supply and to osteoblasts and osteoclasts on bone forming and resorbing surfaces. This provides support for the postulate of transport modulated bone remodeling in which osteocytes are influenced by and modulate the local permeability of their surroundings as a means for survival (Knothe Tate et al. 1998, [28]) and has profound implications for osteocyte viability and intercellular communication in bone.
Fluid flow induced PGE2 release by bone cells is reduced by glycocalyx degradation whereas calcium signals are not
Authors: Reilly Gwendolen C. , Haut Traci R. , Yellowley Clare E. , J. Donahue Henry , Jacobs Christopher R.
Published: November 2024

It has been hypothesized that bone cells have a hyaluronic acid (HA) rich glycocalyx (cell coat or pericellular matrix) and that this contributes to bone cell mechanotransduction via fluid flow. The glycocalyx of bone cells of the MC3T3‐E1 osteoblastic cell line and the MLO‐Y4 osteocytic cell line were characterized. Alcian blue staining and lectin binding experiments suggested that these cells have a glycocalyx rich in HA. Sulphated proteoglycans were not detected. Staining with hyaluronic acid binding protein and degradation by hyaluronidase confirmed that HA was a major component of the glycocalyx. We subjected cells, with and without hyaluronidase treatment, to oscillating fluid flow under standardized in vitro conditions. There was no effect of glycocalyx degradation on the intracellular calcium signal, in either cell type, in terms of the percentage of cells responding (40–80%) or the magnitude of the response (2–5 times baseline). However, a 4‐fold fluid flow induced increase in PGE2 was eliminated by hyaluronidase pre‐treatment in MLO‐Y4 cells. We conclude that under these conditions the calcium and PGE2 responses occur via different pathways. An intact glycocalyx is not necessary in order to initiate a calcium signal in response to oscillating fluid flow. However, in osteocyte‐like cells the PGE2 pathway is more dependent on mechanical signals transmitted through the glycocalyx.
Protection of erythrocytes from sub‐hemolytic mechanical damage by nitric oxide mediated inhibition of potassium leakage
Authors: Baskurt Oguz K. , Uyuklu Murat , Meiselman Herbert J.
Published: November 2024

The effects of mechanical stress on red blood cell (RBC) deformability were evaluated by subjecting cells to a uniform fluid shear stress of 120 Pa for 15–120 seconds at 37°C. This level of stress induced significant impairment of RBC deformability as assessed by ektacytometry, with the degree of impairment independent of extracellular calcium concentration. Inhibition of RBC nitric oxide (NO) synthesis by a competitive inhibitor of NO synthases (N‐omega‐nitro‐L‐arginine methyl ester, L‐NAME) had no effect on deformability after exposure to mechanical stress. The NO donor sodium nitroprusside (SNP) prevented the deterioration of RBC deformability in a dose‐dependent manner with 10−4 M being the most effective concentration. A similar protective effect by the non‐selective potassium channel blocker, tetraethylammonium chloride (TEA) suggests that the effect of NO might be mediated by the inhibition of potassium leakage from RBC. These results suggest that NO may prevent mechanical deterioration of RBC exposed to high shear stresses. While RBC are not exposed to such high levels of shear stresses for prolonged periods under normal circulatory conditions, comparable levels of mechanical stress can be encountered under certain situations (i.e., artificial organs, extracorporeal circulation) and may result in subhemolytic damage and hemorheological alterations.
Passive transverse mechanical properties as a function of temperature of rat skeletal muscle in vitro
Authors: van Turnhout Mark , Peters Gerrit , Stekelenburg Anke , Oomens Cees
Published: November 2024

The objective of the current study was to determine the in vitro passive transverse mechanical properties of skeletal muscle with Dynamic Mechanical Thermal Analysis (DMTA) tests. The starting hypotheses was that the time–temperature‐superposition principle could be used to expand the DMTA results to a 1 kHz frequency range. Experiments were performed with rat hind leg skeletal muscle tissue samples on a rotational rheometer using a parallel plate geometry. Because of the small size and low modulus of the samples, the standard test geometry was altered and the samples were shifted from the center to the edge of the plates. From strain sweep tests it became clear that for strains smaller than 0.003 the muscle tissue behaves linearly. In the linear region storage moduli ranged between 24 kPa (ω=1 rad/s) and 42 kPa (ω=100 rad/s) at T=4°C and 22 kPa and 33 kPa at 29°C within the experimental frequency range. The loss modulus decreased with increasing frequency and ranged between 7 and 4 kPa at 4°C and 4.5 and 3.5 kPa at 29°C. Although the properties are clearly temperature dependent, a temperature shift in phase angle δ could not be detected, thus Time Temperature Superposition is not allowed for skeletal muscle in vitro.
Deformability, dynamics, and remodeling of cytoskeleton of the adherent living cell
Authors: Lenormand Guillaume , Fredberg Jeffrey J.
Published: November 2024

A trail of evidence has led to an unexpected intersection of topical issues in condensed matter physics and cytoskeletal biology. On the one hand, the glass transition and the jammed state are two outstanding unsolved problems; such systems are out-of-equilibrium, disordered, and their transitions between solid-like and liquid-like states are not understood. On the other hand, cellular systems are increasingly being considered as interconnected maps of protein interactions that are highly specific and tightly regulated but, even when such comprehensive maps become available, they may be insufficient to define biological function at the integrative level because they do not encompass principles that govern dynamics at intermediate (meso) scales of organization. It is interesting, therefore, that the cytoskeleton of the living cell shows physical properties and remodeling dynamics with all the same signatures as soft inert condensed systems, although with important differences as well. Data reviewed here suggest that trapping, intermittency, and approach to kinetic arrest represent mesoscale features of collective protein–protein interactions linking underlying molecular events to integrative cellular functions such as crawling, contraction and remodeling. Because these are crucial cell functions, this synthesis may offer new perspectives on a variety of disorders including infectious disease, cardiovascular disease, asthma and cancer.
Electrophysiological demonstration of Na+/Ca2+ exchange in bovine articular chondrocytes
Authors: Sánchez Julio C. , Powell Trevor , Staines Henry M. , Wilkins Robert J.
Published: November 2024

Altered fluxes of Ca2+ across the chondrocyte membrane have been proposed as one pathway by which mechanical load can modulate cartilage turnover. In many cells, Na+/Ca2+ exchange (NCX) plays a key role in Ca2+ homeostasis, and recent studies have suggested it is operative in articular chondrocytes. In this study, an electrophysiological characterisation of NCX in articular bovine chondrocytes has been performed, using the whole-cell patch clamp technique, and the effects of inhibitors and the transmembrane electrochemical gradients of Na+ and Ca2+ on NCX function have been assessed. A Ni2+-sensitive current (INCX) which exhibited outward rectification, was elicited by a voltage ramp protocol. The current was also attenuated by the NCX inhibitors benzamil and KBR7943, without significant differences between the effect of these two compounds upon outward and inward currents. The Ni2+-sensitive current was modulated by changes in extracellular and pipette Na+ and Ca2+ in a manner characteristic of $\[$I\tsub{NCX}$$ . Measured values for the reversal potential differed significantly from those predicted for an exchanger stoichiometry of 3Na+ : 1Ca2+, implying that accumulation of intracellular Ca2+ (from influx or release from stores) or more than one transport mode is occurring. These results demonstrate the operation of NCX in articular chondrocytes and suggest that changes in its turnover rate, as might occur in response to mechanical load, may modify cell composition and thereby dictate cartilage turnover.
Poroelastic numerical modelling of natural and engineered cartilage based on in vitro tests
Authors: Boschetti Federica , Gervaso Francesca , Pennati Giancarlo , Peretti Giuseppe M. , Vena Pasquale , Dubini Gabriele
Published: November 2024

The mechanisms underlying the ability of articular cartilage to withstand and distribute the loads applied across diarthrodial joints have been widely studied. Experimental tests have been done under several configurations to reveal the tissue response to mechanical stimuli, and theoretical models have been developed for the interpretation of the experimental results. The experiments demonstrated that the tissue is non-linear with strain, both in tension and in compression, non-linear with direction of stimulus, anisotropic in tension and compression, non-homogeneous with depth, resulting in depth dependent mechanical properties, and presents fluid dependent and fluid independent viscoelasticity. None of the models up to now developed is able to describe the whole set of responses of such a complex tissue. The purpose of this study was to develop a combined experimental-numerical approach for the proper description of the cartilage response under confined and unconfined compression. We defined a series of experimental tests to be performed on disks of natural and engineered cartilage and we developed a numerical model for cartilage, based on the biphasic theory, which potentially includes the tension–compression non-linearity, the strain non-linearity and the fluid independent viscoelasticity. The model successfully simulated the confined and unconfined compression experiments performed on disks of natural and engineered cartilage, and was also used to identify parameters of difficult experimental evaluation, such as the collagen stiffness and the permeability. In conclusion, the use of our model in combination with biomechanical experimental testing seems a valuable tool to analyze the mechanical properties of natural cartilage and the biofunctionality of tissue engineered cartilage.
Diurnal fluid expression and activity of intervertebral disc cells
Authors: Sivan S. , Neidlinger-Wilke C. , Würtz K. , Maroudas A. , Urban J.P.G.
Published: November 2024

The intervertebral discs are large cartilaginous structures situated between the vertebral bodies, occupying around one third of the length of the spinal column. They act as the joints of the spine and carry mechanical load arising from body weight and muscle activity. Loads change with every alteration of posture and activity and the discs thus undergo a diurnal loading pattern with high loads on the discs during the day's activity and low loads on it at night during rest. As the disc is an osmotic system, around 25% of the disc's fluid is expressed and re-imbibed during each diurnal cycle with consequent changes in the osmotic environment of the disc cells. Here, present information on the effect of osmotic changes in disc cell metabolism is reviewed; results indicate that prevailing osmolarity is a powerful regulator of disc cell activity.
A mandibular propulsive appliance modulates collagen-binding integrins distribution in the young rat condylar cartilage
Authors: Marques Mara Rúbia , Hajjar Denise , Oliveira Crema Virgínia , Kimura Edna Teruko , Santos Marinilce Fagundes
Published: November 2024

We have previously shown that a mandibular propulsive appliance (MPA) stimulates cell proliferation and the synthesis of growth factors in the rat condylar cartilage. The aim of this study was to evaluate the effects of a MPA in the distribution of the integrin subunits α1 and α2 in this cartilage. Twenty eight days-old male Wistar rats were divided into treated (T) and age-matched control groups (C). Treated rats wore the appliance during 3, 5, 7, 9, 11, 15, 20, 30 and 35 days. The condyles were fixed, decalcified and paraffin-embedded. The distribution of α1 and α2 was studied by immunohistochemistry. Alpha1 distribution was uniform along the cartilage, increasing in 48 days-old rats (C20). Treated animals anticipated this increase to the age of 36 days (T9). The number of α2-positive cells was increased in C9 in the anterior condylar region, in C9 and C20 in the middle region and showed no differences in the posterior region. The MPA apparently abolished all variations, leading to a single increase at T30 in all regions. These results suggest that integrins containing the α1 and α2 subunits are modulated by forces promoted by the MPA, participating of the biological response to this therapy.