bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of disturbed flow on endothelial cell function: Pathogenic implications of modified leukocyte recruitment
Authors: Matharu Nick M. , Rainger G. Ed , Vohra Rajiv , Nash Gerard B.
Published: November 2024

Numerous studies have shown that intracellular signalling, transcription factor activation and gene expression in endothelial cells are modulated by the magnitude and patterns of shear stress to which they are exposed. Although these responses suggest that the haemodynamic environment will consequently modulate the ability of the endothelial cells to support leukocyte recruitment as part of an inflammatory response, direct evidence is quite sparse. It seems that disturbances of flow (such as local spatial or temporal variation or sudden cessation) are likely to be pathogenic co-factors, combined with mediators such as cytokines, oxidised lipids or hypoxia, in conditions such as atherosclerosis, post-surgical intimal hyperplasia and ischaemia/reperfusion injury. In fact there have been few experimental investigations of these scenarios that include measurement of leukocyte adhesion and migration. We recently demonstrated that the level of steady shear to which EC are exposed has a powerful effect on their ability to support cytokine-induced leukocyte adhesion and migration. However, more combined studies of flow and agonist-mediated responses, with functional readouts, appear necessary if we are to develop a better understanding of the mechanisms pre-disposing to vascular inflammatory responses and pathology.
Micropatterned polymer surfaces improve retention of endothelial cells exposed to flow-induced shear stress
Authors: Daxini Sachin C. , Nichol Jason W. , Sieminski Alisha L. , Smith Geoffrey , Gooch Keith J. , Shastri V. Prasad
Published: November 2024

The use of synthetic polymeric vascular grafts is limited by the thrombogenecity of most biomaterials. Efforts to reduce thrombogenicity by seeding grafts with endothelial cells, the natural non-thrombogenic lining of blood vessels, have been thwarted by flow-induced cell detachment. We hypothesized that by creating well-defined micro-textured patterns on a surface, fluid flow at the surface can be altered to create discrete regions of low shear stress. We further hypothesized that, due to reduced shear stress, these regions will serve as sanctuaries for endothelial cells and promote their retention. To test these hypotheses, well-defined micro-textured polyurethane (PU) surfaces consisting of arrays of parallel 95-micron wide and 32-micron deep channels were created using an etched silicon template and solvent casting techniques. Based on computational fluid dynamics, under identical bulk flow conditions, the average local shear stress in the channels (46 dyn/cm2) was 28% lower than unpatterned surfaces (60 dyn/cm2). When PU surfaces pre-seeded with endothelial cells (EC) were exposed to the same bulk flow rate, EC retention was significantly improved on the micropatterned surfaces relative to un-patterned surfaces (92% vs. 58% retention).
An in vitro model for analysing neutrophil migration into and away from the sub-endothelial space: Roles of flow and CD31
Authors: Chakravorty Srabasti J. , McGettrick Helen M. , Butler Lynn M. , Buckley Christopher D. , Rainger G. Ed , Nash Gerard B.
Published: November 2024

To model the later stages of neutrophil migration into tissue, we developed an assay in which human umbilical vein endothelial cells (HUVEC) were cultured on porous filters, treated with the inflammatory cytokine tumour necrosis factor-α (TNF), and then incorporated in a flow chamber. Video-microscopic observations were made of neutrophils as they were perfused over the HUVEC. When 3 μm pore filters were used (as opposed to 0.4 μm pore filters), neutrophils could be observed to migrate not only through the endothelial monolayer but also through the filter within minutes. The proportion of adherent neutrophils migrating through the endothelial monolayer and velocity of migration underneath it, were similar on the different filters, and also when neutrophils were perfused over cultures in glass capillaries, or settled on HUVEC cultured in standard plastic dishes. However, neutrophils migrated through HUVEC/filter constructs more rapidly in the flow chamber than in a standard, static, Transwell system, even though the velocities of migration under HUVEC were similar when directly observed under flow or static conditions. A function-blocking antibody against CD31 did not alter movement through the endothelial monolayer or the filter in the new flow system, but did reduce the migration velocity of neutrophils underneath the HUVEC (by 24%). Thus, we have developed a method for following each stage of neutrophil migration, including exit from the sub-endothelial space, and shown how they may be modified by applied fluid shear stress and blockade of a regulatory adhesion molecule.
Static and dynamic compression regulate cartilage metabolism of PRoteoGlycan 4 (PRG4)
Authors: Nugent G.E. , Schmidt T.A. , Schumacher B.L. , Voegtline M.S. , Bae W.C. , Jadin K.D. , Sah R.L.
Published: November 2024

The boundary lubrication function of articular cartilage is mediated in part by molecules at the articular surface and in synovial fluid, encoded by Prg4. The objective of this study was to determine whether static and dynamic compression regulate PRG4 biosynthesis by cartilage explants. Articular cartilage disks were harvested to include the articular surface from immature bovines. Some disks were subjected to 24 h (day 1) of loading, followed by 72 h (days 2–4) of free-swelling culture to assess chondrocyte responses following unloading. Loading consisted of 6 or 100 kPa of static compression, with or without superimposed dynamic compression (10 or 300 kPa peak amplitude, 0.01 Hz). Other disks were cultured free-swelling as controls. PRG4 secretion into culture medium was inhibited by all compression protocols during day 1. Following unloading, cartilage previously subjected to dynamic compression to 300 kPa exhibited a rebound effect, secreting more PRG4 than did controls, while cartilage previously subjected to 100 kPa static loading secreted less PRG4. Immunohistochemistry revealed that all compression protocols also affected the number of cells expressing PRG4. The paradigm that mechanical stimuli regulate biosynthesis in cartilage appears operative not only for load bearing matrix constituents, but also for PRG4 molecules mediating lubrication.
Mechanical responses and integrin associated protein expression by human ankle chondrocytes
Authors: Orazizadeh M. , Cartlidge C. , Wright M.O. , Millward-Sadler S.J. , Nieman J. , Halliday B.P. , Lee H.-S. , Salter D.M.
Published: November 2024

Metabolic, biochemical and biomechanical differences between ankle and knee joint cartilage and chondrocytes including resistance to the effects of catabolic cytokines and fibronectin fragments may be relevant to differences in prevalence of OA in these joints. Although there is increasing information available on how chondrocytes from knee and hip joint cartilage recognise and respond to mechanical stimuli, knowledge of mechanotransduction in ankle joint chondrocytes is limited. This study was undertaken to (i) establish whether the response of normal ankle joint derived chondrocytes to mechanical stimulation in vitro was similar to that of normal and osteoarthritic knee joint derived chondrocytes and (ii) to investigate whether these chondrocytes showed differences in expression of integrin associated regulatory and signalling molecules. Unlike normal knee joint chondrocytes, ankle joint chondrocytes did not show an increase in relative levels of aggrecan mRNA when mechanically stimulated. No obvious change in protein tyrosine phosphorylation was seen in ankle chondrocytes subsequent to mechanical stimulation but these cells expressed elevated levels of tyrosine phosphorylated proteins at rest when compared to normal knee joint chondrocytes. Ankle joint chondrocytes showed an increase in protein kinase B phosphorylation following 1 min 0.33 Hz stimulation which was inhibited by the presence of antibodies to α5β1 integrin. Ankle joint chondrocytes appeared to show significant differences in levels of the integrin-associated proteins CD98, CD147 and galectin 3, PKCγ and differences in responses to glutamate were seen. Chondrocytes from ankle and knee joint cartilage respond differently to 0.33 Hz mechanical stimulation. This may be related to modified integrin-dependent mechanotransduction as a result of changes in expression of integrin regulatory molecules such as CD98 or differential expression and function of downstream components of the mechanotransduction pathway such as PKC or NMDA receptors.
Chondrocyte gene expression under applied surface motion
Authors: Grad Sibylle , Lee Cynthia R. , Wimmer Markus A. , Alini Mauro
Published: November 2024

A cartilage bioreactor has been designed that is intended to approximate the kinematics of natural joints and allows for functional cartilage tissue engineering studies. In particular, interface motion can be generated by oscillation of a ball over the surface of a construct. The present study investigated the specific effect of applied articular motion on the gene expression of chondrocytes cultured in 3D scaffolds, with a particular emphasis on different superficial zone protein (SZP)/lubricin transcripts. Cylindrical porous polyurethane scaffolds were seeded with bovine articular chondrocytes and subjected to dynamic compression, with or without articulation against a ceramic hip ball. Articular motion markedly up-regulated the mRNA expression of the four previously described and two newly identified SZP/lubricin isoforms and of cartilage oligomeric matrix protein (COMP), and, to a lesser extent, aggrecan, type II collagen and TIMPs, while axial compression alone had no effect on the chondrocytes' gene expression levels. These results demonstrate the beneficial effect of articular motion not only for stimulation of important lubricating molecules, but also for the preservation of the chondrocytic phenotype.
Ultrasound stimulates proteoglycan synthesis in bovine primary chondrocytes
Authors: Kopakkala-Tani Milla , Leskinen Jarkko J. , Karjalainen Hannu M. , Karjalainen Tero , Hynynen Kullervo , Töyräs Juha , Jurvelin Jukka S. , Lammi Mikko J.
Published: November 2024

Mechanical forces can stimulate the production of extracellular matrix molecules. We tested the efficacy of ultrasound to increase proteoglycan synthesis in bovine primary chondrocytes. The ultrasound-induced temperature rise was measured and its contribution to the synthesis was investigated using bare heat stimulus. Chondrocytes from five cellular isolations were exposed in triplicate to ultrasound (1 MHz, duty cycle 20%, pulse repetition frequency 1 kHz) at average intensity of 580 mW/cm2 for 10 minutes daily for 1–5 days. Temperature evolution was recorded during the sonication and corresponding temperature history was created using a controllable water bath. This exposure profile was used in 10-minute-long heat treatments of chondrocytes. Heat shock protein 70 (Hsp70) levels after one-time treatment to ultrasound and heat was analyzed by Western blotting, and proteoglycan synthesis was evaluated by 35S-sulfate incorporation. Ultrasound treatment did not induce Hsp70, while heat treatment caused a slight heat stress response. Proteoglycan synthesis was increased approximately 2-fold after 3–4 daily ultrasound stimulations, and remained at that level until day 5 in responsive cell isolates. However, chondrocytes from one donor cell isolation out of five remained non-responsive. Heat treatment alone did not increase proteoglycan synthesis. In conclusion, our study confirms that pulsed ultrasound stimulation can induce proteoglycan synthesis in chondrocytes.
Mandibular repositioning modulates IGFBP-3, -4, -5 and -6 expression in the mandibular condylar cartilage of young rats
Authors: Hajjar Denise , Santos Marinilce F. , Kimura Edna Teruko
Published: November 2024

Functional orthopedic appliances correct dental malocclusion partially by exerting indirect mechanical stimulus on the condylar cartilage, modulating growth and the adaptation of orofacial structures. However, the exact nature of the biological responses to this therapy is not well understood. Insulin-like growth factors I and II (IGF-I and II) are important local factors during growth and differentiation in the condylar cartilage [D. Hajjar, M.F. Santos and E.T. Kimura, Propulsive appliance stimulates the synthesis of insulin-like growth factors I and II in the mandibular condylar cartilage of young rats, Arch. Oral Biol. 48 (2003), 635–642]. The bioefficacy of IGFs at the cellular level is modulated by IGF binding proteins (IGFBP). The aim of this study was to verify the mRNA and protein expression of IGFBP-3, IGFBP-4, IGFBP-5 and IGFBP-6 in the condylar cartilage of young male Wistar rats that used a mandibular propulsive appliance for 3, 9, 15, 20, 30 or 35 days. For this purpose, sagittal sections of decalcified and paraffin-embedded condyles were submitted to immunohistochemistry and the condylar cartilage to RT–PCR. The control group showed a gradual increase in the protein expression of all IGFBPs, except IGFBP-4. Following use of the appliance, IGFBP-3 and IGFBP-6 expression decreased in the early stage of the treatment. At 20 days of treatment there was a decline in the IGFs and IGFBP-3, IGFBP-4 and IGFBP-5 expression and at 30 days there was a peak in the IGFs and all IGFBPs expression except for IGFBP-3 where the peak was observed in the control animals. The expression patterns of all IGFBPs in the condylar cartilage were similar. The modulation of IGFBP-3, -4, -5 and -6 expression in the condylar cartilage in response to the propulsive appliance suggests that those peptides are involved in the mandibular adaptation during this therapy.
Physical signals and solute transport in human intervertebral disc during compressive stress relaxation: 3D finite element analysis
Authors: Yao Hai , Gu Wei Yong
Published: November 2024

A 3D finite element model for charged hydrated soft tissues containing charged/uncharged solutes was developed based on the multi-phasic mechano-electrochemical mixture theory (Lai et al., J. Biomech. Eng. 113 (1991), 245–258; Gu et al., J. Biomech. Eng. 120 (1998), 169–180). This model was applied to analyze the mechanical, chemical and electrical signals within the human intervertebral disc during an unconfined compressive stress relaxation test. The effects of tissue composition [e.g., water content and fixed charge density (FCD)] on the physical signals and the transport rate of fluid, ions and nutrients were investigated. The numerical simulation showed that, during disc compression, the fluid pressurization was more pronounced at the center (nucleus) region of the disc while the effective (von Mises) stress was higher at the outer (annulus) region. Parametric analyses revealed that the decrease in initial tissue water content (0.7–0.8) increased the peak stress and relaxation time due to the reduction of permeability, causing greater fluid pressurization effect. The electrical signals within the disc were more sensitive to FCD than tissue porosity, and mechanical loading affected the large solute (e.g., growth factor) transport significantly, but not for small solute (e.g., glucose). Moreover, this study confirmed that the interstitial fluid pressurization plays an important role in the load support mechanism of IVD by sharing more than 40% of the total load during disc compression. This study is important for understanding disc biomechanics, disc nutrition and disc mechanobiology.
Mechanical regulation of secondary chondrogenesis
Authors: Archer Charles W. , Buxton Paul , Hall Brian K. , Francis-West Philippa
Published: November 2024

This article has been retracted. The original article can be found on: http://dev.biologists.org/cgi/reprint/130/19/4729.
Influence of mechanical stress on cell viability
Authors: Huselstein C. , de Isla N. , Kolopp-Sarda M.N. , Kerdjoudj H. , Muller S. , Stoltz J.F.
Published: November 2024

The cartilage is a hydrated connective tissue in joints that withstands and distributes mechanical forces. The chondrocytes utilize mechanical signals to regulate their metabolic activity through complex biological and biophysical interactions with the extracellular matrix (ECM). The aim of this work was to study the influence of mechanical stress on cells behavior cultured in 3D biosystems (alginate and alginate supplemented with hyaluronate). After mechanical stimulation, cell viability and cell death process were the main studied parameters. Our results indicated that viability and cell cycle progression were inhibited under mechanical stimulation, as far as the extracellular matrix was not yet synthesized. In contrast, on day 21, the mechanical stimulation had positive effect on these parameters.
Dynamic compression counteracts IL-1β induced iNOS and COX-2 activity by human chondrocytes cultured in agarose constructs
Authors: Chowdhury Tina T. , Bader Dan L. , Lee David A.
Published: November 2024

.NO and PGE2 are inflammatory mediators derived from the inducible iNOS and COX enzymes and are potentially important pharmacological targets in OA. Both mechanical loading and IL-1β will influence the release of .NO and PGE2. Accordingly, the current study examines the effect of dynamic compression on .NO and PGE2 release by human chondrocytes cultured in agarose constructs in the presence and absence of selective iNOS and COX-2 inhibitors. The current data demonstrate that IL-1β induced nitrite and PGE2 release and inhibited [3H]-thymidine and 35SO4 incorporation. Inhibitor experiments indicate that 1400W and NS-398 either partially reversed or abolished IL-1β induced nitrite and PGE2 release. IL-1β induced inhibition of cell proliferation and proteoglycan synthesis was partially reversed with 1400W but was not influenced by NS-398. For the dynamic loading experiments, 1400W and NS-398 either reduced or abolished the compression-induced inhibition of .NO and PGE2 release in the presence of IL-1β. The IL-1β induced inhibition of cell proliferation was not influenced by 1400W or NS-398 whereas strain-induced stimulation of proteoglycan synthesis in the presence of IL-1β was enhanced by 1400W. The data obtained using human chondrocytes demonstrate that IL-1β induced .NO and PGE2 release via an iNOS-driven-COX-2 inter-dependent pathway. This response could be reversed by dynamic compression. These data indicate interactions exist between the NOS and COX pathways, a finding which will provide new insights in the development of pharmacological or biophysical treatments for cartilage disorders such as OA.
Uniform tissues engineered by seeding and culturing cells in 3D scaffolds under perfusion at defined oxygen tensions
Authors: Wendt D. , Stroebel S. , Jakob M. , John G.T. , Martin I.
Published: November 2024

In this work, we assessed whether culture of uniformly seeded chondrocytes under direct perfusion, which supplies the cells with normoxic oxygen levels, can maintain a uniform distribution of viable cells throughout porous scaffolds several milimeters in thickness, and support the development of uniform tissue grafts. An integrated bioreactor system was first developed to streamline the steps of perfusion cell seeding of porous scaffolds and perfusion culture of the cell-seeded scaffolds. Oxygen tensions in perfused constructs were monitored by in-line oxygen sensors incorporated at the construct inlet and outlet. Adult human articular chondrocytes were perfusion-seeded into 4.5 mm thick foam scaffolds at a rate of 1 mm/s. Cell-seeded foams were then either cultured statically in dishes or further cultured under perfusion at a rate of 100 μm/s for 2 weeks. Following perfusion seeding, viable cells were uniformly distributed throughout the foams. Constructs subsequently cultured statically were highly heterogeneous, with cells and matrix concentrated at the construct periphery. In contrast, constructs cultured under perfusion were highly homogeneous, with uniform distributions of cells and matrix. Oxygen tensions of the perfused medium were maintained near normoxic levels (inlet ≅ 20%, outlet > 15%) at all times of culture. We have demonstrated that perfusion culture of cells seeded uniformly within porous scaffolds, at a flow rate maintaining a homogeneous oxygen supply, supports the development of uniform engineering tissue grafts of clinically relevant thicknesses.
Evaluation of human MSCs cell cycle, viability and differentiation in micromass culture
Authors: Yang Jing-Wei , Isla Natalia de , Huselstein Céline , Sarda-Kolopp Marie-Nathalie , Li Na , Li Yin-Ping , Jing-Ping Ou-Yang , Stoltz Jean-François , Eljaafari Assia
Published: November 2024

Mesenchymal stem cells (MSCs) have the potential to differentiate into distinct mesenchymal tissue cells. They are easy to expand while maintaining their undifferentiated state, which suggests that these cells could be an attractive cell source for tissue engineering of cartilage. In vitro high density micromass culture has been widely used for chondrogenesis induction. Our objective was to investigate human MSCs cell cycle, viability and differentiation in these conditions. Therefore, to induce human MSCs chondrogenesis, micromasses were cultured in the presence of transforming growth factor-β1 in serum free medium for 21 days. Cell cycle, cell viability and cell phenotype were analyzed by flow cytometry. From day 0 to 7, the G0/G1 phase increased, whereas the S phase decreased gradually, but cell cycle phases (S, G0/G1 and G2/M) did not significantly change after day 7. Less than 10% of cells were apoptotic, but no necrosis was observed, even at day 21. We observed a decrease in CD90 and CD105 expression, from day 0 to 21. In conclusion, our results demonstrate a good viability of human MSCs in micromass culture during the whole period of culture. Moreover, micromass culture allowed human MSCs to be synchronized at the G0/G1 phase, while their phenotype suggested some degree of differentiation.
Dynamic deformational loading results in selective application of mechanical stimulation in a layered, tissue-engineered cartilage construct
Authors: Ng Kenneth W. , Mauck Robert L. , Statman Lauren Y. , Lin Evan Y. , Ateshian Gerard A. , Hung Clark T.
Published: November 2024

The application of dynamic physiologic loading to a bilayered chondrocyte-seeded agarose construct with a 2% (wt/vol) top layer and 3% (wt/vol) bottom layer was hypothesized to (1) improve overall construct properties and (2) result in a tissue that mimics the mechanical inhomogeneity of native cartilage. Dynamic loading over the 28 day culture period was found to significantly increase bulk mechanical and biochemical properties versus free-swelling culture. The initial depth-distribution of the compressive Young's modulus (EY) reflected the intrinsic properties of the gel in each layer and a similar trend to the native tissue, with a softer 2% gel layer and a much stiffer 3% gel layer. After 28 days in culture, free-swelling conditions maintained this general trend while loaded constructs possessed a reverse profile, with significant increases in EY observed only in the 2% gel. Histological analysis revealed preferential matrix formation in the 2% agarose layer, with matrix localized more pericellularly in the 3% agarose layer. Finite element modeling revealed that, prior to significant matrix elaboration, the 2% layer experiences increased mechanical stimuli (fluid flow and compressive strain) during loading that may enhance chondrocyte stimulation and nutrient transport in that layer, consistent with experimental observations. From these results, we conclude that due to the limitations in 3% agarose, the use of this type of bilayered construct to construct depth-dependent inhomogeneity similar to the native tissue is not likely to be successful under long-term culture conditions. Our study underscores the importance of other physical properties of the scaffold that may have a greater influence on interconnected tissue formation than intrinsic scaffold stiffness.
Three-dimensional tissue constructs built by bioprinting
Authors: Jakab Karoly , Damon Brook , Neagu Adrian , Kachurin Anatolij , Forgacs Gabor
Published: November 2024

Bioprinting is an evolving tissue engineering technology. It utilizes computer controlled three-dimensional printers for rapid and high-precision construction of three-dimensional biological structures. We employed discrete and continuous bioprinting to build three-dimensional tissue constructs. In the former case bioink particles – spherical cell aggregates composed of many thousands of cells – are delivered one by one into biocompatible scaffolds, the biopaper. Structure formation takes place by the subsequent fusion of the bioink particles due to their liquid-like and self-assembly properties. In the latter case a mixture of cells and scaffold material is extruded from the biocartridge akin to toothpaste to arrive at the desired construct. Specifically, we built rectangular tissue blocks of several hundred microns in thickness as well as tubular structures of several millimeters in height. The physical basis of structure formation was studied by computer simulations.
Acoustic properties of articular cartilage under mechanical stress
Authors: Nieminen Heikki J. , Töyräs Juha , Laasanen Mikko S. , Jurvelin Jukka S.
Published: November 2024

Mechano-acoustic and elastographic techniques may provide quantitative means for the in vivo diagnostics of articular cartilage. These techniques assume that sound speed does not change during tissue loading. As articular cartilage shows volumetric changes during compression, acoustic properties of cartilage may change affecting the validity of mechano-acoustic measurements. In this study, we examined the ultrasound propagation through human, bovine and porcine articular cartilage during stress-relaxation in unconfined compression. The time of flight (TOF) technique with known cartilage thickness (true sound speed) as well as in situ calibration method [Suh, Youn, Fu, J. Biomech. 34 (2001), 1347–1353] were used for the determination of sound speed. Ultrasound speed and attenuation decreased in articular cartilage during ramp compression, but returned towards the level of original values during relaxation. Variations in ultrasound speed induced an error in strain and compressive moduli provided that constant ultrasound speed and time-of-flight data was used to determine the tissue thickness. Highest errors in strain (−11.8±12.0%) and dynamic modulus (15.4±17.9%) were recorded in bovine cartilage. TOF and in situ calibration methods yielded different results for changes in sound speed during compression. We speculate that the variations in acoustic properties in loaded cartilage are related to rearrangement of the interstitial matrix, especially to that of collagen fibers. In human cartilage the changes, are, however relatively small and, according to the numerical simulations, mechano-acoustic techniques that assume constant acoustic properties for the cartilage will not be significantly impaired by this phenomenon.
The mechanical environment of chondrocytes in articular cartilage
Authors: Adams Michael A.
Published: November 2024

There is a growing literature concerning chondrocyte responses to mechanical loading, but relatively little is known about the mechanical environment these cells experience in a living joint. Calculations indicate that high forces are applied to limb joints whenever the joints are flexed, because flexion can cause body weight to act on long lever arms compared to the joint centre, whereas the muscles which extend the joint act on much shorter lever arms. As a result, joint reaction forces (which compress the cartilage) can rise to 3–6 times body weight during activities such as stair climbing. Articular cartilage tends to spread this load evenly over the joint surface, but is too thin to do this well, and compressive stresses can rise to 10–20 MPa. Within cartilage, matrix stresses vary locally, possibly as a result of variation in composition or undulations in the subchondral bone, and further modifications of stress occur within each chondron. Articular cartilage is a fibrous solid and cells within it are deformed by mechanical loading rather than subjected to a hydrostatic pressure. The mechanical environment of chondrocytes can best be reproduced in vitro by direct compression of the articular surface of cartilage which is supported naturally by adjacent cartilage and subchondral bone.
Numerical simulations of pulsatile blood flow using a new constitutive model
Authors: Fang Jiannong , Owens Robert G.
Published: November 2024

In the present paper we use a new constitutive equation for whole human blood [R.G. Owens, A new microstructure-based constitutive model for human blood, J. Non-Newtonian Fluid Mech. (2006), to appear] to investigate the steady, oscillatory and pulsatile flow of blood in a straight, rigid walled tube at modest Womersley numbers. Comparisons are made with the experimental results of Thurston [Elastic effects in pulsatile blood flow, Microvasc. Res. 9 (1975), 145–157] for the pressure drop per unit length against volume flow rate and oscillatory flow rate amplitude. Agreement in all cases is very good. In the presentation of the numerical and experimental results we discuss the microstructural changes in the blood that account for its rheological behaviour in this simple class of flows. In this context, the concept of an apparent complex viscosity proves to be useful.
An extended relationship for the characterization of Young's modulus and Poisson's ratio of tunable polyacrylamide gels
Authors: Boudou Thomas , Ohayon Jacques , Picart Catherine , Tracqui Philippe
Published: November 2024

Substrates with tunable mechanical properties are crucial for the study of cellular processes, and polyacrylamide gels (PAGs) are frequently used in this context. Several experimental techniques have been proposed to obtain the mechanical properties of PAGs. However, the range of the considered Poisson's ratio values remains quite large and no attempt has been made to propose an analytical relationship allowing the estimation of PAG Young's modulus when both bis-acrylamide and acrylamide concentrations are known. In order to complete the actual knowledge on the mechanical properties of PAGs, we took benefit of our original method based on the micropipette aspiration technique (Boudou et al., J. Biomech. 2006) for characterizing gels made with concentrations in the range 0.02% ≤[Bis]≤0.20% and 3% ≤[Acry]≤10%. We found that the PAGs Young's modulus varies nonlinearly with the acrylamide amount. Moreover, our study validates the quasi-incompressibility hypothesis usually made in studies using PAGs (mean Poisson's ratio of 0.480±0.012). More generally, and in agreement with data published by other groups, we propose an original nonlinear mathematical relationship allowing the computation of Young's modulus of PAG for any given acrylamide and bis-acrylamide amounts taken in the range of values we considered.
Red blood cell aggregation quantitated via Myrenne aggregometer and yield shear stress
Authors: Lee Byoung Kwon , Alexy Tamas , Wenby Rosalinda B. , Meiselman Herbert J.
Published: November 2024

Although the study of red blood cell (RBC) aggregation continues to be of basic science and clinical interest, aggregation standards for calibration do not exist, and most aggregation studies report data in terms of arbitrary units: quantitative comparisons between studies are thus essentially precluded. However, use of low shear viscometry plus the Casson equation provides a yield shear stress that has defined units and is known to reflect RBC aggregation. Employing human RBC–plasma suspensions exhibiting a wide range of aggregation, the present study examined relations between yield shear stress values and aggregation indices obtained using the Myrenne aggregometer: the latter approach uses a light-transmission technique and provides an “M” index at stasis and an “M1” at very low shear. Our results for normal controls and for angina patients without coronary artery disease indicate highly significant correlations (p<0.001) between the yield stress and both M and M1. Thus, within the range of aggregation studied, these findings lend support to the rheological validity of the Myrenne approach; extension of our findings to intensely aggregating RBC suspensions may require additional validation studies.
A mathematical model for the dissolution of non-occlusive blood clots in fast tangential blood flow
Authors: Serša I. , Tratar G. , Mikac U. , Blinc A.
Published: November 2024

Our aim was to study the effect of an axially directed blood plasma flow on the dissolution rate of cylindrical non-occlusive blood clots in an in vitro flow system and to derive a mathematical model for the process. The model was based on the hypothesis that clot dissolution dynamics is proportional not only to the biochemical proteolysis of fibrin but also to the power of the flowing blood plasma dissipated along the clot. The predicted rate of thrombolysis is then proportional to the square of the average blood plasma velocity for laminar flow and to the third power of the average velocity for turbulent flow. To verify the model, the time dependence of the clot cross-sectional area was measured by dynamic magnetic resonance microscopy during fast (turbulent) and slow (laminar) flow of plasma through an axially directed channel along the clot. The flowing plasma contained a magnetic resonance imaging contrast agent (Gd-DTPA) and a thrombolytic agent (recombinant tissue-type plasminogen activator). The experimental data fitted well to the model, and confirmed the predicted increase in the dissolution rate when blood flow changed from a laminar to a turbulent flow regime.
Changes in the integrin-mediated adhesion of human neutrophils in the cold and after rewarming
Authors: Jetha Karim A. , Egginton Stuart , Nash Gerard B.
Published: November 2024

Changes in the mechanical and adhesive properties of neutrophils may modify perfusion of the microcirculation in cooled tissue. We tested how integrin-mediated adhesion of isolated human neutrophils was altered by cooling, or cooling and rewarming. First, adhesion was tested in a static assay. In the presence or absence of integrin-activating agents (formyl peptide, fMLP or Mn++), there were significant reductions in adhesion to immobilised albumin at 10°C or 0°C compared to 37°C, although a slight increase in adhesion was induced by fMLP or Mn++ at 10°C or 0°C. If cells were cooled for 5 or 20 min at 10°C and rewarmed (in the absence of activators) there was >100% increase in adhesion compared to cells held at 37°C. In a flow assay, neutrophils perfused over P-selectin at 37°C formed rolling attachments, but if neutrophils were cooled to 10°C and rewarmed for 1 or 5 min, there was transformation to stationary adhesion, which was reversed by antibody against CD18. After 20 minutes of rewarming, rolling was restored. Cooling and rewarming did not cause de novo expression of CD11b/CD18, and so appears to transiently activate constitutively-expressed integrin. Thus, integrin-mediated adhesion may be impaired in cold tissue but on return to normal temperature, neutrophils may transiently adhere locally or in remote vessels.
Participation of caspase-3-like protease in oxidation-induced impairment of erythrocyte membrane properties
Authors: Suzuki Yoji , Ohkubo Nobutaka , Aoto Mamoru , Maeda Nobuji , Cicha Iwona , Miki Tetsuro , Mitsuda Noriaki
Published: November 2024

Erythrocytes are very susceptible to oxidative stress, having a high content of intracellular oxygen and hemoglobin. In the present study, exposure to oxidative stress resulted in a significant impairment of erythrocyte membrane functions, such as deformability and anion exchange. Band 3 protein, also known as anion exchanger-1, plays an important role in these two functions. We show that oxidative stress activated caspase-3 inside the erythrocytes, which resulted in band 3 protein cleavage. Interestingly, inhibition of the caspase-3 with its specific inhibitor not only suppressed the digestion of band 3 protein, but also blunted the functional damage to erythrocytes, such as deformability and anion exchange, without changing the level of peroxidation of membrane lipids. These results provide experimental evidence that activation of caspase-3 plays an important role in the oxidative stress-induced impairment of membrane functions of erythrocytes.
Investigation of platelet margination phenomena at elevated shear stress
Authors: Zhao Rui , Kameneva Marina V. , Antaki James F.
Published: November 2024

Thrombosis is a common complication following the surgical implantation of blood contacting artificial organs. Platelet transport, which is an important process of thrombosis and strongly modulated by flow dynamics, has not been investigated under the shear stress level associated with these devices, which may range from tens to several hundred Pascal.

The current research investigated platelet transport within blood under supra-physiological shear stress conditions through a micro flow visualization approach. Images of platelet-sized fluorescent particles in the blood flow were recorded within microchannels (2 cm × 100 μm × 100 μm). The results successfully demonstrated the occurrence of platelet-sized particle margination under shear stresses up to 193 Pa, revealing a platelet near-wall excess up to 8.7 near the wall (within 15 μm) at the highest shear stress. The concentration of red blood cells was found to influence the stream-wise development of platelet margination which was clearly observed in the 20% Ht sample but not the 40% Ht sample. Shear stress had a less dramatic effect on the margination phenomenon than did hematocrit. The results imply that cell–cell collision is an important factor for platelet transport under supra-physiologic shear stress conditions. It is anticipated that these results will contribute to the future design and optimization of artificial organs.
Development of a flow-through system to create occluding thrombus
Authors: Ku David N. , Flannery Conor J.
Published: November 2024

Occlusive thrombosis accounts for many heart attacks and strokes. These acute events are difficult to catch in patients and animal test methods may be misleading because anti-thrombotic therapeutics often do not cross-react with different species. This paper presents a new flow-through system that leads to rapid occlusive thrombosis in arterial flow conditions. Whole porcine blood is perfused through a tubular test section. The growing thrombus is visualized in real time from early platelet attachment, through accumulation, to occlusion. The progression of flow rate reduction provides a clear distinguishing parameter between thrombus formation and embolization. Thrombus growth rate is a linear function of very high shear rate beyond 40,000 s−1. The histology of the thrombus reveals predominantly platelet accumulation and growth as a rough surface with tendrils. This flow-through system may be useful for the economic testing of new anti-thrombosis therapies.
Mechanotransduction in leukocyte activation: A review
Authors: Makino Ayako , Shin Hainsworth Y. , Komai Yutaka , Fukuda Shunichi , Coughlin Mark , Sugihara-Seki Masako , Schmid-Schönbein Geert W.
Published: November 2024

We review recent evidence which suggests that leukocytes in the circulation and in the tissue may readily respond to physiological levels of fluid shear stress in the range between about 1 and 10 dyn/cm2, a range that is below the level to achieve a significant passive, viscoelastic response. The response of activated neutrophilic leukocytes to fluid shear consists of a rapid retraction of lamellipodia with membrane detachment from integrin binding sites. In contrast, a subgroup of non-activated neutrophils may project pseudopods after exposure to fluid shear stress. The evidence suggests that G-protein coupled receptor downregulation by fluid shear with concomitant downregulation of Rac-related small GTPases and depolymerization of F-actin serves to retract the lamellipodia in conjunction with proteolytic cleavage of β2 integrin to facilitate membrane detachment. Furthermore, there exists a mechanism to up- and down-regulate the fluid shear-response, which involves nitric oxide and the second messenger cyclic guanosine monophosphate (cGMP). Many physiological activities of circulating leukocytes are under the influence of fluid shear stress, including transendothelial migration of lymphocytes. We describe a disease model with chronic hypertension that suffers from an attenuated fluid shear-response with far reaching implications for microvascular blood flow.
Mechanical response of a living human epidermal keratinocyte sheet as measured in a composite diaphragm inflation experiment
Authors: Selby John C. , Shannon Mark A.
Published: November 2024

Sheets of normal human epidermal keratinocytes (NHEKs) were reconstituted in vitro on tensed but highly compliant, freestanding polydimethylsiloxane (PDMS) membranes, 5.0 mm in diameter and 10 μm thick. NHEK-PDMS composite diaphragm (CD) specimens were then subjected to cyclical axisymmetric inflation tests to investigate epithelial sheet rheology under conditions of physiologically severe deformations (∼50% nominal polar biaxial strains). Because the compliance of the specially formulated PDMS membrane was greater than that of the attached cell layer, the finite load-deformation behavior (mechanical response) of the living NHEK sheet was inferred from differences between the mechanical behavior of the CD specimen and the response of the underlying PDMS membrane measured prior to cell culture. In these composite diaphragm inflation (CDI) experiments, interconnected NHEKs exhibited rheological behaviors that were suggestive of a viscoelastic–plastic stress response. Remarkably, specimens returned to quiescent culture following a sequence of inflation tests recovered at least 80% of their original ability to store elastic strain energy, evidence of biological adaptation and recovery or restitutio ad integrum. Unlike methodologies that assay the morphological or biochemical response of cultured cells to an applied mechanostimulus, CDI experiments can be used to probe the load-bearing functions of desmosomes and adherens junctions within a living epithelial sheet, as well as to assess the rheological behaviors of the intermediate filament and microfilament networks that these cell–cell junctions serve to interconnect.
Influence of gearbox oil on 3D printed carbon fiber reinforced polymer
Authors: Kazda Lukas , Matušů Martin , Padovec Zdenek , Jenikova Zdenka
Published: November 2024

This study builds upon prior research investigating the effects of gearbox oil on filament wound carbon fiber reinforced polymer (CFRP) materials. Here, short carbon fiber composite material was examined, motivated by the intention to use such materials in vehicle gearboxes. Automotive sector faces pressures to reduce CO2 emissions, therefore car manufacturers explore possibilities to implement CFRP into their gearboxes for parts such as shafts or casings to save weight, and also improve NVH behavior. Also, e-bike manufacturers aim to use polymers with short carbon fibers for making gears in their gearboxes. The important caveat to using these materials in gearboxes is the operating environment which is oil. While numerous studies have explored the influence of water on CFRP mechanical properties, research on the effects of oil remains scarce. Our experiment, conducted on 3D printed specimens, revealed predominantly positive effects of 60°C oil on the material’s ultimate tensile strength, with increases ranging from 2 to 10% depending on printing orientation, and on Young’s modulus, which increased by 7% in the longitudinal direction but decreased by 5% in the transversal direction. Interestingly, there was no significant change in glass transition temperature, and only negligible and inconsistent diffusion behavior was observed.
Physico-mechanical characteristics of horsehair/jute fiber-based nonwoven fabric reinforced LLDPE composites: Effect of alkali treatment and maleic anhydride
Authors: Üstüntağ Sümeyye
Published: November 2024

Horsehair/jute fiber reinforced linear low-density polyethylene (LLDPE) laminated composites were prepared by compression molding using the film-stacking method. The objective of this study is to assess the impact of modifying reinforcement materials through alkaline treatment and incorporating maleated coupling agent on the mechanical, morphological, degradation performance, and water absorption properties of composites. Horsehair, which constitutes approximately 70% of the reinforcing material, preserved its keratin structure after alkaline treatments (NaOCI and NaOH) and the scale layer became more prominent. The alkali treatment slightly improved the mechanical properties of the composites but led to an increase in water uptake. The maleated coupling agent was included in the composite structure as a sheet. The compatibilizer significantly enhanced the tensile and flexural properties while also reducing water uptake of the composites. The greatest enhancement in mechanical properties was attained when alkaline treatment and compatibilizer were utilized in conjunction.
Is China-Taiwan Rapprochement Possible? Experimental Evidence From Taiwan
Authors: Pan Hsin-Hsin , Kastner Scott L. , Pearson Margaret M.
Published: November 2024

Any peaceful resolution to the Cross-Strait conflict between China and Taiwan is likely to be composed of give-and-take between the two sides, and any agreement will ultimately require the support of Taiwan’s citizens, by whom Taiwan’s leaders are held accountable. Yet little is known about the actual tradeoffs Taiwanese citizens are willing to make in pursuit of an agreement in a time of peace. In conjoint experiments fielded in Taiwan in April 2022, we present Taiwanese respondents with hypothetical Cross-Strait agreements that randomly assign economic, security, and sovereignty-related concessions by the two sides. We find that support for agreements is conditioned by the concessions included, with sovereignty-related or security-related concessions by Taiwan lowering support, and sovereignty or security-related concessions by China increasing support. Additionally, respondents indicate that neither US support nor PRC threats significantly influence support for agreements, and that Taiwan's acceptance of an agreement substantially reduces the perceived likelihood of conflict.
Cardiorespiratory, hemodynamic, and sedative effects of dexmedetomidine in sheep
Authors: Gomes Janainne Hilbig , Bittar Isabela Plazza , Moura Rauane Sousa de , Prado Bruna Ginú , Franco Leandro Guimarães
Published: November 2024

An alternative in an attempt to minimize the effects triggered by intravenous (IV) bolus administration of α-2 adrenergic receptor agonists are continuous rate infusions (CRI). The requirement for sedation protocols in sheep for procedures to be performed without physical restraint and with reduced adverse effects, commonly observed with bolus use, justifies the study of CRI. The aim of study was to compare the cardiopulmonary and sedative effects of IV bolus injection and CRI of dexmedetomidine (DEX) in sheep. Six adult male sheep (38.3 ± 7.6 kg) received DEX as a bolus (5 µg kg−1, DEXbolus treatment) or CRI (5 µg kg−1 h−1 for 1 h, DEXCRI treatment). We recorded heartrate (HR), respiratory rate, systemic arterial blood pressure, pulse oximetry, hemodynamic parameters, blood gases and sedation scores over 120 min. HR was significantly lower in DEXbolus at 5 and 15 min than in DEXCRI, with HR reduction observed for 30 min in DEXbolus. Hypoxemia was noted in DEXbolus at 10 and 30 min. Pulmonary vascular resistance index increased at 5 min, and cardiac index (CI) decreased at all timepoints compared with baseline in DEXbolus. In DEXCRI, CI decreased only at 45 min. Sedation scores were higher in DEXbolus at 15 and 30 min. DEX CRI administration resulted in fewer cardiorespiratory and hemodynamic changes compared with bolus injection and lower sedation scores (<4/10), which would not allow animal handling without a reaction. The load dose used in CRI was a limitation to constant infusion.