Biorheology - Volume 41, issue 3-4

Authors: Huyghe, J.M. | Drost, M.R.

Article Type: Research Article

Abstract: Recent modelling efforts in the field of mechanics of the intervertebral disc, demonstrate that the deformation properties of intervertebral disc tissue are intimately linked to compositional changes. This paper presents uniaxial tensile relaxation experiments of canine annulus fibrosus tissue under stepwise changes of external salt concentration.

Citation: Biorheology, vol. 41, no. 3-4, pp. 255-261, 2004

Authors: Volokh, K.Y.

Article Type: Research Article

Abstract: A phenomenological continuum mechanics framework for modeling growth of living tissues is proposed. Tissue is considered as an open system where mass is not conserved. The momentum balance is completed with the full‐scale mass balance. Constitutive equations define simple growing materials. ‘Thermoelastic’ formulation of a simple growing material is specified. Within this framework traction free growth of a cylinder is considered. It is shown that the theory accommodates the case where stresses are not generated in uniform volumetric growth. It is also found that surface growth corresponds to a boundary layer solution of the governing equations.

Keywords: Living tissue, volumetric growth, surface growth, mass balance

Citation: Biorheology, vol. 41, no. 3-4, pp. 263-269, 2004

Authors: Wiseman, Mike | Bader, Dan L. | Reisler, Tom | Lee, David A.

Article Type: Research Article

Abstract: This study tests the hypothesis that expansion by passage in monolayer influences the response of isolated articular chondrocytes to dynamic compression. Chondrocytes, isolated from bovine articular cartilage, were seeded in monolayer and passaged 4 times (P1–4). For assessment of chondrocytic and fibroblastic phenotype, freshly isolated and passaged cells were seeded on glass coverslips or in 2% alginate beads and cultured for 7 days in DMEM + 10% FCS. Samples were assayed for DNA and GAG content and stained for collagen types I and II. In separate experiments, freshly isolated or passaged chondrocytes were seeded at 10×106 cells.ml−1 in …4% cylindrical agarose constructs and subjected to 15% dynamic compressive strain at 1 Hz for 24 hours. [3 H]‐thymidine incorporation, SO4 incorporation and nitrite release were analysed. Immediately following isolation (P0), chondrocytes seeded in alginate expressed high levels of type II collagen, but did not stain for type I collagen. Following repeat passage the cells expressed enhanced levels of type I collagen, with an associated reduction in type II collagen staining. These data indicate a modulation to a fibroblastic phenotype during monolayer expansion which was not rapidly reversed by culture in a 3D hydrogel. Dynamic compression down‐regulated SO4 incorporation at P0, but did not affect [3 H]‐thymidine incorporation. By contrast the incorporation of both SO4 and [3 H]‐thymidine was enhanced by dynamic compression at both P1 and to a lesser extent P2. SO4 and [3 H]‐thymidine incorporation were inhibited at P3 and P4. Nitrite release was down‐regulated by dynamic compression at all passages. These data demonstrate a clear modulation in the response of bovine articular chondrocytes to dynamic compression following passage in monolayer. Show more

Keywords: Chondrocyte, dynamic compression, tissue engineering, cell phenotype, cell expansion, monolayer culture

Citation: Biorheology, vol. 41, no. 3-4, pp. 283-298, 2004

Authors: Browning, J.A. | Saunders, K. | Urban, J.P.G. | Wilkins, R.J.

Article Type: Research Article

Abstract: The intracellular milieu of chondroctyes is regulated by an array of proteins in the cell membrane which operate as transport pathways, allowing ions and nutrients such as glucose and amino acids and metabolites such as lactate to cross the plasma membrane. Here we investigated the influence of hydrostatic pressure on intracellular calcium concentrations ([Ca2+ ]i ) in isolated bovine articular chondrocytes. We found that short applications of high hydrostatic pressures led to a significant increase in [Ca2+ ]i . The pressure‐induced rise was abolished for long (240 sec) but not short (30 sec) pressure applications by removal of extracellular Ca2+ …. The rise in pressure was also blocked by the inhibitors neomycin and thapsigargin confirming that pressure, by generating IP3 , led to an increase in [Ca2+ ]i by mobilising the pool of Ca2+ ions contained within intracellular stores. We also found that intracellular [Na+ ] was affected by a rise in osmotic pressure and further affected by application of hydrostatic pressure. The effect of hydrostatic pressure on sulphate incorporation depended strongly on extracellular osmolality. Since significant gradients in extracellular osmolality exist across intact cartilage, the results imply that responses of chondrocytes to the same pressure will vary depending on location in the joint. The results also indicate that hydrostatic pressures can affect several different transporter systems thus influencing the intracellular milieu and chondrocyte metabolism. Show more

Keywords: Calcium, sodium pump, mechanotransduction, ion transport, osmotic pressure

Citation: Biorheology, vol. 41, no. 3-4, pp. 299-308, 2004

Authors: Lammi, Mikko J. | Elo, Mika A. | Sironen, Reijo K. | Karjalainen, Hannu M. | Kaarniranta, Kai | Helminen, Heikki J.

Article Type: Research Article

Abstract: Hydrostatic pressure is a well‐known effector of cellular protein synthesis. High continuous hydrostatic pressure inhibits protein synthesis in general. It has been known for a long time that 30S ribosomal subunit is associated with the effects of pressure on protein synthesis in prokaryotes, however, the mechanisms of action are still not completely understood. Our new data suggest that synthesis of eukaryotic elongation factor‐2 (eEF‐2) is decreased under 30 MPa continuous hydrostatic pressure. Thus, eEF‐2 may have a role in the synthesis of pressure‐regulated proteins in eukaryotic cells. The presence of pressure‐sensitive proteins indicate that hydrostatic pressure can induce very specific …responses in stressed cells. Accumulation of heat shock protein 70 and 90 beta occurs under high pressure, independent of the general inhibition of protein synthesis, although this response appears clearly weaker than during heat stress. Show more

Keywords: Hydrostatic pressure, translation, chondrocyte

Citation: Biorheology, vol. 41, no. 3-4, pp. 309-313, 2004

Authors: Edlich, Maximilian | Yellowley, Clare E. | Jacobs, Christopher R. | Donahue, Henry J.

Article Type: Research Article

Abstract: Many studies have shown that a loading‐induced (bio)physical signal regulates chondrocyte behavior. In a recent study our group has demonstrated the shear stress level‐ and frequency‐dependent effect of sinusoidal oscillatory fluid flow on bovine articular chondrocyte (BAC) cytosolic calcium concentration ([Ca2+ ]i ), neglecting the fact that chondrocytes are not likely to see these ideal waveform in vivo or in vitro. Furthermore, possible overload of articular cartilage or excessive shear stress in chondrocyte cultures are more likely to be of a short nature. Therefore, in this study we choose to investigate a saw‐tooth waveform oscillating fluid flow at varying exposure …times in comparison to the established sinusoidal oscillatory waveform. [Ca2+ ]i , as an early signaling molecule, was quantified using the fluorescent dye fura‐2. BAC were exposed to 1 Hz sinusoidal or saw‐tooth waveform oscillating fluid flow at 2.2 Pa flow rates in a parallel plate flow chamber for 8 different loading times. As little as 5 cycles of oscillatory fluid flow were sufficient to increase [Ca2+ ]i significantly over baseline. The number of responding cells could not be increased any further after a sufficient number of cycles (11), regardless of the waveform. Furthermore, a saw‐tooth waveform appeared to be more stimulatory than regular sinusoidal oscillating flow at higher cycle numbers. BAC appear to be able to respond to these biophysical stimuli in a differentiated manner. This ability might give every single chondrocyte the capability to maintain its territory autonomously, since chondrocytes distributed in articular cartilage without the possibility to interact, e.g., via cell processes. Show more

Keywords: Chondrocytes, in vitro, mechanotransduction, fluid flow, shear stress, calcium

Citation: Biorheology, vol. 41, no. 3-4, pp. 315-322, 2004

Authors: Scherer, Katrin | Schünke, Michael | Sellckau, Roland | Hassenpflug, Joachim | Kurz, Bodo

Article Type: Research Article

Abstract: Tissue engineering of articular cartilage from chondrocytes or stem cells is considered to be a potential aspect in the treatment of cartilage defects. In order to optimize culture conditions the influence of low oxygen tension (5%) – single or in combination with intermittent hydrostatic pressure (HP: 30/2 min on/off loading; 0.2 MPa) – on the biosynthetic activity (sulfate and proline incorporation) of human osteoarthritic chondrocytes cultured on collagen I/III membranes was investigated. Additionally, chondrogenesis from high density or monolayer cultures of bovine adherent bone marrow cells (aBMC) with and without chondrogenic medium supplements (CM) was analyzed by RT‐PCR (mRNA expression …of aggrecan and collagen type II). We could show that low oxygen tension increases significantly the biosynthesis of collagen I/III membrane‐associated chondrocytes and even higher under co‐stimulation with HP. While there is no chondrogenesis in monolayer cultures, CM induces expression of cartilage matrix molecules in high density cultures of aBMC which is even increased under the influence of low oxygen tension. Both, low oxygen tension and HP without CM are alone not sufficient stimuli for chondrogenesis. It can be concluded that low oxygen tension and HP might be useful tools in cartilage tissue engineering and that these physico‐chemical factors promote but do not induce chondrogenesis under the given conditions. Show more

Keywords: Chondrogenesis, biosynthesis, high density culture, collagen I/III membrane

Citation: Biorheology, vol. 41, no. 3-4, pp. 323-333, 2004

Authors: Angele, Peter | Schumann, Detlef | Angele, Martin | Kinner, Bernd | Englert, Carsten | Hente, Reiner | Füchtmeier, Bernd | Nerlich, Michael | Neumann, Carsten | Kujat, Richard

Article Type: Research Article

Abstract: The effects of cyclic, mechanical compression on human bone marrow‐derived mesenchymal progenitor cells undergoing chondrogenic differentiation were examined in this study. Mesenchymal progenitor cells were injected into cylindrical biodegradable scaffolds (hyaluronan–gelatin composites), cultured in a defined, serum‐free chondrogenic medium and subjected to cyclic, mechanical compression. Scaffolds were loaded for 4 hours daily in the first 7 days of culture. At 1, 7, 14 and 21 days of culture, scaffolds were harvested for reverse transcriptase Polymerase Chain Reaction (RT‐PCR), histology, quantitative DNA, proteoglycan and collagen analysis. Scaffolds loaded for 7 days showed a significant upregulation especially of chondrogenic markers (type II …collagen, aggrecan; p<0.0001). No significant difference could be found for DNA content between loaded samples and unloaded controls. At day 1 in culture no significant differences in proteoglycan‐ and collagen contents could be detected between unloaded and loaded samples. After 21 days the proteoglycan (p<0.001) and collagen contents (p<0.0001) were significantly higher in the loaded samples compared to unloaded controls. By histological analysis (toluidine blue) a higher amount of proteoglycan‐rich, extracellular matrix production throughout the matrix could be detected for loaded samples compared to unloaded controls. This study indicates that cyclic, mechanical compression enhances the expression of chondrogenic markers in mesenchymal progenitor cells differentiated in vitro resulting in an increased cartilaginous matrix formation, and suggests that mechanical forces may play an important role in cartilage repair. Show more

Keywords: Chondrogenesis, stem cell, bone marrow, mechanobiology, compression

Citation: Biorheology, vol. 41, no. 3-4, pp. 335-346, 2004

Authors: Jakab, Karoly | Neagu, Adrian | Mironov, Vladimir | Forgacs, Gabor

Article Type: Research Article

Abstract: Aggregates of living cells (i.e. model tissue fragments) under appropriate conditions fuse like liquid drops. According to Steinberg's differential adhesion hypothesis (DAH), this may be understood by assuming that cells are motile and tissues made of such cells possess an effective surface tension. Here we show that based on these properties three‐dimensional cellular structures of prescribed shape can be constructed by a novel method: cell aggregate printing. Spherical aggregates of similar size made of cells with known adhesive properties were prepared. Aggregates were embedded into biocompatible gels. When the cellular and gel properties, as well as the symmetry of the …initial configuration were appropriately adjusted the contiguous aggregates fused into ring‐like organ structures. To elucidate the driving force and optimal conditions for this pattern formation, Monte Carlo simulations based on a DAH motivated model were performed. The simulations reproduced the experimentally observed cellular arrangements and revealed that the control parameter of pattern evolution is the gel‐tissue interfacial tension, an experimentally accessible parameter. Show more

Keywords: Tissue engineering, differential adhesion, fusion, spherical aggregate, tissue liquidity

Citation: Biorheology, vol. 41, no. 3-4, pp. 371-375, 2004

Authors: Connelly, John T. | Vanderploeg, Eric J. | Levenston, Marc E.

Article Type: Research Article

Abstract: While not generally viewed as physiologically significant in articular cartilage, substantial tension can develop in fibrocartilage structures and in articular cartilage injuries. This study examined how different amplitudes of cyclic tension influence chondrocyte matrix synthesis. Bovine articular chondrocytes seeded in fibrin gels were loaded continuously for 48 hours at 1.0 Hz with displacements of 5%, 10%, or 20%. Protein and proteoglycan synthesis were measured by 3 H‐proline and 35 S‐sulfate incorporation, respectively. A poroelastic finite element model of the fibrin gel was developed to determine the strain distributions, hydrostatic pressures, and fluid velocities within the constructs at the various levels …of displacement. Compared to unloaded controls, 10% and 20% displacements inhibited proteoglycan synthesis to the same extent, while 5% displacement had no effect. Tensile loading did not significantly affect protein synthesis. The finite element model predicted a wide range of strains and fluid velocities within the region of the gel analyzed for matrix synthesis, and the ranges overlapped for the different levels of displacement. These results indicate that the cyclic tension amplitude influences chondrocyte proteoglycan synthesis and that there may be a threshold in the response. Show more

Keywords: Cartilage, poroelastic, fibrin, tissue engineering

Citation: Biorheology, vol. 41, no. 3-4, pp. 377-387, 2004