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Response of cultured nasal goblet cells to wall shear stresses
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Journal o f Biomechanics 2006, Vol. 39 (Suppl 1)
images as detailed in [1]. Airway diameter ranges from approx. 2 to 14mm. The flow in the airway model was simulated using CFD software: Fluent (Fluent 6.1.22, Fluent. Inc.). The resultant flow showed differences compared with that observed in a simplified planar multi-branching model reported in [2]. The inspiratory flow patterns were relatively similar to the patterns observed in a simplified airway model, but the expiratory flow patterns strongly depended on the realistic airway geometry and showed more complicated secondary flow structures. Secondary flow velocities were higher in the realistic airway model than in the simplified airway model in both the inspiratory and expiratory flows. Performing Lagrangian fluid particle tracking, we discussed the convective dispersion due to asymmetric inspiratory and expiratory velocity profiles. Supported by a Grant-in-Aid for Young Scientists (15760123) from the MEXT, Japan References [1] Ue H, Sato Y, Haneishi H, Toyama H, Miyamoto T, Yamamoto N, Mori Y. Med. Image. Tech. 2003; 21: 122-29. [2] Tanaka G, Ogata T, Oka K, Tanishita K. J. Biomech. Eng. 1999; 121: 565-73. 5686 We-Th, no. 42 (P64) Response of cultured nasal goblet cells to wall shear stresses N. Even-Tzur 1, U. Zaretsky 1, M. Wolf 2, D. Elad 1. 1Department of Biomedical Engineering, Tel Aviv University, Tel Aviv, Israel, 2Department of Otorhinolaryngology, Sheba Medical Center, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel Goblet cells of the respiratory tract contribute to the first-line defense of the lungs by secretion of mucus in response to a wide variety of biological, chemical and environmental stimuli. The objective of this work was to explore the response of cultured nasal goblet cells to airflow induced wall shear stress (WSS). Human nasal epithelial cells were cultured in custom designed wells using the air-liquid interface (ALl) technique that mimics the in vivo condition of the inner nasal respiratory epitheluim that is rich with goblet cells. Once a confluent layer of cultured cells has been grown, the wells were disassembled in a way that a continuous field of WSS could be applied on the cells surface without any obstacle. Then, the disassembled wells with the cultured cells were mounted in a designed flow chamber which was connected to a respiratory simulator that drove the airflow above the cells surface. The specific tests were to evaluate geometrical modifications, cytoskeletal adjustments and mucus secretion in response to WSS of different flow fields. Biological assays were implemented in these tests. Initial results showed that WSS, introduced by steady airflow of the magnitude of heavy breathing, has a significant effect on nasal goblet cells behavior. Both, the cell's shape and the volume of mucus secretion were affected by the airflow direction and the increased WSS. We expect that the results of this study will help in understanding issues related to nasal irritation and sensitivity, especially when responses of mucus secretion are involved. 5208 We-Th, no. 43 (P65) Measurement o f single-cell generated tractions in response to localized repetitive mechanical loading R. Krishnan 1, S. Hu 1, J.T. Dennerlein 1, N. Wang 1,2. 1Physiology Program, Dept of Environmental Health, Harvard School of Public Health, Boston, USA, 2Department of Mechanical and Industrial Engineering, University of Illinois, Urbana-Champaign, USA It has been shown that activation of contractile cells by a mechanical or pharmacological stimulus triggers a series of biochemical events accompanied by changes in cell prestress (Wang et al. 2001, 2002) and cytoskeletal stiffness (Hubmayr et al 1996; Wang et al. 2002). However, the relationship between external mechanical stimulus and cell-generated contractile forces on the same single cell has not been directly investigated. The current study describes a novel approach to quantify this relationship. Localized twisting loads of physiological magnitudes were applied via integrin receptors to the apical surface of C2C12 murine myoblasts. Temporal changes in interfacial tractions between the cell basal surface and its underlying flexible gel substrate were quantified using traction force microscopy. Using synchronous detection methods (Hu et al. 2003), displacements and tractions induced by external oscillatory loads were uncoupled from cell-generated active response. Displacement and traction plots were generated to map real-time tractions before, during, and after application of external loads. Preliminary results show that cell-generated contractile forces increased after the external loading. This approach can be used to quantify dynamic changes in cell tractions in response to localized mechanical forces. References Hu S., et al. (2003). Am J Physiol Cell Physiol 285: C1082-90. Hubmayr R.D., et al. (1996). Am J Physiol 271: C1660-8. Wang N., et al. (2001). Proc Natl Acad Sci USA 98: 7765-70. Wang N. et al. (2002). Am J Physiol Cell Physiol 282: C606-16.
Poster Presentations 5092 We-Th, no. 44 (P65) Structural contribution of the cytoskeleton to the dynamic response of adherent cells assessed by a viscoelastic tensegrity model P. CaSadas 1, S. Wendling-Mansuy 2, D. Isabey3. 1CNRS, LMGC UMR 5508, Universit6 de Montpellier 2, Montpellier, France, 2CNRS, LABM USR 2164, Universit6 de la M6diterran~e, Marseille, France, 31NSERM, UMR 651, Universit6 de Paris 12, Facult~ de M~decine, Cr~teil, France In the aim of studying dynamically the role of structural rearrangement of cytoskeleton onto cell viscoelastic mechanical properties, we simulated numerically the behaviour of a viscoelastic tensegrity structure (VTS model made of 24 tensed viscoelastic cables and 6 rigid bars) loaded by various external forces. The mechanical response to creep tests and various sinusoidal oscillatory Ioadings of the overall structure was studied as a function of (i) the overall strain amplitude, (ii) the frequency of the applied forces, and (iii) the viscoelastic properties of local elements. The results reveal the role of the various strain/amplitude-dependences and frequency-dependence of the normalized elasticity and viscosity modulus of the overall VTS model as well as the role of normalized length and normalized internal tension of elements on these structural properties. The study reveals that the mechanism behind the oscillatory behaviour of the structure is related to the contribution of spatial rearrangement of VTS elements which varies from high when elastic effects predominate (low frequencies, large amplitudes) to low when viscous effects predominate (high frequencies, low amplitudes). More precisely, the elasticity modulus increases when force-amplitude, frequency and/or internal tension increase, while it decreases when the size of the structural elements increases. By contrast, the viscosity modulus, which also increases with force-amplitude, decreases with frequency and structure-size and remains independent on internal tension. Present numerical results have been found in satisfactorily agreement with results reported in the literature for in vitro cell experiments, suggesting that the highly variable contribution of spatial rearrangement of the cytoskeleton elements, especially encountered in a transitional zone of frequency, could play a significant and predictable role in the dynamic response of adherent cells. 5077 We-Th, no. 45 (P65) The steady propagation of an air finger into a partially collapsed, fluid-filled, elastic tube A. Heap, A. Juel. School of Mathematics, University of Manchester, Manchester, UK The reopening of a partially collapsed, fluid-filled, elastic tube is investigated experimentally. The origin of this problem lies in the field of lung airway reopening. Airway closure can occur as a result of pulmonary disease and thus greater understanding of the reopening dynamics is essential in order to prevent damage during mechanical ventilation. The laboratory model consists of a 1 m long, uniformly collapsed, fluid-lined tube into which air is injected at a constant flow rate. This leads to the steady propagation of an air finger, whose velocity is characterised by the non-dimensional capillary number Ca =flU~a* (ratio of viscous to surface tension forces). Pressure measurements and video footage are combined to describe the reopening dynamics. Controlled experiments were performed for 70% and 80% tube collapse. At 70% collapse, the effect of viscosity on the reopening dynamics was investigated by using three different grades of silicone oil. A direct comparison between the experimental pressure dependence on Ca and the numerical simulations of the zero-gravity, three-dimensional airway reopening model of Hazel and Heil (2005) highlighted some significant differences. Within the experimental parameter range, gravity was found to profoundly influence the reopening mechanics in several ways. Recent experiments conducted at 80% collapse indicate the presence of multiple steady reopening states, including the propagation of one asymmetric air finger, two fingers and a low pressure pointed finger. References Hazel A.L., Heil M. (2005). Finite Reynolds number effects in steady, threedimensional airway reopening. ASME J. Biomech. Eng., in press. 5332 We-Th, no. 46 (P65) Coupled mechanics and airflow o f a human lung K.L. Hedges, P.J. Hunter, M.H. Tawhai. Bioengineering Institute, University of Auckland, Auckland, New Zealand To study the ventilation distribution within a human lung a model has been produced that couples soft tissue mechanics and a simplified airflow solution. The model takes account of the regional changes in the material properties of the lung which affect the pressures developed by the lung tissue during ventilation and determine the patency of the airways. The lung geometry was constructed using CT scanned data as far as the 9 th generation. Further airways are grown within the CT-based tissue lobes using a volume filling algorithm. Equations for large deformation elasticity are used to compute
Journal o f Biomechanics 2006, Vol. 39 (Suppl 1)
images as detailed in [1]. Airway diameter ranges from approx. 2 to 14mm. The flow in the airway model was simulated using CFD software: Fluent (Fluent 6.1.22, Fluent. Inc.). The resultant flow showed differences compared with that observed in a simplified planar multi-branching model reported in [2]. The inspiratory flow patterns were relatively similar to the patterns observed in a simplified airway model, but the expiratory flow patterns strongly depended on the realistic airway geometry and showed more complicated secondary flow structures. Secondary flow velocities were higher in the realistic airway model than in the simplified airway model in both the inspiratory and expiratory flows. Performing Lagrangian fluid particle tracking, we discussed the convective dispersion due to asymmetric inspiratory and expiratory velocity profiles. Supported by a Grant-in-Aid for Young Scientists (15760123) from the MEXT, Japan References [1] Ue H, Sato Y, Haneishi H, Toyama H, Miyamoto T, Yamamoto N, Mori Y. Med. Image. Tech. 2003; 21: 122-29. [2] Tanaka G, Ogata T, Oka K, Tanishita K. J. Biomech. Eng. 1999; 121: 565-73. 5686 We-Th, no. 42 (P64) Response of cultured nasal goblet cells to wall shear stresses N. Even-Tzur 1, U. Zaretsky 1, M. Wolf 2, D. Elad 1. 1Department of Biomedical Engineering, Tel Aviv University, Tel Aviv, Israel, 2Department of Otorhinolaryngology, Sheba Medical Center, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel Goblet cells of the respiratory tract contribute to the first-line defense of the lungs by secretion of mucus in response to a wide variety of biological, chemical and environmental stimuli. The objective of this work was to explore the response of cultured nasal goblet cells to airflow induced wall shear stress (WSS). Human nasal epithelial cells were cultured in custom designed wells using the air-liquid interface (ALl) technique that mimics the in vivo condition of the inner nasal respiratory epitheluim that is rich with goblet cells. Once a confluent layer of cultured cells has been grown, the wells were disassembled in a way that a continuous field of WSS could be applied on the cells surface without any obstacle. Then, the disassembled wells with the cultured cells were mounted in a designed flow chamber which was connected to a respiratory simulator that drove the airflow above the cells surface. The specific tests were to evaluate geometrical modifications, cytoskeletal adjustments and mucus secretion in response to WSS of different flow fields. Biological assays were implemented in these tests. Initial results showed that WSS, introduced by steady airflow of the magnitude of heavy breathing, has a significant effect on nasal goblet cells behavior. Both, the cell's shape and the volume of mucus secretion were affected by the airflow direction and the increased WSS. We expect that the results of this study will help in understanding issues related to nasal irritation and sensitivity, especially when responses of mucus secretion are involved. 5208 We-Th, no. 43 (P65) Measurement o f single-cell generated tractions in response to localized repetitive mechanical loading R. Krishnan 1, S. Hu 1, J.T. Dennerlein 1, N. Wang 1,2. 1Physiology Program, Dept of Environmental Health, Harvard School of Public Health, Boston, USA, 2Department of Mechanical and Industrial Engineering, University of Illinois, Urbana-Champaign, USA It has been shown that activation of contractile cells by a mechanical or pharmacological stimulus triggers a series of biochemical events accompanied by changes in cell prestress (Wang et al. 2001, 2002) and cytoskeletal stiffness (Hubmayr et al 1996; Wang et al. 2002). However, the relationship between external mechanical stimulus and cell-generated contractile forces on the same single cell has not been directly investigated. The current study describes a novel approach to quantify this relationship. Localized twisting loads of physiological magnitudes were applied via integrin receptors to the apical surface of C2C12 murine myoblasts. Temporal changes in interfacial tractions between the cell basal surface and its underlying flexible gel substrate were quantified using traction force microscopy. Using synchronous detection methods (Hu et al. 2003), displacements and tractions induced by external oscillatory loads were uncoupled from cell-generated active response. Displacement and traction plots were generated to map real-time tractions before, during, and after application of external loads. Preliminary results show that cell-generated contractile forces increased after the external loading. This approach can be used to quantify dynamic changes in cell tractions in response to localized mechanical forces. References Hu S., et al. (2003). Am J Physiol Cell Physiol 285: C1082-90. Hubmayr R.D., et al. (1996). Am J Physiol 271: C1660-8. Wang N., et al. (2001). Proc Natl Acad Sci USA 98: 7765-70. Wang N. et al. (2002). Am J Physiol Cell Physiol 282: C606-16.
Poster Presentations 5092 We-Th, no. 44 (P65) Structural contribution of the cytoskeleton to the dynamic response of adherent cells assessed by a viscoelastic tensegrity model P. CaSadas 1, S. Wendling-Mansuy 2, D. Isabey3. 1CNRS, LMGC UMR 5508, Universit6 de Montpellier 2, Montpellier, France, 2CNRS, LABM USR 2164, Universit6 de la M6diterran~e, Marseille, France, 31NSERM, UMR 651, Universit6 de Paris 12, Facult~ de M~decine, Cr~teil, France In the aim of studying dynamically the role of structural rearrangement of cytoskeleton onto cell viscoelastic mechanical properties, we simulated numerically the behaviour of a viscoelastic tensegrity structure (VTS model made of 24 tensed viscoelastic cables and 6 rigid bars) loaded by various external forces. The mechanical response to creep tests and various sinusoidal oscillatory Ioadings of the overall structure was studied as a function of (i) the overall strain amplitude, (ii) the frequency of the applied forces, and (iii) the viscoelastic properties of local elements. The results reveal the role of the various strain/amplitude-dependences and frequency-dependence of the normalized elasticity and viscosity modulus of the overall VTS model as well as the role of normalized length and normalized internal tension of elements on these structural properties. The study reveals that the mechanism behind the oscillatory behaviour of the structure is related to the contribution of spatial rearrangement of VTS elements which varies from high when elastic effects predominate (low frequencies, large amplitudes) to low when viscous effects predominate (high frequencies, low amplitudes). More precisely, the elasticity modulus increases when force-amplitude, frequency and/or internal tension increase, while it decreases when the size of the structural elements increases. By contrast, the viscosity modulus, which also increases with force-amplitude, decreases with frequency and structure-size and remains independent on internal tension. Present numerical results have been found in satisfactorily agreement with results reported in the literature for in vitro cell experiments, suggesting that the highly variable contribution of spatial rearrangement of the cytoskeleton elements, especially encountered in a transitional zone of frequency, could play a significant and predictable role in the dynamic response of adherent cells. 5077 We-Th, no. 45 (P65) The steady propagation of an air finger into a partially collapsed, fluid-filled, elastic tube A. Heap, A. Juel. School of Mathematics, University of Manchester, Manchester, UK The reopening of a partially collapsed, fluid-filled, elastic tube is investigated experimentally. The origin of this problem lies in the field of lung airway reopening. Airway closure can occur as a result of pulmonary disease and thus greater understanding of the reopening dynamics is essential in order to prevent damage during mechanical ventilation. The laboratory model consists of a 1 m long, uniformly collapsed, fluid-lined tube into which air is injected at a constant flow rate. This leads to the steady propagation of an air finger, whose velocity is characterised by the non-dimensional capillary number Ca =flU~a* (ratio of viscous to surface tension forces). Pressure measurements and video footage are combined to describe the reopening dynamics. Controlled experiments were performed for 70% and 80% tube collapse. At 70% collapse, the effect of viscosity on the reopening dynamics was investigated by using three different grades of silicone oil. A direct comparison between the experimental pressure dependence on Ca and the numerical simulations of the zero-gravity, three-dimensional airway reopening model of Hazel and Heil (2005) highlighted some significant differences. Within the experimental parameter range, gravity was found to profoundly influence the reopening mechanics in several ways. Recent experiments conducted at 80% collapse indicate the presence of multiple steady reopening states, including the propagation of one asymmetric air finger, two fingers and a low pressure pointed finger. References Hazel A.L., Heil M. (2005). Finite Reynolds number effects in steady, threedimensional airway reopening. ASME J. Biomech. Eng., in press. 5332 We-Th, no. 46 (P65) Coupled mechanics and airflow o f a human lung K.L. Hedges, P.J. Hunter, M.H. Tawhai. Bioengineering Institute, University of Auckland, Auckland, New Zealand To study the ventilation distribution within a human lung a model has been produced that couples soft tissue mechanics and a simplified airflow solution. The model takes account of the regional changes in the material properties of the lung which affect the pressures developed by the lung tissue during ventilation and determine the patency of the airways. The lung geometry was constructed using CT scanned data as far as the 9 th generation. Further airways are grown within the CT-based tissue lobes using a volume filling algorithm. Equations for large deformation elasticity are used to compute