Track 16. Reproductive Biomechanics

6550 Mo-Tu, no. 18 (P66) Reduced myocardial flow heterogeneity under exchange transfusion with liposomal hemoglobin explained by a branching tree model with effective blood viscosity and red cell distribution T. Matsumoto, K. Mano, S. Adachi, N. Hanafusa, H. Naito, M. Tanaka. Bioengineering Division, Osaka University Graduate School of Engineering Science, Toyonaka, Japan

Exchange transfusion with liposomal hemoglobin (LH) reduced regional my- ocardial flow heterogeneity with fairly preserving coronary vascular tone and cardiac function (1). However, an explanation of why the flow heterogeneity is decreased by the transfusion is still lacking. Considering the rheological effect of blood-LH exchange transfusion as the primary cause for the reduced flow heterogeneity, we proposed an arterial-to-capillary tree model. The arterial tree was constructed on the basis of the statistical morphometric data on segment lengths, diameters, and connectivities [2], where the apparent viscosity and the phase separation were described as functions of vessel diameter and hematocrit [3]. Myogenic response [4] was also incorporated into the model, allowing the vessel constriction/dilation due to a rise/fall in luminal pressure. Each terminal arteriole was connected to a capillary bed, in which the flow- dependent increase of resistance due to capillary obstruction was consid- ered [5]. Assuming flows through the network to be steady under a constant perfusion pressure, the numerical results for six statistically reconstructed trees showed that the 30% blood-LH exchange increases the flow rate by 50% according to the decrease of fluid viscosity and decreases the degree of regional flow heterogeneity (coefficient of variation) by 6%. The 50% exchange leads to a further increase in flow rate but not in flow heterogeneity.

References [1] Matsumoto et al. Am J Physiol. 2005; 288: H1909-14. [2] Kassab et al. Am J Physiol. 1993; 265: H350-65. [3] Pries and Secomb. Am J Physiol. 2005; 289: H2657-64. [4] Cornelissen et al. Am J Physiol. 2000; 278: H1490-9. [5] Hudetz. Microvasc Res. 1993; 45: 1-10.

4058 Mo-Tu, no. 19 (P66) Multiscale combination of microcontinual and microfluidic biorheological studies of blood with suspended microspheres E.'~ Taran, '~V. Pridatchenko, V.A. Gryaznova. Faculty of Mechanics and Mathematics, Kyiv Taras Shevchenko National University, Kyiv, Ukraine

The analytical expression for the effective viscosity of a dilute suspension in blood of rigid microspheres of the same size possessing zero buoyancy is obtained. Suspensions in blood can arise on addition of particles of contrast agents for the purposes of X-ray visualization of blood vessels, on addition of particles of medical substances with the aim of delivery of drugs to affected organs and so on. We assume that the diameter of the suspended spheres, on the one hand, is significantly greater than the characteristic size of blood erythrocytes, but, on the other hand, is much smaller than the characteristic size of the suspension macroflow region. Due to the such correlation of the scales, we combine the microcontinual description of blood [1,2] by the Cowin polar fluid [3] and Einsteinian microfluidic study of the dilute suspension of beads in the Cowin polar fluid carried out in [4] in the scale of suspended particles. The evaluation in [2] of parameters of the Cowin polar fluid as function of hematocrit value of blood allows us to use the obtained here analytical expression for the effective viscosity of the considered suspension in order to find the numerical values of its characteristic viscosity. The obtained numerical values show that the account of the polar properties of blood as a carrier fluid of the suspension leads to the increase of characteristic viscosity of the suspension in comparison with the dilute suspension with the Newtonian model of blood. In particular, the characteristic viscosity is increased in this case from the well-known Einsteinian value 2.5 [5] to 3.2 for the dilute suspension of beads of 70 microns in diameter in blood with the hematocrit value 40%.

References [1] Ariman T., Turk M.A. and Sylvester N.D.J. Appl. Mech., Trans. ASME, 1974;

41(1): pp.1-7. [2] Chaturani P., Biswas D. Rheol. Acta 1984; 23(4): pp.435-445. [3] Cowin S.C. Phys. Fluids 1968; 11(9): pp.1919-1927. [4] Erdogan M.E., Kadioglu N. Rheol. Acta 1971; 10: pp.378-381. [5] Einstein A. Ann. Physik 1906; 19: pp.289-306.

5263 Mo-Tu, no. 20 (P66) Association and dissociation rates of adhesion for red blood cells in the presence of large polymers

B. Neu 1 , H.J. Meiselman 2. 1Division of Bioengineering, Nanyang Technological University, Singapore, 2Department of Physiology and Biophysics, University of Southern California, Los Angeles, USA

Cell-cell interactions are governed by interplay of various cell-receptor- mediated interactions and non-specific forces, with non-specific forces (e.g.,

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electrostatic repulsion) often responsible for allowing or preventing cells ap- proaching sufficiently to establish adhesion via lock and key forces. One non- specific force that has only found little attention in this area is macromolecular depletion interaction. Polymer depletion occurs at cell surfaces if adsorption energy is low, and if depletion zones of adjacent surfaces overlap fluid moves away from the intercellular gap and cell-cell attractive forces develop. The present study was designed to examine the impact of depletion forces on cell adhesion. Human red blood cells (RBC) were allowed to settle onto albumin-coated glass in polymer-free buffer and in solutions of 10 to 500 kDa dextran. Subsequently RBC adhesion and dissociation were investigated via interference reflection microscopy and a parallel plate flow system. Our re- sults indicate decreasing cell-substrate separation and significantly faster cell- substrate binding (increase of the on-rate) in the presence of higher molecular weight dextrans (>40 kDa). The off rate constants, which were calculated based on the lifetimes of the adherent cells under flow, revealed that the presence of large polymers during the settling of the cells lead to a decrease of the off rate constant of up to two orders of magnitude. In conclusion adhesion of RBC is significantly faster and stronger in the presence of these large polymers due to depletion interaction. These results demonstrate the importance of depletion forces for RBC-surface interactions. While these results originate in a "model" system, we believe they are relevant to a wide variety of cell-cell and cell- surface interactions (e.g., RBC or WBC vs. endothelial cells, endocytosis).

Track 16

Reproductive Biomechanics

7810 Mo-Tu, no. 1 (P67) Finite element studies of the deformation of the pelvic floor J.A.C. Martins 1 , M.P.M. Pato 2, E.B. Pires 1 , R.M.N. Jorge 3, M. Parente 3, T. Mascarenhas 4. I I.S.T., 21.S.E.L., Lisbon, Portugal, 3EE.U.P, 3EM.U.P, Oporto, Portugal

The present paper describes research involving numerical simulations of women's pelvic floor, undertaken in the engineering schools of Lisbon and Oporto, in collaboration with the medical school of Oporto. These studies are motivated by the pelvic floor dysfunctions that lead namely to urinary incontinence and pelvic organ prolapse. The ultimate goals of this research are: (i) to contribute to clarity the primary mechanism behind such disorders: neuropathy or damage of connective tissues and muscles of the pelvic floor; (ii) to provide tools to simulate the pelvic floor function and the effects of its dysfunctions; (iii) to contribute to planning and performing correcting surgeries in a more controlled and reliable way. The finite element meshes of the levator ani used here are based in the geo- metric dataset published by Janda et al. (2003): triangular thin shell elements or special brick elements that behave well in the thin-structure limit are used. Muscle and soft tissues are generically assumed as (quasi-)incompressible hyperelastic materials. Skeletal muscles are transversely isotropic with a single fibre direction assumed to be embedded in an isotropic matrix. The fibres considered in this work may be: (i) purely passive, (ii) active with a (variable) prescribed activation level, or (iii) active with input of neuronal excitation and consideration of the muscle activation process. These different assumptions may be adequate to simulate passive deformations of the pelvic muscles and tissues (namely, under the extreme loading conditions of childbirth), slow activation processes (quasi-static contractions), or faster contractions occurring in time intervals of the same order as those of muscle activation and deactivation (to prevent urinary incontinence in coughing or sneezing). We present numerical results for the passive deformation of the levator ani muscle under constant pressure or under neural excitation and consequent active contraction. In order to estimate the deformation field induced by a vaginal childbirth, a vaginal delivery is simulated. For this purpose, the pelvic floor is modelled using hexahedral elements and the foetus is modelled as a set of rigid bodies.

6419 Mo-Tu, no. 2 (P67) About a medical device for non-invasive reversible vasectomy C. Tanase, C. Gachon, P. Delassus. Department of Mechanical & Industrial Engineering, Galway Mayo Institute of Technology, Galway, Ireland

The paper presents a possible non-invasive and reversible vasectomy pro- cedure based on a new medical device. The existing standard procedures as well as their main disadvantages are mentioned and shortly described by the authors. The current vasectomy techniques aim to remove a small section of each vas deferens and to seal off the ends, blocking the passage of spermatozoa from epididymis. Usually, they are fast, taking between 10 and 30 minutes and most patients go home after surgery. However, the