Session H29: Biofluids: Cellular IV: Disease and Microorganisms

Imaging Morphological Changes in Live-cells at various time-scales using Heterodyne Mach-Zehnder Interferometer

Measurement of the dynamic behavior of the cell will provide new insights about the state of the live cells, since this response depends upon its structure and functional state. Studies have shown that all mammalian cells exhibit continuous regional motion and shape changes. This is controlled by the dynamic cytoskeleton of the cell. Existing measurement techniques are either limited to point observation or do not have required speed and accuracy. The optical arrangement consists of a Mach-Zehnder interferometer integrated to a microscope. Heterodyning is achieved using a pair of AOMs. Temporal phase shifting technique is used to extract the continuously varying phase information, which is caused by the changes in cell. Due to dynamic phase change, the continuous wave signal reaching the detector is a frequency modulated signal. To extract dynamic phase, at first the instantaneous frequency of the phase modulated signal is determined, which is then integrated with respect to time to obtain time-varying phase. Results obtained for in vitro live 3T3 Fibroblast cells and REH Leukocyte cell lines are presented. Phase imaging of live leukemic cells, can be used for studying morphological differences between various sub-types of the cancerous cells.   

How malaria merozoites reduce the deformability of infected RBC

This talk presents a three-dimensional particle-based model for the red blood cell (RBC), and uses it to explore the changes in the deformability of RBC due to presence of malaria parasite. The cell membrane is represented by a set of discrete particles connected by nonlinear springs that represent shear and bending elasticity. The cytoplasm and the external liquid are modeled as homogeneous Newtonian fluids, and discretized by particles as in standard smoothed-particle-hydrodynamics models. The merozoite is modeled as an aggregate of particles constrained to rigid-body motion. The fluid flow and membrane deformation are computed, via the particle motion, by a two-step explicit scheme, with model parameters determined from experiments. The stretching of healthy and infected RBC by optical tweezers has been simulated to investigate the contribution of rigid merozoites to the decrease in deformability.   

Wetting dynamics of living drops

Tissue spreading is a fundamental process in embryonic development, wound healing, and cancer invasion. We study the spreading dynamics of cell aggregates on solid substrates by means of an analogy with the wetting of a viscoelastic drop. At long times, a precursor film of cells spreads around the aggregate with two possible states: either a liquid state (cohesive migration) or a 2D gas state (where cells escape individually) depending on the cell-cell adhesion. These results provide insight into the progression of a non-invasive tumor into a metastatic malignant carcinoma.   

Gold nanoparticle incorporation in the cancer cells : imaging and treatment

Surface modified gold nanoparticles ($\sim$ 20 nm) are selectively incorporated in the various cancer cells. Depending on the attached molecules on the gold nanoparticle surface, incorporation efficiency of the gold nanoparticles in the cancer cells are differentiated. Two-photon fluorescence microscopy, energy dispersive X-ray spectroscopy (EDS) and second ion mass spectroscopy (SIMS) are utilized to quantify the gold nanoparticles incorporated in the cancer cells. Static images of the cancer cell are obtained by scanning electron microscopy (SEM) and zone-plate X-ray nanoscopy. On the other hand, dynamic flow images are captured by dynamic X-ray imaging. To enhance the selective incorporation into the cancer cells, specially designed aptamer is introduced on the gold nanoparticles, which changes the mechanisms of gold nanoparticle incorporation through the cancer cell membrane. Anti-cancer drugs are also incorporated, by which sustained drug delivery mechanisms are investigated. This study would contribute to the basic understanding on the nanoparticle- mediated disease treatment and advanced imaging technology.   

Effect of Magnetic Field on Ion Transport in bacterial cells

We calculate the fluid parameters as a function of the constant static magnetic field. The ion transport is affected by the strength and the direction of the magnetic field. This effect can indicate unusual behavior of micro and nano systems. A possible explanation of the abnormal behavior is, therefore, investigated using quantum electrodynamics of many body systems. We have demonstrated the effect of magnetic field on fluid parameters through the transport of ions in the bacterial cells. We could experimentally observe an impact of this effect on the bacterial growth. However, it is still difficult to precisely estimate or compute this effect theoretically.   

Hydrodynamic Contributions to Amoeboid Cell Motility

Understanding the methods by which cells move is a fundamental problem in modern biology. Recent evidence has shown that the fluid dynamics of cytoplasm can play a vital role in cellular motility. The slime mold Physarum polycephalum provides an excellent model organism for the study of amoeboid motion. In this research, we use both analytic and computational models to investigate intracellular fluid flow in a simple model of Physarum. In both models, of we are specifically interested in stresses generated by cytoplasmic flow which act in the direction of cellular motility. In our numerical model, the Immersed Boundary Method is used to account for such stresses. We investigate the relationship between contraction waves, ?ow waves and locomotive forces, and attempt characterize conditions necessary to generate directed motion.   

Intrinsic viscosity of actively swimming microalgae suspensions

Suspensions of actively swimming microorganisms exhibit an effective viscosity which may depend on volume fraction, cell shape, and the nature of locomotion (e.g. ``pushers'' vs. ``pullers''). Although several dilute-regime theories have been offered for active suspensions, no experimental study to our knowledge has been able to resolve the dilute-regime intrinsic viscosity of actively swimming microorganism suspensions. Here we use a cone-and-plate rheometer to experimentally measure the dynamic shear viscosity for motile and non-motile suspensions of unicellular green algae (Dunaliella primolecta, a biflagellated ``puller''). The low viscosity biological samples require careful experimental protocols to avoid settling and flow-induced migration, and to minimize precision error. With these protocols in place we can distinguish the intrinsic viscosity which we show is higher for the motile ``puller'' swimmers compared to the immobilized counterparts. This observation is consistent with recently proposed dilute-regime theories which predict that ``pullers'' should have a higher viscosity than non-motile suspensions.   

Hydrodynamics of cell--cell mechanical signaling

Mechanotactic cell motility, i.e. directed motion mediated by a mechanical stress at the cell's surface, has recently been shown to be a key player in the initial aggregation of crawling cells such as leukocytes and amoebae. The effects of mechanotactic signaling in the early aggregation of amoeboid cells has been investigated using a general mathematical model based upon known biological evidence. We elucidate the hydrodynamic fundamentals of the direct guiding of a cell through mechanotaxis in the case where one cell transmits a mechanotactic signal through the fluid flow by changing its shape. It is found that any mechanosensing cells placed in the stimulus field of mechanical stress are able to determine the signal transmission direction with a certain angular dispersion which does not preclude the aggregation from happening. The ubiquitous presence of noise is accounted for by the model.   

Micro PIV Measurements of the Internal Flow of an \textit{Amoeba proteus}

We report about micro PIV measurements of the internal flow in the protoplasm of an amoeba. The velocity data shall give information about the mechanism of the change of amoeba's contour during its locomotion in water. The experimental data is used for an analytical modeling of the locomotion mechanism with the help of a variable contour and finally for the development of locomotion principles for micro robots. The experimental set-up consists of a microscope and a CCD camera with 12 frames per second and image analysis software. The illumination of the amoeba was done by the built-in microscope halogen lamp. We use the phase contrast configuration to capture images of the amoeba moving in water. We applied an electrical field to the water channel in order to control the movement of the amoeba in one direction. During this motion we measured time dependent velocity vector fields of the protoplasm flow, estimated velocity profiles and analyzed time series of the maximum velocity. The velocity vector plots are calculated from the images by using cross correlation and naturally occurring particles in the protoplasm. Beside the analyses of the internal flow we recorded the motion of the center of gravity and the variation of the sectional area.   

Numerical study on the dynamics and oxygen transport of a healthy red blood cell and a malaria-infected red blood cell

In the present work, a red blood cell (RBC) and a malaria-infected red blood cell (IRBC) moving along a capillary are simulated with including their permeable properties of the membranes by using a numerical technique based on the two-dimensional immersed interface method. The adhesiveness of the IRBC membrane is modeled by means of a potential function. Then, the model is employed to simulate the motion of a biconcave RBC in the absence of membrane stickiness and a more rigid and circular IRBC in the presence of membrane stickiness. The results show that the RBC gradually moves away from the capillary wall while the IRBC rolls on the capillary wall due to its stickiness. This rolling behavior of the IRBC agrees well with experimental findings. It is found that the resistance on the plasma flow given by the IRBC is larger than the corresponding resistance given by the RBC revealing that macrovascular blockage could happen due to malaria infection. Furthermore, oxygen transport in capillaries and oxygen absorption by nearby muscles are investigated in the presence of a RBC and an IRBC.