Ivan V. Fedosov

Use of dynamic speckle field space-time correlation function estimates for the direction and velocity determination of blood flow

A method of flow direction and velocity determination using statistical properties of dynamic speckles is proposed. Two point detection of scattered light intensity fluctuations allows for slow flows velocity measuring and flow direction determination without incident beam frequency shifting and with using one focused incident beam. The space-time correlation functions estimated for two position of the incident beam waist allows for the flow space localization and the absolute flow velocity measuring. The described method has the principal advantages for the bioflow investigations in comparison of the traditional laser Doppler velocimetry.

In Vitro and in Vivo Visualization and Trapping of Fluorescent Magnetic Microcapsules in a Bloodstream

Remote navigation and targeted delivery of biologically active compounds is one of the current challenges in the development of drug delivery systems. Modern methods of micro- and nanofabrication give us new opportunities to produce particles and capsules bearing cargo to deploy and possess magnetic properties to be externally navigated. In this work we explore multilayer composite magnetic microcapsules as targeted delivery systems in vitro and in vivo studies under natural conditions of living organism. Herein, we demonstrate magnetic addressing of fluorescent composite microcapsules with embedded magnetite nanoparticles in blood flow environment. First, the visualization and capture of the capsules at the defined blood flow by the magnetic field are shown in vitro in an artificial glass capillary employing a wide-field fluorescence microscope. Afterward, the capsules are visualized and successfully trapped in vivo into externally exposed rat mesentery microvessels. Histological analysis shows that capsules infiltrate small mesenteric vessels whereas large vessels preserve the blood microcirculation. The effect of the magnetic field on capsule preferential localization in bifurcation areas of vasculature, including capsule retention at the site once external magnet is switched off is discussed. The research outcome demonstrates that microcapsules can be effectively addressed in a blood flow, which makes them a promising delivery system with remote navigation by the magnetic field.

Double-wavelength laser scanning microphotometer (DWLSM) for in-vitro hair shaft and surrounding tissue imaging

The double-wavelength laser scanning microphotometer (DWLSM) with high spatial resolution had been developed for in vitro measuring of hair shaft and follicle absorbance. The instrument allows for determining the absorbance distribution across and along hair shaft and follicle. The instrument is based on standard universal binocular microscope. The construction of the instrument and the data processing reduces the influence of the light scattering on the hair and tissue samples.

The Space-Time Correlation of the Intensity of a Speckle Field Formed as a Result of Scattering of Focused Coherent Radiation by a Capillary Liquid Flow Containing Scattering Particles

The properties of a dynamic speckle field formed as a result of scattering of a focused laser beam by a flow of a scattering liquid in a capillary, which are the most important from the viewpoint of practical application, were studied experimentally. The dependences of the parameters of the mutual correlation function of the dynamic speckle-field intensities, which are measured at spatially separated points, on the flow velocity and the geometry of the experiment have been established. A new method for measuring the mean absolute velocity in absolute units and direction of a biological liquid flow in microcapillaries on the basis of the results obtained is proposed.

The Stress and Vascular Catastrophes in Newborn Rats: Mechanisms Preceding and Accompanying the Brain Hemorrhages

In this study, we analyzed the time-depended scenario of stress response cascade preceding and accompanying brain hemorrhages in newborn rats using an interdisciplinary approach based on: a morphological analysis of brain tissues, coherent-domain optical technologies for visualization of the cerebral blood flow, monitoring of the cerebral oxygenation and the deformability of red blood cells (RBCs). Using a model of stress-induced brain hemorrhages (sound stress, 120 dB, 370 Hz), we studied changes in neonatal brain 2, 4, 6, 8 h after stress (the pre-hemorrhage, latent period) and 24 h after stress (the post-hemorrhage period). We found that latent period of brain hemorrhages is accompanied by gradual pathological changes in systemic, metabolic, and cellular levels of stress. The incidence of brain hemorrhages is characterized by a progression of these changes and the irreversible cell death in the brain areas involved in higher mental functions. These processes are realized via a time-depended reduction of cerebral venous blood flow and oxygenation that was accompanied by an increase in RBCs deformability. The significant depletion of the molecular layer of the prefrontal cortex and the pyramidal neurons, which are crucial for associative learning and attention, is developed as a consequence of homeostasis imbalance. Thus, stress-induced processes preceding and accompanying brain hemorrhages in neonatal period contribute to serious injuries of the brain blood circulation, cerebral metabolic activity and structural elements of cognitive function. These results are an informative platform for further studies of mechanisms underlying stress-induced brain hemorrhages during the first days of life that will improve the future generations health.

Measurements of the diffusion coefficient of nanoparticles by selective plane illumination microscopy

A laser-based selective plane illumination microscope is developed for the visualization of polystyrene nanospheres about 100 nm in diameter in water at a distance more than 600 μm from microcell walls. The contrast and brightness of particle images are high enough to record them by a video camera with a frame rate of up to 60 frames per second without using an image intensifier. The diffusion coefficients of monodisperse polystyrene nanospheres obtained using this microscope and the image processing software developed by the authors are presented. The measured diffusion coefficients provide the possibility to determine nanosphere diameters with a relative error not exceeding 5%.

Laser speckle flow velocity sensor for functional biomicroscopy

Laser speckle based direction sensitive flow velocity sensor has been developed for use with transmission microscope for in vivo bioflow monitoring. The instrument allows for measurements of blood and lymph flow parameters in micro vessels simultaneously with biomicroscopic measurements. The performance of the instrument was tested using the model of lymph micro vessel and was illustrated by the results of in vivo experiments on micro vessels of rat mesentery.

In-vivo lymph dynamic monitoring using speckle-correlation technique and light microscopy

In this work we described the new modification of experimental setup designed on the basis of transmission microscopy and high-resolution speckle-correlation technique. This combined technique provides the simultaneous speckle and video registration of lymph dynamics that allows one to calibrate the speckle-correlation velocity sensor and to determine an absolute flow velocity and its direction. As a result many parameters of lymph dynamic were measured quickly, conveniently and simultaneously and a new data about the lymph flow velocity and other functions of microcirculation were received. The results of the experimental study of lymph microcirculation in small intestine mesentery of rat in vivo are presented.

Micro-PIV quantification of capillary blood flow redistribution caused by laser-assisted vascular occlusion

We propose μPIV-based technique for quantitative assessment of blood flow redistribution in microcirculatory networks. Our approach is based on per-segment averaging of measured quantities so we can avoid most of problems that are typical for point-wise measurements. The key point of our technique is the digital processing algorithms of recorded data that include: capillary network axial line construction; interrogation regions centering; blood flow velocity local estimate using PIV approach; blood flow velocity calculation by means of averaging over entire vessel segment; the calculation of blood volume flow rate map. We illustrate the application of developed technique with in vivo measurements and blood flow velocity map reconstruction for chorioallantoic membrane (CAM) of chicken embryo, in which the local vascular occlusion was produced using continuous wave laser light irradiation..

In-vivo study of blood flow in capillaries using μPIV method

A digital optical system for intravital capillaroscopy has been developed. It implements the particle image velocimetry (PIV) based approach for measurements of red blood cells velocity in individual capillary of human nailfold. We propose to use a digital real time stabilization technique for compensation of impact of involuntary movements of a finger on results of measurements. Image stabilization algorithm is based on correlation of feature tracking. The efficiency of designed image stabilization algorithm was experimentally demonstrated.