Fundamentals of photoelectrocatalysis

Photoelectrocatalysis combines heterogeneous photocatalysis and electrocatalysis principles for numerous processes including the degradation of harmful compounds, the generation of H2 and O2 from water splitting, the reduction of CO2 or the photoelectrocatalytic synthesis of valuable organic molecules otherwise difficult to be synthetized with classical approaches. The recent progress of photoelectrocatalysis is heavily related to the development of materials, especially in 2D and nano materials. Highly ordered nanomaterials such as graphene, nanotubes, nanowires, etc. are gaining more attention due to their high surface area and excellent conductivity. Other challenges are the development of stable semiconductor materials able to be activated by solar radiation. In fact, the method is based on the use of a semiconductor irradiated by light energy equal or greater than its band gap energy simultaneously biased by a gradient potential. Therefore, to better understand the photoelectrocatalytic processes it is important to handle both the fundamental aspects related to photocatalysis and electrocatalysis, and the scope of this chapter is actually to fulfil this gap

Glycaemic Control Achieves Sustained Increases of Circulating Endothelial Progenitor Cells in Patients Hospitalized for Decompensated Diabetes: An Observational Study

Diabetes reduces the levels of circulating endothelial progenitor cells (EPCs), which contribute to vascular homeostasis. In turn, low EPCs levels predict progression of chronic complications. Several studies have shown that hyperglycaemia exerts detrimental effects on EPCs. Improvement in glucose control with glucose-lowering medications is associated with an increase of EPCs, but only after a long time of good glycaemic control. In the present study, we examined the effect of a rapid glycaemic amelioration on EPC levels in subjects hospitalized for decompensated diabetes

von Willebrand factor-mediated platelet adhesion in flowing blood is influenced by hematocrit.

We have studied the influence of hematocrit on the capture and rolling of platelets on von Willebrand factor (VWF) as well as the biomechanical properties of the interaction. When fluorescently-labeled platelets in whole blood (in the presence of anti-aIIbb3 MoAb LJ-CP8 to avoid platelet stable arrest) were perfused onto immobilized VWF through rectangular flow chambers, platelets formed numerous rolling attachments. The characterization is based on information obtained from a tailored-specific image analysis method applied to continuous sequences of microscopical images. Platelet movement on the surface, the duration of each arrest (lifetime), the frequency of this movement, and the distance traveled before its resumes the velocity of a non-interacting cell were measured. Our data indicated that hematocrit influenced not just the rate of capture from the flowing stream, enhancing platelet diffusivity to the wall, but also the ability to sustain interactions with the surface. Possibly due to the augmented intercellular collisions, as the hematocrit was increased from 5% to 40% the frequency of attachment increased 1.5 times. The removal rate constant was faster at high hematocrit (29.5 s-1 at 40% Hct and 21.1 s-1 at 5% Hct). Variation of hydrodynamic forces was used to sample the on-rate and bond resistance, ultimately resulting in different association and dissociation constants. The number of adhering platelets revealed a bell-shaped dependence on the wall shear rate, also affected by the hematocrit. Increasing hematocrit, platelets showed a faster saltatory movement, i.e., stayed on the surface for shorter durations, traveling longer distances. In rapid flow conditions (3000 s-1), increasing the hematocrit from 5% to 40%, the mean translational velocity increased exponentially (from 0.03 to 0.21 \ub5m/s). Our findings support the concept of transport-enhancing capability of red cells but also suggest their influence on platelet rolling on immobilized VWF before adhering firmly to form thrombi

Characterization of platelet adhesion under flow using microscopic image sequence analysis

A method for quantitative analysis of platelet deposition under flow is discussed here. The model systemis based uponperfusion of blood platelets on an adhesive subtrate immobilized over a glass coverslip acting as the lower surface of a rectangular flow chamber. the perfusion apparatus is mountedonto an inverted microscope equipped with epifluorescentillumination and intesified CCD vide camera. Characterization is based on information derived from a specific image analysis method applied to continuous sequences of microscopical images. Platelet recognition across the sequence of images is based on a time-dependent bidimensional, gausssian-like pdf. Once a platelet is located, the variation of its position and shaped as a function of time (i.e., the platelet history) can be determined. Analyzing the history we can establish if the platelet is moving on the surface, the frequency of this movement and the distance traveled before its resumes the velocity of a non-interacting cell. Therefore, we can determine how long the adhesion would last which is correlated to the resistence of the platelet-substrate bond. This algorithm enables the dynamic quantification of trajectories, as well as residence times, arrest and release frequencies for a high number of platelets at the same time. Statstically significant conclusions on platelet-surface interaction can be obtained. An image analysis tool of this kind candramatically help the investigation and characterization of the thrombogenic properties of artificial surfaces such as those used in artificial organs and biomedical devices

Single particle tracking across sequences of microscopical images: Application to platelet adhesion under flow

A versatile and automated image processing technique and data extraction procedure from videomicroscopic data is presented. The motivation is a detailed quantification of blood platelet adhesion from laminar flow onto a surface. The characteristics of the system under observation (type of cells, their speed of movement, and the quality of the optical image to analyze) provided the criteria for developing a new procedure enabling tracking for long image sequences. Specific features of the novel method include: automatic segmentation methodology which removes operator bias; platelet recognition across the series of images based on a probability density function (two-dimensional, gaussian-like) tailored to the physics of platelet motion on the surface; options to automatically tune the procedure parameters to explore different applications; integrated analysis of the results (platelet trajectories) to obtain relevant information, such as deposition and removal rates, displacement distributions, pause times and rolling velocities. Synthetic images, providing known reference conditions, are used to test the method. The algorithm operation is illustrated by application to images obtained by fluorescence microscopy of the interaction between platelets and von Willebrand factor-coated surfaces in parallel-plate flow chambers. Potentials and limits are discussed, together with evaluation of errors resulting from an inaccurate tracking