In vitro investigations of red blood cell phase separation in a complex microchannel network.

Microvascular networks feature a complex topology with multiple bifurcating vessels. Nonuniform partitioning (phase separation) of red blood cells (RBCs) occurs at diverging bifurcations, leading to a heterogeneous RBC distribution that ultimately affects the oxygen delivery to living tissues. Our understanding of the mechanisms governing RBC heterogeneity is still limited, especially in large networks where the RBC dynamics can be nonintuitive. In this study, our quantitative data for phase separation were obtained in a complex in vitro network with symmetric bifurcations and 176 microchannels. Our experiments showed that the hematocrit is heterogeneously distributed and confirmed the classical result that the branch with a higher blood fraction received an even higher RBC fraction (classical partitioning). An inversion of this classical phase separation (reverse partitioning) was observed in the case of a skewed hematocrit profile in the parent vessels of bifurcations. In agreement with a recent computational study [P. Balogh and P. Bagchi, Phys. Fluids 30,051902 (2018)], a correlation between the RBC reverse partitioning and the skewness of the hematocrit profile due to sequential converging and diverging bifurcations was reported. A flow threshold below which no RBCs enter a branch was identified. These results highlight the importance of considering the RBC flow history and the local RBC distribution to correctly describe the RBC phase separation in complex networks.

A novel single compartment in vitro model for electrophysiological research using the perfluorocarbon FC-770.

Electrophysiological studies of whole organ systems in vitro often require measurement of nerve activity and/or stimulation of the organ via the associated nerves. Currently two-compartment setups are used for such studies. These setups are complicated and require two fluids in two separate compartments and stretching the nerve across one chamber to the other, which may damage the nerves. We aimed at developing a simple single compartment setup by testing the electrophysiological properties of FC-770 (a perfluorocarbon) for in vitro recording of bladder afferent nerve activity and electrical stimulation of the bladder. Perflurocarbons are especially suitable for such a setup because of their high oxygen carrying capacity and insulating properties. In male Wistar rats, afferent nerve activity was recorded from postganglionic branches of the pelvic nerve in vitro, in situ and in vivo. The bladder was stimulated electrically via the efferent nerves. Organ viability was monitored by recording spontaneous contractions of the bladder. Additionally, histological examinations were done to test the effect of FC-770 on the bladder tissue. Afferent nerve activity was successfully recorded in a total of 11 rats. The bladders were stimulated electrically and high amplitude contractions were evoked. Histological examinations and monitoring of spontaneous contractions showed that FC-770 maintained organ viability and did not cause damage to the tissue. We have shown that FC-770 enables a simple, one compartment in vitro alternative for the generally used two compartment setups for whole organ electrophysiological studies.

Can an algorithm predict a voiding contraction in unconscious rats?

Urinary incontinence (UI) is a very common and serious disorder which can be classified in stress and urge incontinence, the latter mainly caused by an overactive bladder (OAB). A definitive treatment for OAB does not exist yet due to its complex nature. Therefore, more attention must be focused on improving the patient's quality of life. A device able to alert the patient to development of a voiding contraction would be highly desirable, enabling actions to avoid incontinence. The main hypothesis of this work is that a voiding contraction is preceded by a consistent change in the pattern of intravesical pressure (p(ves)). We developed an algorithm based on frequency analysis of p(ves) recordings of two strains of rats whose bladders were first filled with saline (S fillings) and then with acetic acid (AA fillings); the latter was used as model for OAB in rats. The algorithm was designed to provide an alarm when an increase in the range 0.2-0.6 Hz of the amplitude spectrum was detected. The accuracy of the algorithm has been tested and quantified, successful alarms were those taking place within fifty seconds before the start of voiding. Although the results are still very preliminary, due to the low number of tested animals, they seem encouraging since, in five rats, only one showed a percentage of success lower than 50%, with one rat reaching 100%. The accuracy of the algorithm is affected by the choice of the values for the controlling parameters, which have been set the same for all rats; future developments might include individual values for each rat.

A novel single compartment in vitro model: Perflurocarbons for electrophysiological studies of the rat urinary bladder.

This study presents a novel single compartment model for in vitro electrophysiological studies of the rat urinary bladder. We tested the functionality and suitability of FC-770 (a Perflurocarbon) for in vitro recording of nerve activity arising from the bladder in a single compartment setup. We have also favorably tested stimulation of the bladder via the bladder nerves in FC-770. The organ viability was monitored by recording spontaneous contractions of the bladder for a certain time. We propose the use of FC-770 as a fluid for nerve recording/stimulation in vitro as well as for maintaining organ viability, over the commonly used two compartmental methods.

An artificial model for studying fluid dynamics in the obstructed and stented ureter.

Fluid dynamics in the obstructed and stented ureter represents a non-trivial subject of investigation since, after stent placement, the urine can flow either through the stent lumen or in the extra-luminal space located between the stent wall and the ureteric inner wall. Fluid dynamic investigations can help understanding the phenomena behind stent failure (e.g. stent occlusions due to bacterial colonization and encrustations), which may cause kidney damage due to the associated high pressures generated in the renal pelvis. In this work a microfluidic-based transparent device (ureter model, UM) has been developed to simulate the fluid dynamic environment in a stented ureter. UM geometry has been designed from measurements on pig ureters. Pressure in the renal pelvis compartment has been measured against three variables: fluid viscosity (µ), volumetric flow rate (Q) and level of obstruction (OB%). The measurements allowed a quantification of the critical combination of µ, Q and OB% values which may lead to critical pressure levels in the kidney. Moreover, an example showing the possibility of applying particle image velocimetry (PIV) technology to the developed microfluidic device is provided.