A mathematical model for cell-induced gel contraction incorporating osmotic effects

Biological tissues are composed of cells surrounded by the extracellular matrix (ECM). The ECM can be thought of as a fibrous polymer network, acting as a natural scaffolding to provide mechanical support to the cells. Reciprocal mechanical and chemical interactions between the cells and the ECM are crucial in regulating the development of tissues and maintaining their functionality. Hence, to maintain in vivo-like behaviour when cells are cultured in vitro, they are often seeded in a gel, which aims to mimic the ECM. In this paper, we present a mathematical model that incorporate cell-gel interactions together with osmotic pressure to study the mechanical behaviour of biological gels. In particular, we consider an experiment where cells are seeded within a gel, which gradually compacts due to forces exerted on it by the cells. Adopting a one-dimensional Cartesian geometry for simplicity, we use a combination of analytical techniques and numerical simulations to investigate how cell traction forces interact with osmotic effects (which can lead to either gel swelling or contraction depending on the gel's composition). Our results show that a number of qualitatively different behaviours are possible, depending on the composition of the gel (i.e. the chemical potentials) and the strength of the cell traction forces. We observe an unusual case where the gel oscillates between swelling and contraction. We also consider on how physical parameters like drag and viscosity affect the manner in which the gel evolves.

Heat Transport Phenomena for the Darcy–Forchheimer Flow of Casson Fluid over Stretching Sheets with Electro-Osmosis Forces and Newtonian Heating

In this study, an investigation has been carried out to analyze the impact of electro-osmotic effects on the Darcy–Forchheimer flow of Casson nanofluid past a stretching sheet. The energy equation was modelled with the inclusion of electro-osmotic effects with viscous and Joule dissipations. The governing system of partial differential equations were transformed by using the suitable similarity transformations to a system of ordinary differential equations and then numerically solved by using the Runge–Kutta–Fehlberg method with a shooting scheme. The effects of various parameters of interest on dimensionless velocity and temperature distributions, as well as skin friction and heat transfer coefficient, have been adequately delineated via graphs and tables. A comparison with previous published results was performed, and good agreement was found. The results suggested that the electric and Forchheimer parameters have the tendency to enhance the fluid velocity as well as momentum boundary layer thickness. Enhancements in temperature distribution were observed for growing values of Eckert number. It was also observed that higher values of electric field parameter diminished the wall shear stress and local Nusselt number.

Modelling the Effect of Salt and PEG on Water Uptake in Wheat Seeds

Water uptake is a seminal process in seed germination. Salt and polyethylene glycol (PEG) are known to retard seed germination rates and percentages, which is often attributed to osmotic effects. Here, we quantified water uptake in wheat seeds killed with a hot needle, finding evidence of three distinct water uptake pools. The fast pool was unaffected by salt, and likely represents cell walls and other apoplastic material. Water uptake into the medium and slow pools was slowed by salt addition, with the medium pool thought to be cellular, while the slow pool is presumably related to endosperm hydration. Salt caused a minor decrease in the water uptake rates and maximum seed water content, while PEG strongly suppressed both parameters. Seeds transferred between water and salt solutions followed the water uptake trajectories of the solution into which they were transferred. Seeds transferred from PEG to water achieved final seed water contents similar to water control seeds, while seeds transferred from water to PEG achieved significantly higher final water contents than PEG controls. This work confirms that salt and PEG have distinct effects on water uptake by wheat seeds.

Salt stress slows down dynamic photosynthesis mainly through osmotic effects on dynamic stomatal behavior

Salt stress affects stomatal behavior and photosynthesis, by a combination of osmotic and ionic components, but it is unknown how these components affect photosynthesis dynamics under fluctuating light. Tomato (Solanum lycopersicum) plants were grown using a reference nutrient solution (Control, EC: 2.3 dS m-1), the reference containing extra macronutrients (only osmotic effect; EC: 12.6 dS m-1), or the reference containing an additional 100 mM NaCl (osmotic and ionic effects; EC: 12.8 dS m-1). Steady-state and dynamic photosynthesis along with leaf biochemistry were characterized throughout leaf development. Osmotic effects resulted in increased leaf chlorophyll content per unit leaf area, induced stomatal closure along with rapid stomatal responses to changes in light intensity, and limited dynamic but not steady-state photosynthesis. Ionic effects were barely observed in plant growth and dynamic photosynthesis, but led to a reduction in leaf chlorophyll content and photosynthetic capacity in old leaves. Steady-state and dynamic photosynthesis traits decreased with leaf age, due to increases in stomatal and non-stomatal limitations. With increasing leaf age, rates of light-triggered stomatal movement decreased across treatments, which is more strongly for stomatal opening rather than closure. We conclude that osmotic effect strongly impacts dynamic stomatal and photosynthetic behavior under salt stress.

Modeling and Simulations of Buongiorno’s Model for Nanofluid in a Microchannel with Electro-Osmotic Effects and an Exothermal Chemical Reaction

The article presents a mathematical model for the magnetized nanofluid flow and heat transfer with an exothermic chemical reaction controlled by Arrhenius kinetics. Buongiorno’s model with passive boundary condition is employed to formulate the governing equation for nanoparticles concentration. The momentum equation with slip boundary conditions is modelled with the inclusion of electroosmotic effects which remain inattentive in the study of microchannel flows with electric double layer (EDL) effects. Conclusions are based on graphical and numerical results for the dimensionless numbers representing the features of heat transfer and fluid flow. Frank-Kamenetskii parameter resulting from the chemical reaction showed significant effects on the optimization of heat transfer, leading to increased heat exchangers’ effectiveness. The Hartmann number and slip parameter significantly affect skin friction, demonstrating the notable effects of electroosmotic flow and the exothermic chemical reaction on heat transfer in microchannels. This analysis contributes to prognosticating the convective heat transfer of nanofluids on a micro-scale for accomplishing successful thermal designs.

Molecular Imprinted Based Quartz Crystal Microbalance Sensors for Bacteria and Spores

A molecular imprinting strategy was combined with mass-sensitive transducers to generate robust and reliable biomimetic sensor systems for the detection of bioparticles. The patterning of polymers with bioanalytes enabled us to detect Escherichia coli (E. coli) bacteria with quartz crystal microbalance (QCM). The QCM sensor results were compared with direct Atomic Force Microscopy (AFM) measurements—bacteria cells adhering to the sensor coatings were counted. The recognition sites generated by Bacillus subtilis (B. subtilis) spores could successfully and reversibly recognize the template analyte and ensured rapid sensing. Cross sensitive measurements clearly showed the advantage of the molecular imprinting strategy, by which spores of Bacillus species (subtilis and thuringiensis) could easily be differentiated and selectively detected. The growth of B. subtilis from its spores was observed at 42 °C in appropriate nutrient solution of glucose and ammonium sulfate over a period of 15 h. Moreover, the growth of B. subtilis bacteria from its respective spores was studied by increasing the glucose concentration until saturation effect of the sensor. The polymeric sensor coatings were patterned to fix the B. subtilis in order to investigate osmotic effects according to a frequency response of 400 Hz by altering the ionic strength of 0.1 M.

P0105THE ROLE OF PROTEOGLYCANS IN GLOMERULAR PHYSIOLOGY AND PATHOPHYSIOLOGY

Background and Aims Damage to the filtration barrier in the kidney may result in proteinuria, a hallmark of kidney disease. The glomerular filtration barrier consist of 3 layers: the endothelial cells with their endothelial surface layer (ESL), the glomerular basement membrane and podocytes. The ESL is rich in negatively charged molecules, such as proteoglycans (PGs). The negatively charged molecules restrain the flow of charged molecules, as albumin, over the barrier. Loss of ESL has been shown to lead to proteinuria without damage to the other structures of the filtration barrier. In order to gain further knowledge about the function and composition of the glomerular ESL we eluted the glomerular ESL from rats and analyzed the PG content as well as the effect of loss of the ESL on the function of the glomerular filtration. Method The basic principles of ion exchange chromatography were applied in this study. In order to elute highly negatively charged proteoglycans of the ESL, we used 1 M NaCl solution (HS). 1 M mannitol (HO) was included to evaluate osmotic effects. A control fraction was eluted with normal saline solution (0,15 M NaCl) (NS). Solutions were introduced intraarterially to rat kidneys under anesthesia in vivo. Venous effluent was collected and analyzed using proteomics and mass spectrometry. Fractional clearance of albumin was measured as well as GFR. Electron microscopy (EM) was used to investigate changes to the filtration barrier and the thickness of the glomerular ESL. Immunohistochemistry was used to confirm the presence of identified PGs in human tissue. Results We identified 15 PGs and PG candidates in ESL as well as hyaluronan. The most abundant PGs were lumican, glypican-1, syndecan-4, perlecan, podocan, decorin, serglycan, agrin and biglycan. In general, PGs were found in in all HS, NS and HO fractions, but in higher yields in the HS samples. EM demonstrated that the glomerular ESL thickness was significantly reduced in HS perfused rats – 28% (p<0.05) compared to rats perfused with NS. Rats perfused with HS also had increased fractional clearance of albumin compared to NS and HO, and a large reduction of GFR 10 minutes after perfusion. Conclusion The ESL itself represents a dynamic structure with significant molecular turnover and is formed by PGs, glycosaminoglycans, glycoproteins and soluble proteins. In our study, we identified several PGs in the glomerular endothelial ESL. We show that loss of ESL leads to increased albumin fractional clearance and reduction in GFR after perfusion, strongly suggesting that the ESL is important for preventing proteinuria. Characterizing the composition of the glomerular ESL is therefore of great importance, and can give new possible targets for treatment of proteinuria.