Osmotic Pressure Gradient Research Articles

A Mathematical Model of Interstitial Fluid Flow and Retinal Tissue Deformation in Macular Edema.

This study aims to develop a mathematical model to elucidate fluid circulation in the retina, focusing on the movement of interstitial fluid (comprising water and albumin) to understand the mechanisms underlying exudative macular edema (EME). The model integrates physiological factors such as retinal pigment epithelium (RPE) pumping, osmotic pressure gradients, and tissue deformation. It accounts for spatial variability in hydraulic conductivity (HC) across the retina and incorporates the structural role of Müller cells (MCs) in maintaining retinal stability. The model predicts that tissue deformation is maximal at the center of the fovea despite fluid exudation from blood capillaries occurring elsewhere, aligning with clinical observations. Additionally, the model suggests that spatial variability in HC across the thickness of the retina plays a protective role against fluid accumulation in the fovea. Despite inherent simplifications and uncertainties in parameter values, this study represents a step toward understanding the pathophysiology of EME. The findings provide insights into the mechanisms underlying fluid dynamics in the retina and fluid accumulation in the foveal region, showing that the specific conformation of Müller cells is likely to play a key role.

Manipulation of artificial and living small objects by light driven diffusioosmotic flow

Here we report on light-triggered generation of local flow utilizing a bio-compatible non-ionic photo-active surfactant. The mechanism is based on diffusioosmotic phenomenon, where the gradient of relative concentration with respect to different chemical species near a surface leads to an osmotic pressure gradient driving liquid flow along the surface. The application of a photo-responsive surfactant allows for easy and reversible changes in concentration gradient by positioning a light source at the desired place. Along with the so-inscribed concentration gradient one can change reversible the direction and strength of the flow even in a closed system. The phenomenology of light-driven diffusioosmotic flow (LDDO) can be used in a rather flexible way: colloids can be gathered or dispersed and bio-compatibility extends the range of colloid types also to living microorganisms such as soil bacterium Pseudomonas putida. We show that DO flow can be considered a versatile method to set hydrodynamic conditions along the sample for investigating the motility of living cells. Further advantages of employing LDDO are the flexibility of flow generation in a reversible way and with spatiotemporal control, without the need to either change the channel geometry by loading a different device, or the periphery of pumps and connectors.

Polymer colloidal motors with photodynamic-regulated propulsion

Artificial colloidal motors capable of converting various external energy into mechanical motion, have emerged as attractive photosensitizer (PS) nanocarriers with good deliverability for photodynamic therapy. However, photoactivated 3O2-to-1O2 transformation as the most crucial energy transfer of the photodynamic process itself is still challenging to convert into autonomous transport. Herein, we report on PS-loaded thiophane-containing semiconducting conjugated polymer (SCP)-based polymer colloidal motors with asymmetric geometry for photodynamic-regulated propulsion in the liquid. The asymmetrical presence of the SCP phases within the colloidal motors would lead to significant differences in the 3O2-to-1O2 transformation and 1O2 release manners between asymmetrical polymer phases, spontaneously creating asymmetrical osmotic pressure gradients across the nanoparticles for powering the self-propelled motion under photodynamic regulation. This photoactivated energy-converting behavior can be also combined with the photothermal conversion of the SCP phases to create two energy gradients exerting diffusiophoretic/thermophoretic force on the colloidal motors for achieving multimode synergistic propulsion. This unique motile feature endows the light-driven PS nanocarriers with good permeability against various physiological barriers in the tumor microenvironment for enhancing antitumor efficacy, showing great potential in phototherapy.

Lumen expansion is initially driven by apical actin polymerization followed by osmotic pressure in a human epiblast model

Post-implantation, the pluripotent epiblast in a human embryo forms a central lumen, paving the way for gastrulation. Osmotic pressure gradients are considered the drivers of lumen expansion across development, but their role in human epiblasts is unknown. Here, we study lumenogenesis in a pluripotent-stem-cell-based epiblast model using engineered hydrogels. We find that leaky junctions prevent osmotic pressure gradients in early epiblasts and, instead, forces from apical actin polymerization drive lumen expansion. Once the lumen reaches a radius of ∼12μm, tight junctions mature, and osmotic pressure gradients develop to drive further growth. Computational modeling indicates that apical actin polymerization into a stiff network mediates initial lumen expansion and predicts a transition to pressure-driven growth in larger epiblasts to avoid buckling. Human epiblasts show transcriptional signatures consistent with these mechanisms. Thus, actin polymerization drives lumen expansion in the human epiblast and may serve as a general mechanism of early lumenogenesis.

Osmosis-driven stiffening of structured hydrogels

Plant cells harness osmotic pressures to stiffen their leaves through strong turgor pressures. Key to this osmosis-driven stiffening is the confinement of liquids within semipermeable membranes that can regulate the transport of water molecules and ions. Inspired by the turgor effect in plants, we fabricate rather stiff hydrogels with inclusions and fill them with polyelectrolytes possessing a high degree of swelling. The swelling of these polyelectrolytes is spatially confined by the stiffer inert hydrogel surrounding, resulting in an up to three-fold increase in the stiffness of these structured hydrogels compared to that of the matrix with water-filled inclusions. We leverage osmotic pressure gradients to change the morphology of cm-sized hydrogel leaves by immersing their bottom parts in water, without the need for additional stimuli that consume energy or require a change in the environmental conditions. Similarly, we exploit the osmosis-driven stiffening to release a ball. We foresee these materials to open up new possibilities to actuate soft materials in a benign, energy-efficient manner.

Complexes of photosensitive surfactant and fluorescent dye for light-induced manipulation of colloids

Light-driven diffusioosmosis is a membrane-free method for manipulating colloidal ensembles at solid–liquid interfaces based on photo-sensitive molecules inducing fluid flows along solid surfaces. In this study, we present our findings on porous colloids settled at a solid wall in an aqueous solution comprising a photo-sensitive azobenzene-containing cationic surfactant and a cyanine-based dye, capable of ionically binding to each other. The surfactant acts as an activation agent for diffusioosmotic flow. When exposed to modulated light, it undergoes photo-isomerization from a hydrophobic trans-state to a more hydrophilic cis-state, creating a concentration gradient near the irradiated area of the wall. The resulting osmotic pressure gradient sets the flow in motion. Porous colloids actively participate in flow generation by readily incorporating the surfactant molecules in the trans-state and releasing them in the cis-state, creating a constant source of diffusioosmotic flow. Under UV illumination, an excess of cis-isomers near the porous colloids elicits long-range repulsive interactions, tenfold the diameter of a particle. The dye acts as a sensor for the surfactant filling or emptying the pores of the colloids. It forms a complex with the trans-isomer and diffuses into the pores, where photoisomerization to cis-state destroys the complex and causes both the dye and the surfactant to leave the pores, altering the luminescence brightness within the colloids. We demonstrated that the presence of the dye affects cis-trans isomer ratios of the surfactant at photo-stationary states, thereby influencing the process of diffusioosmosis. This process enables the manipulation of colloidal particles and remote control of the interaction potential between them, facilitating the formation of well-ordered surface aggregates.

Highly effective emulsion liquid membrane based on Triethylamine for extraction of heavy metals: Investigation of extraction, de-extraction, swelling, and osmotic pressure gradient

The aim of this work is to produce a stable W/O primary emulsion which is able to extract a wide variety of heavy metals, namely Cu2+, Zn2+, Pb2+, Ni2+, Co2+ and Hg2+. The appropriate conditions through which a better extraction was obtained are: concentration of Span 80 (4 wt%); concentration of TEA (10 wt%); internal phase (HCl 0.5 M); emulsification time (4 min); Vmemb/Vint (2.08); Vemul/Vext (0.1); pH of the external solution (4.7) and stirring speed (150 rpm). A second recycling of the emulsion resulted in a drop in extraction about 40 %. The morphological study confirmed a good dispersion of internal globules and a good stability of emulsion for up to 60 days. The extraction of metal cations showed very high extraction (> 90 %) with very fast kinetics. However, it has been shown that the type of anion to which the metal cation is bound, only affects the extraction efficiency above 100 mg/L. Results extraction of heavy metals are in good analogy with evolution of the osmotic pressure difference between the internal and external phases, leading to a significant swelling of emulsion, while de-extraction also appears to be in accord with extraction with a slightly slower rate.

Dramatic mitigation of capacity decay and volume variation in vanadium redox flow batteries through modified preparation of electrolytes

Electrolyte imbalance caused by the undesired vanadium-ions cross-over and water transport through the membrane is one of the main critical issues of vanadium redox flow batteries, leading to battery capacity loss and electrolytes volume variation. In this work, the evolution of discharged capacity and electrolyte volume variation were firstly investigated adopting commercial electrolyte for hundreds of charge-discharge cycles in vanadium redox flow batteries employing different membranes, varying thickness and equivalent weight. Subsequently, with the support of a 1D physics-based model, the origin of the main phenomena regulating capacity decay and volume variation has been identified and different modifications in the preparation of electrolytes have been proposed. Electrolytes characterized by an equal proton concentration between the two tanks at the beginning of cycling operation turned out to limit capacity decay, while increasing electrolyte proton concentration was effective also in the mitigation of volume variation. The most promising electrolyte preparation combined the effect of high proton concentration and null osmotic pressure gradient between the two tanks: compared to commercial electrolyte this preparation reduced the capacity decay from 47.7% to 20.9%, increased the coulombic efficiency from 96.2% to 98.9% and the energy one from 79.9% to 83.4%, and also implied a negligible volume variation during cycles. The effectiveness of this electrolyte preparation has been verified with different membranes, increasing the range of validity of the results, that could be thus applied in a real system regardless of the adopted membrane.

Concentration of phycocyanin and coffee extracts in aqueous solutions with osmotically-assisted membrane distillation

Osmotic membrane distillation (OMD) is a dewatering process that exploits combined temperature and osmotic pressure gradients to drive water vapor fluxes under mild operation conditions. In this study, the feasibility of OMD is evaluated for the concentration of phycocyanin and coffee extract solutions, with the goal to safeguard the quality of the extracts. Different feed solution temperatures were studied, namely, 35 °C, 45 °C, 55 °C, while keeping a concentration of 4 M CaCl2 in the extraction solution. The target concentration factor was set to 4, equivalent to a water recovery rate of 75 %. The results suggest that a temperature equal to or below 45 °C should be chosen for the concentration of phycocyanin to prevent degradation and to minimize fouling, while higher temperatures may be used for the recovery of the coffee extract. The combined gradients provided water fluxes around or above 4 L m−2h−1 with both extracts under relatively mild conditions, even at high concentration factors. Qualitative membrane fouling inspection was corroborated by estimating the fraction of productivity lost due to fouling, which was larger for higher feed temperatures and for the phycocyanin extracts, and had values between roughly 20 and 70 %. Results also suggest that the quality of the extracts was maintained, based on the measured purity and content of the target compounds in the concentrated solutions. Specifically, no trace of extraneous compounds was found, and no salt passage was observed from the extraction solution to the feed solution, suggesting that OMD has the potential to concentrate sensitive components.

Nutrient recovery from freshwater aquaculture effluent by employing seawater driven zeolite-assisted forward osmosis process

This study focused on recovering nutrients from inland freshwater aquaculture effluent which contains dilute nutrients such as ammonium (NH4+) and phosphate (PO43-) ions. Forward osmosis (FO) process with the assistance of Mg-zeolite Y was employed to recover PO43- through chemical precipitation while NH4+ recovery was achieved by regenerating the zeolite. It showed that zeolite-assisted FO process requires 56.56 ± 2.88 h to dewater 87.5% of the feed solution while standalone FO process took only 51.08 ± 2.99 h. The difference in duration was due to the supplement of Mg2+ that reduces osmotic pressure gradient. The ammonium sorption process of Mg-zeolite Y introduced Mg2+ into the feed solution and facilitated the precipitation of PO43-. Phosphate recovery from the Ca-rich solution from standalone FO process resulted in amorphous calcium phosphate (ACP) with co-precipitation of calcite and dolomite. The zeolite-assisted FO process at pH 10.5 yielded optimal results with 98.46% phosphate recovery, forming mainly amorphous magnesium phosphate (AMP). Subsequently, a two-step precipitation process was proposed to recover Mg2+ as brucite. The concentrated feed solutions from the cycles underwent the proposed two-step precipitation study, resulting in 0.507 g/L of AMP and 5.4077 g/L of brucite. An average of 88.7% NH4+ recovery with high reuse efficiency of Mg-zeolite Y using magnesium sulfate as regenerating solution could be achieved. Reusability studies showed consistent or slightly higher water flux during the dewatering process. The composition of spent regenerant was investigated, and its reuse as liquid fertilizer was feasible after dilution.

Preparation of Forward osmosis composite membrane with Chitosan/Tannic acid co-deposition interlayer and its fluoride removal performance

The treatment of fluorine-containing wastewater has very important significance for environmental protection. Forward osmosis (FO), using osmotic pressure gradient as driving force, can remove ion from aqueous solutions effectively. The key to improve the separation efficiency of FO is to prepare the membrane of excellent performance. In this work, chitosan (CS)/tannic acid (TA) interlayer was constructed by the strategy of polyphenol/polyamine liquid phase co-deposition, then three-layer FO membranes with more uniform surface and higher hydrophilicity were obtained by interfacial polymerization on the interlayer. And the effects of co-deposition time and mass ratio of CS/TA on the performance of FO treating simulated fluorine-containing wastewater were also investigated. Experimental results showed that the optimal co-deposition time was 60 min and the mass ratio of CS/TA was 0.5. The water flux of the TFC-CS/TA0.5–60 membrane (TFC means thin film composite, 0.5 is the mass ratio of CS/TA, 60 means the co-deposition time is 60 min) reached 22.3 LMH and the fluorine rejection was 99.93%, when it was applied to treat model waste water containing fluoride of 300 mg/L. In FO test on fluorine-containing wastewater from a semiconductor factory, compared with commercial Aquaporin InsideTM FO membrane, the water flux of TFC-CS/TA0.5–60 membrane was 49.3% higher than that of the commercial membrane. This study provides a new idea for the preparation of high-efficiency FO membranes and has a good prospect for the treatment of industrial fluorine-containing wastewater.

Gradient-Charged Hydrogels for Highly Efficient Solar Steam Generation and Desalination.

Solar-driven interface desalination (SDID) is a promising and sustainable technology that produces freshwater from brine. Ionic hydrogels are effective evaporators, providing enhanced interaction with water and ions due to the charged groups on hydrophilic polymer networks. In this study, we developed a hydrogel-based solar steam generator with a gradient-charged (GC) structure for desalination. The gradient-charged groups' distribution on the hydrogels creates gradients of free water and osmotic pressure, realizing rapid water supplement as well as desalination of concentrated brine. Consequently, the GC hydrogel demonstrated an exceptional water evaporation rate, achieving a value as high as 2.61 kg m-2 h-1 in pure water and 1.72 kg m-2 h-1 on treating with 20 wt % NaCl solution under one sun illumination. Following the substantial solar-driven evaporation, impurities, including salt and other pollutants, were removed, thereby ensuring the purity of the condensed water. Overall, the GC hydrogel-based evaporator is a promising solution for SDID to achieve effective and sustainable water desalination.

Transition from nanobubble-induced-blockage to enhancing water flux

Gas bubbles often form and accumulate in microfluidic devices, which is a critical obstacle in microfluidic applications. Here, we report by molecular dynamics simulations that “nanobubbles” can form and hinder water flow through the carbon nanotubes which are core components of nanofluidic devices. It is exceedingly difficult to remove the “nanobubble” trapped in the nanotube by a conventional method of hydrostatic or osmotic pressure gradient. Ratchet-like mechanics is applied to resume water flow powered by mechanical resonance. Interestingly, the water flow is even faster as compared to the pure water system without nanobubbles. Our findings provide a new means for solving pore-blocking problems in nanochannels and have potential applications in the design of high-flux nanofluidic systems.

Osmotic Pressure Gradient Effects on Water Diffusion in Porous Rock: Can They Pervert Permeability Tests?

Abstract Generation of a large network of hydraulic cracks is of key importance not only for the success of fracking of shale but also for the recent scheme of sequestration of CO2 in deep formations of basalt and peridotite, which are mafic and ultramafic rocks that combine chemically with CO2. In numerical simulation of the creation of a fracture network in porous rock, an important goal is to enhance the rock permeability. The objective of this article is to calculate the effect of osmotic pressure gradients caused by gradients of concentration of the ions of Ca, Mg, Na, etc. on the effective permeability of the rock. The basic differential equations are formulated, and their explicit solutions for appropriate initial and boundary conditions are obtained under certain plausible simplifications. The main result is explicit approximate formulas for the critical time before which no water permeation through a test specimen can be observed. Depending on various parameters, this time can be unacceptably long, which is manifested as a zero water outflow. The solution may also explain the unreasonably small permeability values reported for some shales.

Forward Osmosis for Metal Processing Effluents under Similar Osmotic Pressure Gradients.

Water recovery from aqueous effluents in the mining and metals processing industry poses a unique challenge due to the high concentration of dissolved salts typically requiring energy intensive methods of treatment. Forward osmosis (FO) is a lower energy technology which employs a draw solution to osmotically extract water through a semi-permeable membrane further concentrating any feed. Successful FO operation relies on using a draw solution of higher osmotic pressure than the feed to extract water while minimizing concentration polarization to maximize the water flux. Previous studies employing FO on industrial feed samples commonly used concentration instead of osmotic pressures for feed and draw characterization; this led to misleading conclusions on the impact of design variables on water flux performance. By employing a factorial design of experiments methodology, this study examined the independent and interactive effects on water flux by: osmotic pressure gradient, crossflow velocity, draw salt type, and membrane orientation. With a commercial FO membrane, this work tested a solvent extraction raffinate and a mine water effluent sample to demonstrate application significance. By optimizing with osmotic gradient independent variables, water flux can be improved by over 30% without increasing energy costs or compromising the 95-99% salt rejection of the membrane.

The Nature and Properties of Tonicity

We proposed that tonicity has a physical nature and three properties 1 . In this abstract, we prove this hypothesis to be true by logical reasoning. Two key terms will be used: 1) S 1 -m-S 2 (a composite osmosis system that can be deconstructed into two simple osmosis systems: S 1 -m-H 2 O and H 2 O-m-S 2 1 ; and 2) OC 0 , the initial osmotic concentration (concentration of the impermeant solute particles (impSP)) before osmosis occurs (time = 0) 2 . Results are as follows. 1) Since we defined tonicity to be a relational concept that reflects a comparison of two OC 0 in S 1 -m-S 2 1 , if OC 0 (S 1 ) = 90 mOsm/L and OC 0 (S 2 )= 30 mOsm/L, then Δ OC0 (S 1 -S 2 ) = 90 – 30 = 60 mOsm/L, which contributes to the force that drives osmosis and an osmotic pressure gradient (Δ π) results 3 . Δ OC 0 informs the tonicity (i.e., S 1 is hypertonic to S 2 ) directly and Δ π indirectly, so both can be used to express tonicity (the comparison) 4 . Either Δ OC 0 or Δ π is a form of energy, thus tonicity has a physical nature. Tonicity is often inappropriately described as a solution's ability to change a cell’s volume 5 . As shown in this work, it is Δ OC 0 (S 1 -S 2 ) that has the ability to cause a change in cell volume, not any single solution in S 1 ‐m‐S 2 . 2) The first property of tonicity is m-dependent: Facing different m, different fractions of the impSP result, so OC 0 is m-dependent 2 ; tonicity compares two OC 0 separated by a given m, thus is m-dependent too. 3) The second property is relativity (reference-solution dependency: S 2 in S 1 -m-S 2 can be replaced by S X (X = 1, 2, 3, …n), a reference solution for S 1 . In contrast, in any simple osmosis system (S-m-H 2 O) 1 , the reference solution for S is always water with 0 mOsm/L, which cannot be replaced by any solution. 4) The third property is reciprocity because the same comparison can be described as either “S 1 is hypertonic to S 2 or S 2 is hypotonic to S 1 ” or “ Δ OC 0 (S 1 -S 2 ) or Δ OC 0 (S 2 –S 1 )” etc. Hence, we conclude: Tonicity can be expressed using either Δ OC 0 or Δ π. Either stores a form of energy representing a physical nature. OC 0 (defined in a simple S-m-H 2 O) and tonicity (defined in a composite S 1 -m-S 2 ) are both m-dependent, whereas relativity and reciprocity are properties of tonicity only.

How to Study Osmosis If the Membrane Water Moves Across Is Nonideal

In our past works, we introduced two fundamental osmosis systems (a simple S-m-H 2 O and a composite S 1 -m-S 2 ) to study osmosis 1,2 , where m is a selectively permeable membrane that separates two fluid compartments. A composite S 1 -m-S 2 can be deconstructed into two simple osmosis systems (S 1 -m-H 2 O and H 2 O-m-S 2 ) 1,2 . When applying these two fundamental osmosis systems, a given m can either be permeable to water only (an ideal m) or its permeability to one species of non-charged solute particles (SP, e.g., urea) can be ignored. If m' represents a nonideal membrane whose permeability to urea cannot be ignored, then a new research question emerges: how can osmosis be studied in S-m'-H 2 O and S 1 -m'-S 2 , respectively? This abstract provides the answers by logical reasoning. First, S-m'-H 2 O can be viewed as the overlap of a pure osmosis system with an ideal m (S-m-H 2 O) and a permeant SP (pSP), urea diffusion system: S-m'-H 2 O = S-m-H 2 O + S urea -m'-H 2 O, so that osmosis and urea diffusion can be studied separately. The former is governed by van ’t Hoff’s law and the latter by Fick’s law. Second, similarly, S 1 -m'-S 2 = S 1 -m-S 2 + S 1urea -m'-S 2urea . Third, the effect of urea diffusion on osmosis depends on several conditions: 1) In S-m'-H 2 O, urea diffusion and osmosis are always in opposite directions, so urea diffusion reduces the resulting osmotic pressure (π). 2) In S 1 -m'-S 2 , if S 1 is hypertonic to S 2 and [urea] S1 > [urea] S2 , then the diffusion and osmosis are in opposite directions, so the diffusion reduces the resulting osmotic pressure gradient (Δ π). 3) If S 1 is hypotonic to S 2 and [urea] S1 > [urea] S2 , then osmosis and diffusion are in the same direction, so the diffusion augments the resulting Δ π. In conclusion: 1) Deconstruction of an osmosis system that has a nonideal m' allows separate studies of osmosis and pSP diffusion, respectively. 2) The effect of pSP diffusion on osmosis needs to be differentiated according to the type of osmosis systems and the direction of osmosis and pSP diffusion. 3) While the simple S-m-H 2 O and composite S 1 -m-S 2 are fundamental osmosis systems, S-m'-H 2 O and S 1 -m'-S 2 are complex passive membrane transport systems that transport both water and pSP. 4) If a given nonideal m' is permeable to two types of pSP (e.g., urea and glucose), then the diffusion system needs to be further deconstructed into a urea diffusion system and a glucose diffusion system.

Biodegradable Preformed Particle Gel (PPG) Made of Natural Chitosan Material for Water Shut-Off Application.

Oil and gas extraction frequently produces substantial volumes of produced water, leading to several mechanical and environmental issues. Several methods have been applied over decades, including chemical processes such as in-situ crosslinked polymer gel and preformed particle gel, which are the most effective nowadays. This study developed a green and biodegradable PPG made of PAM and chitosan as a blocking agent for water shutoff, which will contribute to combating the toxicity of several commercially used PPGs. The applicability of chitosan to act as a crosslinker has been confirmed by FTIR spectroscopy and observed by scanning electron microscopy. Extensive swelling capacity measurements and rheological experiments were performed to examine the optimal formulation of PAM/Cs based on several PAM and chitosan concentrations and the effects of typical reservoir conditions, such as salinity, temperature, and pH. The optimum concentrations of PAM with 0.5 wt% chitosan were between 5-9 wt%, while the optimum chitosan amount with 6.5 wt% PAM was in the 0.25-0.5 wt% range, as these concentrations can produce PPGs with high swellability and sufficient strength. The swelling capacity of PAM/Cs is lower in high saline water (HSW) with a TDS of 67.2976 g/L compared with fresh water, which is related to the osmotic pressure gradient between the swelling medium and the PPG. The swelling capacity in freshwater was up to 80.37 g/g, while it is 18.73 g/g in HSW. The storage moduli were higher in HSW than freshwater, with ranges of 1695-5000 Pa and 2053-5989 Pa, respectively. The storage modulus of PAM/Cs samples was higher in a neutral medium (pH = 6), where the fluctuation behavior in different pH conditions is related to electrostatic repulsions and hydrogen bond formation. The increase in swelling capacity caused by the progressive increment in temperature is associated with the amide group's hydrolysis to carboxylate groups. The sizes of the swollen particles are controllable since they are designed to be 0.63-1.62 mm in DIW and 0.86-1.00 mm in HSW. PAM/Cs showed promising swelling and rheological characteristics while demonstrating long-term thermal and hydrolytic stability in high-temperature and high-salinity conditions.

The Vagus Nerve Mediates Gut-Brain Response to Duodenal Nutrient Administration.

Obesity contributes significant disease burden worldwide, including diabetes, cardiovascular disease, and cancer. While bariatric surgery is the most effective and durable obesity treatment, the mechanisms underlying its effects remain unknown. Although neuro-hormonal mechanisms have been suspected to mediate at least some of the gut-brain axis changes following bariatric surgery, studies examining the intestine and its regionally specific post-gastric alterations to these signals remain unclear. Vagus nerve recording was performed following the implantation of duodenal feeding tubes in mice. Testing conditions and measurements were made under anesthesia during baseline, nutrient or vehicle solution delivery, and post-delivery. Solutions tested included water, glucose, glucose with an inhibitor of glucose absorption (phlorizin), and a hydrolyzed protein solution. Vagus nerve signaling was detectable from the duodenum and exhibited stable baseline activity without responding to osmotic pressure gradients. Duodenal-delivered glucose and protein robustly increased vagus nerve signaling, but increased signaling was abolished during the co-administration of glucose and phlorizin. Gut-brain communication via the vagus nerve emanating from the duodenum is nutrient sensitive and easily measurable in mice. Examination of these signaling pathways may help elucidate how the nutrient signals from the intestine are altered when applied to obesity and bariatric surgery mouse models. Future studies will address quantifying the changes in neuroendocrine nutrient signals in health and obesity, with specific emphasis on identifying the changes associated with bariatric surgery and other gastrointestinal surgery.

Neutral polymers partial exclusion in ionic solutions near charged membranes.

Neutral polymers have become a useful tool in biophysics. They are currently used in a variety of single-channel conductance measurements, to change solution conductivity and viscosity, to induce osmotic stress in polymer-excluded regions, or simply as crowding agents. Many experiments involve the proximity of neutral polymers to charged membranes or their confinement in aqueous pores formed by protein channels with charged residues. A well-known phenomenon relevant to this problem is the polarization of a neutral particle with dielectric properties different from the surrounding medium under the effect of an electric field. This polarization causes a dielectrophoretic force when inhomogeneous electric fields act on the particle and it has been extensively used in many biomedical applications involving particle trapping and cell separation, among others. In addition, whenever a neutral particle perturbs the equilibrium electric double layer near a charged surface, the osmotic pressure gradient acts as a net repulsive force that pushes the particle away from that surface. Both the dielectrophoretic force and the hydrostatic force contribute to exclude a neutral particle from a charged surface, provided the polarizability is lower in the particle than in the solution. Here we report analytical predictions and simulations of the exclusion of polyethylene glycol (PEG) molecules of different molecular weight from charged surfaces. Molecular dynamics of PEG near charged DPPS membranes and neutral DPPC membranes show a region of PEG exclusion near the membrane-solution interface for charged membranes. The simulations also point to a preferential alignment of PEG molecules near the charged membrane. The simulations are confirmed by preliminary neutron reflectometry data, which are consistent with an exclusion region of concentrated PEG solutions near the highly charged silicon dioxide/water interface.