Increasing Polymer Concentration Research Articles

Vajinal İlaç Taşıyıcı Sistem Olarak Polivinil Alkol Nanoliflerinin Mekanik ve Mukoadezif Özelliklerinin Değerlendirilmesi

Electrospinning is a versatile and inexpensive technique to produce nanofibers. Nanofibers can be a good alternative to classical dosage forms in vaginal applications due to high surface area/volume ratio, high encapsulation efficenciacy and mucoadhesive properties. Polyvinyl alcohol (PVA) is a biocompatible, easily degradable and flexible polymer with mucoadhesive properties used in industrial, commercial and medical applications. The scope of this study is to characterize electropsun nanofibers produced with different PVA types for vaginal use. PVA nanofibers were produced using the electrospinning method. Nanofiber formulations were prepared by dissolving PVA in dimethylformamide (DMF):distilled water (1:1) solvent system. Nanofibers were produced with three different types (PVA M 13/140, PVA G 26/140 and PVA G 40/140) PVA at 5%, 7.5% and 10% concentrations. The surface tension, viscosity and conductivity properties of the polymer mixtures were measured for electrospinning process and these parametres were found suitable for nanofiber production. While the viscosity increased with increasing polymer concentration, the surface tension values were found to be close to each other since the solvent system was the same. The mechanical and the mucoadhesive properties of nanofibers were examined and compared. Mucoadhesive and mechanical properties of nanofiber formulations differed depending on molecular weight and electrospinning process. The nanofiber formulations produced with PVA M 13/140 were found suitable for vaginal applications in terms of their mechanical and mucoadhesive properties. PVA nanofibers can be a good alternative as a drug delivery system in vaginal applications.

Influence of Polymer Combınatıon Concentratıon on The Characterıstıcs, In Vıtro Release And In Vıvo Lung Deposıtıon of Algınate-Carrageenan Mıcrospheres Encapsulatıng Cıprofloxacın HCl

Inhalation Ciprofloxacin HCl microspheres were formulated with combination of alginate and kappa carrageenan with a total of 1% (F1), 1.5% (F2), and 2% (F3). Aim of this research is to examine effect of polymer concentration on characteristics, release, and lung deposition of microspheres. Microspheres were characterized including loading, efficiency, yield, size, moisture content, mucoadhesivity, and release. Deposition was studied by fluorescence microscopy. Results showed spherical and smooth with size ofless than 2 µm. Loading showed about 18.55% to 29.65%. Entrapment efficiency was 52.86-76.29%. Yield was 49.83-70.72%. Swelling index was less than 10. For moisture content, all formulas demonstrated less than 6.5%. For mucoadhesivity, F1, F2, and F3 showed 0.0090 kg, 0.0217 kg, and 0.0329 kg respectively. It was found that increasing polymer concentration did not affect size, loading, efficiency, and yield of microspheres. Cumulative release at F1, F2, and F3 was 72.64%, 59.25%, and 47.66% respectively in 10 minutes at PBS pH 7.4 with burst release profile. In vivo showed that all formulas were able to deposit on rat lungs and it was found that the intensity were decreased at the 4th hour due to increase of polymer. Remaining intensity indicated that microspheres were able to maintain the drugs loaded.

Rheo-electric measurements of carbon black suspensions containing polyvinylidene difluoride in N-methyl-2-pyrrolidone

Lithium-ion battery cathode slurries have a microstructure that depends sensitively on how they are processed due to carbon black's (CB) evolving structure when subjected coating flows. While polyvinylidene difluoride (PVDF), one of the main components of the cathode slurry, plays an important role in modifying the structure and rheology of CB, a quantitative understanding is lacking. In this work, we explore the role of PVDF in determining the structural evolution of Super C65 CB in N-methyl-2-pyrrolidinone (NMP) with rheo-electric measurements. We find that PVDF enhances the viscosity of NMP resulting in a more extensive structural erosion of CB agglomerates with increasing polymer concentration and molecular weight. We also show that the relative viscosity of all suspensions can be collapsed by the fluid Mason number (Mnf), which compares the hydrodynamic forces imposed by the medium to cohesive forces holding CB agglomerates together. Using simultaneous rheo-electric measurements, we find at high Mnf, the dielectric strength (Δε) scales with Mnf, and the power-law scaling can be quantitatively predicted by considering the self-similar break up of CB agglomerates. The collapse of the relative viscosity and scaling of Δε both suggest that PVDF increases the hydrodynamic force of the suspending medium without directly changing the CB agglomerate structure. These findings are valuable for optimizing the rheology of lithium ion battery cathode slurries. We also anticipate that these findings can be extended to understand the microstructure of similar systems under flow.

Preparation of Poly(4-methyl-1-pentene) Membranes by Low-Temperature Thermally Induced Phase Separation

As a widely used method for the preparation of membranes, thermally induced phase separation (TIPS) is usually performed at high temperatures (200–260 °C) and has the disadvantages of high energy consumption, usage of large amounts of solvents, and easy decomposition of polymers. To solve these problems, this article presents a low-temperature thermally induced phase separation (LT-TIPS) method for the preparation of porous poly(4-methyl-1-pentene) (PMP) membranes at 70 °C. The PMP/cyclohexane solution was cast on a glass plate and quenched in water for a few minutes, and then the solvent was recovered by vacuum evaporation and condensation. The effects of quenching medium, quenching temperature, time, wet membrane thickness, and polymer concentration on the membrane porosity and air permeability were studied. The results showed that the elevated quenching temperature and extended quenching time in water favor the increase of air permeability. The increase of wet membrane thickness and polymer concentration results in reduced air permeability. The method displays convenience in process control, low energy consumption, less solvent usage, easy recovery of solvent, and environmental friendliness, exhibiting great promises for the preparation of membranes.

Enhancing pollutant removal from contaminated soils using yield stress fluids as selective blocking agents

This work presents a novel technique consisting in the use of yield stress fluids as blocking agents in porous media presenting pore-scale heterogeneities. The key feature of this method is that yield stress fluids only flow through the pores having a minimum size that depends on the applied pressure gradient. These fluids remain immobile in more and more pores as the pressure gradient is decreased. Therefore, the dimension of the pores which are invaded by the yield stress fluid can be controlled by adjusting the applied pressure gradient. Moreover, yield stress fluids are highly suitable blocking agents given the extremely high viscosity values that they exhibit in the pores. This allows for the diversion of the flow from greater to smaller pores during subsequent waterflooding stages, thus enhancing pollutant removal from the flow paths of small hydraulic conductance. A series of multiphase flow experiments were conducted in this study using well-characterized cores of artificial A10 sintered silicate. In these experiments, semidilute aqueous solutions of xanthan gum biopolymer were used as yield stress fluids to block the greatest pores. By doing so, considerably more pollutant was recovered by waterflooding. Furthermore, it was shown that an increase in polymer concentration does not always lead to a decrease in the size of the pores invaded by the blocking agent. Indeed, concentrated polymer solutions generate higher pressure gradients throughout the porous medium, which facilitates the invasion of small pores. Nevertheless, depending on the value of the yield stress-pressure gradient ratio, they may also develop extremely high viscosities that slow down their flow through such small pores. This work also presents a method to measure the volume of blocked pores using the results of tracer tests. The reported results suggest that using a polymer solution developing a yield stress as a selective blocking agent is a promising technique for soil remediation.

Structural Insights into Polymer-Bounded Lipid Nanodiscs.

Membrane proteins are an essential part of signaling and transport processes and are targeted by multiple drugs. To isolate and investigate them in their native state, polymer-bounded nanodiscs have become valuable tools. In this study, we investigate the lipid model system dimyristoyl-phosphocholine (DMPC) with the nanodisc-forming copolymers styrene maleic acid (SMA) and diisobutylene maleic acid (DIBMA). Using small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS), we studied the influence of polymer concentration and temperature on the nanodisc structure. In Tris buffer, the size of nanodiscs formed with SMA is smaller compared to DIBMA at the same polymer ratio. In both cases, the size decreases monotonically with increasing polymer concentration, and this effect is more pronounced when using SMA. Measurements at temperatures (T) between 5 and 30 °C in phosphate buffer showed an incomplete solubilization at high T even at polymer/lipid ratios above that required for complete lipid solubilization. For DIBMA, the nanodiscs developed at lower temperatures are stable and the net repulsion increases, while for SMA, the individual nanodiscs possess smaller sizes and are less affected by T. However, using DLS, one can observe SMA agglomerates at low T. Interestingly, for both polymers, no drastic changes of the observable parameters (radius and bilayer thickness) are seen upon cooling, which would indicate a sharp (first-order) phase transition from liquid-crystalline to gel, but only gradual changes. Hence, we conclude that the transition from a gel toward a liquid-crystalline lipid phase proceeds over a broad T-range compared to a continuous lipid bilayer. These results can pave the way toward the development of better protocols for studying membrane proteins stabilized in this type of membrane mimics.

Insight into polymer concentration, temperature, CO2 content, and Cl− content on corrosion of N80 steel tubing in polymer flooding

AbstractThe corrosion of N80 steel in polymer flooding is studied, and the safe service life of N80 steel tubing is calculated. The results show that the temperature is the main factor affecting the corrosion of tubing during the process of polymer flooding, and the safe service life of N80 carbon steel tubing at 75°C is only 11.1 years. The polymer is connected by molecular chains to form a network structure and then adsorbed on the surface of the steel. As the polymer concentration increases, the space between polymer molecules becomes smaller; the exposed surface area decreases; and the corrosion rate of N80 steel decreases. Both temperature and Cl− ions destroy the adsorption capacity of the polymer on the carbon steel substrate. The negatively charged chloride ion repels the negatively charged polymer, leading to the resolution of the polymer and reduction of the corrosion inhibition of the polymer. High temperature destroys the polymer's intramolecular and intermolecular aggregation, and also wrecks the long molecular chain polymer structure, significantly inhibiting the corrosion inhibition effect of the polymer.

Confinement-Induced Fractionation and Liquid-Liquid Phase Separation of Polymer Mixtures.

The formation of (bio)molecular condensates via liquid-liquid phase separation in cells has received increasing attention, as these aggregates play important functional and regulatory roles within biological systems. However, the majority of studies focused on the behavior of pure systems in bulk solutions, thus neglecting confinement effects and the interplay between the numerous molecules present in cells. To better understand the physical mechanisms driving condensation in cellular environments, we perform molecular simulations of binary polymer mixtures in spherical droplets, considering both monodisperse and polydisperse molecular weight distributions for the longer polymer species. We find that confinement induces a spatial separation of the polymers by length, with the longer ones moving to the droplet center. This partitioning causes a distinct increase in the local polymer concentration near the droplet center, which is more pronounced in polydisperse systems. Consequently, the confined systems exhibit liquid-liquid phase separation at average polymer concentrations where bulk systems are still in the one-phase regime.

Alginate Hydrogels Reinforced by Dehydration under Stress-Application to a Soft Magnetic Actuator.

We investigated the effect of partial dehydration under mechanical stress in the properties of alginate hydrogels. For this aim, we characterized the mechanical properties of the hydrogels under tensile and shear stress, as well as their swelling behavior, macroscopic appearance, and microscopic structure. We found that the processes of dehydration under a mechanical stress were irreversible with fully rehydration being impossible. What is more, these processes gave rise to an enhancement of the mechanical robustness of the hydrogels beyond the effect due to the increase in polymer concentration caused by dehydration. Finally, we analyzed the applicability of these results to alginate-based magnetic hydrogel grippers that bended in response to an applied magnetic field. Remarkably, our study demonstrated that the dehydration of the magnetic hydrogels under compression facilitated their bending response.

Self-Healing Capability and Mechanical Properties of Asphalt Mixtures Prepared With Light-Activated Polyurethane Prepolymer Modified Asphalt Binder

The objective of this study was to develop a new generation of ultraviolet (UV) light-activated self-healing polyurethane prepolymer modified asphalt binder using a reactive approach and to optimize the production parameters. Rheological tests were conducted on the prepared binder blends to evaluate the effect of the modification on rutting and fatigue cracking. The effect of the modification on asphalt mixtures was also evaluated using a self-healing experiment and various mechanical laboratory tests. The formation of urethane bond was confirmed using Fourier transformed infrared spectroscopy (FT-IR). Rheological test results of the modified binder demonstrated an increase in the high-temperature grading, while no significant effect was observed on the low-temperature grade. Self-healing testing of the asphalt mixtures showed that mixtures with 10% polymer and continuous exposure to UV light exhibited the highest crack healing rate. Loaded Wheel Tracking (LWT) results showed an improvement in rutting resistance of the mixtures prepared with polymer. In addition, Semi-Circular Bending (SCB) test results showed an improvement in the cracking resistance with 5% polymer. An increase in high-temperature grade was also observed for the extracted binders from the prepared asphalt mixtures. Multiple Stress Creep Recovery (MSCR) test results of the extracted binders showed an improvement in the elastic behavior and rutting resistance with an increase in polymer content. Furthermore, the extracted binders from aged mixtures showed an improved fatigue performance with the increase in polymer content.

Effects of polymer addition on transition and length scales of flow structures in transitional channel flow

The effect of polymer addition on transition to turbulence in a two-dimensional water-flow channel was experimentally investigated by flow visualization using reflective flakes. The flow entering the channel test section maintains a high disturbance level by expanding laterally after reaching a high Reynolds number upstream the test section. In order to obtain the intermittency factor (turbulence fraction), the visualized images were classified into non-turbulent and turbulent regions, and the streamwise scale of the streaks appearing in the non-turbulent region was estimated from the autocorrelation coefficient computed by shifting the images in the streamwise direction. The visualization results show that similar to the pure water case, intermittent flow with a patch-like distribution of turbulent and non-turbulent areas clustered by streamwise streaks is observed. The Reynolds number at which the intermittency increases shifts toward higher Reynolds numbers with increasing polymer concentration, indicating a delay of transition. The streaks appearing in the non-turbulent region elongate with increasing polymer concentration. At high concentrations, straight elongated streaks penetrate through the turbulent regions, suggesting that the polymer addition affects the stability of the streaks. These changes of the streak behavior indicate that the polymer affects not only the transition Reynolds number but also the flow structure during the transition process.

Multiscale investigation of viscoelastic properties of aqueous solutions of sodium alginate and evaluation of their biocompatibility.

In order to get better knowledge of mechanical properties from microscopic to macroscopic scale of biopolymers, viscoelastic bulk properties of aqueous solutions of sodium alginate were studied at different scales by combining macroscopic shear rheology (Hz), diffusing-wave spectroscopy microrheology (kHz-MHz) and Brillouin spectroscopy (GHz). Structural properties were also directly probed by small-angle X-ray scattering (SAXS). The results demonstrate a change from polyelectrolyte behavior to neutral polymer behavior by increasing polymer concentration with the determination of characteristic sizes (persistence length, correlation length). The viscoelastic properties probed at the phonon wavelength much higher than the ones obtained at low frequency reflect the variation of microscopic viscosity. First experiments obtained by metabolic activity assays with mouse embryonic fibroblasts showed biocompatibility of sodium alginate aqueous solutions in the studied range of concentrations (2.5-10 g L-1) and consequently their potential biomedical applications.

Improved permselectivity and mechanical properties of sulfonated poly dimethyl phenylene oxide cation exchange membrane using MXene nanosheets

In the current research, sulfonated poly (phenylene oxide) (SPPO)/MXene nanosheets cation exchange membranes (CEM) were prepared by solution casting technique. SPPO with different sulfonation degrees (DS) were synthesized, and MXene nanosheets were etched from the MAX phase. The effect of sulfonation degrees (31, 36, and 43 %), polymer concentration (19, 22, and 25 wt%), and MXene loading (0.5, 1, and 2 wt%) on mechanical properties, electrochemical characteristics, and permselectivity of the CEMs were studied. The results showed that an increase in DS, the presence of hydrophilic MXene nanosheets, and a decrease in polymer concentration had synergistic effects on enhancing the hydrophilicity and conductivity of the fabricated CEMs. The ion exchange capacity (IEC) increased with enhancement of DS and MXene loading due to more attaching the functional groups to the polymer structure. On the other hand, an increase in polymer concentration resulted in the reduction of IEC. The tensile strength of CEMs had a reduction trend when the sulfonation degree increased, and polymer concentration decreased. Presence of MXene nanosheets significantly improved the values of permselectivity and tensile strength; For example, permselectivity increased from 80.92 % to 92.30 % by adding 2 % of MXene to the casting solution containing 25 wt% of SPPO with a sulfonation degree of 36 %.

Investigation of Cell Aggregation on the Printing Performance in Inkjet-Based Bioprinting of Cell-Laden Bioink.

During 3D bioprinting, when the gravitational force exceeds the buoyant force, cell sedimentation will be induced, resulting in local cell concentration change and cell aggregation which affect the printing performance. This paper aims at studying and quantifying cell aggregation and its effects on the droplet formation process during inkjet-based bioprinting and cell distribution after inkjet-based bioprinting. The major conclusions of this study are as follows: (1) Cell aggregation is a significant challenge during inkjet-based bioprinting by observing the percentage of individual cells after different printing times. In addition, as polymer concentration increases, the cell aggregation is suppressed. (2) As printing time and cell aggregation increase, the ligament length and droplet velocity generally decrease first and then increase due to the initial increase and subsequent decrease of the viscous effect. (3) As the printing time increases, both the maximum number of cells within one microsphere and the mean cell number have a significant increase, especially for low polymer concentrations such as 0.5% (w/v). In addition, the increased rate is the highest using the lowest polymer concentration of 0.5% (w/v) because of its highest cell sedimentation velocity.

A new mathematical model derived from transient (creep) analysis to estimate the vaginal retention of semi-solid dosage forms

The performance of vaginal drug delivery systems is dependent on their retention. This study presents a novel mathematical method to estimate the vaginal retention of semi-solids. Using creep analysis, the elastic and residual compliances are determined from the discrete retardation spectrum and used to determine the retention times (RT), defined as the time required for the formulations to enter the terminal viscous zone of deformation and hence flow. RT of commercially available products (CAP) and selected prototype formulations were determined, the estimated RT of CAP broadly aligning with their prescribed clinical usage. Candidate formulations composed of hydroxyethylcellulose (HEC, 3%/5%w/w) and polyacrylic acid (PAA, 1%/3%w/w) were manufactured using, and further diluted with simulant vaginal fluid (SVF) or simulant seminal fluid (SSF) and their RT subsequently determined. Increasing polymer concentration and pH enhanced the estimated RT whereas dilution reduced RT. Notably, the formulation composed of 5%HEC/3% PAA (SSF) maintained its RT on dilution due to swelling of suspended PAA particles, thus representing a strategy to develop vaginal semi-solids that are resistant to dilution and hence removal. The mathematical model described is reproducible, straightforward to use and is recommended as a tool in formulation development to estimate the retention of vaginal semi-solids.

Effects of network connectivity on viscoelastic relaxation in transient networks using experimental approach

The effect of network connectivity on viscoelastic relaxation in transient networks with well-defined structures (Tetra-PEG slime) was experimentally evaluated and compared to bond dissociation kinetics. To control the connectivity and discuss the pure effect precisely, we mixed the precursors in off-stoichiometric ratio. With decreasing network connectivity, the viscoelastic relaxation time accelerated and became shorter than the bond dissociation time. With increasing polymer concentration, the connectivity at which the viscoelastic relaxation time matched the dissociation time shifted to the high-connectivity region. The dependence of viscoelastic relaxation on connectivity can be adequately explained within the framework of the lifetime of a backbone. The backbone has numerous breakage points in low-connectivity region nearby the gelation point, resulting in a shorter lifetime than the dissociation time. However, the Rubinstein-Semenov model based on backbone relaxation does not predict the concentration dependence, suggesting that the formation of the network in the dilute/semi-dilute region deviates from a random branching process. These findings provide a crucial foundation for the molecular comprehension of transient network materials.

Development of Besifloxacin HCL Loaded Ocular İn Situ Gels; In Vitro Characterization Study

Objective: The aim of this study is to develop in situ gel formulations containing besifloxacin hydrochloride are heat triggered, which are prepared by using different poloxomer and derivatives different polymers that will change the gelling temperature to increase corneal contact time, regulate drug release, improve ocular bioavailability and increase patient compliance increase mucoadhesion.
 Material and Method: Various concentrations of poloxamer 188 (P188) and poloxamer 407 (P407) were used to create the in situ forming gels. To increase the gel's capacity for bioadhesion, mucoadhesives such hydroxypropylmethyl cellulose (HPMC) or hydroxyethyl cellulose (HEC) were included in the formulations. Drug release in vitro, sol-gel transition temperature, rheological behavior, pH, clarity, and mucoadhesion force were all assessed for the produced formulations. 
 Result and Discussion: The developed formulations' gelation temperatures ranged from 29 to 35°C. The preparations' viscosity and mucoadhesion force increased with increasing P407, HPMC, and HEC concentrations. Besifloxacin HCl forms in situ gel formulas with K1, K2, K3, and K6 suited for mucoadhesion characteristics, gelation temperature, and viscosity. These formulations exhibit pseudoplastic flow. Increasing polymer concentrations resulted in a reduction in the burst release of the formulations. However, at the end of 6 hours, drug release was finished in all formulations. The results show that in situ gels containing P407 and P188 show promise for besifloxacin HCl application

Mechanism of Phase Separation in Aqueous Two-Phase Systems.

Liquid-liquid phase separation underlies the formation of membrane-less organelles inside living cells. The mechanism of this process can be examined using simple aqueous mixtures of two or more solutes, which are able to phase separate at specific concentration thresholds. This work presents the first experimental evidence that mesoscopic changes precede visually detected macroscopic phase separation in aqueous mixtures of two polymers and a single polymer and salt. Dynamic light scattering (DLS) analysis indicates the formation of mesoscopic polymer agglomerates in these systems. These agglomerates increase in size with increasing polymer concentrations prior to visual phase separation. Such mesoscopic changes are paralleled by changes in water structure as evidenced by Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) spectroscopic analysis of OH-stretch bands. Through OH-stretch band analysis, we obtain quantitative estimates of the relative fractions of four subpopulations of water structures coexisting in aqueous solutions. These estimates indicate that abrupt changes in hydrogen bond arrangement take place at concentrations below the threshold of macroscopic phase separation. We used these experimental observations to develop a model of phase separation in aqueous media.

Effect of Sand Grain on Adsorption of Xanthan Gum and Polyacrylamide

Polymer flooding is an Enhanced oil recovery (EOR) method using chemicals, such as xanthan gum and polyacrylamide which are widely used in the field. Polymer flooding can improve the mobility of the injection fluid, but in the reservoir the polymer has an interaction with sand known as adsorption which causes some of the polymer to be bound to the surface of the pore of sand, so that it has an impact on the ineffectiveness of the injection. The purpose of this study want to determine and compare the effect of sand grain on the adsorption of xanthan gum and polyacrylamide polymer solutions. Based on the experiment results, it was found that the increase in adsorption was proportional to the increase in polymer concentration. From two polymers used, xanthan gum showed lower adsorption than polyacrylamide. Based on the sand grain, the adsorption that occurs is greater in the grain size for large sand compare small.

PBPK modelling of ceftriaxone Na-loaded starch-sodium alginate polymeric blend prepared by water-in-oil emulsification for oral delivery

Ceftriaxone is a third-generation cephalosporin antibiotic effective against many bacterial infections. However, owing to its instability in the gastrointestinal tract (GIT), it is administered by injections, which is an unfavourable route of administration. Therefore, the aim of this study was to formulate ceftriaxone into biodegradable and thermally stable polymeric blend microparticles that are suitable for oral delivery. The drug-loaded microparticles were prepared by the water-in-oil (W/O) emulsion method and consisted of starch and sodium alginate (NaAlg) as a polymeric matrix and glutaraldehyde (GA) as a cross-linking agent. Characterization of these particles using scanning electron microscopy (SEM) showed that the particles were spherical in shape with a smooth surface. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) of these particles showed no drug-polymer interactions. The highest percentage yield of particles was obtained at 3% polymer concentration. The particle size increased slightly after drug loading. The drug loading and entrapment efficiency appeared to increase with increasing polymer concentration. In vitro drug release at pH 1.2 and pH 7.4, revealed that drug release was below 20% at the acidic pH, while at pH 7.4, drug release of up to 85% was observed. The release mechanism followed first-order and Fickian diffusion patterns. Plasma concentration-time profiles were simulated for subcontinental Asian populations using commercial PBPK software, and the results suggest that microencapsulation of ceftriaxone sodium in a polymeric blend could represent a promising approach for controlled oral delivery of the drug, with enhanced absorption and bioavailability of the drug.