Adsorption of poly(ethylene oxide)-containing amphiphilic polymers on solid-liquid interfaces: Fundamentals and applications

Development of an Injectable Formulation of a Water-Insoluble Glycyrrhizin Derivative That Potently Inhibits High-Mobility Group Box 1 in Murine Intracerebral Hemorrhage

High-mobility group box (HMGB) 1, a nuclear protein that acts as an inflammatory mediator, exacerbates injury following intracerebral hemorrhage (ICH). Glycyrrhizin, a natural HMGB1 inhibitor derived from licorice, alleviates ICH-induced inflammatory responses, including brain edema formation. In our previous study, inspired by the bioconversion of endophytes living symbiotically in licorice, we discovered a glycyrrhizin derivative with more potent anti-HMGB1 activity than glycyrrhizin. However, this derivative is poorly soluble in water, and some issues remain to be resolved when applying it to treat ICH. The aim of this study was to develop an injectable formulation of a water-insoluble glycyrrhizin derivative (WIGLD) to treat acute ICH. Screening of Pluronic surfactants revealed that Pluronic P103 significantly improved the solubility of WIGLD. The micelles had a particle size of approximately 20 nm; therefore, this formulation was considered suitable for intravenous injection. Thus, we investigated the therapeutic efficacy of an intravenously injected solubilized WIGLD formulation in a murine model of ICH induced by intrastriatal collagenase injection. The injected WIGLD formulation increased brain penetration compared to that after oral administration. Additionally, it inhibited microglial activation by HMGB1, decreased brain edema, and ameliorated neurological deficits. These findings suggested that the injectable WIGLD formulation, with its potent anti-HMGB1 activity, represents a promising therapeutic strategy for managing ICH-related brain edema and associated injuries.

A Preformulation Experiment: The Influence of Poloxamer 188 and Poloxamer 407 on the Binding Coefficients (Single Molecule) and the Partitioning Coefficients (Micelle) of Ketoprofen (Probe Molecule) with Sodium Cholate, Dodecyl Trimethylammonium Bromide and BrijC10 Surfactants

INTRODUCTION

Ketoprofen, a Biopharmaceutics Classification System (BCS) class II drug, exhibits poor water solubility, necessitating solubilization strategies for effective drug delivery. Surfactants and poloxamers are commonly employed to enhance solubilization via micellar encapsulation and host-guest interactions.

AIM

This study investigates the binding interactions, stoichiometry, and partitioning behavior of ketoprofen with surfactants-sodium cholate (SC), dodecyltrimethylammonium bromide (DTAB), and Brij C10 (BC10)-and examines the impact of Poloxamer 188 (P188) and Poloxamer 407 (P407) as modifiers.

MATERIALS AND METHODS

Complexation stoichiometry was evaluated using Job's plots, while binding constants (Kb​) were derived from Benesi-Hildebrand plots. Partition coefficients (Kx) and Gibbs energies (ΔGx​) were determined using Kawamura's equation. Measurements were conducted at 25°C with constant ketoprofen concentrations.

RESULTS AND DISCUSSION

Job's plots indicated 1:1 complexation for most systems, except DTAB + P407, which exhibited a 1.67:1 ratio. DTAB displayed the highest Kx (81386.259 with P188), attributed to electrostatic interactions and micelle stabilization. SC showed moderate Kx​, reduced by poloxamers due to competitive hydrogen bonding. BC10, the least efficient solubilizer, improved slightly with poloxamers by enabling micellar core partitioning. Gibbs energy (ΔGx < 0) confirmed spontaneous solubilization, with the most favorable values for DTAB + P188. Discrepancies between Job's and Benesi-Hildebrand plots highlighted the limitations of the latter for low-CMC surfactants.

CONCLUSION

DTAB, particularly with P188, demonstrated the greatest potential for ketoprofen solubilization, providing valuable insights for designing surfactant-based drug delivery systems.

Decoding the suppressing effects of Pluronic triblock copolymers on copper electrodeposition

Triblock Pluronics of polyoxyethylene (PEO) and polyoxypropylene (PPO) are identified as competent suppressors for copper (Cu) electroplating in advanced electronics manufacturing. However, the specific interfacial roles of PEO and PPO blocks in Pluronic suppressors, are not yet fully understood, which is crucial for the rational design of effective suppressors. Herein, the influences of composition and block arrangement of such Pluronics on the inhibition against Cu plating are systematically investigated. The decrease in Cu deposition mass with increasing PPO content suggests that the PPO blocks are the main contributor to the inhibition strength of Pluronics, as demonstrated by the positive correlation between electrodeposited Cu mass and hydrophilic-lipophilic balance (HLB) value. Comparative analysis of normal and reverse Pluronic pairs with similar compositions indicates that an adequately long PEO block is indispensable to maintain the inhibition stability of Pluronics. Moreover, electrochemical attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) offers direct evidence that the PEO block, rather than the PPO block, compactly adsorbs on the chloridion (Cl-) adlayer covered Cu surface. This work highlights the importance of balancing the PPO-dominated inhibition strength and the PEO-dominated inhibition stability in the design of practical copolymer suppressors, for which the HLB may serve a valuable indicator, together with the PEO block length.

Highly sensitive plasmonic paper substrate fabricated via amphiphilic polymer self-assembly in microdroplet for detection of emerging pharmaceutical pollutants

We report an innovative and facile approach to fabricating an ultrasensitive plasmonic paper substrate for surface-enhanced Raman spectroscopy (SERS). The approach exploits the self-assembling capability of poly(styrene-b-2-vinyl pyridine) block copolymers to form a thin film at the air-liquid interface within the single microdroplet scale for the first time and the subsequent in situ growth of silver nanoparticles (AgNPs). The concentration of the block copolymer was found to play an essential role in stabilizing the droplets during the mass transfer phase and formation of silver nanoparticles, thus influencing the SERS signals. SEM analysis of the morphology of the plasmonic paper substrates revealed the formation of spherical AgNPs evenly distributed across the surface of the formed copolymer film with a size distribution of 47.5 nm. The resultant enhancement factor was calculated to be 1.2 × 107, and the detection limit of rhodamine 6G was as low as 48.9 pM. The nanohybridized plasmonic paper was successfully applied to detect two emerging pollutants-sildenafil and flibanserin-with LODs as low as 1.48 nM and 3.45 nM, respectively. Thus, this study offers new prospects for designing an affordable and readily available, yet highly sensitive, paper-based SERS substrate with the potential for development as a lab-on-a-chip device.

Nonequilibrium Colloids: Temperature-Induced Bouquet Formation of Flower-like Micelles as a Time-Domain-Shifting Macromolecular Heat Alert

Climate change requires enhanced autonomous temperature monitoring during logistics/transport. A cheap approach comprises the use of temperature-sensitive copolymers that undergo temperature-induced irreversible coagulation. The synthesis/characterization of pentablock copolymers (PBCP) starting from poloxamer PEO130-b-PPO44-b-PEO130 (poly(ethylene oxide)130-b-poly(propylene oxide)44-b-poly(ethylene oxide)130) and adding two terminal qPDMAEMA85 (quaternized poly[(2-dimethylamino)ethyl methacrylate]85) blocks is presented. Mixing of PBCP solutions with hexacyanoferrate(III)/ferricyanide solutions leads to a reduction of the decane/water interfacial tension accompanied by a co/self-assembly toward flower-like micelles in cold water because of the formation of an insoluble/hydrophobic qPDMAEMA/ferricyanide complex. In cold water, the PEO/PPO blocks provide colloidal stability over months. In hot water, the temperature-responsive PPO block is dehydrated, leading to a pronounced temperature dependence of the oil-water interfacial tension. In solution, the sticky PPO segments exposed at the micellar corona cause a colloidal clustering above a certain threshold temperature, which follows Smoluchowski-type kinetics. This coagulation remains for months even after cooling, indicating the presence of a kinetically trapped nonequilibrium state for at least one of the observed micellar structures. Therefore, the system memorizes a previous suffering of heat. This phenomenon is linked to an exchange of qPDMAEMA-blocks bridging the micellar cores after PPO-induced clustering. The addition of ferrous ions hampers the exchange, leading to the reversible coagulation of Prussian blue loaded micelles. Hence, the Fe2+ addition causes a shift from history monitoring to the sensing of the present temperature. Presumably, the system can be adapted for different temperatures in order to monitor transport and storage in a simple way. Hence, these polymeric "flowers" could contribute to preventing waste and sustaining the quality of goods (e.g., food) by temperature-induced bouquet formation, where an irreversible exchange of "tentacles" between the flowers stabilizes the bouquet at other temperatures as well.

Block Copolymer Adsorption on the Surface of Multi-Walled Carbon Nanotubes for Dispersion in N,N Dimethyl Formamide

This research aims to characterize the adsorption morphology of block copolymer dispersants of the styrene-block-4-vinylpyridine family (S4VP) on the surface of multi-walled carbon nanotubes (MWCNT) in a polar organic solvent, N,N-dimethyl formamide (DMF). Good, unagglomerated dispersion is important in several applications such as fabricating CNT nanocomposites in a polymer film for electronic or optical devices. Small-angle neutron scattering (SANS) measurements, using the contrast variation (CV) method, are used to evaluate the density and extension of the polymer chains adsorbed on the nanotube surface, which can yield insight into the means of successful dispersion. The results show that the block copolymers adsorb onto the MWCNT surface as a continuous coverage of low polymer concentration. Poly(styrene) (PS) blocks adsorb more tightly, forming a 20 Å layer containing about 6 wt.% PS, whereas poly(4-vinylpyridine) (P4VP) blocks emanate into the solvent, forming a thicker shell (totaling 110 Å in radius) but of very dilute (<1 wt.%) polymer concentration. This indicates strong chain extension. Increasing the PS molecular weight increases the thickness of the adsorbed layer but decreases the overall polymer concentration within it. These results are relevant for the ability of dispersed CNTs to form a strong interface with matrix polymers in composites, due to the extension of the 4VP chains allowing for entanglement with matrix chains. The sparse polymer coverage of the CNT surface may provide sufficient space to form CNT-CNT contacts in processed films and composites, which are important for electrical or thermal conductivity.

Rhamnolipid Micellization and Adsorption Properties

Biosurfactants are naturally occurring amphiphiles that are being actively pursued as alternatives to synthetic surfactants in cleaning, personal care, and cosmetic products. On the basis of their ability to mobilize and disperse hydrocarbons, biosurfactants are also involved in the bioremediation of oil spills. Rhamnolipids are low molecular weight glycolipid biosurfactants that consist of a mono- or di-rhamnose head group and a hydrocarbon fatty acid chain. We examine here the micellization of purified mono-rhamnolipids and di-rhamnolipids in aqueous solutions and their adsorption on model solid surfaces. Rhamnolipid micellization in water is endothermic; the CMC (critical micellization concentration) of di-rhamnolipid is lower than that of mono-rhamnolipid, and both CMCs decrease upon NaCl addition. Rhamnolipid adsorption on gold surface is mostly reversible and the adsorbed layer is rigid. A better understanding of biosurfactant self-assembly and adsorption properties is important for their utilization in consumer products and environmental applications.

Direct separation and enumeration of CTCs in viscous blood based on co-flow microchannel with tunable shear rate: a proof-of-principle study

Circulating tumor cells (CTCs), which have extremely low density in whole blood, are an important indicator of primary tumor metastasis. Isolation and enumeration of these cells are critical for clinical applications. Separation of CTCs from massive blood cells without labeling and addition of synthetic polymers is challenging. Herein, a novel well-defined co-flow microfluidic device is presented and used to separate CTCs in viscous blood by applying both inertial and viscoelastic forces. Diluted blood without any synthetic polymer and buffer solution were used as viscoelastic fluid and Newtonian fluid, respectively, and they were co-flowed in the designed chip to form a sheath flow. The co-flow system provides the function of particle pre-focusing and creates a tunable shear rate region at the interface to adjust the migration of particles or cells from the sample solution to the buffer solution. Successful separation of CTCs from viscous blood was demonstrated and enumeration was also conducted by image recognition after separation. The statistical results indicated that a recovery rate of cancer cells greater than 87% was obtained using the developed method, which proved that the direct separation of CTCs from diluted blood can be achieved without the addition of any synthetic polymer to prepare viscoelastic fluid. This method holds great promise for the separation of cells in viscous biological fluid without either complicated channel structures or the addition of synthetic polymers.

GenX in water: Interactions and self-assembly

2,3,3,3-tetrafluoro-2-(heptafluoropropoxy) propanoate, a.k.a. "GenX", is a surfactant introduced as a safer alternative to replace perfluorooctanoate (PFOA) in the manufacturing of fluorinated polymers, however, GenX is shown to cause adverse health effects similar to, or even worse than, those of the legacy PFOA. With an overarching goal to understand the behavior of GenX molecules in aqueous media, we report here on GenX micelle formation and structure in aqueous solutions, on the basis of results obtained from a combination of experimental techniques such as surface tension, fluorescence, viscosity, and small-angle neutron scattering (SANS), and molecular dynamics (MD) simulations. To our best knowledge, this is the first report on GenX micelles. The critical micelle concentration (CMC) of GenX ammonium salt in water is 175 mM. GenX forms small micelles with association number 6-8 and 10 Å radius. GenX molecules prefer to align along the micelle surface, and the ether oxygen of GenX has very little interaction with and exposure to water. Information on the surfactant and interfacial properties of GenX is crucial, since such properties are manifestations of interactions between GenX molecules and between GenX and water molecules and, in turn, the amphiphilic character of GenX dictates its fate and transport in the aqueous environment, its interactions with various biomolecules, and its binding to adsorbent materials.

SBA-15 obtained from rice husk ashes wet-impregnated with metals (Al, Co, Ni) as efficient catalysts for 1,4-dihydropyridine three-component reaction

A fully characterized mesoporous silica prepared from industrial waste was impregnated with metals and applied as a green heterogeneous catalyst.

Curcumin-tannic acid-poloxamer nanoassemblies enhance curcumin's uptake and bioactivity against cancer cells in vitro

Curcumin (CUR) is a bioactive natural compound with potent antioxidant and anticancer properties. However, its poor water solubility has been a major limitation against its widespread clinical use. The aim of this study was to develop a nanoscale formulation for CUR to improve its solubility and potentially enhance its bioactivity, by leveraging the self-assembly behavior of tannic acid (TA) and amphiphilic poloxamers to form CUR-entrapped nanoassemblies. To optimize drug loading, formulation variables included the CUR: TA ratio and the type of amphiphilic polymer (Pluronic® F-127 or Pluronic® P-123). The optimal CUR nanoparticles (NPs) were around 200 nm in size with a high degree of monodispersity and 56% entrapment efficiency. Infrared spectroscopy confirmed the presence of intermolecular interactions between CUR and the NP formulation components. X-ray diffraction revealed that CUR was entrapped in the NPs in an amorphous state. The NPs maintained excellent colloidal stability under various conditions. In vitro release of CUR from the NPs showed a biphasic controlled release pattern up to 72 h. Antioxidant and antiproliferative assays against a panel of human cancer cell lines revealed significantly higher activity for CUR NPs compared to free CUR, particularly in MCF-7 and MDA-MB-231 breast cancer cells. This was attributed to greater cellular uptake of the NPs compared to the free drug as verified by confocal microscopy imaging and flow cytometry measurements. Our findings present a highly promising NP delivery platform for CUR prepared via a simple self-assembly process with the ability to potentiate its bioactivity in cancer and other diseases where oxidative stress is implicated.

Determination of Interfacial Tension of Nanomaterials and the Effect of Particle Size on Interfacial Tension

The unique physical and chemical properties and performances of nanomaterials are closely related to the interfacial tension. However, there is no method to accurately measure the interfacial tension of nanomaterials. In addition, the effect of particle size on the interfacial tension of nanoparticles is unclear, and there exist conflicting conclusions about the value and sign of Tolman length. In this paper, a novel method of determining the interfacial tension (solid-liquid and solid-gas interfaces), temperature coefficient of interfacial tension, and Tolman lengths of nanomaterials by adsorption thermodynamics and kinetics was presented. The interfacial tension and its temperature coefficient of the solid-liquid interface of nano cadmium sulfide before adsorption were obtained, and further, the Tolman length was also obtained. The experimental results show that the particle size of nanoparticles has significant effects on the interfacial tension and its temperature coefficient. When the radius is larger than 10 nm, the interfacial tension and its temperature coefficient are almost constant with the decrease of the radius. When the radius is less than 10 nm, the interfacial tension decreases sharply and the temperature coefficient increases sharply with the decrease of the radius, and the temperature coefficient of the interfacial tension is negative. The Tolman length of the solid-liquid interface of nanoparticles is proved to be positive, and the particle size also has a significant effect on the Tolman length. The Tolman length decreases with the decrease of particle size. However, the effects of particle size on the Tolman length become significant only when the particle radius approach or reach the order of magnitudes of molecular (or atomic) radius. The effects of particle size on interfacial tension and Tolman length of nano cadmium sulfide obtained in this paper can provide significant references for the research and applications of interface thermodynamics of other nanomaterials.

Structure and composition of mixed micelles formed by nonionic block copolymers and ionic surfactants in water determined by small-angle neutron scattering with contrast variation

HYPOTHESIS

Complex fluids comprising polymers and surfactants exhibit interesting properties which depend on the overall composition and solvent quality. The ultimate determinants of the macroscopic properties are the nano-scale association domains. Hence it is important to ascertain the structure and composition of the domains, and how they respond to the overall composition.

EXPERIMENTS

The structure and composition of mixed micelles formed in aqueous solution between poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers (Pluronics or Poloxamers) and the ionic surfactant sodium dodecylsulfate (SDS) are determined from an analysis of small-angle neutron scattering (SANS) intensity data obtained at different contrasts. Different polymers and concentrations have been probed.

FINDINGS

The SDS + Pluronic mixed micelles include polymer and some water in the micelle core that is formed primarily by alkyl chains. This is different than what was previously reported, but is consistent with a variety of experimental observations. This is the first report on the structure of SDS + Pluronic P123 (EO₁₉PO₆₉EO₁₉) assemblies. The effects on the mixed micelle structure and composition of the surfactant concentration and the polymer hydrophobicity are discussed here in the context of interactions between the different components.

Amphiphilic triblock copolymer as the gas chromatographic stationary phase with high-resolution performance towards a wide range of isomers and the components of lemon essential oil

This work presents the investigation of using the amphiphilic triblock copolymer composed of poly(ethylene oxide)(PEO)-poly(propylene oxide) (PPO)-poly(ethylene oxide) (PEO) (denoted as EPE) as the stationary phase for gas chromatographic (GC) analyses. The EPE capillary column exhibited moderate polarity and column efficiency of 4348 plates/m determined by naphthalene at 120 °C (k = 11.52). Different from the PEG and polysiloxane homopolymers, it showed high-resolution performance towards a wide range of aliphatic and aromatic isomers in terms of polarity and acid-base properties. Particularly, the EPE column displayed distinct advantages for separating the critical isomers of alkanes, anilines and phenols and the components of the lemon essential oil over the commercial PEG and polysiloxane columns. In addition, the EPE column exhibited excellent separation repeatability and reproducibility with the relative standard deviation (RSD) values in the range of 0.03% - 0.08% for run-to-run, 0.14% - 0.61% for day-to-day and 3.1% - 4.0% for column-to-column, respectively. Moreover, the EPE column was investigated in terms of thermal stability, the minimum allowable operating temperature (MiAOT) and sample loadability. Its application to GC-MS analysis of the essential oil demonstrated its feasibility for practical analyses. This work demonstrates the promising future of triblock copolymers as a new class of selective stationary phases for GC analyses, which is barely reported up to date. The findings of this work is of important value for fundamental researches and practical applications.

Avoiding artifacts in liposome leakage measurements via cuvette- and liposome-surface modifications

The barrier properties of lipid membranes are often determined by investigating their solute permeability with the help of spectroscopic methods and the use of liposome-encapsulated self-quenching fluorescent dyes, for example, Carboxyfluorescein (CF). It was shown previously that liposome-surface interactions, and thus the choice of cuvette material, influence the result of such spectroscopic permeability/leakage experiments. In this work, we explore different methods to minimize the artifacts observed in spontaneous leakage measurements performed with cholesterol-containing liposomes. The spontaneous leakage of CF from liposomes with different composition and surface properties is monitored in cuvettes composed of quartz, polystyrene (PS), and Poly(methyl methacrylate) (PMMA). Our results show that significantly different leakage profiles are recorded for the exact same liposome batch depending on the cuvette material used. Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D) experiments indicate that these discrepancies likely arise from side processes occurring at the solution-cuvette interface, mainly, the attaching and spreading of liposomes. Further, we show that in some cases it is possible to minimize liposome-cuvette interactions, and reduce the experimental artifacts, by supplementing the liposomes with polyethylene glycol (PEG)-grafted lipids or gangliosides, and/or by pre-adsorbing free PEG to the cuvette walls. The collected data suggest that quartz cuvettes modified by adsorption of PEG8000 are suitable for spontaneous leakage experiments with POPC:cholesterol-based liposomes, while other cuvette materials perform poorly in the same experiments.

Development and In Vitro Evaluation of Controlled Release Viagra® Containing Poloxamer-188 Using Gastroplus™ PBPK Modeling Software for In Vivo Predictions and Pharmacokinetic Assessments

Sildenafil is the active substance in Viagra^® tablets, which is approved by the FDA to treat sexual dysfunction in men. Poor solubility and short half-life, however, can limit the span of its effectiveness. Therefore, this study focused on an oral controlled release matrix system with the aim to improve solubility, control the drug release, and sustain the duration of drug activity. The controlled release matrices were prepared with poloxamer-188, hydroxypropyl methylcellulose, and magnesium stearate. Various formulations of different ratios were developed, evaluated in vitro, and assessed in silico. Poloxamer-188 appeared to have a remarkable influence on the release profile of sildenafil citrate. In general, the rate of drug release decreased as the amount of polymer was gradually increased in the matrix system, achieving a maximum release period over 12 h. The in silico assessment by using the GastroPlus™ PBPK modeling software predicted a significant variation in C_max, t_max, t_1/2, and AUC_0-t among the formulations. In conclusion, the combination of polymers in matrix systems can have substantial impact on controlling and modifying the drug release pattern.

Controlling the self-assembly of perfluorinated surfactants in aqueous environments

Surface active per- and polyfluoroalkyl substances (PFAS) released in the environment generate great concern in the US and worldwide. The sequestration of PFAS amphiphiles from aqueous media can be limited by their strong tendency to form micelles that plug the pores in the adsorbent material, rendering most of the active surface inaccessible. A joint experimental and simulation approach has been used to investigate the structure of perfluorooctanoate ammonium (PFOA) micelles in aqueous solutions, focusing on the understanding of ethanol addition on PFOA micelle formation and structure. Structurally compact and slightly ellipsoidal in shape, PFOA micelles in pure water become more diffuse with increasing ethanol content, and break into smaller PFOA clusters in aqueous solutions with high ethanol concentration. A transition from a co-surfactant to a co-solvent behavior with the increase of ethanol concentration has been observed by both experiments and simulations, while the latter also provide insight on how to achieve co-solvent conditions with other additives. An improved understanding of how to modulate PFAS surfactant self-assembly in water can inform the fate and transport of PFAS in the environment and the PFAS sequestration from aqueous media.

Fluorinated Surfactant Adsorption on Mineral Surfaces: Implications for PFAS Fate and Transport in the Environment

Fluorinated surfactants, which fall under the class of per- and polyfluoroalkyl substances (PFAS), are amphiphilic molecules that comprise hydrophobic fluorocarbon chains and hydrophilic head-groups. Fluorinated surfactants have been utilized in many applications, e.g., fire-fighting foams, paints, household/kitchenware items, product packaging, and fabrics. These compounds then made their way into the environment, and have been detected in soil, fresh water, and seawater. From there, they can enter human bodies. Fluorinated surfactants are persistent in water and soil environments, and their adsorption onto mineral surfaces contributes to this persistence. This review examines how fluorinated surfactants adsorb onto mineral surfaces, by analyzing the thermodynamics and kinetics of adsorption, and the underlying mechanisms. Adsorption of fluorinated surfactants onto mineral surfaces can be explained by electrostatic interactions, hydrophobic interactions, hydrogen bonding, and ligand and ion exchange. The aqueous pH, varying salt or humic acid concentrations, and the surfactant chemistry can influence the adsorption of fluorinated surfactants onto mineral surfaces. Further research is needed on fluorinated surfactant adsorbent materials to treat drinking water, and on strategies that can modulate the fate of these compounds in specific environmental locations.

Association between Nonionic Amphiphilic Polymer and Ionic Surfactant in Aqueous Solutions: Effect of Polymer Hydrophobicity and Micellization

The interaction in aqueous solutions of surfactants with amphiphilic polymers can be more complex than the surfactant interactions with homopolymers. Interactions between the common ionic surfactant sodium dodecyl sulfate (SDS) and nonionic amphiphilic polymers of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) type have been probed utilizing a variety of experimental techniques. The polymer amphiphiles studied here are Pluronic F127 (EO₁₀₀PO₆₅EO₁₀₀) and Pluronic P123 (EO₁₉PO₆₉EO₁₉), having the same length PPO block but different length PEO blocks and, accordingly, very different critical micellization concentrations (CMC). With increasing surfactant concentration in aqueous solutions of fixed polymer content, SDS interacts with unassociated PEO-PPO-PEO molecules to first form SDS-rich SDS/Pluronic assemblies and then free SDS micelles. SDS interacts with micellized PEO-PPO-PEO to form Pluronic-rich SDS/Pluronic assemblies, which upon further increase in surfactant concentration, break down and transition into SDS-rich SDS/Pluronic assemblies, followed by free SDS micelle formation. The SDS-rich SDS/Pluronic assemblies exhibit polyelectrolyte characteristics. The interactions and mode of association between nonionic macromolecular amphiphiles and short-chain ionic amphiphiles are affected by the polymer hydrophobicity and its concentration in the aqueous solution. For example, SDS binds to Pluronic F127 micelles at much lower concentrations (~0.01 mM) when compared to Pluronic P123 micelles (~1 mM). The critical association concentration (CAC) values of SDS in aqueous PEO-PPO-PEO solutions are much lower than CAC in aqueous PEO homopolymer solutions.

Curcumin encapsulated colloidal amphiphilic block co-polymeric nanocapsules: colloidal nanocapsules enhance photodynamic and anticancer activities of curcumin

Curcumin-based novel colloidal nanocapsules were prepared from amphiphilic poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (F108). These colloidal nanocapsules appeared as spherical particles with size ranging between 270 and 310 nm. Curcumin fluorescence spectra exhibited an aggregation-induced 23 nm red-shift of the emission maximum in addition to the enhancement of the fluorescence quantum yield in these nanocapsules. The cytotoxicity of curcumin and colloidal nanocapsules was assessed using human derived immortalized cell lines (A549 and A375 cells) in the presence and absence of light irradiation. The nanocapsules exhibited a >30-fold decrease in IC₅₀, suggesting enhanced anticancer activity associated with curcumin encapsulation. Higher toxicity was also reported in the presence of light irradiation (as shown by the IC₅₀ data), indicating their potential for future application in photodynamic therapy. Finally, A375 cells treated with curcumin and the nanocapsules showed a significant increase in single- and/or double-strand DNA breaks upon exposure to light, indicating promising biological effects.

Transport of Flexible, Oil-Soluble Diblock and BAB Triblock Copolymers to Oil/Water Interfaces

The connection between block copolymer architecture and adsorption at fluid/fluid interfaces is poorly understood. We characterize the interfacial properties of a well-defined series of polyethylene oxide/polydimethyl siloxane (PDMS) diblock and BAB triblock copolymers at the dodecane/water interface. They are oil-soluble and quite flexible because of their hydrophobic PDMS block. Rather than relying on equilibrium interfacial measurements for which it is difficult to mitigate experimental uncertainty during adsorption, we combine measurements of steady-state adsorption, dilatational rheology, and adsorption/desorption dynamics. Steady-state interfacial pressure is insensitive to interfacial curvature and mostly agrees with theory. Adsorption does not occur in the diffusive limit as is the case for many aqueous, small-molecule surfactants. Dilatational rheology reveals differences in behavior between the diblocks and triblocks, and all interfaces possess elasticities below the thermodynamic limit. Desorption dynamics show that material exchange between the interface and the neighboring fluid occurs too slowly to relax dilatational stresses. The mechanism of relaxation occurs at the interface, likely from the reorientation of adsorbed chains.

Investigation of Formulation and Process Parameters of Wet Media Milling to Develop Etodolac Nanosuspensions

PURPOSE

Etodolac (ETD) is one of the non-steroidal anti-inflammatory drugs which has low aqueous solubility issues. The objective of this study was to develop ETD nanosuspensions to improve its poor aqueous solubility properties while investigating formulation and process parameters of wet media milling method via design of experiment (DoE) approach.

METHODS

The critical formulation parameters (CFP) were selected as ETD amount, stabilizer type and ratio as well as critical process parameters (CPP) which were bead size, milling time and milling speed. The two-factorial-2³ and The Box-Benkhen Designs were generated to evaluate CFP and CPP, respectively. Particle size (PS), polydispersity index (PDI) and zeta potential (ZP) were analyzed as dependent variables. Characterization, physical stability and solubility studies were performed.

RESULTS

Optimum nanosuspensions stabilized by PVP K30 and Poloxamer 188 showed 188.5 ± 1.6 and 279.3 ± 6.1 nm of PS, 0.161 ± 0.049 and 0.345 ± 0.007 PDI, 14.8 ± 0.3 and 16.5 ± 0.4 mV of ZP values, respectively. The thermal properties of ETD did not change after milling and lyophilization process regarding to DSC analysis. Also, the crystalline state of ETD was preserved. The morphology of particle was smooth and spherical on SEM. The dry-nanosuspensions stayed physically stable for six months at room temperature. The solubility of nanosuspensions increased up to 13.0-fold in comparison with micronized ETD.

CONCLUSIONS

In conclusion, it is found that the poor solubility issue of ETD can be solved by nanosuspension. DoE approach provided benefits such as reducing number of experiments, saving time and improving final product quality by using wet media milling.

Rapid characterization of neutral polymer brush with a conventional zetameter and a variable pinch of salt

The fundamental and practical importance of particle stabilization has motivated various characterization methods for studying polymer brushes on particle surfaces. In this work, we show how one can perform sensitive measurements of neutral polymer coating on colloidal particles using a commercial zetameter and salt solutions. By systematically varying the Debye length, we study the mobility of the polymer-coated particles in an applied electric field and show that the electrophoretic mobility of polymer-coated particles normalized by the mobility of non-coated particles is entirely controlled by the polymer brush and independent of the native surface charge, here controlled with pH, or the surface-ion interaction. Our result is rationalized with a simple hydrodynamic model, allowing for the estimation of characteristics of the polymer coating: the brush length L, and the Brinkman length ξ, determined by its resistance to flows. We demonstrate that the Debye layer provides a convenient and faithful probe to the characterization of polymer coatings on particles. Because the method simply relies on a conventional zetameter, it is widely accessible and offers a practical tool to rapidly probe neutral polymer brushes, an asset in the development and utilization of polymer-coated colloidal particles.

Comprehensive Bioanalysis of Ultrahigh Molecular Weight, Highly Disperse Poly(ethylene oxide) in Rat via Microsolid Phase Extraction and RPLC-Q-Q-TOF Coupled with the MSALL Technique

Ultrahigh molecular weight (UHMW) poly(ethylene oxide) (PEO) is a synthetic hydrophilic polymer with wide dispersity which shows considerable promise as a hemostatic agent in the treatment of gastrointestinal bleeding. Currently there is no analytical method for the determination of highly disperse UHMW PEO in biological samples that would allow its characterization in vivo and support its clinical development. Although liquid chromatography-tandem mass spectrometry (LC-MS/MS) is a powerful bioanalytical tool, it faces major challenges when applied to UHMW PEO. In this work, we report a novel bioanalytical method for the determination of UHMW PEO involving microsolid phase extraction (μ-SPE), chromatography on a PLRP-S 1000 Å reversed phase column and detection by positive ion Q-Q-TOF MS using the MS^ALL technique. In this mode, dissociation of all precursor ions in Q2 generated a series of product ions at m/z 89.0715, 133.0854, 177.1047, and 221.1475 of which the product ion at m/z 133.0854 was common to all precursor ions and enabled quantitation of all polymers in UHMW PEO. The method was successfully applied to the determination of UHMW PEO polymers in rat plasma, urine, and feces after oral administration of 1700 kDa PEO. The results show that UHMW PEO is not absorbed into the blood and is largely eliminated unchanged in feces over 48 h. We maintain the method is sufficiently robust to be used in routine bioanalysis of polymers with UHMW and wide dispersity.

Biosurfactants, natural alternatives to synthetic surfactants: Physicochemical properties and applications

Biosurfactants comprise a wide array of amphiphilic molecules synthesized by plants, animals, and microbes. The synthesis route dictates their molecular characteristics, leading to broad structural diversity and ensuing functional properties. We focus here on low molecular weight (LMW) and high molecular weight (HMW) biosurfactants of microbial origin. These are environmentally safe and biodegradable, making them attractive candidates for applications spanning cosmetics to oil recovery. Biosurfactants spontaneously adsorb at various interfaces and self-assemble in aqueous solution, resulting in useful physicochemical properties such as decreased surface and interfacial tension, low critical micellization concentrations (CMCs), and ability to solubilize hydrophobic compounds. This review highlights the relationships between biosurfactant molecular composition, structure, and their interfacial behavior. It also describes how environmental factors such as temperature, pH, and ionic strength can impact physicochemical properties and self-assembly behavior of biosurfactant-containing solutions and dispersions. Comparison between biosurfactants and their synthetic counterparts are drawn to illustrate differences in their structure-property relationships and potential benefits. Knowledge of biosurfactant properties organized along these lines is useful for those seeking to formulate so-called green or natural products with novel and useful properties.

Perfluorooctanoate in Aqueous Urea Solutions: Micelle Formation, Structure, and Microenvironment

Fluorinated surfactants are used in a wide range of applications that involve aqueous solvents incorporating various additives. The presence of organic compounds such as urea is expected to affect the self-assembly of fluorinated surfactants, however, very little is known about this. We investigated the effect of urea on the micellization in water of the common fluorinated surfactant ammonium perfluorooctanoate (APFO), and on the structure and microenvironment of the micelles that APFO forms. Addition of urea to aqueous APFO solution decreased the critical micellization concentration (CMC) and increased the counterion dissociation. The observed increase in surface area per APFO headgroup and decrease in packing density at the micelle surface suggest the localization of urea at the micelle surface in a manner that reduces headgroup repulsions. Micropolarity data further support this picture. The results presented here indicate that significant differences exist between urea effects on fluorinated surfactant and on hydrocarbon surfactant micellization in aqueous solution. For example, the CMC of sodium dodecyl sulfate (SDS) increased with urea addition, while the increase in surface area per headgroup and packing density of SDS with urea addition are much lower than those observed for APFO. This study informs fluorinated surfactant fate and transport in the environment, and also applications involving aqueous media in which urea or similar additives are present.

How does temperature impact the conformation of single DNA molecules below melting temperature?

The double stranded DNA molecule undergoes drastic structural changes during biological processes such as transcription during which it opens locally under the action of RNA polymerases. Local spontaneous denaturation could contribute to this mechanism by promoting it. Supporting this idea, different biophysical studies have found an unexpected increase in the flexibility of DNA molecules with various sequences as a function of the temperature, which would be consistent with the formation of a growing number of locally denatured sequences. Here, we take advantage of our capacity to detect subtle changes occurring on DNA by using high throughput tethered particle motion to question the existence of bubbles in double stranded DNA under physiological salt conditions through their conformational impact on DNA molecules ranging from several hundreds to thousands of base pairs. Our results strikingly differ from previously published ones, as we do not detect any unexpected change in DNA flexibility below melting temperature. Instead, we measure a bending modulus that remains stable with temperature as expected for intact double stranded DNA.

Block Copolymers as Dispersants for Single-Walled Carbon Nanotubes: Modes of Surface Attachment and Role of Block Polydispersity

When using amphiphilic polymers to exfoliate and disperse carbon nanotubes in water, the balance between the hydrophobic and hydrophilic moieties is critical and nontrivial. Here, we investigate the mode of surface attachment of a triblock copolymer, Pluronics F127, composed of a central hydrophobic polypropylene oxide block flanked by hydrophilic polyethylene oxide blocks, onto single-walled carbon nanotubes (SWNTs). Crucially, we analyze the composition in dispersant of both the as-obtained dispersion (the supernatant) and the precipitate-containing undispersed materials. For this, we combine the carefully obtained data from ¹H NMR peak intensities and self-diffusion and thermogravimetric analysis. The molecular motions behind the observed NMR features are clarified. We find that the hydrophobic blocks attach to the dispersed SWNT surface and remain significantly immobilized leading to ¹H NMR signal loss. On the other hand, the hydrophilic blocks remain highly mobile and thus readily detectable by NMR. The dispersant is shown to possess significant block polydispersity that has a large effect on dispersibility. Polymers with large hydrophobic blocks adsorb on the surface of the carbonaceous particles that precipitate, indicating that although a larger hydrophobic block is good for enhancing adsorption, it may be less effective in dispersing the tubes. A model is also proposed that consistently explains our observations in SWNT dispersions and some contradicting findings obtained previously in carbon nanohorn dispersions. Overall, our findings help elucidating the molecular picture of the dispersion process for SWNTs and are of interest when looking for more effective (i.e., well-balanced) polymeric dispersants.

Determination Method and Size Dependence of Interfacial Tension between Nanoparticles and a Solution

Interfacial tension plays an important role in the processes of preparation, research, and application of nanomaterials. Because the interfacial tension is fairly difficult to be determined by experiments, it is still unclear about the effect of particle size on interfacial tension. In this paper, we proposed a method to determine the interfacial tensions and its temperature coefficients by determining the electrode potential of the nanoparticle electrode. Nano-Au with different radii (from 0.9 to 37.4 nm) in an aqueous solution was taken as a research system; we determined the interfacial tension and its temperature coefficient of the interface and discussed the size dependence. At the same time, we found surprisingly that this method can also be applied to determine the Tolman length and the atomic radius. The results show that the particle size of nano-Au has remarkable influences on the interfacial tension and its temperature coefficient. As the particle size decreases, the interfacial tension and the absolute value of its temperature coefficient increase. With the decrease of radius, the influences of the particle size on the interfacial tension and its temperature coefficient become more significant, whereas the influences can be neglected when the radius exceeds 10 nm. In addition, the results also show that the Tolman length is a negative value, and temperature has little effect on the Tolman length. This research can provide a new method to conveniently and reliably determine the interfacial tension on interfaces between nanoparticles and solutions, the temperature coefficients, the Tolman lengths, and the atomic radii; and the size dependences can provide important references for preparation, research, and application of nanomaterials.

Photoresponsive Drug/Gene Delivery Systems

Light as an external stimulus can be precisely manipulated in terms of irradiation time, site, wavelength, and density. As such, photoresponsive drug/gene delivery systems have been increasingly pursued and utilized for the spatiotemporal control of drug/gene delivery to enhance their therapeutic efficacy and safety. In this review, we summarized the recent research progress on photoresponsive drug/gene delivery, and two major categories of delivery systems were discussed. The first category is the direct responsive systems that experience photoreactions on the vehicle or drug themselves, and different materials as well as chemical structures responsive to UV, visible, and NIR light are summarized. The second category is the indirect responsive systems that require a light-generated mediator signal, such as heat, ROS, hypoxia, and gas molecules, to cascadingly trigger the structural transformation. The future outlook and challenges are also discussed at the end.

Formulation of Poloxamers for Drug Delivery

Poloxamers, also known as Pluronics®, are block copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), which have an amphiphilic character and useful association and adsorption properties emanating from this. Poloxamers find use in many applications that require solubilization or stabilization of compounds and also have notable physiological properties, including low toxicity. Accordingly, poloxamers serve well as excipients for pharmaceuticals. Current challenges facing nanomedicine revolve around the transport of typically water-insoluble drugs throughout the body, followed by targeted delivery. Judicious design of drug delivery systems leads to improved bioavailability, patient compliance and therapeutic outcomes. The rich phase behavior (micelles, hydrogels, lyotropic liquid crystals, etc.) of poloxamers makes them amenable to multiple types of processing and various product forms. In this review, we first present the general solution behavior of poloxamers, focusing on their self-assembly properties. This is followed by a discussion of how the self-assembly properties of poloxamers can be leveraged to encapsulate drugs using an array of processing techniques including direct solubilization, solvent displacement methods, emulsification and preparation of kinetically-frozen nanoparticles. Finally, we conclude with a summary and perspective.

Micellization Thermodynamics of Pluronic P123 (EO20PO70EO20) Amphiphilic Block Copolymer in Aqueous Ethylammonium Nitrate (EAN) Solutions

Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers (commercially available as Pluronics or Poloxamers) can self-assemble into various nanostructures in water and its mixtures with polar organic solvents. Ethylammonium nitrate (EAN) is a well-known protic ionic liquid that is expected to affect amphiphile self-assembly due to its ionic nature and hydrogen bonding ability. By proper design of isothermal titration calorimetry (ITC) experiments, we determined the enthalpy and other thermodynamic parameters of Pluronic P123 (EO20PO70EO20) micellization in aqueous solution at varied EAN concentration. Addition of EAN promoted micellization in a manner similar to increasing temperature, e.g., the addition of 1.75 M EAN lowered the critical micelle concentration (CMC) to the same extent as a temperature increase from 20 to 24 °C. The presence of EAN disrupts the water solvation around the PEO-PPO-PEO molecules through electrostatic interactions and hydrogen bonding, which dehydrate PEO and promote micellization. At EAN concentrations lower than 1 M, the PEO-PPO-PEO micellization enthalpy and entropy increase with EAN concentration, while both decrease above 1 M EAN. Such a change can be attributed to the formation by EAN of semi-ordered nano-domains with water at higher EAN concentrations. Pyrene fluorescence suggests that the polarity of the mixed solvent decreased linearly with EAN addition, whereas the polarity of the micelle core remained unaltered. This work contributes to assessing intermolecular interactions in ionic liquid + polymer solutions, which are relevant to a number of applications, e.g., drug delivery, membrane separations, polymer electrolytes, biomass processing and nanomaterial synthesis.