Polymer Solution Interface Research Articles

Does Media Choice Matter When Evaluating the Performance of Hydroxypropyl Methylcellulose Acetate Succinate-Based Amorphous Solid Dispersions?

Hydroxypropyl methylcellulose acetate succinate (HPMCAS) is a weakly acidic polymer that is widely used in the formulation of amorphous solid dispersions (ASDs). While the pH-dependent solubility of HPMCAS is widely recognized, the role of other solution properties, including buffer capacity, is less well understood in the context of ASD dissolution. The goal of this study was to elucidate the rate-limiting steps for drug and HPMCAS release from ASDs formulated with two poorly water soluble model drugs, indomethacin and indomethacin methyl ester. The surface area normalized release rate of the drug and/or polymer in a variety of media was determined. The HPMCAS gel layer apparent pH was determined by incorporating pH sensitive dyes into the polymer matrix. Water uptake extent and rate into the ASDs were measured gravimetrically. For neat HPMCAS, the rate-limiting step for polymer dissolution was observed to be the polymer solubility at the polymer-solution interface. This, in turn, was impacted by the gel layer pH which was found to be substantially lower than the bulk solution pH, varying with medium buffer capacity. For the ASDs, the HPMCAS release rate was found to control the drug release rate. However, both drugs reduced the polymer release rate with indomethacin methyl ester having a larger impact. In low buffer capacity media, the presence of the drug had less impact on release rates when compared to observations in higher strength buffers, suggesting changes in the rate-limiting steps for HPMCAS dissolution. The observations made in this study can contribute to the fundamental understanding of acidic polymer dissolution in the presence and absence of a molecularly dispersed lipophilic drug and will help aid in the design of more in vivo relevant release testing experiments.

Low cross-linked terpenes-based porous polymers with reduced content of divinylbenzene: synthesis, physicochemical properties and sorption abilities

The low cross-linked porous polymers were prepared using terpene compounds (citral, limonene and pinene) and divinylbenzene with a suspension method. The prepared materials were characterized by: ATR-FTIR, low temperature nitrogen adsorption–desorption, TGA, swelling ratio and solid phase extraction (SPE) experiments. ATR-FTIR verified the chemical structures of the polymers. All the materials had developed internal structure with SBET in the range of 45–190 m2/g and high thermal stability. Sorption properties of the terpene-based polymers were tested for phenolic compounds (phenol, 2-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol) and popular non-steroidal anti-inflammatory drugs (aspirin, paracetamol and ibuprofen) and an antibiotic (ampicillin) with a dynamic solid phase extraction (SPE) method. The recoveries of 2,4-dichlorophenol and 2,4,6-trichlorophenol remained at a level 80–100% for all new materials even for 10–13 concentration cycles. Very high recoveries (70–100%) were also obtained for ibuprofen and aspirin from the citral- and limonene-based polymers using one-component solutions. However, when using ternary component solutions, the maximum recoveries of ibuprofen reached 70%. Paracetamol recoveries did not exceed 20%, while these for ampicillin ranged from 40 to 80%. The performed studies have proven that the process is affected by both chemical nature of adsorbents and adsorbates. Especially in the case of multicomponent solutions, the acid—base balance of solutes in the solution and on the polymer—solution interface should be taken into account as an important factor determining obtained recoveries.

Electrocatalytic Properties of Ni(II) Schiff Base Complex Polymer Films.

Platinum electrodes were modified with polymers of the (±)-trans-N,N′-bis(salicylidene)-1,2-cyclohexanediaminenickel(II) ([Ni(salcn)]) and (±)-trans-N,N′-bis(3,3′-tert-Bu-salicylidene)-1,2-cyclohexanediaminenickel(II) ([Ni(salcn(Bu))]) complexes to study their electrocatalytic and electroanalytical properties. Poly[Ni(salcn)] and poly[Ni(salcn(Bu))]) modified electrodes catalyze the oxidation of catechol, aspartic acid and NO2−. In the case of poly[Ni(salcn)] modified electrodes, the electrocatalysis process depends on the electroactive surface coverage. The films with low electroactive surface coverage are only a barrier in the path of the reducer to the electrode surface. The films with more electroactive surface coverage ensure both electrocatalysis inside the film and oxidation of the reducer directly on the electrode surface. In the films with the most electroactive surface coverage, electrocatalysis occurs only at the polymer–solution interface. The analysis was based on cyclic voltammetry, EQCM (electrochemical quartz crystal microbalance) and rotating disc electrode method.

Convective meniscus splitting of polysaccharide microparticles on various surfaces

In contrast to convective self-assembly methods for colloidal crystals etc., “convective meniscus splitting method” was developed to fabricate three-dimensionally ordered polymeric structures. By controlling the geometry of evaporative interface of polymer solution, a deposited membrane with uniaxial orientation and layered structures can be prepared. Here it is demonstrated that xanthan gum polysaccharide microparticles with diameter ~ 1 µm can bridge a millimeter-scale gap to form such a membrane because the capillary force among the particles is more dominant than the gravitational force on the evaporative interface. This method is applicable for various substrates with a wide range of wettability (water contact angle, 11°–111°), such as glass, metals, and plastics. The specific deposition can be also confirmed between frosted glasses, functional-molecules-modified glasses, and gold-sputtered substrates. By using such a universal method, the membrane formed on a polydimethylsiloxane surface using this method will provide a new strategy to design a functional polysaccharide wall in microfluidic devices, such as mass-separators.

Laser-induced carbon nanotube microcapsules formation through depletion enhanced deposition

We report a method to fabricate carbon nanotube (CNT) microcapsule through laser-induced bubble formation in a polyethylene glycol-modified CNT (PEG-CNT) solution in the presence of PEG. A low-power laser is focused on a heat-absorbing surface to create a bubble. While PEG-CNTs in the solution are deposited on the bubble surface to form a microcapsule. The shape stability of microcapsule during swelling process is measured in different concentrations of PEG solutions. The stable CNTs microcapsules form with uniform spherical shape within 8 seconds in a 2% PEG solution, while PEG-CNTs only randomly aggregate without the presence of PEG molecules. Thus, we propose that the deposition of PEG-CNTs is enhanced by PEG molecules due to depletion interaction. Comparing with other methods, assembling PEG-CNTs microcapsules at liquid-air interface of polymer solution by optical heating greatly reduce the time and provide good quality of CNTs microcapsules. This study may enable applications of PEG-CNTs microcapsules.

The formation and properties of polypyrrole doped with an immobile antibiotic

Oxacillin, a semisynthetic penicillinase-resistant penicillin, was incorporated as a dopant within polypyrrole. The oxacillin-doped polymer was deposited at gold, platinum and the biocompatible substrate, titanium. A doping level of 0.12 was obtained during the early stages of polymer formation. Smooth polymer films were deposited, but more structure was observed in the cross sections of the polymer. This was attributed to a reduction in the concentration of the anionic oxacillin as the interfacial pH decreased due to the electropolymerisation reaction, shifting the equilibrium in favour of the undissociated oxacillin, HOx. Although HOx has poor solubility and may precipitate at the polymer solution interface during formation of the polymer, there was no evidence of any reduction in the conducting properties of the polymer. High charging capacitance values of 12 to 15 mF cm−2 were estimated for the oxidised polymer. These conducting properties were attributed to a slow rate of electropolymerisation that prevented significant acidification at the electrode interface, preventing the build-up of HOx. The oxacillin-doped polypyrrole showed cation exchange properties. Oxacillin was maintained within the polymer, as the polymer was cycled between its oxidised and reduced states to give an immobilised antibiotic with very little oxacillin detected in the solution phase. The application of a layer of chitosan gave rise to a slight reduction in the charging capacitance of PPyOx. However, improved adhesion was observed for the reduced PPyOx with the application of the chitosan layer.

Stable hydrophilic poly(dimethylsiloxane) via glycan surface functionalization

Polydimethylsiloxane (PDMS) is an extremely important and versatile polymeric material for biomedical and microfluidic devices due to a range of desirable properties. Control of the hydrophilicity of PDMS surfaces is of significant interest due to the potential for developing surfaces with tunable protein adsorption or cell adhesion properties. We report the formation of stable hydrophilic PDMS surfaces by covalent modification with glycans via aryldiazonium chemistry. The PDMS surface was modified by a two step-process including an activation of the PDMS surface, followed by reaction with aryldiazonium glycosides in aqueous solution. The functionalized PDMS was characterized by atomic force microscopy, infrared and X-ray photoelectron spectroscopy, water contact angle measurements and fluorescence microscopy. Our results demonstrate that glycans immobilized via this methodology have the dual function of imparting hydrophilicity and stabilizing the modified surface against hydrophobic recovery. Importantly, the presentation of thus immobilized glycosides makes them available to specific lectin-glycan binding interactions at the polymer-solution interface while, in the absence of specific binding interactions, leads to a reduction in albumin adsorption. This approach provides a novel and efficient route to stable hydrophilic PDMS surfaces with a broad range of applications.

Correlation between adhesion of aqueous solutions of nonionic and anionic surfactant mixture with short-chain alcohols to polymer surface and their adsorption at interfaces. I. Adhesion tension and adsorption

Contact angle measurements of aqueous solutions of a p-(1,1,3,3-tetramethylbutyl) phenoxypoly(ethylene glycol) (Triton X-100)/sodium dodecylsulfate (SDDS) mixture with a short-chain alcohol (methanol, ethanol or propanol) on polytetrafluoroethylene (PTFE) and nylon-6 surfaces were made. Complete spreading of the studied solutions was observed only in the case of nylon-6. Contact angle isotherms were considered with regard to alcohol activity as well as the adsorption of the surfactant mixture and alcohol at the polymer-solution interface. For this analysis solid-liquid interfacial tension and changes of adhesion tension as a function of the surface tension of the solution were taken into account. It appeared that in the range of alcohol concentration in which it is present in the monomeric form in the bulk phase, the Gibbs surface excess concentration of the surfactant mixture and alcohol at the PTFE-solution interface is close to that at the solution-air interface. However, alcohol activity at these interfaces differ from each other. The adsorption of the surface active agents at the nylon-6-solution interface is much lower than at the solution-air interface.

Dispersion of hydroxyapatite nanoparticles in solution and in polycaprolactone composite scaffolds.

The dispersion behaviour of hydroxyapatite nanoparticles (HAP) and surface-modified HAP was studied in 1,4-dioxane (DO), water and poly(ε-caprolactone) (PCL) solutions and the relationship between these and the dispersion in composite PCL scaffolds prepared by thermally induced phase separation (TIPS) was examined. Investigation of the change in particle sizes by dynamic light scattering, showed that the modification of HAP by adsorption or covalent attachment of heparin via a 3-aminopropyltriethoxysilane (APTES) layer improved the dispersion stability of the particles in water/DO mixtures, while no improvement was observed in DO. The distribution of the particles within the composite scaffolds was determined using a combination of transmission electron microscopy and a calcium quantification method which was used to determine distribution of the particles in the vertical direction. While the scaffolds fabricated in DO had particles embedded within the walls of the scaffold, the scaffolds fabricated in a DO/water mixed solvent showed the particles partitioned to the surface of the scaffold walls, which is likely because the particles acted as interface stabilisers and were not miscible with the PCL rich phase. Therefore, it can be concluded that the polymer-solvent system used, as well as the phase separation mechanism that occurs, significantly influences the distribution of the particles in the scaffolds and thus the particle behaviour in solution is not necessarily a good predictor for the ability to fabricate scaffolds with a high degree of particle dispersion and hence for overall materials performance. Bulk crystallinity and compressive modulus were examined and it was determined that no significant changes occurred compared with the pristine PCL, while the surface bioactivity of the scaffolds had improved significantly, indicating that the particles were present at the polymer-solution interface.

Comparison of the influence of polyaspartic acid and polylysine functional groups on the adsorption at the Cr2O3—Aqueous polymer solution interface

Polyamino acids are a group of synthesized polymers obtained by polymerization of a given kind of amino acid monomer. Because of high biodegradability of this class of polymers, they can be used as flocculation or stabilization agents in the environmental aspects. Therefore determination of their influence on the stability of the aqueous suspension of metal oxides is important. An influence of different functional groups of polyamino acids, their molecular weight and concentration on the adsorption at the chromium (III) oxide (Cr2O3)—aqueous solution interface was determined. Experiments were carried out for four values of solution pH varying from 3 to 10 (3, 4, 7.6 and 10, respectively). Two polymers were used: anionic polyaspartic acid (ASP) of 6800 and 27,000 as well as polylysine (LYS) of 4900 and 33,000 molecular weights. Changes of surface charge density of colloidal Cr2O3 in the presence and in the absence of macromolecular substances were determined using potentiometric titration. In these studies the influence of the concentration and molecular weight of the ionic polymers on the pHpzc value was determined. Additionally, due to the lack of appropriate literature data, potentiometric titration of the selected polymers was performed to determine pKa values.

Correlation between wetting, adhesion and adsorption in the polymer–aqueous solutions of ternary surfactant mixtures–air systems

The correlation between the wettability of polymers and adsorption of ternary mixtures including CTAB, TX-100 and TX-114 at the polymer–aqueous solution interface as well as the adhesion of aqueous solution of these mixtures to apolar polytetrafluoroethylene (PTFE), monopolar polymethyl methacrylate (PMMA) and nylon 6 was considered on the basis of the contact angle measurements and the literature data of the solutions surface tension. From these considerations it appeared that the efficiency and effectiveness of the adsorption at the PTFE–water interface are comparable to those at the water–air one, but for the PMMA–water and nylon 6–water interfaces they are lower than those for the water–air one for a given series of solutions. The efficiency and effectiveness are reflected in the composition of the mixed monolayer at the polymer–solution interface which even for the PTFE–solution interface is somewhat different from the water–air interface. The properties of the mixed monolayer at these interfaces influence the critical surface tension of polymer wetting which for PTFE is somewhat higher but for PMMA and nylon 6 considerably lower than their surface tension. From these considerations it also appeared that the work of adhesion of aqueous solutions of ternary mixtures of surfactants to the PTFE surface does not depend on the composition and concentration of solution contrary to PMMA and nylon 6. The adhesion work of these solutions to the PMMA and nylon 6 surface can be determined on the basis of van Oss et al. and Neumann et al. equations.

Work of adhesion and activity of aqueous solutions of ternary mixtures of hydrocarbon and fluorocarbon nonionic surfactants at the water–air and polymer–water interfaces

The values of the surface tension and contact angle on the polytetrafluoroethylene surface (PTFE) of aqueous solutions of the ternary mixtures of hydrocarbon surfactants, TX100 and TX165, and fluorocarbon FSN100 at different mole fractions of surfactants in the bulk phase were applied for the studies of the correlation between the adsorption of surfactants at the solution–air and polymer–solution interfaces, the work of adhesion determined from the Young–Dupree equation, the parameter of the intermolecular interactions and the spreading coefficient of aqueous solutions of the studied mixtures on the PTFE surface. For this purpose the values of the total mole fraction and activity of surfactants at the polymer–solution interface obtained from the Sprow and Prausnitz equation were compared to those at the solution–air one. Also on the basis of the mole fraction of the particular surfactants at the PTFE–solution and water–air interface and on the assumption of the additivity of the adhesion work, the work of adhesion of the fluorocarbon tail to the PTFE surface as well as the Lifshitz–van der Waals component of the PTFE surface tension were calculated.

Wetting and Adsorption Properties of Aqueous Solutions of Ternary Mixtures of Hydrocarbon and Fluorocarbon Nonionic Surfactants in PTFE-Solution–Air Systems

The surface tensions and contact angles of aqueous solutions of ternary mixtures of hydrocarbon, TX100 and TX165, and fluorocarbon, FSN100, surfactants at different mole fractions in the bulk phase on a poly(tetrafluoroethylene) (PTFE) surface were studied. The measured values were used in the Young equation for calculations of the polymer–solution interfacial tension in two ways, first, assuming that the surface tension of PTFE is constant and, second, assuming that this tension is not constant and is equal to the value determined for FSN100 at a given concentration. Next, the Gibbs surface excess concentrations of the studied mixtures at the polymer–solution interface were calculated and compared to the corresponding values at the solution–air interface. Also, the critical surface tension of polymer wetting was obtained from the relationship between the adhesion tension and the surface tension of aqueous solutions of the studied mixtures and then related to the adsorption of the surfactants at the water–air and PTFE–water interfaces.

Polymer microchip impedance spectroscopy through two parallel planar embedded microelectrodes: Understanding the impedance contribution of the surrounding polymer on the measurement accuracy

The present work describes a new methodology for contact free impedance of a solution in a polymer microchip taking into account the role played by the surrounding polymer on the impedance accuracy. Measurements were carried out using a photoablated polyethylene terephthalate (PET) microchannel above two embedded microband electrodes. The impedance diagrams exhibit a loop from high frequencies to medium frequencies (1MHz–100Hz) and a capacitive behavior at low frequencies (100–1Hz). The impedance diagrams were corrected by eliminating from the global microchip response the contribution of the impedance of the PET layer between the two microband electrodes. This operation enables a clear observation of the impedance in the microchannel solution, including the bulk solution contribution and the interfacial capacitance related to the surface roughness of the photoablated microchannel. Models for the impedance of solutions of varying conductivity showed that the capacitance of the polymer–solution interface can be modeled by a constant phase element (CPE) with an exponent of 0.5. The loop diameter was found to be proportional to the microchannel resistivity, allowing a cell constant around 4.93×105m−1 in contactless microelectrodes configuration.

Wettability, adhesion, adsorption and interface tension in the polymer/surfactant aqueous solution system: II. Work of adhesion and adsorption of surfactant at polymer–solution and solution–air interfaces

The values of the surface tension of aqueous solutions of Triton X-100, Triton X-114, Triton X-165, sodium dodecylsulfate, sodium hexadecylsulfonate, cetyltrimethylammonium bromide, cetylpyridinium bromide, sodium N-lauryl sarcosinate, dodecyldimethyethylammonium bromide, tetradecyltrimethylammonium bromide and benzyldimethyldodecylammonium bromide and those of contact angle measured in the polytetrafluoroethylene (polymethyl methacrylate, nylon 6)–solution–air system were applied for the studies of correlation between the adsorption of surfactants at the solution–air and polymer–solution interfaces, critical surface tension of polymer wetting and work of adhesion of aqueous solutions of these surfactants to the above mentioned polymer surfaces. On the basis of the surface tension of aqueous solutions of surfactants studied and polymer–solution interface tension the Gibbs surface excess concentration at the polymer–solution interface was calculated and compared to that at the solution–air one. Using the Gibbs surface excess concentration data the molar fraction of surfactants at the polymer–solution interface was determined and compared to that at the solution–air one. The values of the activity of surfactants at the polymer–solution interface obtained from the Sprow and Prausnitz equation were also compared to those at the solution–air one and next used for calculations of the work of adhesion of solution to the polymer surface. The obtained values were compared to those determined from the Young–Dupree equation.

Wettability, adhesion, adsorption and interface tension in the polymer/surfactant aqueous solution system. I. Critical surface tension of polymer wetting and its surface tension

The contact angle of aqueous solutions of Triton X-100, Triton X-114, Triton X-165, sodium dodecylsulfate, sodium hexadecylsulfonate, cetyltrimethylammonium bromide, cetylpyridinium bromide, sodium N-lauryl sarcosinate, dodecyldimethyethylammonium bromide, tetradecyltrimethylammonium bromide and benzyldimethyldodecylammonium bromide on polytetrafluoroethylene, polymethyl methacrylate and nylon 6 was studied. The contact angle values were used in the Young equation for the polymer–solution interface tension calculation and for the determination of the critical surface tension of polymer wetting. The critical surface tension of polymer wetting was obtained on the basis of the relationship between the cosine of contact angle and/or the adhesion tension as a function of the surface tension of aqueous solution of studied surfactants and then was discussed in relation to the Lifshitz–van der Waals components and electron-acceptor and electron-donor parameters of polytetrafluoroethylene, polymethyl methacrylate and nylon 6 surface tension. The role of the parameter of interfacial interactions in the relationship between the critical surface tension of polymer wetting and the surface tension was also considered. This parameter was calculated by using the polymer–solution interface tension as well as the polymer and aqueous solutions of surfactant surface tension.

The wettability of polytetrafluoroethylene and polymethylmethacrylate with regard to interface behaviour of Triton X-165 and short chain alcohol mixtures:: II. Adsorption at water–air and polymer–water interfaces

On the basis of the contact angle data presented in the previous paper, the surface concentration of alcohols and TX-165 at PTFE–water and PMMA–water interfaces was determined. For this determination the polymer–solution interface tension was calculated from the Young equation by using the literature data of the polymers surface tension. Taking into account the Gibbs and Guggenheim-Adam adsorption isotherms of Triton X-165 and alcohols their molar fractions and activity coefficients were determined. Next, the free enthalpy of Triton X-165 and alcohols mixing in the adsorption monolayer at polymer–solution interface was calculated. From the theoretical analysis of the adsorption of the Triton X-165 and alcohols it results that the total adsorption of the mixture and its individual components at PTFE–solution and solution–air interface is nearly the same, but the total adsorption at PMMA–solution interface is considerably lower than that at solution–air one, and the composition of the mixtures at both interfaces is different. It can be also stated that the activity coefficients of Triton X-165 and alcohols in the surface region at solution–air and polymer–solution interface are different.

Label-free DNA electrochemical sensor based on a PNA-functionalized conductive polymer

An electrochemical hybridization biosensor based on peptide nucleic acid (PNA) probe is presented. PNA were attached covalently onto a quinone-based electroactive polymer. Changes in flexibility of the PNA probe strand upon hybridization generates electrochemical changes at the polymer–solution interface. A reagentless and direct electrochemical detection was obtained by detection of the electrochemical changes using square wave voltammetry (SWV). An increase in the peak current of quinone was observed upon hybridization of probe on the target, whereas no change is observed with non-complementary sequence. In addition, the biosensor is highly selective to effectively discriminate a single mismatch on the target sequence. The sensitivity is also presented and discussed.

Fabrication of highly ordered microporous thin films by PS-b-PAA self-assembly and investigation of their tunable surface properties

A facile approach is presented to fabricate three-dimensional ordered microporous thin films by self-assemblyvia an amphiphilic block polymer, polystryene-b-polyacrylic acid (PS-b-PAA). The highly ordered microporous thin films were formed by casting a PS-b-PAA tetrahydrofuran (THF) solution onto a glass slide under high humidity conditions. The condensed water droplets act as sacrificial templates on the air–polymer solution interface based on thermocapillary convection. Some critical influencing factors, such as the concentration of the block polymer solution, the relative humidity of the atmosphere, the properties of the solvent, the spreading volume and the substrates, were investigated to control micropore size and tune film surface properties. The surface composition and wettability of the film were found to be dramatically changed in aqueous solution, and the contact angle of the film surface was interestingly reduced from nearly hydrophobic to super-hydrophilic, which was shown by optical contact angle measurements. The influence of porosity and the ionization degree of PAA on the above properties was investigated. Micropore diameters of the films determine the initial contact angle, while the PAA ionization degree determines the transformation time of the wettability behavior and the final contact angle. The microporous thin films, as potential functional materials, are expected to play an important role in future applications.

Influence of Temperature and Purity of Polyacrylic Acid on its Adsorption and Surface Structures at the ZrO2/Polymer Solution Interface

The influence of temperature and the effect of the purity of polyacrylic acid (PAA) on its conformation on the zirconium oxide surface were studied. Spectrophotometric measurements, potentiometric titrations, electrokinetic and viscosity measurements allowed the determination of the amounts of polymer adsorbed, the surface charge and the zeta potential of solid particles in the absence and presence of the polymer together with the thickness of the polymer adsorption layers. All measurements were carried out over the temperature range 15–40°C.The occurrence of a minimum in the adsorption of PAA between 25–30°C was caused by conformational changes of the polymer macromolecules. For non-filtered PAA, a decrease in polymer adsorption and an increase in the thickness of the adsorbed polymer layers were observed. These result from changes in the polydispersity index of filtered PAA and the blocking of some active sites on the oxide surface by inorganic contamination present in the non-filtered PAA samples.The f...