Hydrophobic and electrostatic interactions in the adsorption of fibronectin at maleic acid copolymer films

Adsorption and desorption of fibronectin (FN) were investigated at thin films of alternating maleic acid copolymers with octadecene (POMA) and with propene (PPMA). The hydrophobicity and charge density of the polymers were modulated by the choice of the comonomer. In consequence, the dominant forces between the substrate and the protein were specified as hydrophobic interaction for POMA and electrostatic interaction for PPMA. The adsorption kinetics were investigated in situ as variations of the optical thickness, adsorbed mass, and viscoelastic properties (detected by reflectometric interference spectroscopy and quartz crystal microbalance technique, respectively) while alterations of the electrosurface properties were derived from surface conductivity data and isoelectric points (by streaming potential/current measurements using a microslit electrokinetic setup). The results demonstrate that the interfacial mode of adsorbed FN depends on the predominant interactions: large amounts of FN were tightly bound to POMA by hydrophobic interactions. In contrast, FN adsorbed on PPMA was concluded to attain an unfolded structure allowing for the "electrostatic matching" of positively charged residues on FN with the maleic acid groups. This conclusion was supported by the acidic IEP of 3.2 found for FN on PPMA and a significant reduction of the surface conductivity of the FN-covered polymer film, whereas FN on POMA showed an IEP of 4.2 (close to the intrinsic IEP of FN), indicating a stochastic orientation of the adsorbed protein.     

Functional films of maleic anhydride copolymers under physiological conditions

Reactivity and swelling of nanometer films of alternating maleic anhydride copolymers were investigated in dependence on the kind of comonomer and molar mass of copolymer in aqueous solution at pH 7.4 and pH 3.0 in order to reveal their characteristics under physiological conditions. Fully hydrolyzed (maleic acid) chains of the copolymers with styrene, propene, and ethylene comonomers covalently bound to SiO2 substrates showed a "mushroom" swelling behavior at pH 7.4 with a layer thickness scaling of N3/5. Decreasing the environmental pH was found to induce a comonomer-dependent shrinking or collapse of the immobilized polymers due to the change in ionization. From the swelling kinetics of non-hydrolyzed chains, the time constants and characteristics of swelling and anhydride hydrolysis were determined and found to depend on the type of comonomer. The short- and long-term swelling kinetics [l approximately t and approximately ln(t)1/2] were found to be in agreement with theoretical models of polymer swelling, while at intermediate time scales enhanced swelling was observed due to hydrolysis reaction of maleic anhydride groups. The findings elucidate the variety of properties of maleic anhydride copolymer films under physiological conditions, which can advantageously be applied for biofunctionalization of different templates.     

Novel method to characterize the hydrolytic decomposition of biopolymer surfaces

Present pharmaceutical research is focused on the development, modification and characterisation of new drug delivery systems. Among the many different substances, biodegradable polymers and copolymers are of practical importance, especially if their degradation byproducts are non-toxic. The polymeric drug carriers are not easily wettable by water or aqueous solutions, i.e. they are hydrophobic. This surface hydrophobicity is unfavourable for keeping drug carriers circulating in the blood long enough to release the drug so that it reaches its target. Therefore, copolymers with components of different hydrophobicity were introduced, to make them less hydrophobic and hence more suitable for drug delivery in the human body. Exploratory experiments with one homopolymer, , -poly(lactic acid), , -PLA and two of its copolymers, , -poly(lactic/glycolic acid), and , -PLGA with 85/15 and 50/50 copolymer ratios were carried out. Films of these substances were prepared by dip coating onto hydrophobic and hydrophilic substrates. The changes in wettability of the polymer layers, caused by the direct contact with an aqueous environment (soaking the samples in distilled water), have been studied to model the hydrolytic decomposition of polymer surfaces and to follow the changes in their wettability by dynamic contact angle measurements in a non-destructive manner. It was found that each polymer film became less hydrophobic (dynamic contact angles decreased) and more heterogeneous as the decomposition progressed with time. Increasingly significant decreases in contact angles were observed for the copolymer films containing 15 and 50% glycolic acid, during the 50–80-day-long study. These findings were supported by gel chromatographic analysis of the soaking liquids. It was concluded that the homopolymer layer of , -PLA was the most resistant to hydrolysis and the stability of copolymer films decreased with increasing glycolic acid ratio in the copolymers. This is accordance with the fact that the less crystalline poly(glycolic acid) is more hydrophilic and hence less resistant to hydrolytic decomposition, than the poly(lactic acid). The effect of pH on the rate of hydrolysis of polymer films was also established; the influence of pH on the decomposition was best demonstrated, again, for the copolymer with 50/50 component ratio. The outcome of these experiments showed that the contact angle measuring method enables us to detect, follow and interpret the hydrolytic decomposition of biopolymer substances in a non-invasive manner.     

Positive working resists sensitive to visible light,I: poly(tert-butyl and 2-phenylpropyl-2 methacrylates) sensitized with diphenyliodonium salt — p-aminobenzylidene dye system

Visible-light-sensitive positive type resists have been developed. The chemistry to form images is based on the cleavage of side chain ester bonds of poly(methacrylates) catalyzed by an acid which is generated on sensitized photodecomposition of a diphenyliodonium (DPI) salt. Homopolymers and copolymers of tert-butyl methacrylate (BMA) and 2-phenylpropyl-2 methacrylate (PPMA) were used as acid labile polymers. Exposure of thin films of the poly(methacrylates) containing DPI salt and p-dimethylaminobenzylidene derivatives to an Ar laser beam emitting 488 nm light and subsequent heat treatment resulted in solubility alteration of the polymers, which became soluble in a protic solvent system. Considerable reduction of film thickness was observed after heating an image-wise exposed thin film of PPMA polymers. The minimum exposure energies of 488 nm light for the positive image formation were 60 mJ/cm² and 40 mJ/cm² for BMA and PPMA homopolymers, respectively.     

Surface properties and swelling behaviour of hyperbranched polyester films in aqueous media

Thin films of hydroxyl (POH) and carboxyl (PCOOH) terminated aromatic hyperbranched polyesters (HBPs) were prepared by spin coating on silicon wafers and subsequently annealed above their glass transition temperature (T_g). The surface properties and the swelling behaviour of these films in aqueous buffer solutions were studied as a function of annealing time using contact angle measurements and ellipsometry. Non-annealed films were hydrophilic with surface free energies of 51 mJ/m² for POH and 49 mJ/m² for PCOOH, respectively. The swelling behaviour of the polymer films in buffer solution with pH 7.4 was described in terms of changes of the thickness and effective refractive index of the swollen layer. Under identical conditions a lower water uptake was found for hydroxyl terminated HBPs (POH) which were annealed more then 2 h. The lower water uptake correlates with the surface properties of the films. The annealed films were less hydrophilic. Their surface free energy was 38 mJ/m² independent of the annealing. Films of carboxyl terminated HBPs (PCOOH) showed similar surface properties after annealing. However, these films were unstable under the same conditions in aqueous solutions. Stable PCOOH films were obtained by additional covalent binding to the substrate using an epoxy silane as a coupling agent.     

Recent progress in the determination of solid surface tensions from contact angles

Advancing contact angles of different liquids measured on the same solid surface fall very close to a smooth curve when plotted as a function of liquid surface tension, i.e., gamma(lv)costheta versus gamma(lv). Changing the solid surface, and hence gamma(sv), shifts the curve in a regular manner. These patterns suggest that gamma(lv)costheta depends only on gamma(lv) and gamma(sv). Thus, an "equation of state for the interfacial tensions" was developed to facilitate the determination of solid surface tensions from contact angles in conjunction with Young's equation. However, a close examination of the smooth curves showed that contact angles typically show a scatter of 1-3 degrees around the curves. The existence of the deviations introduces an element of uncertainty in the determination of solid surface tensions. Establishing that (i) contact angles are exclusively a material property of the coating polymer and do not depend on experimental procedures and that (ii) contact angle measurements with a sophisticated methodology, axisymmetric drop shape analysis (ADSA), are highly reproducible guarantees that the deviations are not experimental errors and must have physical causes. The contact angles of a large number of liquids on the films of four different fluoropolymers were studied to identify the causes of the deviations. Specific molecular interactions at solid-vapor and/or solid-liquid interfaces account for the minor contact angle deviations. Such interactions take place in different ways. Adsorption of vapor of the test liquid onto the solid surface is apparently the only process that influences the solid-vapor interfacial tension (gamma(sv)). The molecular interactions taking place at the solid-liquid interface are more diverse and complicated. Parallel alignment of liquid molecules at the solid surface, reorganization of liquid molecules at the solid-liquid interface, change in the configuration of polymer chains due to contact with certain probe liquids, and intermolecular interactions between solid and liquid molecules cause the solid-liquid interfacial (gamma(sl)) tension to be different from that predicted by the equation of state, i.e., gamma(sl) is not a precise function of gamma(lv) and gamma(sv). In other words, the experimental contact angles deviate from the "ideal" contact angle pattern. Specific criteria are proposed to identify probe liquids which eliminate specific molecular interactions. Octamethylcyclotetrasiloxane (OMCTS) and decamethylcyclopentasiloxane (DMCPS) are shown to meet those criteria, and therefore are the most suitable liquids to characterize surface tensions of low energy fluoropolymer films with an accuracy of +/-0.2 mJ/m2.     

Modification of the wettability of a polymeric substrate by pH effect. Determination of the surface acid dissociation constant by contact angle measurements

The wetting properties of a substrate can be changed by chemical reaction. Here, we studied simple materials with acid-base properties, by preparing poly(vinyl chloride) films containing lauric acid. These substrates constitute simple polymeric surfaces the wettability of which can be easily controlled by the acid-base equilibrium. The roughness of the material was then varied by adding Aerosil (hydrophobic fumed silica). We then studied the wettability of these materials toward aqueous buffer solutions between pH 2 and 12 from contact angle measurements. The variation of the contact angle of a droplet of buffer solution with the pH of the solution was described by a simple thermodynamic model requiring only two parameters. Thus, we could characterize the acid polymer by an effective surface acid dissociation constant the value of which was consistent with those obtained with a similar surface. We showed that the behavior of any substrate could be described even if the surface geometry was not well-known.     

聚乙二醇-聚谷氨酸-聚丙氨酸三嵌段共聚物的合成及其胶束的pH-响应性药物控制释放

通过大分子引发剂ω-胺基-α-甲氧基聚乙二醇引发N-羧基-α-氨基环内酸酐开环聚合和酸性水解制备了一种具有pH-响应性的三嵌段共聚物聚乙二醇-聚谷氨酸-聚丙氨酸(mPEG-PLGA-PLAA).通过核磁共振、ζ-电势、动态光散射、电子显微镜等手段表征了此类三嵌段共聚物的自组装过程及所形成胶束的pH-响应性.使用圆二色谱和红外光谱,分析了胶束结构随环境pH值转变过程中聚氨基酸链段二级结构的变化.以阿霉素作为模型药物,研究了三嵌段共聚物的载药能力和在不同pH条件下的药物释放能力.在碱性条件下,PLGA链段去质子化,链段从疏水性变为亲水性,胶束中间层由于水合作用变得松散,药物释放速率增加;在酸性条件下,PLGA链段质子化,不带电荷,与阿霉素药物分子间的静电相互作用消失.同时,PLGA链段α-螺旋含量增加,形成由链内氢键维持的刚性棒状结构,将链段周围包埋的药物分子"挤出",加速了药物的释放.     

Wettability of biodegradable surfaces

The study of the interfacial characteristics of biodegradable polymers/copolymers is of importance from the point of view of both surface science and pharmaceutical/cosmetic applications. Films formed from biodegradable polymers allow systematic wettability studies on surfaces with a wide range of copolymer (chemical) compositions. The possibility of interchanging these drug carrier polymers, if their wetting characteristics are similar, could be beneficial to diverse applications. Low-rate dynamic contact angles on films (solvent cast on polar substrates, i.e. on silicon wafer) of poly(lactic acid), and its copolymers with poly(glycolic acid), (with four different copolymer ratios of 85/15, 75/25, 65/35 and 50/50) were measured by axisymmetric drop shape analysis-profile (ADSA-P) with four liquids: water, formamide, 2,2′-thiodiethanol and 3-pyridylcarbinol. The solid surface tensions, γ_sv, were calculated from the advancing contact angles, θ_A. The surface topography of the polymer films was investigated by atomic force microscopy (AFM). The surface composition of the polymer layers was analyzed by X-ray photoelectron spectroscopy (XPS). The advancing contact angles were found to be independent of the composition of the copolymers, while the receding angles, θ_R, did decrease with increasing ratio of the polar component [poly(glycolic acid)] in the copolymers. The solid surface tensions calculated from the advancing contact angles of the liquids for all homo- and copolymers were the same within the error limit; the mean value being γ_sv=35.6 ± 0.2 mJ/m². The surface roughness, which was obtained from AFM images, increased with increasing poly(glycolic acid) ratio, without affecting the advancing contact angles. The constancy of γ_sv is attributed to the effect of the surface activity of the nonpolar segments of the polymer chains, which oriented to form the outermost layer of the film. This was confirmed by XPS analysis. Received: 06 November 2000 Accepted: 09 May 2001     

Conversion of solid poly(methyl vinyl ether-alt-maleimide) to poly(methyl vinyl ether-alt-maleic anhydride)

Solid poly(methyl vinyl-alt-maleimide), when subjected to heating at 100°C while being vacuum pumped at 0.1 mm Hg pressure, was converted to a copolymer in which a substantial portion of the imide groups were converted to anhydride groups. Similarly, heating at 100°C at atmospheric pressure in a circulating air oven brought about the same reaction but at a faster rate. This confirms the hypothesis that the formation of maleic anhydride comonomer units from poly(methyl vinyl ether-alt-ammonium maleamate) not only proceeds directly by ring closure of amic acid formed by loss of ammonia but probably also includes, as a parallel pathway, hydrolysis by atmospheric moisture of maleimide comonomer units.     

Adsorption of poly(N‐ethyl‐4‐vinyl pyridinium bromide) onto langmuir‐blodgett films built up from amphiphilic polymers

The interaction of a strong cationic polyelectrolyte, poly(N‐ethyl‐4‐vinyl pyridinium bromide), with Langmuir‐Blodgett (LB) films built up from four monolayers of amphiphilic derivatives of the alternating copolymers of maleic acid and alkenes (one of the monolayers was formed by the amphiphilic copolymer containing pyrenyl groups as fluorescent labels) was examined. Transformations of absorbance spectra and quenching of fluorescence of the LB films were detected after their contact with aqueous solutions of the cationic polyelectrolyte. These changes were attributed to the adsorption of poly(N‐ethyl‐4‐vinyl pyridinium bromide) onto such films. The efficiency of this process was found to be rather sensitive to the variations in pH of the surrounding medium: adsorption of the cationic polyelectrolyte onto the LB films was pronounced in basic media while it became rather weak in acidic media.     

RAFT radical copolymerization of beta‐pinene with maleic anhydride and aggregation behaviors of their copolymer in aqueous solution

RAFT copolymerization of beta‐pinene and maleic anhydride was successfully achieved for the first time, using 1‐phenylethyl dithiobenzoate as chain transfer agent in a mixed solvent of tetrehydrofuran and 1.4‐dioxane (1:9, v/v) at a feed molar ratio of beta‐pinene to maleic anhydride as 3:7, and the alternating copolymer was prepared with predetermined molecular weight and narrow molecular weight distribution. Furthermore, using former alternating copolymer as a macro‐RAFT agent, block copolymer poly(beta‐pinene‐alt‐maleic anhydride)‐b‐polystyrene was synthesized in a chain extending with styrene. Hydrolysis of this block copolymer under acidic conditions formed a new amphiphilic block copolymers poly(beta‐pinene‐alt‐maleic acid)‐b‐polystyrene whose self‐assembly behaviors in aqueous solution at different pH were investigated through SEM and DLS. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1422–1429     

Effect of layer integrity of spin self-assembled multilayer films on surface wettability

We investigated the correlation between surface wettability and internal structure of polyelectrolyte (PE)/PE and PE/inorganic multilayer films prepared by the spin self-assembly (SA) method. Spin self-assembled poly(allylamine hydrochloride) (PAH)/poly(sodium 4-styrenesulfonate) (PSS) multilayer films deposited from PE solutions of 10 mM show the distinct oscillation in contact angles with variation of the outermost PE layer, representing the saturated values in contact angles of individual PAH and PSS layers. These contact angles are also well consistent with the angles measured from respective PE layers (i.e., PAH and PSS) of the spin SA (PAH/CdS-COO-) and (CdS-NH3+/PSS) films carrying the flat interface between PE and inorganic CdS nanoparticle layers as confirmed by X-ray reflectivity. Furthermore, based on the contact angle of CdS-NH3+ layer in the ordered (CdS-NH3+/PSS) films, the change in surface wettability of CdS-NH3+ layers of two different spin SA (CdS-NH3+/poly(methacrylic acid) (PMAA)) multilayer films with ordered and disordered internal structure is also investigated. The films with ordered and disordered internal structure were fabricated by the pH adjustment of PMAA. The CdS-NH3+ layer in both CdS-NH3+/PSS and CdS-NH3+/PMAA multilayer films with the ordered internal structure has the contact angle of about 25 +/- 2 degrees irrespective of the PSS or PMAA sublayer. As a result, the same surface wettability of PE or inorganic layers, despite different sublayers, strongly indicates that the spin SA method in optimum condition allows the top surface to be completely covered with a low level ofinterdigitation with a sublayer at each deposition step, and this leads to the conclusion that physical and chemical characteristics of the sublayers have no significant influence on those of the outermost layer.     

Influence of RAFT end‐groups on the water swelling of poly(N‐propyl methacrylate)

The immersion of poly(n‐propyl methacrylate), PPMA, films (ca., 425 nm) in water induces swelling that is measured in‐situ using spectroscopic ellipsometry. Unexpectedly, the end group of the PPMA resulting from the reversible addition‐fragmentation chain transfer (RAFT) polymerization impacts the temperature dependence of swelling, despite their relatively high molecular weights (ca., 30 kDa). At 25 °C, dithiobenzoate terminated PPMA (PPMA‐DB) leads to significantly less swelling (5.6 vol %) than the dodecylsulfanylthiocarbonyl terminated PPMA (PPMA‐DD, 9.0 vol %). These PPMA films swell significantly more than expected due to a common carboxylic acid end group. As temperature is increased, the swelling for PPMA‐DB increases and that for PPMA‐DD decreases, with a crossover at approximately 35 °C–40 °C where the swelling is indistinguishable between the two polymers. The swelling kinetics exhibit two stages: an initial rapid swelling within the first minute of immersion and then a slow increase in thickness over multiple hours. The water contact angle of PPMA‐DB increases on heating, while the water contact angle of PPMA‐DD is invariant. This difference in the temperature dependence of the hydrophobicity is consistent with that for swelling. These results illustrate the potential unexpected consequences of residual RAFT fragment end groups on physical properties of polymers even at relatively high molecular weights. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 77–84     

pH effects on the complexation, miscibility and radiation-induced crosslinking in poly(acrylic acid)-poly(vinyl alcohol) blends

The effect of pH on the complexation of poly(acrylic acid) with poly(vinyl alcohol) in aqueous solution, the miscibility of these polymers in the solid state and the possibility for crosslinking the blends using gamma radiation has been studied. It is demonstrated that the complexation ability of poly(vinyl alcohol) with respect to poly(acrylic acid) is relatively low in comparison with some other synthetic non-ionic polymers. The precipitation of interpolymer complexes was observed below the critical pH of complexation (pH(crit1)), which characterizes the transition between a compact hydrophobic polycomplex and an extended hydrophilic interpolymer associate. Films prepared by casting from aqueous solutions at different pH values exhibited a transition from miscibility to immiscibility at a certain critical pH, pH(crit2), above which hydrogen bonding is prevented. It is shown here that gamma radiation crosslinking of solid blends is efficient and only results in the formation of hydrogel films for blends prepared between pH(crit1) and pH(crit2). The yield of the gel fraction and the swelling properties of the films depended on the absorbed radiation dose and the polymer ratio. [Diagram: see text] SEM image of an equimolar PAA-PVA blend cast from a pH 4.6 solution.     

Self-doping effect in poly(o-methoxyaniline)/poly(3-thiopheneacetic acid) layer-by-layer films

Nanostructured films from two conducting polymers, poly(o-methoxyaniline) (POMA) and poly(3-thiopheneacetic acid) (PTAA), were fabricated with the layer-by-layer (LBL) technique. The electrochemical response of the LBL films differs from that of a POMA cast film, even in a potential range where PTAA is inactive. This is attributed to differences in the diffusion-controlled charge and mass transport, where distinct ionic species participate in the LBL films, as demonstrated by quartz crystal microbalance measurements. The results show that the transport properties of conducting polymers can be changed by alternation with layers of appropriate materials in LBL films.     

Covalent Immobilization of Subtilisin A onto Thin Films of Maleic Anhydride Copolymers

Enzymes cleaving the biopolymer adhesives of fouling organisms are attracting attention for the prevention of biofouling. We report a versatile and robust method to confine the serine protease Subtilisin A (or Subtilisin Carlsberg) to surfaces to be protected against biofouling. The approach consists of the covalent immobilization of the protease onto maleic anhydride copolymer thin film coatings. High‐swelling poly(ethylene‐alt‐maleic anhydride) (PEMA) copolymer layers permitted significantly higher enzyme loadings and activities than compact poly(octadecene‐alt‐maleic anhydride) (POMA) films. Substantial fractions of the immobilized, active enzyme layers were found to be conserved upon storage in deionized water for several hours. Ongoing studies explore the potentialities of the developed bioactive coatings to reduce the adhesion of various fouling organisms.

     

Optically Triggered Dissociation of Kinetically Stabilized Block Copolymer Vesicles in Aqueous Solution

We demonstrate a strategy for using an optical stimulus to trigger the dissociation of block copolymer (BCP) vesicles in aqueous solution. The BCP, comprising hydrophilic poly(ethylene oxide) (PEO) and a block of poly(methacrylic acid) bearing a number of spiropyran methacrylate comonomer units (P(MAA‐co‐SPMA)), was allowed to firstly self‐assemble into large vesicles in aqueous solution at pH = 3 with protonated carboxylic acid groups, and then become kinetically stable at pH = 8 due to the glassy vesicle membrane of P(MAA‐co‐SPMA). Fast dissociation of the vesicles was achieved through a cascade of events triggered by UV‐induced isomerization from neutral spiropyran to charged merocyanine in the membrane.

     

Experimental Study on Contact Angle Patterns: Liquid Surface Tensions Less Than Solid Surface Tensions

The interpretation of contact angles in terms of solid surface tensions is not trivial. In the past, we and others have postulated that contact angles should be measured with liquid of surface tension larger than the anticipated solid surface tension, i.e., gamma(lv)>gamma(sv). This has recently been disputed. It is also not entirely obvious how to proceed experimentally since gamma(sv) is not known initially. Typically, one starts with a liquid of high gamma(lv) (such as water) and goes lower. We have stopped in the past when the contact angles became small. A question arises as to what would happen if we would go on. Contact angles of liquids with gamma(lv) less than or near gamma(sv) were measured on eight polymer-coated solid surfaces. The experimental contact angle patterns for gamma(lv)gamma(sv) were compared. Results suggest that contact angle interpretation in terms of solid surface tensions requires contact angles to be measured for gamma(lv)>gamma(sv) because the Young equation is not applicable for gamma(lv)相似文献   

Adsorption of hydrophobically modified poly(acrylamide)-co-(acrylic acid) on an amino-functionalized surface and its response to the external solvent environment

The adsorption of hydrophobically modified poly(acrylamide)-co-(acrylic acid), designated as PAM-C14-AA (x%) (x = 5, 10, 20, representing the mole percent of acrylic acid units), at an amino-functionalized silicon surface was studied. The effect of polymer charge density was determined by varying the acrylic acid content of the copolymer. Characteristics of the adsorbed layer were evaluated by atomic force microscopy, water contact angle measurements, and X-ray photoelectron spectroscopy. The results showed that the adsorption behavior of PAM-C14-AA (x%) is influenced by the balance among the electrostatic, hydrogen-bonding, and hydrophobic interactions. Adjusting the solution pH and polymer charge density significantly affects the morphology and thickness of the adsorbed film. Furthermore, it was found that the adsorbed PAM-C14-AA undergoes conformational rearrangements when the surface is wetted by selected organic solvents. The resultant morphology and wettability of the films indicated that the different affinities of the solvents for different segments of PAM-C14-AA (x%) can be considered to be the possible cause of the conformational rearrangements of adsorbed polymer.