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Controlling the surface properties of solid polymers is important for practical applications. We here succeeded in controlling the surface segregation of polymers to display carboxy groups on an outermost surface, which allowed the covalent immobilization of functional molecules via the carboxy groups on a substrate surface. Random methacrylate-based copolymers containing carboxy groups, which were protected with perfluoroacyl (Rf) groups, were dip-coated on acrylic substrate surfaces. X-ray photoelectron spectroscopy and contact-angle measurements revealed that the Rf groups were segregated to the outermost surface of the dip-coated substrates. The Rf groups were removed by hydrolysis of the Rf esters in the copolymers, resulting in the display of carboxy groups on the surface. The quantification of carboxy groups on a surface revealed that the carboxy groups were reactive to a water-soluble solute in an aqueous solution. The surface segregation was affected by the molecular structure of the copolymer used for dip-coating. [ABSTRACT FROM AUTHOR]

Recently, although several unconventional luminescent polymers have been synthesized, it still remains a significant challenge to prepare various new fluorescent polymers by functionalization of nonfluorescent polymers. A nonfluorescent 1H,1H,2H,2H-perfluoro-1-decanol grafted to nonfluorescent polystyrene-b-poly(acrylic acid) block copolymers through simply esterification reaction can exhibit strong blue emission. On the basis of control experiments and theoretical simulation, we have proposed that the luminescence stems from interchain n → π* interaction between the lone pair (n) of hydroxyl O atoms of carboxyl units and empty π* orbital of ester carbonyl unit. In addition, the fluorescent polymers are successfully employed for fluorescence imaging in living HeLa cell. [ABSTRACT FROM AUTHOR]

Stimuli-responsive hydrogels represent a class of materials capable of reversibly switching their morphological and physicochemical characteristics. An ultrathin poly(acrylic acid) film (ca. 6 nm) grafted onto the gate of a p-type EGOFET is studied, and the correlation between the swelling state of the hydrogel and the transistor output characteristics is presented. The hydrogel-related swelling process occurring in basic medium causes an increase in threshold voltage due to the abrupt and intense increase of the negative charge density on the gate electrode. The variation of the drain current during the in situ modification of the pH electrolyte allows a quantitative analysis of the hydrogel switching kinetics. This work shows not only the relevance of EGOFET as an analytical tool in the broad sense, i.e., able to follow in real time phase transition processes of stimuli-responsive materials, but also the relevance of using a hydrogel for field-effect-based (bio)detection according to the ability of such material to overcome the well-known Debye length problematics. [ABSTRACT FROM AUTHOR]

Core-shell-corona silica/polymer hybrid nanoparticles with narrow size distribution were prepared in the template of spherical polyelectrolyte brushes (SPB) which consist of a solid polystyrene (PS) core densely grafted with linear poly(acrylic acid) (PAA) chains. The microstructure of obtained hybrid nanoparticles was studied by small-angle X-ray scattering (SAXS) and in combination with dynamic light scattering (DLS) and transmission electron microscopy (TEM). The generation of silica shell within the brush is confirmed by the significant increase of the electron density in the shell, and the silica shell showed a unique inner-loose-outer-dense structure, whose thickness is pH sensitive but is insensitive to ionic strength as revealed by fitting SAXS data. After dissolving the PS core, hollow silica nanoparticles were obtained and determined by SAXS, which should be ideal carriers for pH-triggered drug delivery. SAXS is confirmed to be a powerful method to characterize the core-shell-corona silica/polymer hybrid and hollow silica nanoparticles. [ABSTRACT FROM AUTHOR]

Thiolated poly(acrylic acid) (PAA-SH) functionalized gold nanoparticles were explored as a colloidal catalyst with potential application as a recoverable catalyst where the PAA provides pH-responsive dispersibility and phase transfer capability between aqueous and organic media. This system demonstrates complete nanoparticle recovery and redispersion over multiple reaction cycles without changes in nanoparticle morphology or reduction in conversion. The catalytic activity (rate constant) was reduced in subsequent reactions when recovery by aggregation was employed, despite unobservable changes in morphology or dispersibility. When colloidal catalyst recovery employed a pH induced phase transfer between two immiscible solvents, the catalytic activity of the recovered nanoparticles was unchanged over four cycles, maintaining the original rate constant and 100% conversion. The ability to recover and reuse colloidal catalysts by aggregation/redispersion and phase transfer methods that occur at low and high pH, respectively, could be used for different gold nanoparticle catalyzed reactions that occur at different pH conditions. [ABSTRACT FROM AUTHOR]

We explore the influence of a selective substrate on the composition and sequence statistics during the free radical copolymerization. In particular, we study the radical copolymerization of styrene and acrylic acid in bulk and in silica pores of different sizes. We show that the substrate affects both polymer composition and sequence statistics. We use dissipative particle dynamics simulations to study the polymerization process in detail, trying to pinpoint the parameters responsible for the observed differences in the polymer chain composition and sequences. The magnitude of the observed effect depends on the fraction of adsorbed monomer units, which cannot be described in the framework of the copolymerization theories based on the terminal unit model. [ABSTRACT FROM AUTHOR]

Polyelectrolyte complex (PEC) films made from oppositely charged polymer chains have applications as drug-delivery vehicles, separation membranes, and biocompatible coatings. Conventional layer-by-layer techniques for polyelectrolyte coatings are low-throughput and multistep processes that are quite slow for building films on the order of micrometers. In this work, PEC films are electrochemically deposited using a rapid one-pot method, yielding thick (1 μm) films within short experimental time scales (5 min). This rapid electrodeposition is achieved by exploiting the reduction of hydrogen peroxide at mild electrode potentials that avoid water electrolysis yet trigger the pH-responsive self-assembly of a PEC film composed of poly(acrylic) acid and poly(allylamine) HCl. In situ rheology using an electrochemical quartz crystal microbalance quantified the shear modulus-density product of the deposited layer to be on the order of 107 Pa g/cm3 at a frequency of 15 MHz, with a viscoelastic phase angle of approximately 50°. This electrodeposition scheme furthers the development of PEC coatings for more high-throughput applications, where a fast and efficient single-step approach would be desirable for obtaining coatings. [ABSTRACT FROM AUTHOR]

We demonstrate a robust and tunable micromolding method to fabricate chemically functional poly(acrylamide-co-acrylic acid) (p(AAm-co-AA)) hydrogel microspheres with uniform dimensions and controlled porous network structures for rapid biomacromolecular conjugation. Specifically, p(AAm-co-AA) microspheres with abundant carboxylate functional groups are fabricated via surface-tension-induced droplet formation in patterned poly(dimethylsiloxane) molds and photoinduced radical polymerization. To demonstrate the chemical functionality, we enlisted rapid EDC/NHS (1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS)) chemistry for fluorescent labeling of the microspheres with small-molecule dye fluorescein glycine amide. Epifluorescence imaging results illustrate the uniform incorporation of carboxylate groups within the microspheres and rapid conjugation kinetics. Furthermore, protein conjugation results using red fluorescent protein R-phycoerythrin demonstrate the highly porous nature of the microspheres as well as the utility of the microspheres and the EDC/NHS scheme for facile biomacromolecular conjugation. Combined, these results illustrate the significant potential for our fabrication-conjugation strategy in the development of biofunctionalized polymeric hydrogel microparticles toward rapid biosensing, bioprocess monitoring, and biodiagnostics. [ABSTRACT FROM AUTHOR]

Chemical cross-linking of layer-by-layer assembled films promotes mechanical stability and robustness in a wide variety of environments, which can be a challenge for polyelectrolyte multilayers in saline environments or for multilayers made from weak polyelectrolytes in environments with extreme pHs. Heating branched poly(ethylenimine)/poly(acrylic acid) (BPEI/PAA) multilayers at sufficiently high temperatures drives amidization and dehydration to covalently cross-link the film, but this reaction is rather slow, typically requiring heating for hours for appreciable cross-linking to occur. Here, a more than one order of magnitude increase in the amidization kinetics is realized through microwave heating of BPEI/PAA multilayers on indium tin oxide (ITO)/glass substrates. The cross-linking reaction is tracked using infrared spectroscopic ellipsometry to monitor the development of the cross-linking products. For thick films (∼1500 nm), gradients in cross-link density can be readily identified by infrared ellipsometry. Such gradients in cross-link density are driven by the temperature gradient developed by the localized heating of ITO by microwaves. This significant acceleration of reactions using microwaves to generate a well-defined cross-link network as well as being a simple method for developing graded materials should open new applications for these polymer films and coatings. [ABSTRACT FROM AUTHOR]

Plasma polymerization is traditionally recognized as a homogeneous film-forming technique. It is nevertheless reasonable to ask whether micrometer thick plasma polymerized structures are really homogeneous across the film thickness. Studying the properties of the interfacial, near-the-substrate (NTS) region in plasma polymer films represents particular experimental challenges due to the inaccessibility of the buried layers. In this investigation, a novel non-destructive approach has been utilized to evaluate the homogeneity of plasma polymerized acrylic acid (PPAc) and 1,7-octadiene (PPOD) films in a single measurement. Studying the variations of refractive index throughout the depth of the films was facilitated by a home-built surface plasmon resonance (SPR)/optical waveguide (OWG) spectroscopy setup. It has been shown that the NTS layer of both PPAc and PPOD films exhibits a significantly lower refractive index than the bulk of the film that is believed to indicate a higher concentration of internal voids. Our results provide new insights into the growth mechanisms of plasma polymer films and challenge the traditional view that considers [ABSTRACT FROM AUTHOR]

We report on the synthesis of novelpH- and electro-responsivepolyelectrolyte brushes from a gold substrate by direct one-step nitroxide-mediatedpolymerization of acrylic acid (AA) or copolymerization of AA andstyrene (S). In the latter case, amphiphilic brushes of block–gradientcopolymers PAA-b-(PAA-grad-PS) comprisingone PAA block and one block with the gradient sequence of AA and Swere obtained. The block–gradient copolymers are initiatedfrom the surface by the start of the PAA block. The brushes were characterizedby XPS and ellipsometry. 1H NMR confirmed the gradientsequence of the PAA-grad-PS copolymer block. ThepH- and electro-responsive properties of the brushes were studiedby quartz crystal microbalance with dissipation monitoring (QCM-D)in combination with electrochemistry. This method provides evidenceof swelling of the PAA brushes proportional to the contour lengthof the chains at elevated pH, whereas the response functions of theblock–gradient copolymers are more complex and point to intermolecularaggregation in the brush at low pH. Monitoring of the changes in resonancefrequency and dissipation of the QCM-D also demonstrates that applicationof negative voltage to the substrate leads to swelling of the brush;application of a positive voltage provokes only a transient collapseof the brush in proportion to the applied voltage. [ABSTRACT FROM AUTHOR]

High proton conductivitywas achieved in a polymer multilayer filmwith a well-defined two-dimensional lamella structure. The multilayerfilm was prepared by deposition of poly(N-dodecylacryamide-co-acrylic acid) (p(DDA/AA)) monolayers onto a solid substrateusing the Langmuir–Blodgett technique. Grazing-angle incidenceX-ray diffraction measurement of a 30-layer film of p(DDA/AA) showedstrong diffraction peaks in the out-of-plane direction at 2θ= 2.26° and 4.50°, revealing that the multilayer film hada highly uniform layered structure with a monolayer thickness of 2.0nm. The proton conductivity of the p(DDA/AA) multilayer film parallelto the layer plane direction was 0.051 S/cm at 60 °C and 98%relative humidity with a low activation energy of 0.35 eV, which iscomparable to perfluorosulfonic acid membranes. The high conductivityand low activation energy resulted from the formation of uniform two-dimensionalproton-conductive nanochannels in the hydrophilic regions of the multilayerfilm. The proton conductivity of the multilayer film perpendicularto the layer plane was determined to be 2.1 × 10–13S/cm. Therefore, the multilayer film showed large anisotropic conductivitywith an anisotropic ratio of 2.4 × 1011. [ABSTRACT FROM AUTHOR]

Polycaprolactone(PCL) is a widely utilized bioresorbable polymerin tissue engineering applications. However, the absence of intrinsicfunctional groups in the polymer backbone necessitates the incorporationof functional chemistries to enable the further addition of bioactivemolecules to PCL-based surfaces and scaffolds. The current study aimedto incorporate two different functional groups, amine and carboxylate,first on two-dimensional (2D) spin-coated PCL films and, thereafter,throughout all surfaces within three-dimensional (3D) porous PCL-basedscaffolds, produced using the thermally induced phase separation (TIPS)method, but in a spatially separated manner. Specifically, gamma irradiationinduced grafting of acrylic acid (AA) and 2-aminoethyl methacrylatehydrochloride (AEMA) onto PCL was performed in selected solvents andthe resulting substrates were characterized using X-ray photoelectronspectroscopy (XPS), atomic force microscopy (AFM), and contact anglemeasurements to determine the surface free energy. Results demonstratedthat stepwise graft copolymerization of AEMA and AA allows the fabricationof dual-functional surfaces, with chemistry depending on the orderof grafting of the two monomers. In addition, 3D scaffolds could bedecorated exclusively with carboxylate groups in the interior, whilethe outer surface displayed dual-functionality. This simple surfacemodification methodology, with the ability to create spatially separatedsurface functional groups throughout 3D porous scaffolds post theirfabrication, has the potential to be applied to many current and futurescaffold systems being investigated in the field of tissue engineering. [ABSTRACT FROM AUTHOR]

This work includes both experimentaland theoretical studies ofthe wetting property changes of water on a surface of poly(dimethylsiloxane)(PDMS) modified with different amounts of acrylic acid (AA). The defaultsurface properties of PDMS were changed from hydrophobic to hydrophilicbehavior which was characterized with contact angle measurements bytwo approaches: (i) experimental tests of samples subjected to a photograftingpolymerization procedure to obtain a functionalized surface and (ii)DPD (dissipative particle dynamics) simulations which also involvethe calculation of sets of repulsive parameters determined followingtwo methods: the use of the “Blends” module in the MaterialsStudio software and the calculation of cohesive energy density withmolecular simulations. Changes of contact angle values observed fromboth experimental and numerical simulation results provide qualitativeand quantitative information on the wetting behavior of photograftedsurfaces. [ABSTRACT FROM AUTHOR]

Inthis study, we proposed a catechol chemistry inspired approachto construct surface self-cross-linked polymer nanolayers for thedesign of versatile biointerfaces. Several representative biofunctionalpolymers, P(SS-co-AA), P(SBMA-co-AA), P(EGMA-co-AA), P(VP-co-AA),and P(MTAC-co-AA), were first synthesized via reversibleaddition–fragmentation chain transfer (RAFT) polymerization,and then the catecholic molecules (dopamine, DA) were conjugated tothe acrylic acid (AA) units by the facile carbodiimide chemistry.Then, the catechol (Cat) group conjugated biofunctional polymers,named PSS-Cat, PSBMA-Cat, PEGMA-Cat, PVP-Cat, and PMTAC-Cat, wereapplied for the construction of self-cross-linked nanolayers on polymericsubstrates via the pH induced catechol cross-linking and immobilization.The XPS spectra, surface morphology, and wettability gave robust evidencethat the catechol conjugated polymers were successfully coated, andthe coated substrates possessed increased surface roughness and hydrophilicity.Furthermore, the systematic in vitro investigation of protein adsorption,platelet adhesion, activated partial thromboplastin time (APTT), thrombintime (TT), cell viability, and antibacterial ability confirmed thatthe coated nanolayers conferred the substrates with versatile biologicalperformances. The PSS-Cat coated substrate had low blood componentactivation and excellent anticoagulant activity; while the PEGMA-Catand PSBMA-Cat showed ideal resistance to protein fouling and inhibitionof platelet activation. The PSS-Cat and PVP-Cat coated substratesexhibited promoted endothelial cell proliferation and viability. ThePMTAC-Cat coated substrate showed an outstanding activity on bacterialinhibition. In conclusion, the catechol chemistry inspired approachallows the self-cross-linked nanolayers to be easily immobilized onpolymeric substrates with the stable conformation and multiple biofunctionalities.It is expected that this low-cost and facile bioinspired coating systemwill present great potential in creating novel and versatile biointerfaces. [ABSTRACT FROM AUTHOR]

Kraftlignin grafted with hydrophilic polymers has been preparedusing reversible addition–fragmentation chain-transfer (RAFT)polymerization and investigated for use as a surfactant. In this preliminarystudy, polyacrylamide and poly(acrylic acid) were grafted from a ligninRAFT macroinitiator at average initiator site densities estimatedto be 2 per particle and 17 per particle. The target degrees of polymerizationwere 50 and 100, but analysis of cleaved polyacrylamide was consistentwith a higher average molecular weight, suggesting not all sites wereable to participate in the polymerization. All materials were readilysoluble in water, and dynamic light scattering data indicate polymer-graftedlignin coexisted in isolated and aggregated forms in aqueous media.The characteristic size was 15–20 nm at low concentrations,and aggregation appeared to be a stronger function of degree of polymerizationthan graft density. These species were surface active, reducing thesurface tension to as low as 60 dyn/cm at 1 mg/mL, and a greater decreasewas observed than for polymer-grafted silica nanoparticles, suggestingthat the lignin core was also surface active. While these lignin surfactantswere soluble in water, they were not soluble in hexanes. Thus, itwas unexpected that water-in-oil emulsions formed in all surfactantcompositions and solvent ratios tested, with average droplet sizesof 10–20 μm. However, although polymer-grafted ligninhas structural features similar to nanoparticles used in Pickeringemulsions, its interfacial behavior was qualitatively different. Whileat air–water interfaces, the hydrophilic grafts promote effectivereductions in surface tension, we hypothesize that the low graftingdensity in these lignin surfactants favors partitioning into the hexanesside of the oil–water interface because collapsed conformationsof the polymer grafts improve interfacial coverage and reduce water–hexanesinteractions. We propose that polymer-grafted lignin surfactants canbe considered as random patchy nanoparticles with mixed hydrophilicand hydrophobic domains that result in unexpected interfacial behaviors.Further studies are necessary to clarify the molecular basis of thesephenomena, but grafting of hydrophilic polymers from kraft ligninvia radical polymerization could expand the use of this importantbiopolymer in a broad range of surfactant applications. [ABSTRACT FROM AUTHOR]

Microgel particles of cross-linkedpoly(NIPAM-co-acrylic acid) with different acrylicacid contents are investigatedin solution and in the adsorbed state. As a substrate, silicon witha poly(allylamine hydrochloride) (PAH) coating is used. The temperaturedependence of the deswelling of the microgel particles was probedwith atomic force microscopy (AFM). The inner structure of the adsorbedmicrogel particles was detected with grazing incidence small angleneutron scattering (GISANS). Small angle neutron scattering (SANS)on corresponding microgel suspensions was performed for comparison.Whereas the correlation length of the polymer network shows a divergencein the bulk samples, in the adsorbed microgel particles it remainsunchanged over the entire temperature range. In addition, GISANS indicateschanges in the particles along the surface normal. This suggests thatthe presence of a solid surface suppresses the divergence of internalfluctuations in the adsorbed microgels close to the volume phase transition. [ABSTRACT FROM AUTHOR]

Thermoresponsive microgels bearingprimary amine groups were preparedby the Hofmann rearrangement of methacrylamide groups present in cross-linkedNIPMAM (N-isopropylmethacrylamide) microgels. Mostthermoresponsive microgels are based on NIPAM (N-isopropylacrylamide).By substituting NIPMAM for NIPAM, and methacrylamide for acrylamide,side reactions and the generation of carboxyl groups were preventedduring the Hofmann reaction. The Hofmann rearrangement is sufficientlyslow under our conditions (1 h for a 51% conversion) to permit finecontrol of the primary amine contents in the microgels. When startingwith PNIPMAM microgels containing both methacrylamide and acrylicacid residues, we prepared a series of amphoteric microgels spanninga range of amine contents, all from a common parent microgel. Therefore,every microgel in the series had the same microstructure, cross-linkdensity, and molecular weight. [ABSTRACT FROM AUTHOR]

Controlled drug binding and releasestand among top requirementspostulated for targeted drug delivery systems of the new generations.“Smart” polymers and gels are highly suitable for thecontrolled delivery due to their structural sensitivity to minor environmentalvariations. The aim of this work was to study thermoresponsive polyanionicand polycationic hydrogels of N-isopropylacrylamidecopolymers with acrylic acid and N-aminopropylmethacrylamidein terms of their interaction with two widely used drugs, propranololand ibuprofen. Binding energetics of these drugs by the gels in swollenand collapsed state was estimated by means of high-sensitivity differentialscanning calorimetry. Thermodynamic parameters of the gel collapse(transition temperature, enthalpy, heat capacity increment, and width)were determined as a dependence of the drug concentrations. From thesedata the excess free energy of collapse was calculated as a functionof drug concentration. Deconvolution of this function resulted inthe evaluation of binding parameters and contributions from interactionsof various types to the free energy of binding. The binding mechanismof both drugs to the swollen and collapsed gels was elucidated. Itsmain features are the cooperative character of the drug binding bythe collapsed gel and the predominant role of the hydrophobicity ofdrugs in their affinity for the swollen gel. [ABSTRACT FROM AUTHOR]

Spray-assistedlayer-by-layer (LbL) assembly is far more rapidthan conventional dip-assisted assembly methods and has gained widespreadinterest recently. Even so, it has remained unclear as to how thestructure and properties of the resulting LbL film vary with processingmethod. Here, we compared the thermal properties of poly(ethyleneoxide) (PEO)/poly(acrylic acid) (PAA) and PEO/poly(methacrylic acid)(PMAA) hydrogen-bonded LbL assemblies prepared using both dip-assistedand spray-assisted deposition methods. While the surface morphologiesof PEO/PAA LbL assemblies were similar, those of PEO/PMAA LbL assemblieswere greatly influenced by deposition method. In both PEO/PAA andPEO/PMAA LbL assemblies, glass transition temperatures were not influencedby deposition method, but the transition’s breadth was consistentlylarger for the spray-assisted LbL films. These results indicate thatthe internal structure of spray-assisted LbL films is slightly moreheterogeneous, possibly arising from the shorter time scale of deposition. [ABSTRACT FROM AUTHOR]

The ability of amphiphilicpolymers to self-assemble and form agel or gel-like layer has been investigated by means of both experimentaland theoretical studies on alkylated derivatives of poly(acrylic acid).Experiments were performed to determine the relationship between amphiphilicpolymer chemistry, structure, water retention, and friction in thepresence of hydrophobic substrates. The results indicate that theamphiphilic polymer forms a water-enriched, friction-reducing adsorbedlayer on hydrophobic surfaces. The shear moduli and viscosities ofthe adsorbed layers, as determined by fitting the Voigt model to QCM-Ddata, were consistent with the presence of a gel. Computational studieson HPAA-12 were performed and are consistent with the presence ofadsorbed conformations, in which the lowest free energy in the modelcorresponded to a partially adsorbed molecule, with a small fractionof hydrophobic side chains being compelled, for configurational reasons,to point into the bulk water. This would support the possibility ofthe formation of either a gel-like layer or surface aggregation. However,because the adsorption experiments showed no evidence of aggregation,this strongly suggests the formation of a gel. [ABSTRACT FROM AUTHOR]

Dual stimuli-responsive hollow nanogel spheres servingas an efficient intracellular drug delivery platform were obtainedfrom the spontaneous coassociation of two graft copolymers into thevesicle architecture in aqueous phase. Both copolymers comprise acrylicacid (AAc) and 2-methacryloylethyl acrylate (MEA) units as the backboneand either poly(N-isopropylacrylamide) (PNIPAAm)alone or both PNIPAAm and monomethoxypoly(ethylene glycol) (mPEG)chain segments as the grafts. The assemblies were then subjected tocovalent stabilization within vesicle walls with ester-containingcross-links by radical polymerization of MEA moieties, thereby leadingto hollow nanogel particles. Taking the advantage of retaining a lowquantity of payload within polymer layer-enclosed aqueous chambersthrough the entire loading process, doxorubicin (DOX) in the externalbulk phase can be effectively transported into the gel membrane andbound therein via electrostatic interactions with ionized AAc residuesand hydrogen-bond pairings with PNIPAAm grafts at pH 7.4. With theenvironmental pH being reduced (e.g., from 7.4 to 5.0) at 37 °C,the extensive disruption of AAc/DOX complexes due to the reduced ionizationof AAc residues within the gel layer and the pronounced shrinkageof nanogels enable the rapid release of DOX species from drug-loadedhollow nanogels. By contrast, the drug liberation at 4 °C wasseverally restricted, particularly at pH 7.4 at which the DOX moleculesremain strongly bound with ionized AAc residues and PNIPAAm grafts.The in vitro characterizations suggest that the DOX-loaded hollownanogel particles after being internalized by HeLa cells via endocytosiscan rapidly release the payload within acidic endosomes or lysosomes.This will then lead to significant drug accumulation in nuclei (within1 h) and a cytotoxic effect comparable to free drug. This work demonstratesthat the novel DOX-loaded hollow nanogel particles show great promiseof therapeutic efficacy for potential anticancer treatment. [ABSTRACT FROM AUTHOR]

Hydrogel films have been used extensively in the preparationofbiosensors and biomedical devices. The characteristics of the aqueousinterface of the polymer layer are significant for the biosensor ordevice function; likewise, the changing mechanical properties of thermoresponsivepolymers are an important feature that affects the polymer behavior.Atomic force microscopy was used here to characterize both the surfaceand the mechanical properties of polymeric hydrogel films preparedfrom a thermoresponsive terpolymer of N-isopropylacrylamideand acrylic acid with benzophenonemethacrylate as a photoreactivecross-linker comonomer. The force–distance curves thus obtainedwere analyzed to assess both the surface forces and the mechanicalresponse that were associated with the hydrogel. These propertieswere investigated as a function of temperature, in water and in Trisbuffer, for different degrees of polymer cross-linking. For samplesin water, the distance over which the surface forces were effectivewas found to remain constant as the temperature was increased from26 to 42 °C, even though the mechanical response indicated thatthe samples had been heated past the lower critical solution temperature,or LCST. The bulk of the polymer becomes less soluble above the LCST,although this does not seem to affect the surface properties. Thismay be due to the segregation of the acrylic acid-rich polymer segmentsnear the gel surface, which is in agreement with reports for relatedsystems. [ABSTRACT FROM AUTHOR]

This article reports a novel method to assemble a small anion with exfoliated Mg–Al-layered double hydroxide (LDH) nanosheets into ordered ultrathin films (UTFs) by employing the layer-by-layer assembly technique. The premixing solution of tris(8-hydroxyquinolate-5-sulfonate)aluminum(III) (AQS3–) with three kinds of polyanionspoly(acrylic acid), ((C3H4O2)n, PAA), poly(styrene 4-sulfonate) ([CH2CH(C6H4)SO3]m, PSS), and poly[5-methoxy-2-(3-sulfopropoxy)-1,4-phenylene vinylene] (C12H13O5S)n, PPV)has been used as building blocks to assemble alternatively with LDH nanosheets. The UV–vis absorption and fluorescence spectroscopy of (AQS-polyanion/LDH)nUTFs presents stepwise growth upon increasing deposited cycles in comparison with the (AQS/LDH)nfilm under the same experimental process. (AQS-PPV/LDH)nUTF displays complex fluorescence originating from AQS and PPV. The (AQS/LDH)nand (AQS-polyanion/LDH)nUTFs exhibit higher blue-polarized photoemission character with a luminescence anisotropy (r) of ca. 0.12–0.20 and a longer fluorescence lifetime than that of the Na3AQS film with r= 0.04. X-ray diffraction, scanning electron microscopy, and atomic force microscopy demonstrated that the UTFs were orderly periodically layered structures with a thickness of ca. 3.0 nm per bilayer. Therefore, this work gives a feasible method for immobilizing small anions into the gallery of LDHs. [ABSTRACT FROM AUTHOR]

Biocide emulsions stabilized with various stabilizing agents were prepared and characterized, and their efficiency in bacteria deactivation was evaluated. A number of stabilizing agents were tested for their stabilizing effect on emulsions of thiocyanomethylthiobenzothiazole (TCMTB) biocide. Two agents, the most successful in stabilizing the biocide, were chosen for further studies: high molecular weight polyethyleneimine (PEI) and an amphiphilic block copolymer of poly(caprolactone)-b-poly(acrylic acid) (PCL33-b-PAA33). The emulsion droplet sizes varied between 325 and 500 nm. Deactivation of bacteria was studied by exposing E. coliATCC 11229 bacteria dispersions to emulsions stabilized by positively charged PEI or negatively charged PCL-b-PAA micelles and by measuring their absorbance; E. colido not grow with time in the presence of biocide emulsions. PEI molecules alone act as biocide and deactivate the bacteria. PCL-b-PAA micelles as stabilizing agent do not affect the growth of the E. coli; bacteria are deactivated by TCMTB released from the emulsion droplets. The kinetics of emulsion dissolution studies revealed for both stabilizing agents a decrease in droplet size with time while the emulsions were subjected to dialysis. The biocide was released from the emulsions within ∼250 min; the droplet shells consist mostly of PEI or PCL-b-PAA insoluble complexes with the biocide, which do not dissolve during dialysis. SEM images confirm the presence of residual crumbled shells with holes after 24 h of dialysis. [ABSTRACT FROM AUTHOR]

We report a comprehensive formalism for the electrokinetics (streaming current, Istr) at soft multilayered polyelectrolyte films. These assemblies generally consist of a succession of permeable diffuse layers that differ in charge density, thickness, and hydrodynamic softness. The model, which extends one that we recently reported for the electrokinetics of monolayered soft thin films (Langmuir2010, 26, 18169−18181), is valid without any restriction in the number and thickness of layers, or in the degree of dissociation and density of ionizable groups they carry. It further covers the limiting cases of hard and free draining films and correctly compares to semianalytical expressions derived for Istrunder conditions where the Debye–Hückel approximation applies. The flexibility of the theory is illustrated by simulations of Istrfor a two-layer assembly of cationic and anionic polymers over a large range of pH values and electrolyte concentrations. On this basis, it is shown that the point of zero streaming current (PZSC) of soft multilayered interphases, defined by the pH value where Istr= 0, generally depends on the concentration of the (indifferent) electrolyte. The magnitude and direction of the shift in PZSC with varying salinity are intrinsically governed by the dissymmetry in protolytic characteristics and density of dissociable groups within each layer constituting the film, together with the respective film thickness and hydrodynamic softness. The fundamental effects covered by the theory are illustrated by streaming current measurements performed on two practically relevant systems, a polyelectrolyte bilayer prepared from poly(ethylene imine) (PEI) and poly(acrylic acid) (PAA) and a polymer-cushioned (PEI) bilayer lipid membrane. [ABSTRACT FROM AUTHOR]

In situnanoindentation was performed on a multilayer of poly(acrylic acid) and a high molecular weight, pendant chain polyviologen under controlled electrochemical potential. The modulus of the thin film of polyelectrolyte complex was reversibly modulated, by about an order of magnitude, upon changing the state of charge within the material using the electrochemically active and addressable viologen repeat units. The applied potential, under aqueous conditions, is believed to control the extent of cross-link formation. Simultaneous quartz crystal microbalance measurements revealed the flux of ions into or out of the multilayer during redox cycling. Apparent film modulus also depends on the identity of the last layer. [ABSTRACT FROM AUTHOR]

This study aims to present the fabrication of colloidal photonic crystals (PC) with increased fluorescence properties. The use of a highly fluorescent perylenediimide derivate (PDI) during the soap-free emulsion polymerization of styrene–acrylic acid resulted in monodisperse core–shell particles which allowed the fabrication of PC films. The properties of the hybrid material were studied in comparison with hybrid materials obtained by impregnation of films with chromophore solutions. In both cases an increase of the fluorescence response was observed in addition to a blue shift for the PDI core particles, proving the incorporation of the dye inside the copolymer particles. [ABSTRACT FROM AUTHOR]

The synthesis, characterization, and evaluation of a novel polymer–protein conjugate are reported here. The covalent conjugation of high-molecular weight poly(acrylic acid) (PAA) to the lysine amino groups of met-hemoglobin (Hb) resulted in the covalent conjugation of Hb to PAA (Hb-PAA conjugate), as confirmed by dialysis and electrophoresis studies. The retention of native-like structure of Hb in Hb-PAA was established from Soret absorption, circular dichroism studies, and the redox activity of the iron center in Hb-PAA. The peroxidase-like activities of the Hb-PAA conjugate further confirmed the retention of Hb structure and biological activity. Thermal denaturation of the conjugate was investigated by differential scanning calorimetry and steam sterilization studies. The Hb-PAA conjugate indicated an improved denaturation temperature (Td) when compared to that of the unmodified Hb. One astonishing observation was that polymer conjugation significantly enhanced the Hb-PAA storage stability at room temperature. After 120 h of storage at room temperature in phosphate-buffered saline (PBS) at pH 7.4, for example, Hb-PAA retained 90% of its initial activity and unmodified Hb retained <60% of its original activity under identical conditions of buffer, pH, and temperature. Our conjugate demonstrates the key role of polymers in enhancing Hb stability via a very simple, efficient, general route. Water-swollen, lightly cross-linked, stable Hb-polymer nanogels of 100–200 nm were produced quickly and economically by this approach for a wide variety of applications. [ABSTRACT FROM AUTHOR]

This article describes the mineralization behavior of CaCO3crystals on electrospun cellulose acetate (CA) fibers by using poly(acrylic acid) (PAA) as a crystal growth modifier and further templating synthesis of CaCO3microtubes. Calcite film coatings composed of nanoneedles can form on the surfaces of CA fibers while maintaining the fibrous and macroporous structures if the concentration of PAA is in a suitable range. In the presence of a suitable concentration of PAA, the acidic PAA molecules will first adsorb onto the surface of CA fibers by the interaction between the OH moieties of CA and the carboxylic groups of PAA, and then the redundant carboxylic groups of PAA can ionically bind Ca2+ions on the surfaces of CA fibers, resulting in the local supersaturation of Ca2+ions on and near the fiber surface, which can induce the nucleation of CaCO3on the CA fibers instead of in bulk solution. Calcite microtube networks on the macroscale can be prepared by the removal of CA fibers after the CA@CaCO3composite is treated with acetone. When the CA fiber scaffold is immersed in CaCl2solution with an extended incubation time, the first deposited calcite coatings can act as secondary substrate, leading to the formation of smaller calcite mesocrystal fibers. The present work proves that inorganic crystal growth can occur even at an organic interface without the need for commensurability between the lattices of the organic and inorganic counterparts. [ABSTRACT FROM AUTHOR]

Multilayers of poly(acrylic acid), PAA, and chitosan, CHI, have been built by the layer-by-layer (LbL) method from aqueous solutions at different pH values and analyzed by the dissipative quartz crystal microbalance (D-QCM) and ellipsometry. The results showed that under all of the assembly conditions considered the growth of the films is nonlinear. The thickness of the PAA layers increases as the pH of the assembling solutions decreases, whereas the adsorption of CHI is almost unaffected by the pH conditions. The comparison of the thickness obtained by D-QCM and by ellipsometry has allowed us to calculate the water content of the films, showing that the multilayers are highly hydrated, with an average water content higher than 20%. The analysis of D-QCM data has provided high-frequency values of the complex shear modulus that are in the megapascal range and shows a transition from mainly viscous to mainly elastic behavior for the added PAA layers, depending on the pH. The monomer surface density in each layer (obtained from the combination of ellipsometry and differential refractive index measurements) indicated that the monomer density depends on the assembly conditions. It was found that the adsorption kinetics is a bimodal process, with characteristic times that depend on the number and nature of the layers. Finally, the possibility of using of these multilayers as a drug storage and delivery system has been evaluated. [ABSTRACT FROM AUTHOR]

We use patterned poly(acrylic acid) (PAA) polymer brushes to explore the effects of surface chemistry and topography on cell–surface interactions. Most past studies of surface topography effects on cell adhesion have focused on patterned feature sizes that are larger than the dimensions of a cell, and PAA brushes have been characterized as cell repellent. Here we report cell adhesion studies for RBL mast cells incubated on PAA brush surfaces patterned with a variety of different feature sizes. We find that when patterned at subcellular dimensions on silicon surfaces, PAA brushes that are 30 or 15 nm thick facilitate cell adhesion. This appears to be mediated by fibronectin, which is secreted by the cells, adsorbing to the brushes and then engaging cell–surface integrins. The result is detectable accumulation of plasma membrane within the brushes, and this involves cytoskeletal remodeling at the cell–surface interface. By decreasing brush thickness, we find that PAA can be ‘tuned’ to promote cell adhesion with down-modulated membrane accumulation. We exemplify the utility of patterned PAA brush arrays for spatially controlling the activation of cells by modifying brushes with ligands that specifically engage IgE bound to high-affinity receptors on mast cells. [ABSTRACT FROM AUTHOR]

A novel Cu2+-imprinted fiber (IIF) was prepared by grafting acrylic acid (AA) onto the surface of a polypropylene (PP) fiber and subsequently modified with polyethylenimine (PEI). An examination by infrared spectroscopy and scanning electron microscopy confirmed that the ion-imprinted polymer was successfully introduced onto the surface of a PP fiber. The modification of PP fibers with AA was beneficial to the grafting of PEI onto the fibers. The highest grafting degree of PEI could reach 120 wt % under optimal grafting conditions. This IIF showed excellent tensile and chemical stability in acid solution, which qualified the IIF for practical applications. Besides having a high adsorption capacity for Cu2+(120 mg/g), the IIF adsorbent showed a high selectivity for Cu2+as compared with that of the non-ion-imprinted fiber (NIF). The dynamic adsorption results indicated that IIF can thoroughly remove Cu2+from the solution in a relatively short contact time. The effective treatment volume was about 910 bed volumes. The selectivity coefficient of IIF for Cu2+with respect to Zn2+could reach 76.4. IIF also has good regeneration performance and could maintain almost the same adsorption capacity for copper ions after 10 adsorption–desorption cycles. [ABSTRACT FROM AUTHOR]

Copolymer hydrogels were prepared from an aqueous micellar solution of the nonionic surfactant monomer (surfmer) ω-methoxy poly(ethylene oxide)40undecyl-α-methacrylate (PEO-R-MA-40) and acrylic acid (AA) in a one-step reaction using γ-irradiation. The hydrogels were transparent if the polymerization was carried out at pH ≥ 4, whereas turbid gels were obtained if the polymerization was carried out at lower pH. Exposure of the turbid gels to an aqueous solution of pH 11 led to swelling and clearing, whereas subsequent exposure to pH 1 had the reverse effect. Clear gels prepared at pH 4 became turbid, if exposed to an aqueous solution of lower pH and became clear again if reswollen at higher pH. The pH at which clouding set in increased with the amount of surfmer copolymerized in the gel. Pure poly(acrylic acid) (P-AA) hydrogels did not show any changes in transparency if the pH was varied. The presence of surfmer led to more pronounced shrinking and swelling, especially if the gels were prepared at pH 4. The mechanical stability of P-AA and copolymer hydrogels was studied using elongational flow measurements. The presence of surfmer led to increased mechanical stability of the hydrogels. The increase originates from copolymerized micellar aggregates acting as additional, stable cross-linking units in the gel. The true stress at break of copolymer hydrogels prepared at pH 2.4 (or 4) was 5.5 (or 3.4) times larger than for surfmer-free P-AA gels. Possible origins for the higher stability such as complex formation between P-AA and oxyethylene segments of copolymerized PEO-R-MA-40 are discussed. [ABSTRACT FROM AUTHOR]