Cell adhesion properties of patterned poly(acrylic acid)/poly(allylamine hydrochloride) multilayer films created by room-temperature imprinting technique

Patterned poly(acrylic acid) (PAA)/poly(allylamine hydrochloride) (PAH) multilayer films with line structures of different lateral size and vertical height were fabricated by a room-temperature imprinting technique, and their cell adhesion properties were investigated. The nonimprinted PAA/PAH multilayer films are cytophilic toward NIH/3T3 fibroblasts and HeLa cells whether PAA or PAH is the outer most layer. In contrast, the PAA/PAH multilayer films with a 6.5-microm-line/3.5-microm-space pattern structure are cytophobic toward NIH/3T3 fibroblasts and HeLa cells when the height of the lines is 1.29 microm. By either increasing the lateral size of the patters to 69-microm-line/43-mum-space or decreasing the height of the imprinted lines to approximately 107 nm, imprinted PAA/PAH multilayer films become cytophilic. This kind of transition of cell adhesion behavior derives from the change of the physical pattern size of the PAA/PAH multilayer films and is independent of the chemical composition of the films. The easy patterning of layer-by-layer assembled polymeric multilayer films with the room-temperature imprinting technique provides a facile way to tailor the cellular behavior of the layered polymeric films by simply changing the pattern dimensions.     

From cloudy to transparent: chain rearrangement in hydrogen-bonded layer-by-layer assembled films.

The cloudiness of hydrogen-bonded LBL films assembled from polyvinylpyrrolidone (PVPON) and poly(acrylic acid) (PAA) is studied in detail by two approaches: spectroscopy (Fabry-Pérot fringes) and microscopy (AFM). Fabrication parameters such as temperature, molecular weight, pH value, and rinsing time, have notable influences on film cloudiness. The buildup of the PVPON/ PAA film is a two-stage process of adsorption and chain rearrangement. Generally, adsorption is fast, while chain rearrangement is slow. The fast adsorption process traps defects, whereas the relatively slow chain-rearrangement process can not heal the defects in time; therefore; the number of defects continuously increases as LBL assembly proceeds, and a cloudy, heterogeneous film is produced. However, the as-prepared cloudy films become transparent and homogeneous on subsequent annealing in acidic water. UV/Vis spectroscopy and fluid AFM were applied to monitor this transition ex situ and in situ, respectively. It is found that increasing the annealing temperature accelerates the transition from cloudy to transparent, and the transition of the film made from higher molecular weight polymer is slower.     

Preparation of Poly(acrylic acid) Nano-films by In-situ Polymerization of Acrylic Acid Macroclusters on Silicon Oxide Surfaces

A new method for preparing poly(acrylic acid) (PAA) films on silicon oxide surfaces with smooth morphology has been developed. Acrylic acid (AA) was preferably adsorbed on silicon oxide surfaces in AA/ chloroform binary liquids and formed a hydrogen-bonded organized structure, which was called molecular macrocluster. AA macroclusters on silicon oxide surfaces were in-situ polymerized to obtain molecularly flat polymer films with thickness up to 10 nm. In-situ polymerizations were conducted by photo-irradiation in the presence of a photo initiator, 2,2-dimethoxy-2-phenylacetophenone (DPA). As a reference, the adsorption of PAA polymerized in the bulk solution was examined on silicon oxide surfaces. A series of techniques such as attenuated total reflection–FTIR (ATR-FTIR) spectroscopy, ellipsometry and atomic force microscopy (AFM) was utilized for characterizing two types of films. It was found that flat PAA films with linear hydrogen-bonded COOH could only be obtained by in-situ polymerization, which demonstrated this method was an effective way for preparing molecularly uniform polymer films. The surface morphology and thickness of obtained PAA films were found to be dependent on the monomer concentration, initiator amount and photoirradiation time. Molecularly uniform and flat PAA films were obtained after 5 min irradiation at 0.8 mol% AA in the presence of 5 wt% DPA.     

Fabry-Perot fringes and their application to study the film growth, chain rearrangement, and erosion of hydrogen-bonded PVPON/PAA films

We observed Fabry-Perot fringes in the absorption spectra of hydrogen-bonded layer-by-layer (LBL) films of poly(vinyl pyrrolidone) (PVPON) and poly(acrylic acid) (PAA), which stem from the interferences between beams transmitted and partially reflected at the highly smooth film-air interface and film-quartz interface. The appearance and disappearance of Fabry-Perot fringes can be used to evaluate the homogeneity of the film. They also provide information about the film thickness. Using this optical phenomenon, with a minimal requirement of instrumentation, we studied the effect of several experimental conditions on the film buildup and structure. The film grows linearly with dipping cycles. Films fabricated from higher molecular weight polymers tend to be thicker. Increasing the concentration of the assembly solutions can also make thicker films. However, films from high molecular weight polymers or high concentration assembly solutions may be heterogeneous and do not display Fabry-Perot fringes in their absorption spectra. The defects in these heterogeneous films can be healed by a postannealing in water or diluted HCl to allow the chain rearrangement to complete. We further found the PVPON/PAA films can be eroded by long-term annealing in water or diluted HCl by monitoring the movement of the Fabry-Perot fringes. In most cases, the erosion rate is constant with annealing time. The erosion rate decreases with a decrease in the pH of the media and an increase in the molecular weight of the polymers.     

The role of hydrogen-bonding interaction in poly(vinyl alcohol)/poly(acrylic acid) blending solutions and their films

<正>The aim of this work is to investigate the hydrogen-bonding interaction in poly(vinyl alcohol)(PVA)/poly(acrylic acid)(PAA) blending system and its influence on rheological properties in solution and the physical properties in solid state. Introducing PAA into PVA solutions resulted in a thickening behavior of blend solutions.The viscosity of the solutions increased with PAA content increasing,and a maximum viscosity could be obtained when the ratio of PVA/PAA was 70/30. The intermolecular hydrogen-bonding and miscibility between PVA and PAA in solid state were investigated by differential scanning calorimetry(DSC),Fourier transform infrared spectroscopy(FTIR) and mechanical measurements.The results displayed the great influence of introducing PAA on the properties of blending films.The tensile strength increased from 89.31 MPa to 119.8 MPa and Young's modulus improved by over 300%with increasing PAA concentration compared with those of pure PVA films.By systematically studying the rheological behaviors of solutions and the physical properties of films,the influence of hydrogen-bonding in solutions and solid states were discussed.     

Composite thin film by hydrogen-bonding assembly of polymer brush and poly(vinylpyrrolidone)

Based on hydrogen-bonding layer-by-layer (LBL) assembly in aqueous solution, poly(vinylpyrrolidone) (PVPON) and a spherical polymer brush with a poly(methylsilsesquioxane) (PSQ) core and poly(acrylic acid) (PAA) hair chains were used to fabricate composite multilayer thin films. Hydrogen bonding as the driving force was confirmed by FT-IR spectrometry. A simple method (Filmetric F20) was introduced to determine the thickness and refractive index of the films. The film thickness was found to be a linear function of the number of bilayers. The average increase in thickness per bilayer is 28.3 nm. The film morphology was characterized with scanning electron microscopy and atomic force microscopy. The images obtained from the two instruments show a great resemblance. The films were further calcined to get an inorganic film by removing the organic components, or treated with tetrabutylammonium fluoride (TBAF) to remove the PSQ core and get an organic film. The optical properties and morphological changes induced by these treatments were also studied.     

Partial poly(glutamic acid) <--> poly(aspartic acid) exchange in layer-by-layer polyelectrolyte films. Structural alterations in the three-component architectures

Layer-by-layer (LBL) polyelectrolyte films were constructed from poly(L-glutamic acid) (PGA) and poly(L-aspartic acid) (PAA) as polyanions, and from poly(L-lysine) (PLL) as the polycation. The terminating layer of the films was always PLL. According to attenuated total reflection Fourier transform infrared measurements, the PGA/PLL and PAA/PLL films, despite their chemical similarity, had largely different secondary structures. Extended beta-sheets dominated the PGA/PLL films, while alpha-helices and intramolecular beta-sheets dominated the PAA/PLL films. The secondary structure of the polyelectrolyte film affected the adsorption of human serum albumin (HSA) as well. HSA preserved its native secondary structure on the PGA/PLL film, but it became largely deformed on PAA/PLL films. Both PGA and PAA were able to extrude to a certain extent the other polyanion from the films, but the structural consequences were different. Adding PAA to a (PGA/PLL)5-PGA film resulted in a simple exchange and incorporation: PGA/PLL and PAA/PLL complexes coexisted with their unaltered secondary structures in the mixed film. The incorporation of PGA into a (PAA/PLL)5-PAA film was up to 50% and caused additional beta-structure increase in the secondary structure of the film. The proportions of the two polyanions were roughly the same on the surfaces and in the interiors of the films, indicating practically free diffusion for both polyanions. The abundance of PAA/PLL and PGA/PLL domains on the film surfaces was monitored by the analysis of the amide I region of the infrared spectrum of a reporter molecule, HSA, adsorbed onto the three-component polyelectrolyte films.     

Hydrogen bonded layer-by-layer assembly of poly(2-vinylpyridine) and poly(acrylic acid): Influence of molecular weight on the formation of microporous film by post-base treatment

This article describes the buildup of hydrogen bonded multilayer film of poly(2-vinylpyridine) (P2VP) and poly(acrylic acid) (PAA), and the influence of polymer molecular weight on the formation of microporous film by post-base treatment. The formation of a microporous film involved a two-step mechanism: the release of PAA from P2VP/PAA multilayer, and the reorganization of the remaining P2VP on the substrate. Fourier transform infrared spectroscopy (FT-IR) indicated that the release of PAA from hydrogen bonded multilayer was a rapid process, which was almost independent of the molecular weight of PAA. Furthermore, the molecular weight of P2VP had a great effect on micropore formation by immersing the P2VP/PAA multilayer in basic solution. The rate of micropore formation increased with increasing molecular weight. We anticipate that a comparative study on P2VP/PAA films containing high or low molecular weight polymer provides a way to control the surface morphology, and will be helpful and constructive for the forthcoming discussion about the formation of the microporous film.     

Synthesis, characterization and hydrolytic stability of poly (amic acid) ammonium salt

A series of new poly (amic acid) ammonium salt (PAAS) precursors were prepared by incorporating different amounts of triethylamine (TEA) into terpolymer polyamic acid (PAA), which was synthesized by pyromellitic dianhydride (PMDA), 4,4’-oxydianiline (ODA) and p-phenylenediamine (PDA) in dimethylacetamide (DMAc). Then, the PAAS films were made by casting their solutions onto glass plates followed by the evaporation of the solvent. The chemical structure of PAAS films was confirmed by ¹H NMR and FTIR spectroscopy. Mechanical properties, intrinsic viscosities and solubility of PAAS precursors were examined, respectively. It was found that the intrinsic viscosity of PAA solution obviously decreased with storage time during 30 days, while no distinct changes were observed in the intrinsic viscosity of the PAAS (the mole ratio of TEA/repeating unit of PAA = 2/1) solution after 90 days. The results suggested that hydrolytic stability of the PAAS films was significantly improved as compared with that of PAA film due to the polyelectrolyte structure of PAAS. Moreover, the thermal and mechanical properties of polyimide (PI) films prepared from PAAS precursors were also investigated, respectively.     

Highly ion conductive poly(ethylene oxide)-based solid polymer electrolytes from hydrogen bonding layer-by-layer assembly

We report the development of a solid polymer electrolyte film from hydrogen bonding layer-by-layer (LBL) assembly that outperforms previously reported LBL assembled films and approaches battery integration capability. Films were fabricated by alternating deposition of poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) layers from aqueous solutions. Film quality benefits from increasing PEO molecular weight even into the 10(6) range due to the intrinsically low PEO/PAA cross-link density. Assembly is disrupted at pH near the PAA ionization onset, and a potential mechanism for modulating PEO:PAA ratio within assembled films by manipulating pH is discussed. Ionic conductivity of 5 x 10(-5) S/cm is achievable after short exposure to 100% relative humidity (RH) for plasticization. Adding free ions by exposing PEO/ PAA films to lithium salt solutions enhanced conductivity to greater than 10(-5) S/cm at only 52% RH and tentatively greater than 10(-4) S/cm at 100% RH. The excellent stability of PEO/PAA films even when exposed to 1.0 M salt solutions led to an exploration of LBL assembly with added electrolyte present in the adsorption step. Fortuitously, the modulation of PEO/PAA assembly by ionic strength is analogous to that of electrostatic LBL assembly and can be attributed to electrolyte interactions with PEO and PAA. Dry ionic conductivity was enhanced in films assembled in the presence of salt as compared to films that were merely exposed to salt after assembly, implying different morphologies. These results reveal clear directions for the evolution of these promising solid polymer electrolytes into elements appropriate for electrochemical power storage and generation applications.     

Fabrication and characterization of poly(vinyl alcohol)/chitosan hydrogel thin films via UV irradiation

A series of poly(vinyl alcohol)/chitosan (PVA/CTS) hydrogel thin films were prepared via ultraviolet (UV) irradiation, with acrylic acid (AA) monomer added as a crosslinker without the addition of any other photo-initiator. The swelling behaviors, intermolecular chemical bonds, molecular structures, thermal behaviors, degrees of crystallinity, morphologies of the surfaces and internal structure, and their relationship to the AA content were characterized using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Poly(acrylic acid) (PAA) and its chemical crosslinks formed in hydrogel films via free-radical reactions were confirmed using FTIR and DSC analyses. The XRD patterns indicated that the degree of crystallinity of the hydrogel films decreased as the PAA content was increased. SEM micrographs showed that a uniform interconnected pore structure was formed through the entire hydrogel structure, and a gradient in the crosslinking density through the film thickness was observed to result from extended irradiation times. The swelling behaviors revealed that the formation of PAA and its crosslinking in the hydrogel thin films improved the pH stability and controlled the degree of swelling while retaining a high swelling rate. The successful formation of chemical crosslinking without any specific photo-initiator improves the natural characteristics of CTS and PVA and imparts the resulting PVA/CTS hydrogel thin films with properties that make them very promising in biomedical applications.     

Room-temperature imprinting poly(acrylic acid)/poly(allylamine hydrochloride) multilayer films by using polymer molds

Layer-by-layer assembled polyelectrolyte multilayer films of poly(acrylic acid) (PAA)/poly(allylamine hydrochloride) (PAH) have been successfully patterned by room-temperature imprinting using a Norland Optical Adhesives (NOA 63) polymer mold. The proper amount of water in the PAA/PAH multilayer film can decrease the viscosity of the film and facilitate the imprinting. Many factors, such as imprinting pressure, length of imprinting time, and the structure and size of the patterns in the polymer mold, can produce an influence on the final imprinted pattern structures on multilayer films. A high imprinting pressure of 100 bar and elongated imprinting time of several hours is needed to achieve a patterned PAA/PAH multilayer film with a feature size of several tens of micrometers. With a twice imprinting, grid structures can be successfully produced when a NOA 63 mold having line structures is used. Room-temperature imprinting by using polymer NOA 63 mold provides a facile way to fabricate layered polymeric films with various kinds of pattern structures.     

Modulation of the functions of osteoblast-like cells on poly(allylamine hydrochloride) and poly(acrylic acid) multilayer films

Deposition of layer-by-layer polyelectrolyte multilayer (PEM) films has been a widely applied surface modification technique to improve the biocompatibility of biomaterials. The objective of this study was to investigate the impact of the deposition of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) multilayer films on adhesion, growth and differentiation of osteoblasts-like MG63 cells. PAH and PAA were deposited sequentially onto tissue culture polystyrene at either pH 2.0 or pH 6.5 with 4-21 layers. While the MG63 cells attached poorly on the PAH/PAA multilayer films deposited at pH 2.0, while the cells adhered to the PEM films deposited at pH 6.5, depending on layer numbers. Cell adhesion, proliferation and osteogenic activities (alkaline phosphatase activity, expression of osteogenic marker genes and mineralization) were highest on the 4-layer PAH/PAA film and decreased with increasing layer numbers. On the other hand, the behavior of MG63 cells did not show any difference on the adjacent even and odd layers, except PEM4 and PEM5, i.e. the surface charges of the PAH/PAA multilayer films with over ten layers seem indifferent to osteoblastic functions. The results in this study suggested that the mechanical properties of PEM films may play a critical role in modulating the behavior of osteoblasts, providing guidance for application of PEM films to osteopaedic implants.     

Robust, functionalizable, nanometer-thick poly(acrylic acid) films spontaneously assembled on oxidized aluminum substrates: structures and chemical properties

Immersion of oxidized aluminum substrates in ethanol solutions of poly(acrylic acid) (PAA), followed by extensive solvent immersion, results in tenaciously chemisorbed, nanometer scale, controllable thickness films for a wide range of solution concentrations and molecular weights. Atomic force microscope images reveal isolated polymer globules from adsorption in low-concentration solutions with crossover to conformal, highly uniform, nanometer-thickness films at higher concentrations, an indication that the chemisorbing chains start to overlap and trap underlying segments to form planar chemisorbed films only two or three chains in thickness. Quantitative IR reflection spectroscopy in combination with chemical derivitization on a standard set of 1.0(±0.2) nm thick films reveals a film structure with 5.5(±1) chemisorbed -CO(-)(2) groups/nm(2) and 6.3 unattached -CO(2)H groups/nm(2), with up to ～3.6/nm(2) available for chemical derivitization, a comparable number to typical self-assembled monolayer coverages of ～4-5 molecules/nm(2). Thermal treatment of the ～1 nm chemisorbed films, at even extreme temperatures of ～150 °C, results in almost no anhydride formation via adjacent -CO(2)H condensation, in strong contrast to bulk PAA, a clear indication that the films have a frozen glass structure with effectively no segment and side group mobility. Overall, these results demonstrate that these limiting thickness nanometer films provide a model surface for understanding the behavior of strongly bound polymer chains at substrates and show potential as a path to creating highly stable, chemically functionalized inorganic substrates with highly variable surface properties.     

Synthesis and self‐assembly of thermosensitive double‐hydrophilic poly(N‐vinylcaprolactam)‐b‐poly(N‐vinyl‐2‐pyrrolidone) diblock copolymers

We report on novel diblock copolymers of poly(N‐vinylcaprolactam) (PVCL) and poly(N‐vinyl‐2‐pyrrolidone) (PVPON) (PVCL‐b‐PVPON) with well‐defined block lengths synthesized by the MADIX/reversible addition‐fragmentation chain transfer (RAFT) process. We show that the lower critical solution temperatures (LCST) of the block copolymers are controllable over the length of PVCL and PVPON segments. All of the diblock copolymers dissolve molecularly in aqueous solutions when the temperature is below the LCST and form spherical micellar or vesicular morphologies when temperature is raised above the LCST. The size of the self‐assembled structures is controlled by the molar ratio of PVCL and PVPON segments. The synthesized homopolymers and diblock copolymers are demonstrated to be nontoxic at 0.1–1 mg mL^?1 concentrations when incubated with HeLa and HEK293 cancer cells for various incubation times and have potential as nanovehicles for drug delivery. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2725–2737     

Preparation of thick silica films in the presence of poly(acrylic acid) by using electrophoretic sol-gel deposition

Thick silica films were fabricated by electrophoretic sol-gel deposition of silica particles on a stainless steel sheet. Using sols prepared by the sol-gel method with poly(acrylic acid) (PAA) films of ca. 25 m in thickness were prepared with no cracks. The films were shown to be agglomerates of monodispersed silica particles with PAA. The size of the silica particles decreased with an increase in the added amount of PAA. The deposited weight was considerably larger for the films with PAA than that of the films without PAA.     

Multilayered assemblies composed of brilliant yellow and poly(allylamine) for an optical pH sensor.

Multilayered thin films containing poly(allylamine) (PAA) and brilliant yellow (BY) were prepared on a quartz slide by a layer-by-layer (LBL) deposition technique. The UV-visible spectra of the PAA/BY films were sufficiently changed depending upon the pH value of the solution in which the film was immersed. The response of the PAA/BY films was very fast (within a second) upon pH change from 9.0 to 5.0, while the response time was ca. 100 s upon pH change from 5.0 to 9.0.     

Voltammetric and waveguide spectroelectrochemical characterization of ultrathin poly(aniline)/poly(acrylic acid) films self-assembled on indium-tin oxide

We report on the spectroelectrochemical characterization of conducting polymer (CP) films, composed of alternating layers of poly(aniline) (PANI) and poly(acrylic acid) (PAA), deposited on ITO-coated, planar glass substrates using layer-by-layer self-assembly. Absorbance changes associated with voltammetrically induced redox changes in ultrathin films composed of only two bilayers (ITO/PANI/PAA/PANI/PAA) were monitored in real time using a unique multiple reflection, broadband attenuated total reflection (ATR) spectrometer. CP films in contact with pH 7 buffer undergo a single oxidation/reduction process, with ca. 12.5% of the aniline centers in the film being oxidized and reduced. The ATR spectra indicate that during an anodic sweep, the leucoemeraldine form of PANI in these films is oxidized to generate both the emeraldine and pernigraniline forms simultaneously. A comparison of the behavior observed during anodic and cathodic sweeps suggests that the rate of oxidation is limited by structural changes in the polymer film originating in electrostatic repulsion between positively charged PANI chains.     

用软刻蚀方法制备PbS纳米晶复合聚丙烯酸微图形

PbS microstructures have several applications such as Pb2+ion-selective sensors and IR detector.The method to prepare PbS nanocrystal embed in poly(acrylicacid) (PAA) microstructures produced by means of soft lithography and solid state polymerizatio n by γ-ray irradiation was described. PbS micro patterns were prepared by Micro molding in Capillaries (MIMIC) with aqueous solution of acrylic acid lead monomer, and then solid state polymerized by γ-ray irradiation. Finally, the sample was treated with aqueous solution of Na2 Stoconvert the Pb2+ to PbS in the matrix. High-resolution micro structures of PAA, which have PbS nanocrystals embedded in them, could be produced successfully in this way. The final products were characterized by TEM, XRD, and XPS. TEM image indicated that the PbS particles embedded in PAA had a diameter of smaller than 20nm. X-ray powder diffraction method was also used to characterize the PbS/PAA nanocomposite film. The XPS analysis showed the element Pb has been converted to PbS nanoparticles in the composite films.     

Assembly of multilayered films using well-defined, end-labeled poly(acrylic acid): influence of molecular weight on exponential growth in a synthetic weak polyelectrolyte system

We report on the influence of polyanion molecular weight on the growth and structure of multilayered thin films fabricated from poly(allylamine) (PAH) and well-defined, end-labeled poly(acrylic acid) (PAA) synthesized by atom transfer radical polymerization. We observed striking differences in the growth of PAH/PAA films fabricated using well-defined PAA compared to films fabricated using higher molecular weight, commercially available PAA. Past studies demonstrate that the thicknesses of PAH/PAA films increase as linear functions of the number of PAH and PAA layers deposited over a broad range of pH (e.g., from pH 2.5 to 4.5). We observed the thicknesses of films fabricated using solutions of PAH and PAA adjusted to pH 7.5 and 3.5, respectively, to increase in a nonlinear manner. Films fabricated using well-defined, low molecular weight samples of PAA under these conditions increased in thickness exponentially. Experiments using samples of PAA having substantially non-overlapping molecular weight distributions demonstrated a clear relationship between the molecular weight of PAA and rates of film growth. We also used confocal microscopy, in combination with fluorescently end-labeled samples of PAA, to characterize the location of PAA in these assemblies. The results of these experiments, when combined, support the general conclusion that PAA is able to penetrate or diffuse into these films over large distances during assembly. The mechanism of growth for these films thus appears similar to that recently reported for the exponential growth of films fabricated using a variety of biologically relevant polyelectrolytes. The use of living/controlled methods of polymerization to synthesize well-defined samples of PAA facilitates an interpretation of these differences in film behavior as arising largely from differences in polymer molecular weight and polydispersity. This work provides insight into the assembly and structure of a well-studied weak polyelectrolyte film system and illustrates the potential of living/controlled methods of polymerization to contribute to the characterization and understanding of the physical properties of these ionically cross-linked materials.