Acid Multilayer Films Research Articles

Development of Biodegradable Polyamide 4/Polyvinyl Alcohol/Poly(lactic acid) Multilayer Films with Tunable Water Barrier Property and Superior Oxygen Barrier Property

Poor mechanical and barrier properties of biopolymer-based packaging materials limit their widespread applications. The combination of biopolymers with different nature is considered an effective strategy to obtain complementary properties, but this method is always restricted by the incompatibility between matrices. To combine polyamide 4 (PA4) and poly(lactic acid) (PLA), which present excellent oxygen barrier and water barrier properties, respectively, this study puts forward the use of polyvinyl alcohol (PVA) as a bonding layer to connect them and form the PA4/PVA/PLA multilayer films by the layer-by-layer solution casting method. PA4 and PLA are successfully linked through hydrogen bonding and electrostatic interactions with PVA. The cross-section morphology and peel test results proved the good interlayer adhesion between layers. After combination with PA4, the tensile strength, elongation at break, and oxygen barrier properties of PLA were greatly improved. The oxygen barrier of the PA4/PVA/PLA multilayer film was more than 260 times higher than that of the PLA monolayer. PA4/PVA/PLA films presented better thermal stability, transparency, and water barrier properties compared to the PA4 monolayer. Besides, PA4/PVA/PLA multilayer films presented a one-way water barrier characteristic, which made them effective in avoiding the condensation phenomenon when used as fruit or vegetable packaging. The study improved the poor interfacial compatibility between PA4 and PLA and provided a simple strategy for developing sustainable packaging with excellent performance.

Polyelectrolyte Multilayers Composed of Polyethyleneimine-Grafted Chitosan and Polyacrylic Acid for Controlled-Drug-Delivery Applications.

In this work, polyethyleneimine (PEI)-grafted chitosan (Chi-g-PEI) was prepared for the fabrication of layer-by-layer (LBL) films for use in sustained-drug-delivery applications. Chi-g-PEI and polyacrylic acid (PAA) multilayer films were formed using the LBL technique. Methylene blue (MB) was used as a model drug for the investigation of loading and release capabilities of the LBL films. Characterizations of the synthesized copolymer were performed using Fourier-transform infrared spectroscopy (FTIR), Nuclear magnetic resonance spectroscopy (NMR), Thermogravimetric analysis (TGA), and X-ray Powder Diffraction (XRD) techniques, and the thickness of the LBL films was measured using Atomic force microscopy (AFM). The drug-loading and -release behaviors of the LBL films were assessed using a UV–visible spectrophotometer. The results showed that the loading capacity and release rate of MB were affected by ionic strength and pH. In addition, it was demonstrated that PEI-grafted chitosan is a good candidate for the assembling of LBL films for drug-delivery applications.

Facile fabrication of thermoplastic starch/poly (lactic acid) multilayer films with superior gas and moisture barrier properties

Multilayer films comprised of thermoplastic starch (TPS) and poly (lactic acid) (PLA) were fabricated via a reactive extrusion, compression molding, and dip coating processes. Maleic anhydride (MA) modification of TPS was employed to improve the interfacial adhesion between TPS and PLA layers of the film. The level and effect of TPS modification were evaluated using Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (H NMR), titration, and thermogravimetric analysis (TGA). Nanoclays were incorporated in the TPS and maleated TPS (MTPS) matrices to further enhance the physico-mechanical properties of the multilayer films. The optimized multilayer film fabricated in this study, which was the nanoclays-filled maleated thermoplastic starch and PLA multilayer film (MTPS-3C/PLA) displayed good transparency and tensile properties, and excellent moisture and oxygen barrier properties. This multilayer film assembly provided 1300% improvement in moisture barrier compared to TPS films, and 3300% improvement in oxygen barrier properties as compared to PLA films adjusted for thickness. Moreover, these multilayer films are composed of compostable, food-grade, inexpensive, and bio-based ingredients and as such they are expected to be compostable with great cost structure and environmentally friendly.

Preparation and Antifouling Property of Polyurethane Film Modified by PHMG and HA Using Layer-by-Layer Assembly.

To reduce the possibility of bacterial infection and implant-related complications, surface modification on polyurethane (PU) film is an ideal solution to endow hydrophobic PU with antibacterial and antifouling properties. In this work, a variety of polyhexamethylene guanidine/ hyaluronic acid (PHMG/HA) multilayer films were self-assembled layer-by-layer on PU films using polyanions, carboxyl-activated HA, and polycations PHMG by controlling the concentration of these polyelectrolytes as well as the number of layers self-assembled. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) spectra, water contact angle (WCA), and A Atomic force microscope (AFM) of PU and modified PU films were studied. Protein adsorption and bacterial adhesion as well as the cytotoxicity against L929 of the film on selected PU-(PHMG/HA)5/5-5 were estimated. The results showed that PU-(PHMG/HA)5/5-5 had the best hydrophilicity among all the prepared films, possessing the lowest level of protein adsorption. Meanwhile, this film showed efficient broad-spectrum antibacterial performance as well as significant resistance of bacterial adhesion of more than a 99.9% drop for the selected bacteria. Moreover, almost no influence on cell viability of L929 enhanced the biocompatibility of film. Therefore, the modified PU films with admirable protein absorption resistance, antimicrobial performance, and biocompatibility would have promising applications in biomedical aspect.

Bio-corrosion behaviors of hyaluronic acid and cerium multi-layer films on degradable implant

Initial corrosion resistance and bioactivity of biodegradable magnesium are major success factors for implant applications. Electrodeposition containing Ce prevent material damage and local corrosion resulting from implantation, and Ce penetrates hydrogels and consequently maximizes surface self-healing. Ce(NO3) was used to form an electrodeposition layer on magnesium, and hyaluronic acid(HA) was coated through hydrothermal treatment, which created a composite layer consisting of a polymer compound with Ce and a thick and stable MgO layer. The morphology, chemical structure, and scratch tests conducted on various surface treatments showed hydrothermally treated Ce to be the most effective self-healing and corrosion-resistance. In the electrodeposition of Ca/Ce, relatively reactive Ce quickly adhered to the surface, and according to the hydrothermal process, Ca and Ce ions diffused inward as water and HA penetrated the irregular layers. The cell viability of osteoblasts showed no toxicity with Ce, and the osteoblasts were showed the highest differentiation especially in treated with the HA hydrothermal group. Implantation into rat tibias resulted in stable bone marrow and osteoblast growth in the hydrothermal treatment group containing Ce. Consequently, Ce(OH)3/CeO2 penetrating the natural polymer HA had a self-healing ability and resistance to initial corrosion, local damage, and the biodegradation of the magnesium implant.

3D porous acellular cartilage matrix scaffold with surface mediated sustainable release of TGF-β3 for cartilage engineering

Acellular tissue matrix scaffolds are much closer to tissue’s complex natural structure and biological characteristics, thus assess great advantages in cartilage engineering. We used rabbit costal cartilage to prepare acellular microfilaments and further 3D porous acellular cartilage scaffold via crosslinking. Poly(l-lysine)/hyaluronic acid (PLL/HA) multilayer film was then built up onto the surface of the resulting porous scaffold. Furthermore, TGF-β3 was loaded into the PLL/HA multilayer film coated scaffold to obtain a 3D porous acellular cartilage scaffold with sustained releasing of TGF-β3 up to 60 days. The success of this project will provide a new way for the treatment of articular cartilage defects. Meanwhile, the anchoring and on-site sustained releasing of growth factors mediated by polyelectrolyte multilayered film can also provide a new method for improving the biocompatibility and the biofunctionality for other implanted biomaterials.

Rapid and In Situ Synthesis of Gold Nanoparticles in Redox Multilayer Film for Biosensor Applications

AbstractFerrocene‐grafted poly(ethyleneimine)/poly(acrylic acid) (PEI‐Fc/PAA) multilayer films were constructed via layer‐by‐layer assembly. When the PEI‐Fc/PAA films were immersed in HAuCl4 solution, Fc and the AuIII were converted to Fc+ and Au0, respectively, via the redox reaction of Fc and HAuCl4, and the PEI‐Fc/PAA@Au nanoparticles (NPs) multilayer films were rapidly fabricated. SEM and TEM results showed Au NPs were distributed homogeneously throughout the thickness of the whole film. The electron transfer behavior of PEI‐Fc/PAA@Au NPs multilayer films was investigated by cyclic voltammetry and AC impedance. The results indicated that the Au NPs greatly improve the conductivity of multilayer films and thus enhance the electrochemical properties of films. The PEI‐Fc/PAA@Au NPs films were further used for the fabrication of a hydrogen peroxide (H2O2) sensor, which showed good catalytic ability for the reduction of H2O2. This approach is expected to expand the routes towards rapid fabrication of Au NPs into multilayer films.

Developing regulatory property of gelatin-tannic acid multilayer films for coating-based nitric oxide gas delivery system

To utilize potentials of nitric oxide (NO) gas in anti-bacterial, anticancer, wound healing applications, numerous studies have been conducted to develop a NO delivery system in the past few decades. Even though a coating method and film types are essential to apply in biomedical device coating from previous NO delivery systems, release control from the coating system is still challenging. In this study, we introduced a multilayered polymeric coating system to overcome the uncontrollable NO release kinetics of film systems. We used biocompatible gelatin and tannic acid to construct a rough, porous structured film based on the layer-by-layer self-assembly method. The multilayered polymeric structure facilitated the controlled amount of NO release from (Gel/TA)n film and showed burst release in early period owing to their large surface area from the rough, porous structure. We synthesized the proton-responsive NO donor, N-diazeniumdiolate (NONOates), into the (Gel/TA)n film through a chemical reaction under high pressure NO gas. NO release profile was analyzed by a real-time NO analysis machine (NOA 280i). Then, the NO-releasing (Gel/TA)n film was tested its toxicity against human dermal fibroblast cells and bactericidal effects against Staphylococcus aureus.

Chitosan/hyaluronic acid multilayer films are biocompatible substrate for Wharton's jelly derived stem cells.

Discovery of mesenchymal stem cells (MSCs) in various adult human tissues opened the way to new therapeutic strategies involving tissue engineering from these cells. More recently, vascular substitutes have opened the era of vascular engineering by making replacement vessels from purely biological material. The objective of our study was to create a vascular substitute from MSCs using a multilayer polyelectrolyte film based on natural polymers (Chitosan and Hyaluronic Acid). Biocompatibility and cellular behavior were evaluated in this study using MSCs from the Wharton's jelly (WJ) of human umbilical cords. WJ-MSCs adherence was assessed and cells morphology was investigated by Scanning Electron Microscopy (SEM) and actin visualization (Phalloidin). The number of WJ-MSCs seeded on the (CHI/HA)10 films was greater than the number of cells seeded on the collagen, as the spectrophotometric measurement showed a large cell proliferation on (CHI/HA)10 in comparison with collagen. After adhesion, WJ-MSCs showed a fibroblastic morphology on CHI/HA as for control (collagen I). These results were confirmed by cytoskeleton staining. The biocompatibility of WJ-MSCs and (CHI/HA)10 showed the possibility to combine the use of WJ-MSCs and (CHI/HA)10 films in vascular tissue engineering.

Adsorption kinetics of tannic acid onto an albumin-terminated multilayer thin films

The protein-polyphenol multilayer film is a promising material for protection functional food ingredients from gastric digestion and their targeted delivery to small intestine. Here, we study the process of layer-by-layer assembly of bovine serum albumin—tannic acid (BSA-TA) multilayer films by precision ellipsometry. We demonstrate that TA adsorption has both irreversible and reversible components which contribute to 43% and 57% of bound TA molecules, respectively. The kinetic of TA adsorption/desorption process is analyzed using a phenomenological function approach. The rate-limiting stage of the process is the kinetics of molecules adsorption (desorption) to (from) a planar surface and not diffusion of TA molecules from (to) a solution bulk. For irreversible adsorption, the rate constant is 3.9 × 103 M−1 s−1. For the reversible process, the adsorption rate constant, Kads is 5.14 × 103 M−1 s−1; desorption rate constant, Kdes is 79.4 s−1; and equilibrium constant, K is 64.7 M−1.

Broadband Antireflection Coatings Based on Low Surface Energy/Refractive Index Silica/Fluorinated Polymer Nanocomposites

We demonstrated the fabrication of broadband antireflection coatings (ARCs) comprising low-surface energy/refractive index (RI) silica/polymer nanocomposites by silica mineralization of layer-by-layer (LbL) assembled poly(2-(dimethylamino)ethyl methacrylate)-block-poly(2,2,3,3-tetrafluoropropyl methacrylate)/poly(L-glutamic acid) (PDMA-b-PTFP/PGA) multilayer films without any post-treatments. The introduction of the fluorinated polymer (PTFP segments) effectively lowered not only the RI of the as-fabricated coatings but also the surface energy of the constituted pore surface, which rendered the ARCs with high transmittance and durable AR performance by preventing the absorption and capillary condensation of moisture at ambient conditions. Moreover, the formation of nanosized PDMA-b-PTFP vesicles can render the ARCs exhibiting small pore size, which can improve their light transmittance. The coated substrate with an average transmittance over 97.0% was obtained at the visible wavelength region. The combina...

Effect of environmental parameters on the nano mechanical properties of hyaluronic acid/poly(l-lysine) multilayers.

Atomic force microscopy (AFM) was used to determine the mechanical properties as the indentation modulus of native and crosslinked poly(l-lysine) (PLL)/hyaluronic acid (HA) multilayer films by static force measurements. The influence of the surrounding medium on the mechanical properties of the films after preparation is investigated. The indentation modulus of native and crosslinked film was measured at different pH values, ionic strengths and temperatures. The native HA/PLL films, which behave like a physical gel, show the highest values of the indentation modulus for an intermediate pH value and low ionic strength. Any changes in the pH or an increase in the ionic strength/temperature decreases the measured indentation modulus. In contrast, the crosslinked films show an increase by a factor of 80 in the indentation modulus but no response to changes in the pH, ionic strength or temperature; they behave like a chemical gel. The pH, ionic strength and temperature used in this work are close to the in vivo conditions and thus give a fundamental point of view on the nanomechanical response of the PLL/HA films. Furthermore, information about the mechanical properties can be used for the understanding and manipulation of cell adhesion.

Synthetic Lift-off Polymer beneath Layer-by-Layer Films for Surface-Mediated Drug Delivery.

A broad range of biomaterials coatings and thin film drug delivery systems require a strategy for the immobilization, retention, and release of coatings from surfaces such as patches, inserts, and microneedles under physiological conditions. Here we report a polymer designed to provide a dynamic surface, one that first functions as a platform for electrostatic thin film assembly and releases the film once in an in vivo environment. Atom transfer radical polymerization (ATRP) was used to synthesize this polymer poly(o-nitrobenzyl-methacrylate-co-hydroxyethyl-methacrylate-co-poly(ethylene-glycol)-methacrylate) (PNHP), embedded beneath multilayered polyelectrolyte films. Such a base layer is designed to photochemically pattern negative charge onto a solid substrate, assist deposition of smooth layer-by-layer (LbL) polyelectrolyte in mildly acidic buffers and rapidly dissolve at physiological pH, thus lifting off the LbL films. To explore potential uses in the biomedical field, a lysozyme (Lys)/poly(acrylic acid) (PAA) multilayer film was developed on PNHP-coated silicon wafers to construct prototype antimicrobial shunts. Film thickness was shown to grow exponentially with increasing deposition cycles, and effective drug loading and in vitro release was confirmed by the dose-dependent inhibition of Escherichia coli (E. coli) growth. The efficacy of this approach is further demonstrated in LbL-coated microscale needle arrays ultimately of interest for vaccine applications. Using PNHP as a photoresist, LbL films were confined to the tips of the microneedles, which circumvented drug waste at the patch base. Subsequent confocal images confirmed rapid LbL film implantation of PNHP at microneedle penetration sites on mouse skin. Furthermore, in human skin biopsies, we achieved efficient immune activation demonstrated by a rapid uptake of vaccine adjuvant from microneedle-delivered PNHP LbL film in up to 37% of antigen-presenting cells (APC), providing an unprecedented LbL microneedle platform for human vaccination.

Protein-tannic acid multilayer films: A multifunctional material for microencapsulation of food-derived bioactives

The benefits of various functional foods are often negated by stomach digestion and poor targeting to the lower gastrointestinal tract. Layer-by-Layer assembled protein-tannic acid (TA) films are suggested as a prospective material for microencapsulation of food-derived bioactive compounds. Bovine serum albumin (BSA)-TA and pepsin-TA films demonstrate linear growth of 2.8±0.1 and 4.2±0.1nm per bi-layer, correspondingly, as shown by ellipsometry. Both multilayer films are stable in simulated gastric fluid but degrade in simulated intestinal fluid. Their corresponding degradation constants are 0.026±0.006 and 0.347±0.005nm−1min−1. Milk proteins possessing enhanced adhesion to human intestinal surface, Immunoglobulin G (IgG) and β-Lactoglobulin (BLG), are explored to tailor targeting function to BSA-TA multilayer film. BLG does not adsorb onto the multilayer while IgG is successfully incorporated. Microcapsules prepared from the multilayer demonstrate 2.7 and 6.3 times higher adhesion to Caco-2 cells when IgG is introduced as an intermediate and the terminal layer, correspondingly. This developed material has a great potential for oral delivery of numerous active food-derived ingredients.

Spray-assisted layer-by-layer assembly of decorated PEI/PAA films: morphological, growth and mechanical behavior

The development and study of new smart materials is an emergent research area with high potential applications. In this study, we have fabricated poly(ethyleneimine)/poly(acrylic acid) multilayer films on glass substrates by automated spray-layer-by-layer (spray-LbL) technique. By analyzing the changes in thickness, roughness and elasticity, with fine-tuning of the operational parameters of the spray-LbL system, evident trends of its effect on the multilayer construction were observed. In the case of its mechanical properties, the stability of Young’s modulus (up to 8.25 GPa) from film thickness at this scale was detected, making it variable for other factors such as pH and molecular weight. This work also identified the healability phenomenon that is present in the exponentially grown PEI/PAA samples, based on the reduction in viscosity of the polymer complexes and the interdiffusion of polyelectrolytes at the damaged zones in the presence of water. These properties allow for the assembly of a highly electrically conductive multilayered film by dispersion of a top layer of silver nanowires whose sheet resistance is increased around 5% after multiple damaging events. These experimental results provide new data for the evaluation and design of polyelectrolyte multilayers assembled with a spin-assisted automated spray deposition system to serve as substrates for mechanoelectrical devices which can benefit from its self-healing and modulated mechanical capabilities.

Combined High Stretchability and Gas Barrier in Hydrogen-Bonded Multilayer Nanobrick Wall Thin Films.

Hydrogen-bonded multilayer thin films are very stretchable, but their gas barrier properties are modest compared to more traditional ionically bonded assemblies. In an effort to improve the gas barrier of poly(ethylene oxide) (PEO)-poly(acrylic acid) (PAA) multilayer films without sacrificing stretchability, montmorillonite (MMT) clay platelets were combined with PAA and alternately deposited with PEO. A ten-bilayer PEO/PAA+MMT film (432 nm thick), deposited on a 1 mm PU substrate, resulted in a 54× reduction in oxygen transmission rate after exposure to a 20% strain. This system is the best combination of stretchability and gas barrier ever reported.

Separation of Storage and Loss Modulus of Polyelectrolyte Multilayers on a Nanoscale: A Dynamic AFM Study

Atomic force microscopy (AFM) is used to carry out rheology measurements on the nanoscale and to determine the mechanical properties of poly(l-lysine) (PLL)/hyaluronic acid (HA) multilayer films. Storage (G') and loss modulus (G″) of the films are calculated and compared with the values obtained from quartz crystal microbalance with dissipation monitoring measurements (QCM-D). A predominant elastic behavior independently of the applied frequencies (5-100 Hz) is observed for native HA/PLL films consisting of 36 double layer. If the layers are cross-linked, the value of G' increases by 2 orders of magnitude, while the loss modulus becomes negligible, making these films a purely elastic chemical gel. The values of G' and G'' extracted from QCM-D measurements on native films are much higher, due to the different frequency regime of the applied shear stress. However, the viscoelastic ratio from the two methods is the same and proves the elastic dominated response of the multilayer in both frequency regimes.

Accelerated Amidization of Branched Poly(ethylenimine)/Poly(acrylic acid) Multilayer Films by Microwave Heating

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.

Mobility of lysozyme in poly(l-lysine)/hyaluronic acid multilayer films

The spatial and temporal control over presentation of protein-based biomolecules such as growth factors and hormones is crucial for in vitro applications to mimic the complex in vivo environment. We investigated the interaction of a model protein lysozyme (Lys) with poly(L-lysine)/hyaluronic acid (PLL/HA) multilayer films. We focused on Lys diffusion as well as adsorption and retention within the film as a function of the film deposition conditions and post-treatment. Additionally, an effect of Lys concentration on its mobility was probed. A combination of confocal fluorescence microscopy, fluorescence recovery after photobleaching, and microfluidics was employed for this investigation. Our main finding is that adsorption of PLL and HA after protein loading induces acceleration and reduction of Lys mobility, respectively. These results suggest that a charge balance in the film to a high extent governs the protein–film interaction. We believe that control over protein mobility is a key to reach the full potential of the PLL/HA films as reservoirs for biomolecules depending on the application demand.

Palladium Nanoparticles Embedded in a Layer-by-Layer Nanoreactor Built with Poly(Acrylic Acid) Using "Electro-Click Chemistry".

Palladium nanoparticles (Pd NPs) were formed by electrochemical reduction of Pd(NH3)4(3+) ions entrapped by ion exchange in poly(acrylic acid) (PAA) multilayer films grown by the Sharpless "click reaction." The alkyne (PAAalk) and azide (PAAaz) groups were covalently bound to the PAA, and the catalyzed buildup of the multilayer film was performed by electrochemical reduction of Cu(2+) to Cu(+). The size of the Pd NPs formed in Au/(PAAalk)3(PAAaz)2 multilayer films by the click reaction, that is, 50 nm, is larger than that of similar Pd NPs formed in electrostatically bound Au/(PAA)3(PAH)2 nanoreactors, that is, 6-9 nm, under similar conditions. A combination of electrochemical methods and electrochemical quartz crystal microbalance, polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), ellipsometry, and scanning electron microscopy has been used to follow these processes. Cyclic voltammetry of the resulting Pd NPs in a 0.1 M H2SO4 solution at 0.1 V·s(-1) shows the PdO reduction peak at the same potential as that on the clean Pd surface unlike the NPs formed in electrostatically self-assembled Au/(PAA)3(PAH)2 nanoreactors with a 0.2 V shift in the cathodic direction most probably because of the strong adsorption of amino groups on the Pd NP surfaces.