Polyelectrolyte Multilayer Films Research Articles

Azo dye polyelectrolyte multilayer films reversibly re-soluble with visible light

Polymeric multilayer films were prepared using a layer-by-layer (LBL) technique on glass surfaces, by repeated and sequential dipping into dilute aqueous solutions of various combinations of water-soluble polyanions (polyacrylic acid (PAA)), polycations (polyallylamine hydrochloride (PAH) or chitosan (CS)), with bi-functional water-soluble cationic azo dyes bismark brown R bismarck brown red or bismark brown Y (BBY), or anionic azo dyes allura red (ALR) or amaranth (AMA), as ionic cross-linkers. The electrostatically-assembled ionically-paired films showed good long-term stability to dissolution, with no re-solubility in water. However, upon exposure to low power visible light under running water, the films photo-disassembled back to their water-soluble constituent components, via structural photo-isomerization of the azo ionic crosslinkers. The relative rate of the disassembly (RRD) of the films was established using UV-Vis spectroscopy, demonstrating that these assemblies can in principle represent fully recyclable, environmentally structurally degradable materials triggered by exposure to sunlight, with full recovery of starting components. A density functional theory treatment of the allura red azo dye rationalizes the geometrical isomerization mechanism of the photo-disassembly and provides insight into the energetics of the optically-induced structural changes that trigger the disassembly and recovery.

Efficient PFOA removal from drinking water by a dual-functional mixed-matrix-composite nanofiltration membrane

Drinking water contamination by per- and polyfluorinated alkyl substances (PFAS) is a global concern. Nanofiltration is a promising PFAS removal technology due to its scalability and cost-effectiveness. However, nanofiltration cannot typically reduce PFAS concentrations below current drinking water recommendations. To enhance PFAS removal, we developed mixed-matrix-composite nanofiltration (MMCNF) membranes—an active nanofiltration layer on porous adsorptive support that synergetically combines filtration and adsorption. We synthesized MMCNF membranes comprising thin polyelectrolyte multilayer films deposited on thick (~400 µm) polyethersulfone supports incorporating β-cyclodextrin microparticles. These membranes achieved near complete removal (>99.9%) of model PFAS (PFOA: perfluorooctanoic acid) for significantly longer filtration times compared to a control membrane without β-cyclodextrin, but otherwise identical. The spent MMCNF membrane was regenerated using ethanol, and high PFOA removal performance was regained during three filtration cycles. Perfluorooctanoic acid was concentrated 38-fold in the ethanol eluent. Further concentration by evaporation is straightforward and can enable eluent recycling and effective PFAS removal.

Adlay Polyelectrolyte Multilayer Films Coated on Titanium: Surface Characteristics and MC3T3-E1 Cell Morphology and Proliferation

Objective: Adlay has been reported to prevent osteoporosis, and promote osteoblast cell proliferation and in vitro calcification. However, it has never been used on modified titanium (Ti) surfaces. Hence, the aim of this study was to ameliorate Ti surfaces, by coating with adlay seed extract via the polyelectrolyte multilayer (PEM) film technique. Material and Methods: Adlay seed extract solution containing 150, 300, 600, or 1500 μg/ml concentrations was coated on Ti discs using a layer-by-layer technique to fabricate PEM films (Ti_Adlay surface). The surface characterizations; including atomic force microscope analysis, contact angle analysis and energy dispersive X-ray analysis were evaluated. The osteoblast cell proliferation on its modified surface was also examined. Results: Adlay seed extract could increase surface irregularity, roughness, hydrophilicity and carbon composition of Ti surface in all Ti_Adlay groups. At 24, 48 and 72 hours of incubation, the osteoblast cells morphology was similar in all groups. At 24 hours, the viable cell numbers on all Ti_Adlay groups were statistically lower than the uncoated Ti group, while no significant difference was found after 48 and 72 hours of incubation. Conclusion: Adlay PEM coating on Ti surface could improve the surface properties of Ti in terms of surface roughness, hydrophilicity and surface chemistry. Even though Ti-Adlay surfaces showed no toxic effect on MC3T3-E1, it was unlikely

Increased liver stiffness promotes hepatitis B progression by impairing innate immunity in CCl4-induced fibrotic HBV+ transgenic mice.

Hepatitis B virus (HBV) infection develops as an acute or chronic liver disease, which progresses from steatosis, hepatitis, and fibrosis to end-stage liver diseases such as cirrhosis and hepatocellular carcinoma (HCC). An increased stromal stiffness accompanies fibrosis in chronic liver diseases and is considered a strong predictor for disease progression. The goal of this study was to establish the mechanisms by which enhanced liver stiffness regulates HBV infectivity in the fibrotic liver tissue. For in vitro studies, HBV-transfected HepG2.2.15 cells were cultured on polydimethylsiloxane gels coated by polyelectrolyte multilayer films of 2 kPa (soft) or 24 kPa (stiff) rigidity mimicking the stiffness of the healthy or fibrotic liver. For in vivo studies, hepatic fibrosis was induced in C57Bl/6 parental and HBV+ transgenic (HBVTg) mice by injecting CCl4 twice a week for 6 weeks. We found higher levels of HBV markers in stiff gel-attached hepatocytes accompanied by up-regulated OPN content in cell supernatants as well as suppression of anti-viral interferon-stimulated genes (ISGs). This indicates that pre-requisite "fibrotic" stiffness increases osteopontin (OPN) content and releases and suppresses anti-viral innate immunity, causing a subsequent rise in HBV markers expression in hepatocytes. In vitro results were corroborated by data from HBVTg mice administered CCl4 (HBVTg CCl4). These mice showed higher HBV RNA, DNA, HBV core antigen (HBcAg), and HBV surface antigen (HBsAg) levels after liver fibrosis induction as judged by a rise in Col1a1, SMA, MMPs, and TIMPs mRNAs and by increased liver stiffness. Importantly, CCl4-induced the pro-fibrotic activation of liver cells, and liver stiffness was higher in HBVTg mice compared with control mice. Elevation of HBV markers and OPN levels corresponded to decreased ISG activation in HBVTg CCl4 mice vs HBVTg control mice. Based on our data, we conclude that liver stiffness enhances OPN levels to limit anti-viral ISG activation in hepatocytes and promote an increase in HBV infectivity, thereby contributing to end-stage liver disease progression.

Self-Patterning of Polyelectrolyte Multilayer Films: The Roles of PSS Molecular Weight, the Top Layer, and Post-Preparation Treatment

The self-patterning of thin films is relevant for both fundamental research and applications. We investigate polyelectrolyte multilayer films made from poly(diallyldimethylammonium) chloride and poly(styrene sulfonate) sodium salt (PDADMA/PSS). Various PSS with low molecular weight were used. First, the film thickness increases exponentially with the number of deposited PDADMA/PSS bilayers. The separation and height of the pillar-like domains increase significantly with each deposited PDADMA/PSS bilayer, as AFM images show. After the exponential growth regime, either a parabolic (and then a linear) or a linear growth regime follows, depending on the PSS molecular weight. The domain separation changes less and correlates with the vertical growth regimes. The domain separation varies between 70 and 750 nm and always exceeds the domain height. PSS-terminated films show the same domain distance in water and air. However, when PDADMA-terminated films are dried, the domain distance in air increases while the domain height decreases, causing a reduction in total area. In the air, the surface energy is greater than in water and a highly textured surface costs a lot of energy. We propose that the changed surface pattern is attributable to energy minimization. Furthermore, the domains are stable when exposed to 1 M NaCl solution but shrink enormously in 2 M NaCl, while their separation increases slightly. Under certain conditions, 50 nm broad filaments consisting of PDADMA/PSS complexes are observed. We suggest that these complexes diffuse between the domains and adjust their separation.

Influence of Ionic Strength and Specific Ion Effects on Polyelectrolyte Multilayer Films with pH-Responsive Behavior

Layer-by-layer assembled multilayer films have shown great potential for different applications owing to their responsive behavior. Herein, we systematically investigated the effects of composition, salt concentration, and ion specificity on the pH responsiveness of covalently crosslinked chitosan and alginate dialdehyde multilayer films. The changes in film swelling were measured using ellipsometry from low (0.01 mM) to high (3 M) salt (NaCl or NaSCN) concentrations at pH 3, 6, and 9. The swelling responses to increasing ionic strength matched the swelling responses observed for polyzwitterionic and weak monocomponent polyelectrolyte films and depended on the multilayer composition, pH, and ion specificity. Finally, we used the ellipsometric data to demonstrate that the pH responsiveness of such multilayer films, as measured using a quartz crystal microbalance with dissipation monitoring, strongly depends on the ionic condition under which the responses were measured. We thus show that erroneous conclusions about the pH responsiveness of polyelectrolyte multilayer films can be easily obtained if the ionic environment of the application does not closely resemble the ionic condition under which the pH responsiveness is tested.

Elastic moduli of polyelectrolyte multilayer films regulate endothelium-blood interaction under dynamic conditions

A broad spectrum of biomaterials has been explored in order to design cardiovascular implants of sufficient hemocompatibility. Most of them were extensively tested for the ability to facilitate repopulation by patient cells. It was shown that stiffness, surface roughness, or hydrophilicity of polyelectrolyte films have an impact on adhesion, proliferation, and differentiation of cells. At the same time, it is still unknown how these properties influence cell functionality and as a consequence interactions with blood components under dynamic conditions. In this study, we aimed to determine the impact of chemical cross-linking of Chitosan (Chi) and Chrondroitin Sulphate (CS) on endothelium-blood cross-talk. We have found that the morphology of the endothelium monolayer was not altered by changes in coating properties. However, free radical generation by endothelial cells varied depending on the elastic properties of the coating. Simultaneously, we have observed a significant decrease in the level of adhering and circulating active platelets as well as aggregates when the endothelium monolayer was formed on stiffer films than on the other coating variants. Moreover, the same type of films has promoted significantly higher adhesion of blood morphotic elements when they were not functionalized by endothelium. The observed changes in hemocompatibility indicate the importance of a design of coatings that will promote cellularization in vivo in a relatively short time and which will regulate cell function.

Nanoarchitectonics for Free‐Standing Polyelectrolyte Multilayers Films: Exploring the Flipped Surfaces

AbstractThe competency of polyelectrolyte multilayer films (PEM) self‐assembly to modulate the surface architecture at the molecular level has emerged as a captivating technique for various biomedical applications. PEM advancement in bio‐applications covered the development of bio‐sensors, stimuli‐responsive drug‐delivery systems, surface modification for creating antibacterial surfaces, and tissue‐engineering architectures. Different PEM blends, from natural to synthetic ones, have been explored to make a free‐standing version of the PEM stack. This review provides a deeper understanding of the free‐standing PEM (FS‐PEM), their fabrication strategies, and essential properties for specified bio‐applications. The most crucial aspect of fabricating FS‐PEM is choosing an application‐specific fabrication protocol to delaminate the PEM stack from the underlying substrates. Post‐fabrication, there are important considerations to improve the mechanical stability of these FS‐PEMs by crosslinking or adding desired nanoparticles. Overall, essential insights are discussed here for using FS‐PEM for specific bio‐application, which has received little attention in the material science community until now.

Quaternized Chitosan/Heparin Polyelectrolyte Multilayer Films for Protein Delivery.

Layer-by-layer (LbL) polyelectrolyte coatings are intensively studied as reservoirs of bioactive proteins for modulating interactions between biomaterial surfaces and cells. Mild conditions for the incorporation of growth factors into delivery systems are required to maintain protein bioactivity. Here, we present LbL films composed of water-soluble N-[(2-hydroxy-3-trimethylammonium)propyl] chitosan chloride (HTCC), heparin (Hep), and tannic acid (TA) fabricated under physiological conditions with the ability to release heparin-binding proteins. Surface plasmon resonance analysis showed that the films formed on an anchoring HTCC/TA bilayer, with TA serving as a physical crosslinker, were more stable during their assembly, leading to increased film thickness and increased protein release. X-ray reflectivity measurements confirmed intermixing of the deposited layers. Protein release also increased when the proteins were present as an integral part of the Hep layers rather than as individual protein layers. The 4-week release pattern depended on the protein type; VEGF, CXCL12, and TGF-β1 exhibited a typical high initial release, whereas FGF-2 was sustainably released over 4 weeks. Notably, the films were nontoxic, and the released proteins retained their bioactivity, as demonstrated by the intensive chemotaxis of T-lymphocytes in response to the released CXCL12. Therefore, the proposed LbL films are promising biomaterial coating candidates for stimulating cellular responses.

Collagen-Based Osteogenic Nanocoating of Microrough Titanium Surfaces.

The aim of the present study was to develop a collagen/heparin-based multilayer coating on titanium surfaces for retarded release of recombinant human bone morphogenic protein 2 (rhBMP2) to enhance the osteogenic activity of implant surfaces. Polyelectrolyte multilayer (PEM) coatings were constructed on sandblasted/acid-etched surfaces of titanium discs using heparin and collagen. PEM films of ten double layers were produced and overlayed with 200 µL of a rhBMP2 solution containing 15 µg rhBMP2. Subsequently, cross-linking of heparin molecules was performed using EDC/NHS chemistry to immobilize the incorporated rhBMP2. Release characteristics for 3 weeks, induction of Alkaline Phosphatase (ALP) in C2C12 cells and proliferation of human mesenchymal stem cells (hMSCs) were evaluated to analyze the osteogenic capacity of the surface. The coating incorporated 10.5 µg rhBMP2 on average per disc and did not change the surface morphology. The release profile showed a delivery of 14.5% of the incorporated growth factor during the first 24 h with a decline towards the end of the observation period with a total release of 31.3%. Cross-linking reduced the release with an almost complete suppression at 100% cross-linking. Alkaline Phosphatase was significantly increased on day 1 and day 21, indicating that the growth factor bound in the coating remains active and available after 3 weeks. Proliferation of hMSCs was significantly enhanced by the non-cross-linked PEM coating. Nanocoating using collagen/heparin-based PEMs can incorporate clinically relevant amounts of rhBMP2 on titanium surfaces with a retarded release and a sustained enhancement of osteogenic activity without changing the surface morphology.

Tailored Polyelectrolyte Multilayer Systems by Variation of Polyelectrolyte Composition and EDC/NHS Cross-Linking: Physicochemical Characterization and In Vitro Evaluation.

The layer-by-layer (LbL) self-assembly technique is an effective method to immobilize components of the extracellular matrix (ECM) such as collagen and heparin onto, e.g., implant surfaces/medical devices with the aim of forming polyelectrolyte multilayers (PEMs). Increasing evidence even suggests that cross-linking influences the physicochemical character of PEM films since mechanical cues inherent to the substrate may be as important as its chemical nature to influence the cellular behavior. In this study, for the first-time different collagen/heparin films have been prepared and cross-linked with EDC/NHS chemistry. Quartz crystal microbalance, zeta potential analyzer, diffuse reflectance Fourier transform infrared spectroscopy, atomic force microscopy and ellipsometry were used to characterize film growth, stiffness, and topography of different film systems. The analysis of all data proves a nearly linear film growth for all PEM systems, the efficacy of cross-linking and the corresponding changes in the film rigidity after cross-linking and an appropriate surface topography. Furthermore, preliminary cell culture experiments illustrated those cellular processes correlate roughly with the quantity of newly created covalent amide bonds. This allows a precise adjustment of the physicochemical properties of the selected film architecture regarding the desired application and target cells. It could be shown that collagen improves the biocompatibility of heparin containing PEMs and due to their ECM-analogue nature both molecules are ideal candidates intended to be used for any biomedical application with a certain preference to improve the performance of bone implants or bone augmentation strategies.

Two Sides of the Same Coin: A Unified Theoretical Treatment of Polyelectrolyte Complexation in Solution and Layer-by-Layer Films

Polyelectrolyte coacervates, obtained by mixing solutions of oppositely charged polyions, and layer-by-layer films, produced by sequential adsorption of polyelectrolytes on a surface, are two types of closely related soft materials. While both types of materials are produced by polyelectrolyte complexation, their theoretical description had so far followed divergent paths. This work reports a unifying theoretical treatment of polyelectrolyte complexation in solution and layer-by-layer self-assembled thin films using a molecular theory that describes polyelectrolyte complexation by using a chemical-equilibrium formalism. The theory is shown to predict both the phase diagrams of polyelectrolyte mixtures in solution and the formation of layer-by-layer thin films in good agreement with experimental evidence. In the latter case, the theory correctly captures the effects of solution pH and ionic strength on the mass of the deposited films as well as the possibility of layer-by-layer deposition without full charge reversal at extreme pHs. The theory is then used to revisit the “universal curve” for the effect of salt concentration on layer-by-layer deposition previously proposed on experimental grounds by Salehi et al. [Macromolecules 2015, 48, 400–409]. This universal curve makes predictions about the growth rate of a layer-by-layer film for a given polyanion/polycation pair by using only information obtained from a mixture of the same polyelectrolytes in solution, thereby linking both phenomena. Our theoretical results confirm the validity of the curve. This achievement demonstrates the practical importance of describing polyelectrolyte coacervates and multilayer films within a unified theoretical framework.

Hybrid multilayer coating as the psoralen delivery vehicle promoting bone regeneration on titanium mesh scaffolds in a Posterolateral Spinal Fusion model

The instant and long-term stabilities of the implanted cage between the two vertebras are key factors for successful spinal fusion surgery. Instead of simply induce bone formation by including osteo-inductive cytokines carrying materials in the cavum of the cage, the modification of the cage surfaces to facilitate cage-bone integration yet promoting bone regeneration is becoming more essential. In this study, we used the titanium mesh scaffold (TMS) as the model cage and activated the surface with the synergism of a bone-conductive polyelectrolyte multilayer film (PEM) and the bone-inductive drug psoralen (PSO). The Hyaluronic Acid/Polymerizated Dopamine modified Hydroxyapatite/Chitosan (HA/PDHA/CHI) multilayer film was constructed on the scaffold in layer-by-layer (LBL) fashion, and PSO was loaded on the scaffold via post-diffusion. SEM and FTIR confirmed the successful coating of HA/PDHA/CHI multilayer film on TMS as well as the effective loading of psoralen. The rough and porous surface structure of the hybrid PEM facilitated the proliferation and adhesion of rat bone mesenchymal stem cells (rBMSCs), and the PEM coated scaffolds exhibited advantages in PSO loading and retention. In vitro experiments demonstrated that psoralen had direct and effective osteogenic ability and the ability was closely related to the activation of the autophagy, while PEM promotes new bone formation by favoring cell proliferation and adhesion. In the Rat Model of L4-L5 Posterolateral Spinal Fusion, HA/PDHA/CHI PEM synergized with PSO greatly improved proliferation, adhesion and osteogenesis of rBMSCs, and promoted new bone formation, and therefore accelerated spinal fusion rate. This study provides a new treatment for spinal fusion therapy and may have great potential in bone regeneration and bone integration for implants.

Layer-by-layer assembly of cation exchange membrane for highly efficient monovalent ion selectivity

The development of cation exchange membranes (CEMs) with high monovalent/divalent cation selectivity has great potential for enhanced salt separation for wastewater reclamation, and layer-by-layer (LbL) self-assembly of polyelectrolyte films with high monovalent selectivities among cations has expanded the applications of such membranes. However, the structure–property relationship for constructing multilayered polyelectrolyte films with enhanced separation performance remains poorly understood. This study reports a novel CEM engineered by coating a [polyethyleneimine/polystyrene sulfonate (PEI/PSS)]n alternate electro-deposition multilayer on a polyacrylate substrate membrane. The newly developed CEM exhibited a monovalent selectivity of 4.59 for Li+/Mg2+ with an optimal permeation of 0.16 mmol·cm−2·h−1 for Li+, demonstrating a competitive separation property compared to state-of-the-art permselective membranes. A detailed quantitative investigation provides the underlying insights into the monovalent selectivity for each polyelectrolyte layer. The results indicate negligible interface impedance toward monovalent cations but strengthened repulsion against divalent cations, thereby promoting a quick passage for monovalent cations while imposing temporal retardation on divalent cations during the electrodialysis (ED) process. Therefore, this study elucidates the characteristic reason for the enhanced monovalent ion permselectivity of LbL polyelectrolyte membranes in electro-driven separation processes.

Conformation-dependent thermoelectric power factor of multilayer nanocomposites

Polyelectrolyte multilayer thin films, assembled by sequentially depositing bilayer (BL) of poly(allyamine hydrochloride) (PAH) and double-walled carbon nanotubes (DWNT) stabilized in polyacrylic acid (PAA) using the layer-by-layer assembly technique, are studied in an effort to establish the relationships between the conformational changes and thermoelectric performances. Controlling the charge density of weak polyelectrolytes with assembly pH conditions gives rise to a different physical, structural, and mechanical properties. The 7.5PAH/3.5(DWNT-PAA) films exhibit an exponentially-grown thickness behavior due to in-and-out diffusion of the partially charged polyelectrolytes with coiled polymeric conformation, which results in randomly distributed nanotubes within the multilayers. Films made with the same sequences, but with extended polymeric conformation due to high charge density along the polymer chain (PAH at pH 6 and PAA at pH 6.5), show the linear growth behavior with a uniformly oriented nanotube structure and relatively higher elastic modulus. The precise control of the polymeric conformation upon charge density at the nanoscale level significantly affects the thermoelectric performances. A 14 BL 6PAH/6.5(DWNT-PAA) film exhibits an electrical conductivity of 417 S cm−1 and Seebeck coefficient of 85 μV K−1. This translates to a power factor of 301 μW m−1 K−2, which is 75 times higher than the same films made at pH 7.5/3.5.

Quantification of Water–Ion Pair Interactions in Polyelectrolyte Multilayers Using a Quartz Crystal Microbalance Method

Water existing within thin polyelectrolyte multilayer (PEM) films has significant influence on their physical, chemical, and thermal properties, having implications for applications including energy storage, smart coatings, and biomedical systems. Ionic strength, salt type, and terminating layer are known to influence PEM swelling. However, knowledge of water’s microenvironment within a PEM, whether that water is affiliated with intrinsic or extrinsic ion pairs, remains lacking. Here, we examine the influence of both assembly and post-assembly conditions on the water–ion pair interactions of poly(styrene sulfonate)/poly(diallyldimethylammonium) (PSS/PDADMA) PEMs in NaCl and KBr. This is accomplished by developing a methodology in which quartz crystal microbalance with dissipation monitoring is applied to estimate the number of water molecules affiliated with an ion pair (i), as well as the hydration coefficient, πsaltH2O. PSS/PDADMA PEMs are assembled in varying ionic strengths of either NaCl and KBr and then exposed post-assembly to increasing ionic strengths of matching salt type. A linear relationship between the total amount of water per intrinsic ion pair and the post-assembly salt concentration was obtained at post-assembly salt concentrations >0.5 M, yielding estimates for both i and πsaltH2O. We observe higher values of i and πsaltH2O in KBr-assembled PEMs due to KBr being more effective in doping the assembly because of KBr’s more chaotropic nature as compared to NaCl. Lastly, when PSS is the terminating layer, i decreases in value due to PSS’s hydrophobic nature. Classical and ab initio molecular dynamics provide a microstructural view as to how NaCl and KBr interact with individual polyelectrolytes and the involved water shells. Put together, this study provides further insight into the understanding of existing water microenvironments in PEMs and the effects of both assembly and post-assembly conditions.

Quenching the Macroporous Collapse of Polyelectrolyte Multilayer Films for Repeated Drug Loading

Macroporous structures can be developed within polyelectrolyte multilayer films for efficient drug loading, but these structures tend to collapse or fracture during conventional drying procedures. Herein, a facile dehydrating method for macroporous polyelectrolyte multilayer films is proposed using solvent exchange to ethanol and then spontaneous evaporation. During these processes, the collapse of the macroporous structures can be effectively avoided, which can be ascribed to a combined effect of two factors. On one hand, capillary pressure during ethanol evaporation is relatively small since the surface tension of ethanol is much lower than that of water. On the other hand, solvent exchange suppresses the interdiffusion of polyelectrolytes and substantially increases the mechanical strength of the macroporous films, more than three orders of magnitude, making the pore walls highly tolerant of the capillary pressure. The stability of macroporous polyelectrolyte films to ethanol enables the repeated wicking from the ethanol solution of drugs, leading to a higher loading beyond previous studies. Such a high loading is favorable for the long-term release of drugs from the surfaces of modified substrates and maintaining a local drug concentration above the minimum effective concentration.

Electrodialysis through nafion membranes coated with polyelectrolyte multilayers yields >99% pure monovalent ions at high recoveries

Separation of monovalent and multivalent ions is important in processes ranging from water softening to recycling of Li. Previous studies show that cation-exchange membranes coated with multilayer polyelectrolyte films exhibit monovalent/divalent ion selectivities as high as 1000 in electrodialysis (ED) under ideal conditions with low ion recoveries. This work shows that even at 60–80% monovalent-ion recoveries, ED through Nafion membranes coated with protonated poly(allylamine)/poly(4-styrenesulfonate) multilayers can separate equimolar K + and Mg 2+ or Li + and Mg 2+ to give 99.5% pure monovalent ion. Moreover, the use of a low-volume receiving phase allows ED to concentrate the monovalent ion. Typical current efficiencies are around 70% for these separations. Selectivities appear to increase when the membrane-coating procedure uses a higher polyelectrolyte concentration in the deposition solution. Because the limiting current declines with ED time due to depletion of the monovalent ion in the source phase, use of a gradually decreasing applied current enhances current efficiency compared to ED at a constant high current. The membranes also show Li + /Mg 2+ selectivities around 100 when Mg 2+ is in a 20-fold excess in the source phase at an ionic strength of 0.6 M, but selectivity decreases at even higher ionic strengths. • Electrodialysis through coated membranes gives 99.5% pure monovalent ions. • High purity accompanies 60–80% recovery. • Underlimiting currents lead to high current efficiencies with high purities. • Electrodialysis can concentrate monovalent ions in the receiving phase. • High selectivities occur for Li + over Mg 2+ or K + over Mg 2+ .

The Potential of Polyelectrolyte Multilayer Films as Drug Delivery Materials.

Polyelectrolyte multilayers (PEMs) represent a group of polyelectrolyte complex (PEC)–based materials widely investigated in the biomedical and pharmaceutical sciences. Despite the unflagging popularity of the aforementioned systems in tissue engineering, only a few updated scientific reports concerning PEM potential in drug administration can be found. In fact, PEM coatings are currently recognized as important tools for functionalizing implantable scaffolds; however, only a small amount of attention has been given to PEMs as drug delivery materials. Scientific reports on PEMs reveal two dominant reasons for the limited usability of multilayers in pharmaceutical technology: complex and expensive preparation techniques as well as high sensitivity of interacting polyelectrolytes to the varieties of internal and external factors. The aim of this work was to analyze the latest approaches, concerning the potential of PEMs in pharmacy, chemical technology, and (primarily) tissue engineering, with special attention given to possible polymer combinations, technological parameters, and physicochemical characteristics, such as hydrophilicity, adhesive and swelling properties, and internal/external structures of the systems formed. Careful recognition of the above factors is crucial in the development of PEM-based drug delivery materials.

Fluorescence Signal Enhancement by a Spray-Assisted Layer-by-Layer Technique on Aluminum Tape Devices for Biosensing Applications

Layer-by-layer (LbL) self-assembled polyelectrolyte multilayer (PEM) films are a simple yet elegant bottom-up technology to create films at the nano-microscale. This low-cost technology has been widely used as a universal functionalization technique on a broad spectrum of substrates. Biomolecules under investigation can be incubated onto films based on complementary charge interactions between the films and biomolecules. There is a great demand for developing an ultralow-cost biosensing device, which can optimally enhance the fluorescence signal of the adsorbed biomolecules from the traditional labeled sensing platforms. In this work, we have incorporated a blend of the conventional metal enhanced fluorescence technology and the PEM as a dielectric spacer and functionalized film, coated on an aluminum paper (tape)-based substrate. These device has been found to be capable of holding biomolecules in three-dimensional PEM space. The devices fabricated by the proposed spray LbL technique provide significant fluorescence signal enhancement by holding a relatively higher mass per volume of the adsorbed biomolecules, when compared to traditional spin- and dip-coating techniques. Interestingly, our proposed device has expressed a fluorescence enhancement factor, which is 9 times higher than PEM-functionalized glass-based devices. To demonstrate the practical utility of our devices, we also compared our devices to Whatman FAST slides. Our experimental fluorescence results are almost comparable to Whatman FAST slides. Such PEM devices fabricated on top of low-cost aluminum tape using a spray LbL technique give new insights into the future development of ultralow-cost, high-throughput, and disposable lab-on-chip diagnostic applications.