Red Blood Cell Templated Polyelectrolyte Capsules: A Novel Vehicle for the Stable Encapsulation of DNA and Proteins

Summary: A novel method for the encapsulation of biomacromolecules, such as nucleic acids and proteins, into polyelectrolyte microcapsules is described. Fluorescence‐labelled double‐stranded DNA and human serum albumin (HSA) are used as model substances for encapsulation in hollow microcapsules templated on human erythrocytes. The encapsulation procedure involves an intermediate drying step. The accumulation of DNA and HSA in the capsules is observed by confocal laser scanning microscopy, UV spectroscopy, and fluorimetry. The mechanism of encapsulation is discussed.

Confocal fluorescence microscopy images of encapsulated TRITC‐HSA (left) and dsDNA (right). Inserts demonstrate fluorescence profiles for both compounds.     

Enhancing Gelation Ability of a Dendritic Gelator through Complexation with a Polyelectrolyte

Let's stick together : The gelation ability of a dendritic gelator has been enhanced by its complexation with a polyelectrolyte (see figure). This concept provides a route to construct novel functional or ordered materials by complexation of other low‐molecular‐mass functional species with polyelectrolytes.

     

Controlled Stripping of Polyelectrolyte Multilayers by Quaternary Ammonium Surfactants

The quartz crystal microbalance with dissipation technique (QCM‐D) and atomic force microscopy (AFM) have been employed to study the interaction of N‐tetradecyl trimethyl ammonium bromide (TdTmAB) with polyelectrolyte multilayers containing poly(sodium 4‐styrene sulfonate) (PSS) as the polyanion and either poly(allylamine hydrochloride) (PAH) or poly(diallyl dimethyl ammonium chloride) (PDADMAC) as the polycations. The multilayers were exposed to aqueous solutions of TdTmAB. This resulted in a selective removal of PDADMAC PSS layers while layers with PAH as polycation remained stable. It is suggested that PDADMAC/PSS multilayers can be employed as strippable protecting layers.

     

pH‐Switchable Bioelectrocatalysis Based on Weak Polyelectrolyte Multilayers

Weak polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) were assembled into {PAH/PAA}_n layer‐by‐layer films on electrodes. The cyclic voltammetry (CV) response of ferrocenecarboxylic acid (Fc(COOH)) at {PAH/PAA}₅ film electrodes assembled under the specific condition showed pH‐sensitive “on‐off” switching property. This property was further used to control the electrocatalytic oxidation of glucose by glucose oxidase (GOD) with Fc(COOH) as the electron transfer mediator, so that the pH‐switchable bioelectrocatalysis could be realized. The mechanism of pH‐sensitive behavior of the system was explored and believed to originate from the pH‐dependent structure change of the films.     

Polyelectrolyte micelles in salt‐free solutions: Micelle size and electrostatic potential

The structural and electrical characteristics of polyelectrolyte micelles formed by diblock copolymers with one charged block and one solvophobic block are studied by the means of molecular dynamics simulations using the Primitive model at different Bjerrum lengths. The properties of interest are the mean aggregation number, the shape, the electrical potential as a function of the distance of the micelle's center of mass and the zeta potential. We found that for partially charged short A blocks the micelles’ mass distribution function is at least bimodal, indicating the coexistence of small and large micelles in agreement with theoretical and experimental findings. The zeta potential is not a monotonic function of the length of the charged block. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 924–934     

Stimuli‐Responsive Multilayered Hybrid Nanoparticle/Polyelectrolyte Capsules

Gold nanoparticles (Au_NP) with carboxyl groups on their surface were used in combination with PAH for the layer‐by‐layer coating of CaCO₃ microparticles, followed by the dissolution of the CaCO₃ core. SEM, TEM, and confocal microscopy are used to characterize the hybrid nanoparticles/polyelectrolyte capsules. As the Au_NP have carboxyl groups on their surface, their charge density is pH dependent; therefore, the capsules exhibit a pH‐dependent swelling and can be deconstructed both at low and high pH. By covalent cross‐linking of the carboxyl groups of the Au_NP and the amino groups of the PAH, it is possible to suppress the pH‐responsive behavior. Au_NP are used as activation centers using IR light and this ability is used to release encapsulated material from the nanoparticles/polyelectrolyte capsules as well as for the enhancement of detection and imaging of such capsules by Raman microspectrosopy.

     

Polyelectrolyte multilayers prepared on hydrogel surfaces

Poly(vinyl alcohol) hydrogels were alternately immersed in aqueous solutions of oppositely charged polymers. The adsorption of the cationic dye methylene blue to the immersed hydrogels suggested the presence of a coating on the hydrogel surfaces. Static contact angles with an air bubble in water showed layer‐by‐layer growth of the films. The films could be transferred onto solid substrates for mechanical strength after the hydrogels were placed on the solid substrates, and this resulted in an estimation of the film thickness. The number of assembly steps could regulate the film thickness. We present here coatings of hydrogels with thin polymer films prepared by layer‐by‐layer assembly. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1062–1067, 2005     

Polyelectrolyte Capsules as Carriers for Growth Factor Inhibitor Delivery to Hepatocellular Carcinoma

The efficient internalization of TGF‐beta inhibitor‐loaded polyelectrolyte capsules and particles is studied in two HCC cell lines. Two polyelectrolyte pairs (biocompatible but not degradable and biodegradable crosslinked with gluteraldehyde) are employed for coating. The capsules are characterized by SEM. LY is successfully loaded inside the core and embedded between polymer layers. MS is used to quantify the loading efficiency by comparing post‐loading and core‐loading methods, since both coated templates and hollow shells are used as carriers. CLSM confirms dissolution of the pre‐formed multilayer upon enzymatic degradation as the method of release, and migration assays demonstrate a higher inhibition efficiency of TGF‐beta in tailored biodegradable capsules compared to free LY administration.

     

Ordered Polyelectrolyte Multilayers: Unidirectional FRET Cascade in Nanocompartmentalized Polyelectrolyte Multilayers

Multifunctional polyelectrolyte (or layer‐by‐layer, LbL) multilayers consisting of a set of nanocompartments separated by impermeable ultrathin barriers, whereby the thickness of the compartments is tuned in the range 1–10 nm, are synthesized. Each compartment contains a different dye, introduced by co‐adsorption during multilayer deposition. Different LbL barriers are tested for impermeability towards dye diffusion while simultaneously allowing energy transfer to occur between the compartmentalized dyes. Cross‐linked LbL multilayers based on poly(acrylic acid) and poly(allyl amine) are shown to provide the desired impermeability for thicknesses as small as about 2.5 nm. A proof‐of‐concept system is then realized involving a cascade of two FRET processes, whereby the light energy is collected in a first nanocompartment containing pyranine, sent to a second nanocompartment loaded with fluorescein, before finally being transferred to a third, Nile blue‐filled compartment located at the external surface of the film. This demonstrates the possibility to fabricate complex light‐harvesting antenna systems by LbL assembly while controlling the architecture of the antenna down to a few nanometers.     

Responsive Polyelectrolyte Multilayers Assembled at High Ionic Strength with an Unusual Collapse at Low Ionic Strength

Responsive polyelectrolyte multilayers (PEMs) of poly(diallyl dimethyl ammonium chloride) (PDADMAC) and poly(styrene sodium sulfonate) (PSS) with thicknesses between 350 and 400 nm for 11 deposited polyelectrolyte layers were fabricated assembling the polyelectrolytes at 3 M NaCl. When the 3 M NaCl bulk solution is replaced by water, the PEMs release water, approximately a 46% of the total mass, and experience a thickness reduction of more than 200 nm. Changes in thickness and water content are fully reversible. The film recovers its original thickness and water content when it is exposed again to a 3 M NaCl solution. A responsive polymer film is achieved with the capability of swelling at high ionic strength and collapsing in water with variations in thickness of hundred of nanometers.     

Photocatalytically Active Polyelectrolyte/Nanoparticle Films for the Elimination of a Model Odorous Gas

Virtually transparent films of Aeroxide TiO₂ P25 were fabricated via layer‐by‐layer assembly with sodium poly(styrene sulfonate). Nanoscale films are formed on model surfaces for characterization or inside of cylindrical reactors for investigating the catalytic properties. Films are fairly homogeneous and smooth over large areas and show different optical interference colors depending on film thickness. The application‐relevant photocatalytic performance of such films toward on‐flow degradation of hydrogen sulfide under UV‐A irradiation was investigated. Scanning electron microscopy reveals a nanoporous structure allowing for the permeation of gas. Consequently, the catalytic efficiency of the films increases with increasing film thickness retaining a considerable activity of the corresponding nanoparticle powder. Scheme 1 depicts in a general way the functionalized reactor and the principle of the measurement.     

Modeling the Interactions between Membranes and Inclusions: Designing Self‐Cleaning Films and Resealing Pores

The design of responsive membranes whose interactions with inclusions can be controlled through the application of an external stimulus is reviewed with the aim to establish guidelines for introducing functionality into the materials. For a photo‐reactive AB membrane, we find that a gradient in light intensity can be harnessed to clean the system of any C “impurities”, or target the delivery of C to specific locations. By modeling the interactions between a lipid bilayer and Janus nanoparticles, we design a synthetic membrane with stable pores that can be controllably opened and closed. This leads to design rules for creating nanoparticle‐bilayer assemblies where the pores open and the cargo is released only when local environmental conditions reach a critical value.

     

Salt Responsive Morphologies of ssDNA‐Based Triblock Polyelectrolytes in Semi‐Dilute Regime: Effect of Volume Fractions and Polyelectrolyte Length

A comprehensive study is reported on the effect of salt concentration, polyelectrolyte block length, and polymer concentration on the morphology and structural properties of nanoaggregates self‐assembled from BAB single‐strand DNA (ssDNA) triblock polynucleotides in which A represents polyelectrolyte blocks and B represents hydrophobic neutral blocks. A morphological phase diagram above the gelation point is developed as a function of solvent ionic strength and polyelectrolyte block length utilizing an implicit solvent ionic strength method for dissipative particle dynamics simulations. As the solvent ionic strength increases, the self‐assembled DNA network structures shrinks considerably, leading to a morphological transition from a micellar network to worm‐like or hamburger‐shape aggregates. This study provides insight into the network morphology and its changes by calculating the aggregation number, number of hydrophobic cores, and percentage of bridge chains in the network. The simulation results are corroborated through cryogenic transmission electron microscopy on the example of the self‐assembly of ssDNA triblocks.     

Single Polyelectrolyte Microcapsules Fabricated By Glutaraldehyde‐Mediated Covalent Layer‐By‐Layer Assembly

Summary: Single polyelectrolyte component microcapsules and multilayers, exemplified by poly(allylamine hydrochloride) (PAH), have been prepared using a method of glutaraldehyde (GA)‐mediated covalent layer‐by‐layer (LbL) assembly. The GA cross‐linking of the adsorbed PAH results in surfaces covered by reactive aldehyde groups, which can then react with PAH to result in another layer of covalently linked PAH. The repeated assembly of single polyelectrolyte in an LbL manner can be thus achieved. The PAH multilayers can grow linearly along with the layer number, and their thickness can be controlled at the nanometer scale, as verified by UV‐vis absorption spectrometry and ellipsometry. Single polyelectrolyte microcapsules are obtained after removal of the template cores at low pH. The morphology and integrity are confirmed by scanning force microscopy and confocal laser scanning microscopy.

Schematic illustration of the preparation of a single polyelectrolyte component microcapsule by GA‐mediated covalent LbL assembly.     

Polyelectrolyte Multilayers on Weak Polyelectrolyte Brushes

The interaction of surface‐attached weak polyelectrolyte brushes, grown directly from the surface of a solid substrate by surface‐initiated polymerization, with weak polyelectrolyte molecules in solution is studied. In addition, the formation of PEL multilayers onto such brush substrates is investigated. A strong template effect is observed and the thickness of each adsorbed layer is closely related to the thickness of the initial brush. Thus monolayers of more than 100 nm can be adsorbed in one single dipping cycle.

Layer thickness of PEI layers adsorbed to PMAA brushes as a function of the thickness of the surface‐attached monolayer. The solid line represents a case in which the PEI layer has exactly the same thickness as the brush monolayer.