Polyelectrolyte Multilayer Microcapsules Research Articles

Incorporation of CuS nanorods in polyelectrolyte multilayer microcapsules improved cancer cell cytotoxicity and signal intensity in ultrasound imaging

The fabrications of hollow microcapsules (MCs) with new architecture and ability to incorporate different nanomaterials have received great interest for targeted cancer therapy. Recently, CuS based nanomaterials have been demonstrated to possess the ability to mimic Fenton-like activity in tumor environment and inducing cancer cell apoptosis by generating highly reactive oxygen species (ROS). In this study, we have developed poly(allylamine) hydrochloride (PAH)/dextran sulfate (DS) polyelectrolyte MCs capable of carrying doxorubicin (DOX) for targeted cancer therapy and ultrasound imaging. The electron microscopy investigations showed the formation of polymeric MCs of 3 µm in size with incorporated CuS NRs in their interior structure. The surface modification of MCs with folic acid (FA), and encapsulation of model hydrophilic molecules in MCs was studied by UV–Visible (UV–Vis) spectroscopy, Fourier transform infra-red (FTIR) spectroscopy and confocal laser scanning microscopy. The encapsulation efficiency of DOX was found to be 56 % and the release was found to be linear at pH 5.5 and 7.4 in the absence of ultrasound exposure. The ultrasound exposure resulted in sudden rupture of MCs at 1 MHz and 1 W/cm2 and caused burst release of DOX at both pH conditions. The FA decorated PAH/DS/CuS NR MCs exhibited improved anti-cancer activity against MDA-MB-231 cancer cells due to the synergistic effects of ultrasound mediated burst release of chemotherapeutic drug (DOX), glutathione-stimulated ROS and targeted cancer therapy. Further, the capsules showed better echogenicity than that of control PAH/DS MCs when imaged under medical ultrasound-scanning system. Hence, the MCs demonstrated in this study have huge potential for targeted cancer theranostics by offering an option to image the cancer cells during the treatment period.

In Vitro Bioeffects of Polyelectrolyte Multilayer Microcapsules Post-Loaded with Water-Soluble Cationic Photosensitizer.

Microencapsulation and targeted delivery of cytotoxic and antibacterial agents of photodynamic therapy (PDT) improve the treatment outcomes for infectious diseases and cancer. In many cases, the loss of activity, poor encapsulation efficiency, and inadequate drug dosing hamper the success of this strategy. Therefore, the development of novel and reliable microencapsulated drug formulations granting high efficacy is of paramount importance. Here we report the in vitro delivery of a water-soluble cationic PDT drug, zinc phthalocyanine choline derivative (Cholosens), by biodegradable microcapsules assembled from dextran sulfate (DS) and poly-l-arginine (PArg). A photosensitizer was loaded in pre-formed [DS/PArg]4 hollow microcapsules with or without exposure to heat. Loading efficacy and drug release were quantitatively studied depending on the capsule concentration to emphasize the interactions between the DS/PArg multilayer network and Cholosens. The loading data were used to determine the dosage for heated and intact capsules to measure their PDT activity in vitro. The capsules were tested using human cervical adenocarcinoma (HeLa) and normal human dermal fibroblast (NHDF) cell lines, and two bacterial strains, Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. Our results provide compelling evidence that encapsulated forms of Cholosens are efficient as PDT drugs for both eukaryotic cells and bacteria at specified capsule-to-cell ratios.

Hydrogel Microdomain Encapsulation of Stable Functionalized Silver Nanoparticles for SERS pH and Urea Sensing.

Conceptual and commercial examples of implantable sensors have been limited to a relatively small number of target analytes, with a strong focus on glucose monitoring. Recently, surface-enhanced Raman spectroscopy (SERS) pH sensors were demonstrated to track acid-producing enzymatic reactions targeting specific analytes. We show here that SERS pH tracking in the basic regime is also possible, and can be used to monitor urea concentration. To accomplish this, we developed a hydrogel consisting of polyelectrolyte multilayer microcapsules containing a SERS-sensitive pH reporter (4-mercapopyridine capped silver nanoparticles modified with bovine serum albumin). This pH sensing material exhibited a sensitive Raman scattering response to a wide range of pH from 6.5–9.7. By incorporating urease into the hydrogel matrix, the new sensor was capable of distinguishing urea concentrations of 0, 0.1, 1, and 10 mM. We also found that bovine serum albumin (BSA) prevented severe aggregation of the nanoparticle-based pH sensor, which improved sensing range and sensitivity. Furthermore, BSA safeguarded the pH sensor during the encapsulation procedure. Together, the combination of materials represents a novel approach to enabling optical sensing of reactions that generate pH changes in the basic range.

Distribution of PEG-coated hollow polyelectrolyte microcapsules after introduction into the circulatory system and muscles of zebrafish.

ABSTRACTThe use of polyelectrolyte multilayer microcapsules as carriers for fluorescent molecular probes is a prospective technique for monitoring the physiological characteristics of animal vasculature and interstitial environment in vivo. Polyelectrolyte microcapsules have many features that favor their use as implantable carriers of optical sensors, but little information is available on their interactions with complex living tissues, distribution or residence time following different routes of administration in the body of vertebrates. Using the common fish model, the zebrafish Danio rerio, we studied in vivo the distribution of non-biodegradable microcapsules covered with polyethylene glycol (PEG) over time in the adults and evaluated potential side effects of their delivery into the fish bloodstream and muscles. Fluorescent microcapsules administered into the bloodstream and interstitially (in concentrations that were sufficient for visualization and spectral signal recording) both showed negligible acute toxicity to the fishes during three weeks of observation. The distribution pattern of microcapsules delivered into the bloodstream was stable for at least one week, with microcapsules prevalent in capillaries-rich organs. However, after intramuscular injection, the phagocytosis of the microcapsules by immune cells was manifested, indicating considerable immunogenicity of the microcapsules despite PEG coverage. The long-term negative effects of chronic inflammation were also investigated in fish muscles by histological analysis.

SERS-Active Smart Hydrogels With Modular Microdomains: From pH to Glucose Sensing

A sensing hydrogel was demonstrated using pH-sensitive surface-enhanced Raman scattering (SERS) reporters embedded in modular microdomains. The gold nanoparticle-based pH probes capped with 4-mercaptobenzonic acid (MBA-AuNPs) were encapsulated within polyelectrolyte multilayer microcapsules within a surrounding hydrogel matrix. The materials were fully characterized for pH sensitivity and reproducibility of Raman scattering, which revealed low background (hydrogel) signals and a sigmoidal response curve for ratiometric intensity changes at 1430 and 1078 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , respectively. The analytical range was pH 4.43-8.07 (pKa~5.80) with an average sensitivity of 0.07 pH <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . To assess the potential for sensing enzymatic substrates, hydrogels were prepared with the MBA-AuNPs co-encapsulated with glucose oxidase. Raman spectra recorded from hydrogels exposed to physiological glucose levels (0-400 mg/dL) exhibited apparent trends of decreasing pH from pH ~6.50 to pH ~4.50 due to glucose oxidization within the microdomains. The glucose diffusion into the capsules was controlled by crosslinking the polyelectrolyte multilayers with glutaraldehyde, showing an approach to adjust the balance of oxygen and glucose flux into the microcavities, yielding a tunable sensitivity of the glucose-proportional change at steady-state pH. These findings illustrate the potential of hydrogel hosts for a flexible approach to pseudo-solid-state SERS sensing devices for multiple small molecule targets.

Comparative study of cytotoxicity of ferromagnetic nanoparticles and magnetitecontaining polyelectrolyte microcapsules

The cytotoxicity of magnetite nanoparticles (MNP) stabilized with citrate acidand polyelectrolyte multilayer microcapsules containing these particles in the shell is analyzed. Microcapsules were prepared by co-precipitation of iron (II) and (III) chlorides. Polyelectrolyte microcapsules synthesized by the layer-by-layer method from biodegradable polymers polyarginine and dextran sulfate. Cytotoxicity of the synthesized objects was studied on the L929 cells culture and human leucocytes. It was also investigated the phagocytic activity of leukocytes for the MNP and magnetite containing polyelectrolyte microcapsules (MCPM). A set of tests (MTT assay, neutral red uptake assay, lactate dehydrogenase release assay) was used to study the cytotoxicity in vitro. All the tests have shown that the magnetic nanoparticles have a greater cytotoxicity in comparison with microcapsules containing an equivalent amount of magnetite. In contrast to the mouse fibroblast culture, human leukocytes were more resistant to the toxic effects of magnetite. At the concentrations used in our studies no significant reduction in the viability of leukocytes has been registered. Both MNP and MCPM undergo phagocytosis, however, the phagocytic activity of leukocytes for these particles was lower than for the standard objects (latex microparticles).

Release from Polyelectrolyte Multilayer Capsules in Solution and on Polymeric Surfaces

Release from polyelectrolyte multilayer microcapsules represents one of the most important steps enabling practical use of the microcapsules. A number of biological and non‐biological applications are envisaged by proper encapsulation of molecules of interest and their release performance. Since the invention of the microcapsules at the Max‐Planck Institute of Colloids and Interfaces in 1998 the work towards microcapsule assisted release has undergone tremendous progress. Almost simultaneously with development of release approaches an extensive base of applications has been advanced. In this progress report the release from the capsules in a solution and those immobilized on the surface of polymeric films is addressed.

How Leucocyte Cell Membrane Modified Janus Microcapsules are Phagocytosed by Cancer Cells.

Modern drug delivery systems rely on either antibody-based single-surface recognition or on surface-hydrophobicity-based approaches. For a tumor showing various surface mutations, both approaches fail. This publication hereby presents Janus capsules based on polyelectrolyte multilayer microcapsules exhibiting human leucocyte (THP-1 cell line) cell membranes for discriminating HUVEC cells from three different cancer cell lines. Despite destroying the cellular integrity of leucocyte cells, the modified Janus capsules are able to adhere to cancer cells. Leucocyte cell-membrane-coated Janus capsules are phagocytosed with the cellular membrane part pointing to the cells.

Control of Wnt/β-Catenin Signaling Pathway in Vivo via Light Responsive Capsules.

The possibility to remotely manipulate intracellular pathways in single cells is among the current goals of biomedicine, demanding new strategies to control cell function and reprogramming cell fate upon external triggering. Optogenetics is one approach in this direction, allowing specific cell stimulation by external illumination. Here, we developed optical switchers of an ancient and highly conserved system controlling a variety of developmental and adult processes in all metazoans, from Hydra to mammals, the Wnt/β-catenin signaling pathway. An intracellular modulator of the Wnt pathway was enclosed into polyelectrolyte multilayer microcapsules engineered to include self-tracking (i.e., fluorescence labeling) and light mediated heating functionalities (i.e., plasmonic nanoparticles). Capsules were delivered in vivo to Hydra and NIR triggered drug release caused forced activation of the Wnt pathway. The possibility to remotely manipulate the Wnt pathway by optical switchers may be broadly translated to achieve spatiotemporal control of cell fate for new therapeutic strategies.

Controlled release of a microencapsulated arduous semi-hydrophobic active from coatings: Superhydrophilic polyelectrolyte shells as globally rate-determining barriers

Polymethylmethacrylate-based microcapsules containing the antimicrobial agent 2-n-octyl-4-isothiazolin-3-one (OIT) decorated by an anchored polyelectrolyte brush consisting of an amphiphilic diblock copolymer of polymethylmethacrylate-block-poly(sodium methacrylate) type have been formulated via a coacervation technique. The polyelectrolyte brush surface provided the microcapsule with a high and stable surface charge density. This enabled further surface modification of the colloidal particle with a thin and dense polyelectrolyte multilayer using the layer-by-layer technique. The addition of the highly charged and hydrophilic polyelectrolyte multilayer assembled on the microcapsule surface resulted in a considerable decrease of the release rate of the encapsulated OIT in aqueous suspension, corresponding to a 40 times reduction of the effective OIT diffusion coefficient in the polymethylmethacrylate matrix. Moreover, the release of encapsulated or freely dispersed OIT from coatings as a function of the matrix density was evaluated and analyzed within the framework of applied diffusion models. Encapsulation of OIT in polyelectrolyte multilayer composite microcapsules was found to significantly prolong the release and render the release rate more or less independent of the matrix density. In addition, the long-term antimicrobial properties of the coatings were evaluated in terms of their susceptibility for biofouling using the fungus and common biofouler Aspergillus niger as model organism. The results clearly demonstrated that the use of encapsulated OIT gave a significantly prolonged surface protection and allowed for the determination of the critical surface flux. The polyelectrolyte multilayer has therefore been recognized as the rate-determining barrier for OIT. The matrix density has a minor influence on the release rate of encapsulated OIT from these microcapsules and this concept may very well be expanded to cover a broad range of hydrophobic and semi-hydrophobic biocides.

Cellular uptake and cell-to-cell transfer of polyelectrolyte microcapsules within a triple co-culture system representing parts of the respiratory tract

Polyelectrolyte multilayer microcapsules around 3.4 micrometers in diameter were added to epithelial cells, monocyte-derived macrophages, and dendritic cells in vitro and their uptake kinetics were quantified. All three cell types were combined in a triple co-culture model, mimicking the human epithelial alveolar barrier. Hereby, macrophages were separated in a three-dimensional model from dendritic cells by a monolayer of epithelial cells. While passing of small nanoparticles has been demonstrated from macrophages to dendritic cells across the epithelial barrier in previous studies, for the micrometer-sized capsules, this process could not be observed in a significant amount. Thus, this barrier is a limiting factor for cell-to-cell transfer of micrometer-sized particles.

Motion-based, high-yielding, and fast separation of different charged organics in water.

We report a self-propelled Janus silica micromotor as a motion-based analytical method for achieving fast target separation of polyelectrolyte microcapsules, enriching different charged organics with low molecular weights in water. The self-propelled Janus silica micromotor catalytically decomposes a hydrogen peroxide fuel and moves along the direction of the catalyst face at a speed of 126.3 μm s(-1) . Biotin-functionalized Janus micromotors can specifically capture and rapidly transport streptavidin-modified polyelectrolyte multilayer capsules, which could effectively enrich and separate different charged organics in water. The interior of the polyelectrolyte multilayer microcapsules were filled with a strong charged polyelectrolyte, and thus a Donnan equilibrium is favorable between the inner solution within the capsules and the bulk solution to entrap oppositely charged organics in water. The integration of these self-propelled Janus silica micromotors and polyelectrolyte multilayer capsules into a lab-on-chip device that enables the separation and analysis of charged organics could be attractive for a diverse range of applications.

Highly magneto-responsive multilayer microcapsules for controlled release of insulin

In this study, magneto-responsive polyelectrolyte multilayer microcapsules were successfully prepared by the formation of shell with biocompatible iron oxide nanoparticles (Fe3O4 NPs) and polyallylamine hydrochloride (PAH) by layer-by-layer (LbL) self-assembly technique. The self-assembled microcapsules were characterized by SEM, TEM and zeta-potential analyzer. According to the pH sensitivity of the microcapsule membrane permeability, insulin was encapsulated, with the encapsulation efficiency of 92.08±5.57%. The in vitro release behavior in an external alternating magnetic field indicated that once the magnetic field was applied, the drug release was greatly accelerated. In addition, according to the observed pulse release upon cyclic on-off operations of magnetic field, it could be assumed that the magneto-responsive microcapsules had an excellent “switching on” effect, which might be attributed to the rearrangement of shell structure caused by magnetic nanoparticles twisting and polyelectrolyte chains shaking, hence the increase of microcapsule membrane permeability and the enhancement of insulin release.

Aggregation-Resistant Superparamagnetic Noncovalent Hybrid Multilayer Hollow Microcapsules in High Ionic Strength Media

In order to avoid the aggregation and/or fusion of the polyelectrolyte multilayer hollow microcapsules self-assembled via the noncovalent bonds, superparamagnetic polyelectrolyte hybrid hollow microcapsules surface-modified with polyethylene glycol (PEG) brushes were designed and fabricated. After the layer-by-layer (LbL) self-assembly of chitosan (CS) and citric acid-modified magnetic nanoparticles (Fe3O4–CA) as the polycation and the hybrid anion on the polystyrene sulfonate microsphere (PSS) templates, respectively, the aldehyde group terminated polyethylene glycol-4000 (APEG) was grafted onto the surface of the superparamagnetic polyelectrolyte hybrid multilayer coated template microspheres via the nucleophilic addition between the aldehyde groups of APEG and the amino groups of CS. Then, the modified superparamagnetic polyelectrolyte hybrid hollow microcapsules were obtained after the templates were removed by dialysis. It was found that the surface PEGylation could prevent aggregation among the hollow microcapsules in the media with high salt concentration by dynamic light scattering (DLS), besides the increase in biocompatibility. The technique developed is expected to realize the application of the polyelectrolyte multilayer hollow microcapsules in real physiological environments.

Encapsulation of Basic Fibroblast Growth Factor by Polyelectrolyte Multilayer Microcapsules and Its Controlled Release for Enhancing Cell Proliferation

Basic fibroblast growth factor (FGF2) is an important protein for cellular activity and highly vulnerable to environmental conditions. FGF2 protected by heparin and bovine serum albumin was loaded into the microcapsules by a coprecipitation-based layer-by-layer encapsulation method. Low cytotoxic and biodegradable polyelectrolytes dextran sulfate and poly-L-arginine were used for capsule shell assembly. The shell thickness-dependent encapsulation efficiency was measured by enzyme-linked immunosorbent assay. A maximum encapsulation efficiency of 42% could be achieved by microcapsules with a shell thickness of 14 layers. The effects of microcapsule concentration and shell thickness on cytotoxicity, FGF2 release kinetics, and L929 cell proliferation were evaluated in vitro. The advantage of using microcapsules as the carrier for FGF2 controlled release for enhancing L929 cell proliferation was analyzed.

Engineered (hep/pARG)2polyelectrolyte capsules for sustained release of bioactive TGF-β1

Spatial and temporal controlled delivery of growth factors which contribute to efficient repair upon tissue injury or failure remains a major challenge in tissue engineering. In this paper, we evaluated polyelectrolyte multilayer microcapsules to control spatiotemporal release of transforming growth factor-β1 (TGF-β1). Polyelectrolyte microcapsules were bio-specifically engineered to enhance their ability to bind growth factors. Myofibroblast differentiation and contraction demonstrated that the bioactivity of TGF-β1 was not altered upon encapsulation into polyelectrolyte multilayer microcapsules and subsequent incorporation into gelatin based hydrogels. Finally, polyelectrolyte microcapsules were incorporated within a synthetic tissue engineering cryogel scaffold composed of gelatin without affecting the cryogel morphology, cell population capacity or mechanical properties of the scaffold.

Enzyme microcapsules with substrate selective permeability constructed via layer-by-layer polyelectrolyte self-assembly

Polyelectrolyte multilayer microcapsules with entrapped horseradish peroxidase (HRP) have been prepared via a layer-by-layer (LbL) self-assembly strategy of polycation and polyanion on CaCO3 microparticles as templates. Preparation conditions have been studied and optimized. Within the investigated ranges, use of buffer solutions with lower pH value or lower ionic strength in the buffer solution for polyelectrolyte self-assembly has resulted in thinner polyelectrolyte film and higher permeability of the microcapsules. For dissolving the CaCO3 templates, use of weakly acidic (pH 4.0) buffer solution in place of routinely used EDTA reagent has improved the catalytic activity of microcapsules. The HRP-containing microcapsules have exhibited catalytic activity to pyrogallol as substrate, while the catalytic activity to 2,2′-azino-bis(3-ethylbenz-thiazoline-6-sulfonic acid) (ABTS) was severely suppressed. No less than 90% of the maximum enzymatic activity to pyrogallol has remained after 30days. Promising prospects in various biocatalysis applications have been expected for the enzyme microcapsules, due to their selective permeability, stability and reusability.

Raman imaging and photodegradation study of phthalocyanine containing microcapsules and coated particles

AbstractWe present the results of using Raman molecular imaging and atomic force microscopy (AFM) investigation of the composition, stability, and photodegradation of polyelectrolyte multilayer microcapsules and coated microparticles containing copper–phthalocyanine and iron–phthalocyanine. The influence of laser light on degradation of these phthalocyanine dyes embedded in the walls of polyelectrolyte multilayer capsules and shells of microparticles was studied by both AFM and Raman molecular imaging, but only the latter technique gave information on dynamics of photodegradation. Raman peak assignment was performed according to theoretical calculations. The degradation rate of phthalocyanine dyes is estimated from Raman signal measurements and a model is proposed to account for the degradation rate. Practical applications of our approach are outlined. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Secondary Ion Mass Spectrometry of Macromolecules Loading in Individual Polyelectrolyte Multilayer Microcapsules

The control over the amount of a payload in polyelectrolyte multilayer microcapsules is of particular importance for several applications, such as transportation and delivery of drugs, enzymes, and other (bio)active materials. In this work, secondary ion mass spectrometry is applied to measure the content of peroxidase in individual capsules. The distribution of a payload among the capsules in a batch is analyzed for different loading routines. Absorption in porous CaCO3 demonstrates lower enzyme content with a standard deviation of 40 % on average. pH-Controlled post-loading gives two to three times higher content and a standard deviation of 20–25 %. The decrease of pH upon post-loading increases the encapsulation efficiency.

Disintegration-controllable stimuli-responsive polyelectrolyte multilayer microcapsules via covalent layer-by-layer assembly

The disintegration-controllable stimuli-responsive polyelectrolyte multilayer microcapsules have been fabricated via the covalent layer-by-layer assembly between the amino groups of chitosan (CS) and the aldehyde groups of the oxidized sodium alginate (OSA) onto the sacrificial templates (polystyrene sulfonate, PSS) which was removed by dialysis subsequently. The covalent crosslinking bonds of the multilayer microcapsules were confirmed by FTIR analysis. The TEM analysis showed that the diameter of the multilayer microcapsules was <200 nm. The diameter of the multilayer microcapsules decreased with the increasing of the pH values or the ionic strength. The pH and ionic strength dual-responsive multilayer microcapsules were stable in acidic and neutral media while they could disintegrate only at strong basic media.