Investigation of the influence of temperature on polyelectrolyte microcapsules

The heat sensitivity of hollow polyelectrolyte microcapsules consisting of an even or odd number of alternating layers of poly(allylamine) and poly(styrenesulfonate) is investigated by light scattering and confocal microscopy. The polyelectrolyte microcapsules are prepared using CaCO₃ microspherulites as “core” dispersed particles. It is demonstrated that the size of capsules with an even or odd number of layers decreases with an increase in the temperature and time of heat treatment. The heat sensitivity of the polyelectrolyte microcapsules is estimated from the activation energy required for changing the parameters of their initial structure under heating. It is shown that the heat sensitivity of the polyelectrolyte microcapsules with an odd number of layers is higher than the heat sensitivity of the polyelectrolyte microcapsules with an even number of layers. A possible mechanism responsible for the change in the structural parameters of the microcapsules upon heat treatment is proposed.     

Bovine serum albumin gel/polyelectrolyte complex of hyaluronic acid and chitosan based microcarriers for Sorafenib targeted delivery

The development of systems for targeted delivery of Sorafenib in unresectable hepatocellular carcinoma to reduce the systemic toxicity is a challenge. In our article, we successfully prepared core-shell microcapsules based on bovine serum albumin gel with polyelectrolyte complex multilayer shell of polysaccharides with opposite charges, hyaluronic acid, and chitosan, encapsulating Sorafenib, as targeting delivery system for improved hepatocellular carcinoma therapy. A bovine serum albumin gel core was formed by a method based on a sacrificial CaCO₃ template, followed by the multilayer shell build-up of Ca²⁺ cross-linked hyaluronic acid hydrogel, and subsequently alternating multilayers of the polyelectrolyte complex formed between hyaluronic acid and chitosan. The following techniques: Fourier-transform infrared and UV–Vis spectroscopy, X-ray diffraction, differential scanning calorimetry, confocal laser scanning microscopy, atomic force microscopy, and scanning electron microscopy were used for the physicochemical characterization. These tests revealed the spherical shape of core-shell type, the micro-size, as well as the composition of microcapsules after their synthesis and proved the successful encapsulation and release of the drug. The promising results regarding encapsulation efficiency, Sorafenib release profile and cytotoxicity on HepG2 and mesenchymal stem cells, recommend Sorafenib loaded microcapsules as suitable targeted drug carriers for further in vivo studies for hepatocellular carcinoma therapy.     

Design of intelligent chitosan/heparin hollow microcapsules for drug delivery

In this study, a novel strategy has been developed for the assembly of polyelectrolyte multilayer (PEM) on CaCO₃ templates in acidic pH solutions, where consecutive polyelectrolyte layers (heparin/poly(allylamine hydrochloride) or heparin/chitosan) were deposited on PEM hollow microcapsules established previously on CaCO₃ templates. The PEM build‐up, hollow capsule characterization and successful encapsulation of fluorescein 5(6)‐isothiocyanate (FITC)‐Dextran by coprecipitation with CaCO₃ are demonstrated. Improvement by the removal of CaCO₃ core was achieved while the depositions. In the course of the release profile, high retardation for encapsulated FITC‐Dextran was observed. The combined shell capsules system is a significant trait that has potential use in tailoring functional layer‐by‐layer capsules as intelligent drug delivery vehicles where the preliminary in vitro tests showed the responsiveness on the enzymes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44425.     

Polyelectrolyte complexes of sodium alginate with chitosan or its derivatives for microcapsules

Chitosan, a cationic polysaccharide, was heterogeneously deacetylated with a 47% sodium hydroxide solution and followed by a homogeneous reacetylation with acetic anhydrides to control the N-acetyl content of the chitosan having a similar molecular weight. The chitosans having different degrees of N-acetylation were complexed with sodium alginate, an anionic polysaccharide, and the formation behavior of polyelectrolyte complexes (PECs) was examined by the viscometry in various pH ranges. The maximum mixing ratio (R_max) increased with a decrease in the degree of N-acetylation of the chitosan at the same pH, and with a decrease in pH at the same degree of N-acetylation. Similarly, N-acylated chitosans were also prepared. The N-acyl chitosans scarcely affected the formation behavior of PECs with sodium alginates. For the application of the PECs produced, the microencapsulation of a drug was performed and the release property of drug was tested. The microcapsules were prepared in one step by the extrusion of a solution of guaifenesin and sodium alginate into a solution containing calcium chloride and chitosan through interpolymeric ionic interactions. The drug release during the drug-loaded microcapsules storage in saline was found to depend on the pH where the microcapsules were formed and the kind of N-acyl groups introduced to the chitosan. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 425–432, 1997     

Influence of folate conjugation on the cellular uptake degree of poly(allylamine hydrochloride) microcapsules

The microcapsules in drug delivery systems can prevent degradation of drugs and help to control the release rate. To enhance the targeted delivery effect of the microcapsules to cancer cells, some specific ligands such as folic acid (FA) are necessarily further conjugated. Herein, covalent poly(allylamine hydrochloride) (PAH) multilayers were fabricated on CaCO₃ microparticles under the cross‐linking of glutaraldehyde, which were further immobilized with different amount of FA molecules via the spacer of diamino terminated poly(ethylene glycol) (PEG). As a comparison study, four types of microcapsules, i.e., the PAH capsules, the PAH capsules grafted with PEG, and the PAH capsules conjugated with two different amount of FA via the PEG spacer were prepared. Their chemical and physical structures were confirmed by infrared spectroscopy, UV–vis spectroscopy and scanning electron microscopy. In vitro cell culture found that the cellular uptake of the PAH capsules grafted with PEG was reduced significantly compared with that of the pure PAH capsules. The FA‐modified microcapsules could be selectively delivered into HepG2 tumor cells which overexpress FA receptors but not into the endothelial cells. The number of HepG2 cells which ingested the FA‐conjugated capsules showed a positive correlation with FA amount. The results indicate that these FA conjugated capsules have a high selectivity to be delivered to tumor cells, endowing them with a larger opportunity functioning as targeted delivery vehicle for anticancer drugs. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and nanotribological properties of polyelectrolyte multilayers with in situ Au nanoparticles

Polyelectrolyte multilayers with in situ Au nanoparticles were prepared by alternate immersion of a substrate in poly(allylamine hydrochloride) (PAH)-AuCl₄⁻ complexes solution and poly(acrylic acid) solution for layer-by-layer self assemble process followed by reduction of the metal cations Au³⁺ through immersion into a fresh NaBH₄ solution. UV–vis spectrum, atomic force microscopy (AFM), X-ray photoelectron spectra (XPS), and transmission electron microscope (TEM) were used to confirm the construction of multilayers and synthesis of the Au nanoparticles. The nanotribological behaviors also have been studied using AFM. The polyelectrolyte multilayers with in situ Au nanoparticles exhibited a lower surface adhesion and friction force than the pure polyelectrolyte multilayers due to the nanoparticles improved the mutilayers surface structure and possess a good load-carrying capacity in nanoscale.     

Control of release characteristics in pH‐sensitive poly(vinyl alcohol)/poly(acrylic acid) microcapsules containing chemically treated alumina core

The pH‐sensitive poly(vinyl alcohol)/poly(acrylic acid) hydrogel microcapsules containing vitamin B₁₂‐loaded Al₂O₃ core were prepared with a three‐step emulsion polymerization. Al₂O₃ was chemically treated with HCl or NaOH solutions at room temperature for 24 h to modify the binding properties with vitamin B₁₂. The colon‐targeted release characteristics of vitamin B₁₂ from the microcapsules were evaluated at different pHs. These microcapsules showed the faster and larger release of vitamin B₁₂ due to the high swelling of microcapsule shell as the pH was changed into more basic condition. However, these microcapsules showed the slower and less release of vitamin B₁₂ as the acid value of Al₂O₃ increased due to the strong binding interaction between Al₂O₃ core and vitamin B₁₂ even though the initial loading of vitamin B₁₂ was higher. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Polyelectrolyte platform for sensitive detection of biological analytes via reversible fluorescence quenching

Non-conjugated polyelectrolytes were used to quench oppositely charged fluorescent dye–ligand conjugate (DLC) molecules by bringing them to the vicinity of the polyelectrolyte backbone to form aggregates and hence quench the dye fluorescence. As target protein molecules are added to the solution, the specific interaction between the DLC and the protein disrupts the aggregate structure, thus recovering the luminescence. The binding of DLC to oppositely charged polyelectrolyte and the disruption of the aggregates are investigated by fluorescence spectroscopy. The static-quenching mechanism is clearly manifested in the Stern–Volmer plots that show the decrease in slope with increasing temperature. This polyelectrolyte-based sensing platform has a sensitivity of <100 pM. We also show the selectivity of this platform by comparing the fluorescence recovery between two proteins (avidin and bovine serum albumin) with similar molecular weight. Our results suggest a highly sensitive approach for detecting biological analytes.     

Preferential mineralization of CaCO3 layers on polymer surfaces from CaCl2 and water‐soluble carbonate salt solutions supersaturated by poly(acrylic acid)

CaCO₃ was mineralized from solutions supersaturated only by poly(acrylic acid) (PAA), without bubbling any CO₂ gas in the solution. For example, a layer of CaCO₃ was built up on the surface of a chitosan membrane from a supersaturated aqueous solution containing CaCl₂, Na₂CO₃, and PAA. In this newly developed method, the PAA alone suppresses the precipitation of CaCO₃ from the bulk solution, and therefore, increases the supersaturated concentration. This concentration is estimated to be the same order as that attained in the method in which both CO₂ gas and PAA were used. At the same time, PAA supplies nucleation fields by forming a polymer complex with chitosan. The crystal system obtained was different from those obtained when using CO₂ gas. Self‐organization of aragonite crystallites led to the formation of uniform, concentric, or branching patterns in the surface‐domain structure. These patterns had morphologies similar to those discovered by other researchers, typically in the crystallization of ascorbic acid. Thicker layers of CaCO₃ could be formed on chitosan membranes, the surfaces of which had been converted to a polyelectrolyte complex (PEC) by exposure to PAA solution before the onset of mineralization. Under certain conditions, the CaCO₃ layer had a small spherical curvature, similar to a half‐lens, and generated Newton's ring pattern from the interference fringes of visible light. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:3627–3634, 2004     

Preparation of poly(vinyl alcohol)/poly(acrylic acid) microcapsules and microspheres and their pH-responsive release behavior

The pH-responsive poly(vinyl alcohol)/poly(acrylic acid) hydrogel microparticles containing vitamin B₁₂ were prepared with emulsion polymerization. Both microcapsule and microsphere were easily produced by simply changing the sequence of ingredient addition during the emulsion polymerization. The microparticles showed the faster and larger release of vitamin B₁₂ due to the higher swelling of hydrogel by electrostatic repulsion of carboxylate groups in poly(acrylic acid) as the pH was changed into more basic condition. The microcapsules showed a faster release than the microspheres did due to the less hindered passage through the thinner shell of microcapsules. The poly(vinyl alcohol)/poly(acrylic acid) hydrogel microparticles either protected or released the vitamin B₁₂ effectively depending on pH.     

Microcapsules prepared from a polycondensate‐based cement dispersant via layer‐by‐layer self‐assembly on melamine‐formaldehyde core templates

Novel microcapsules were prepared from colloidal core–shell particles by acid dissolution of the organic core. Weakly crosslinked, monodisperse and spherical melamine‐formaldehyde polycondensate particles (diameter ～ 1 μm) were synthesized as core template and coated with multilayers of an anionic polyelectrolyte via layer‐by‐layer deposition technique. As polyelectrolytes, an anionic naphthalenesulfonate formaldehyde polycondensate that is a common concrete superplasticizer and thus industrially available, and cationic poly(allylamine hydrochloride) were used. Core removal was achieved by soaking the core–shell particles in aqueous hydrochloric acid at pH 1.6, resulting in hollow microcapsules consisting of the polyelectrolytes. Characterization of the template, the core–shell particles, and the microcapsules plus tracking of the layer‐by‐layer polyelectrolyte deposition was performed by means of zeta potential measurement and scanning electron microscopy. The microcapsules might be useful as microcontainers for cement additives. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of surface modifiers and surface modification methods on properties of acrylonitrile–butadiene–styrene/poly(methyl methacrylate)/nano‐calcium carbonate composites

Nano‐calcium carbonate (nano‐CaCO₃) was used in this article to fill acrylonitrile–butadiene–styrene (ABS)/poly(methyl methacrylate) (PMMA), which is often used in rapid heat cycle molding process (RHCM). To achieve better adhesion between nano‐CaCO₃ and ABS/PMMA, nano‐CaCO₃ particles were modified by using titanate coupling agent, aluminum–titanium compound coupling agent, and stearic acid. Dry and solution methods were both utilized in the surface modification process. ABS/PMMA/nano‐CaCO₃ composites were prepared in a corotating twin screw extruder. Influence of surface modifiers and surface modification methods on mechanical and flow properties of composites was analyzed. The results showed that collaborative use of aluminum–titanium compound coupling agent and stearic acid for nano‐CaCO₃ surface modification is optimal in ABS/PMMA/nano‐CaCO₃ composites. Coupling agent can increase the melt flow index (MFI) and tensile yield strength of ABS/PMMA/nano‐CaCO₃ composites. The Izod impact strength of composites increases with the addition of titanate coupling agent up to 1 wt %, thereafter the Izod impact strength shows a decrease. The interfacial adhesion between nano‐CaCO₃ and ABS/PMMA is stronger by using solution method. But the dispersion uniformity of nano‐CaCO₃ modified by solution method is worse. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Chitosan nanoparticles as particular emulsifier for preparation of novel pH-responsive Pickering emulsions and PLGA microcapsules

In this work, we describe a novel and simple method for fabricating biocompatible microcapsules. Chitosan colloidal nanoparticle-coated micrometer-sized poly(lactic-co-glycolic acid) (PLGA) microcapsules were fabricated via a combined system of “Pickering-type” emulsion route and solvent volatilization method in the absence of any molecular surfactants. Stable oil-in-water emulsions were prepared using chitosan colloidal nanoparticles as a particulate emulsifier and a dichloromethane (CH₂Cl₂) solution of PLGA as an oil phase. Moreover, this stable emulsion present a good pH-responsive characteristic. The uncross-linked chitosan nanoparticles coated PLGA microcapsules were fabricated by the evaporation of CH₂Cl₂ from the emulsion, and the cross-linked chitosan nanoparticles coated PLGA microcapsules were prepared by cross-linking with glutaraldehyde and evaporation of CH₂Cl₂. The two types of microcapsules were characterized in terms of size, morphology using scanning electronic microscope (SEM), optical microscope, and so on. These observations confirm the robust nature of these cross-linked microcapsules. Moreover, a possible mechanism for the formation of these microcapsules was proposed. The combined system of Pickering emulsion and solvent volatilization opens up a new route to fabricate a variety of microcapsules.     

Biomimetic synthesis of calcium carbonate films on bioinspired polydopamine matrices

We combine the active surface of polydopamine (PDA) with the biomimetic mineralization of CaCO₃ to obtain the macroscopically continuous CaCO₃ films under mild conditions. In this approach, the organic matrices were adhesive PDA coatings, which were dip-coated on silicon wafers by the self-polymerization of dopamine in an alkaline aqueous solution (pH 8.5). The inorganic layers were CaCO₃ films, which were formed in a CaCl₂ solution in the presence of poly(acrylic acid) (PAA) via a CO₂ diffusion method. During the biomimetic mineralization, amorphous calcium carbonate (ACC) was formed on PDA matrices with the help of PAA, which, subsequently, was transformed into a flat continuous calcite film on the PDA matrices. As the mineralization time increased, a new layer of CaCO₃ crystals was formed over the calcite and, as a result, led to continuous CaCO₃ films with rough surfaces. The thicknesses of CaCO₃ films can be controlled by tuning the mineralization time. Our approach may provide a simple, yet efficient way for the preparation of macroscopically continuous organic–inorganic composite CaCO₃ films under mild conditions. Moreover, superhydrophobic surfaces can be successfully achieved via a hydrophobic modification of the rough CaCO₃ films, which make them suitable candidates for a variety of superhydrophobic applications, such as self-cleaning surfaces or anticorrosion, antiadhesive coatings.     

Preparation and characterization of controlled-release microencapsulated acids for deep acidizing of carbonate reservoirs

Based on the deficiency of traditional acidification or acid pressure technology in the development of carbonate oil and gas resources, a microcapsule which wraps hydrochloric acid and can be released through temperature control was prepared by using microcapsule technology. The microcapsules were prepared with polyurethane prepolymer (PUA) and 1,6-hexadiol diacrylate (HDDA) polymer as wall material and hydrochloric acid as core material by two emulsification and photocatalysis methods. Its parcel rate is 61.9%. Fourier transform infrared spectroscopy characterization confirmed the successful photopolymerization of PUA prepolymer and HDDA in a strong acid environment. The microscopic morphology analysis of electron microscope showed that the microcapsule was regular and uniform spherical with smooth and dense surface. The particle size analysis showed that the microcapsules were mainly distributed between 40 and 300 μm, and the average particle size was 114.02 μm.The glass temperature of microcapsule wall material was 97°C by DSC method. The release rate of microcapsules was accelerated with the increase of release temperature. The cumulative release rate of acid solution of microcapsules for 3 h reached 28.4%, and the final release rate of microcapsules for 12 h reached 90.7% under 100°C. In addition, the release of microcapsules is less affected by the formation salinity. At 90°C, the maximum release rate of 7.5 g/L CaCL₂ was 49.1%, lower than that of 59.4% in pure water, showing the good salt resistance of the wall materials of microcapsules.     

Chitosan/CaCO3 solvent‐free nanofluid composite membranes for direct methanol fuel cells

Natural polyelectrolyte chitosan (CS) has been considered to be a promising proton‐exchange membrane material for direct methanol fuel cells due to its low cost and excellent methanol barrier ability. To further improve the ionic conductivity and mechanical property of CS, calcium‐carbonate solvent‐free nanofluids (CaCO₃‐SF) with unique flow behavior were prepared by an ion‐exchange method, and then used a novel nanofiller to modify CS to fabricate composite membranes. The surface‐grafted organic long chains on the surface of CaCO₃ nanoparticles could promote the homogeneous dispersion of CaCO₃ in the CS matrix, and thus improve the interfacial bonding and facilitate the load transfer from the matrix to stiff CaCO₃. When the content of CaCO₃‐SF was 6 wt%, the tensile strength and fracture elongation of the composite membrane were 28.25 MPa and 17.17%, respectively, which increased by 25% and 36% when compared with those of pure membrane. Moreover, the ? SO₃H groups in the structure of organic long chains could form new proton transport sites, and thus enhance the proton conductivity of the membranes. Consequently, when compared with pure CS membrane (0.0131 S cm^?1), incorporation of 6 wt% CaCO₃‐SF (0.0250 S cm^?1) exhibited about onefold increase of proton conductivity. POLYM. ENG. SCI., 59:2128–2135, 2019. © 2019 Society of Plastics Engineers     

Effect of polyethylene glycol on phase and morphology of calcium carbonate

Calcium carbonate (CaCO₃) with different phases and morphologies were prepared and characterized by scanning electron microscopy (SEM), powder X‐ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. The effect of polyethylene glycol (PEG) with different molecular weight and concentrations on the phase and morphology of CaCO₃ was studied. The results showed that aragonite was the only phase in the solution without PEG, while calcite phase could be obtained by the use of PEG as the additive. The possible crystallization mechanism for the formation of CaCO₃ polymorphs in the presence of different PEG was also discussed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Destruction of shells and release of a protein from microcapsules consisting of non-biodegradable polyelectrolytes

Using fluorescent spectroscopy, we examined degradation of PAH/PSS microcapsule shells and release of a protein from them. The processes were controlled by various concentrations of NaCl and (NH₄)₂SO₄ and levels of pH: 5 and 7.4. We found that a high concentration of sodium chloride (2 М) causes essential dissociation of PAH from the upper shell layer and explained this by the layer loosening under the ionic strength. Using the optical spectroscopy, we determined amount of a microcapsule polyelectrolyte (PAH) and found that less than 20% of it can be released into 2М NaCl solution, and only 2% can be released into the water medium. Increase in solution pH up to 7.4 causes peeling of PAH too, however, temperature increase up to 37°С decreases this effect due to the structuring and compacting of the shell demonstrated by electron-microscopic studies. And finally we found that a scarce release of an encapsulated protein from the microcapsules does not depend on the presence of salts in the medium, their concentrations and a medium pH.     

调酸介质对二甲戊灵微胶囊囊形及粒径的影响

[目的]优选出原位聚合法制备二甲戊灵微胶囊的较佳调酸介质,为二甲戊灵的微胶囊化提供一定的理论指导.[方法]以脲醛树脂为壁材采用原位聚合法制备了二甲戊灵微胶囊,研究了不同调酸介质对二甲戊灵微胶囊囊形及粒径的影响.[结果]5％盐酸溶液作为调酸介质形成的微胶囊囊形粗糙,产生粘连,粒径分布较宽;5％硝酸铵溶液、5％硫酸氢铵溶液作为调酸介质形成的微胶囊囊形松散,容易破裂,产生粘连,粒径分布较窄;5％氯化铵溶液作为调酸介质形的微胶囊囊形光滑致密且坚固,粒径分布较窄.[结论]调酸介质对原位聚合法制备的微胶囊囊形及粒径影响很大,选择合适的调酸介质能获得囊形致密、粒径分布窄的微胶囊.     

To prepared fluorescent chitosan capsules by in situ polyelectrolyte coacervation on poly(methacrylic acid)-doped porous calcium carbonate microparticles

To prepare hollow microcapsules composed of native chitosan (CS), a templating method is developed using poly(methacrylic acid) (PMAA)-doped porous calcium carbonate (CaCO₃) microparticles as sacrificial templates. At first, CS was adsorbed onto PMAA-doped porous CaCO₃ microparticles, and then the adsorbed CS was covalently cross-linked with each other by using glutaraldehyde. After the dissolution of the templates, the resultant CS capsules ranged from 2 to 5???m in diameter. Nitrogen adsorption?Cdesorption analysis are applied to characterize the porous CaCO₃ templates, the BET surface area and total pore volume are 160 and 0.50?cm³/g. The structure and morphology of the CS capsules are characterized by FESEM and TEM. Confocal laser scanning microscopy images reveal that the capsules have been labeled with green FITC. The gradual capsule invagination in response to bulk osmotic pressure created by CS solutions has also been discussed.