Porous Calcium Carbonate Microparticles Research Articles

Vaterite microparticle-loaded methylene blue for photodynamic activity in macrophages infected with Leishmania braziliensis.

Calcium carbonate (CaCO3) exhibits a variety of crystalline phases, including the anhydrous crystalline polymorphs calcite, aragonite, and vaterite. Developing porous calcium carbonate microparticles in the vaterite phase for the encapsulation of methylene blue (MB) as a photosensitizer (PS) for use in photodynamic therapy (PDT) was the goal of this investigation. Using an adsorption approach, the PS was integrated into the CaCO3 microparticles. The vaterite microparticles were characterized by scanning electron microscopy (SEM) and steady-state techniques. The trypan blue exclusion method was used to measure the biological activity of macrophages infected with Leishmania braziliensis in vitro. The vaterite microparticles produced are highly porous, non-aggregated, and uniform in size. After encapsulation, the MB-loaded microparticles kept their photophysical characteristics. The carriers that were captured allowed for dye localization inside the cells. The results obtained in this study indicated that the MB-loaded vaterite microparticles show promising photodynamic activity in macrophages infected with Leishmania braziliensis.

Magnetic and silver nanoparticle functionalized calcium carbonate particles—Dual functionality of versatile, movable delivery carriers which can surface-enhance Raman signals

Multifunctional probes play an increasing role even beyond applications in biomedicine. Multifunctionality introduced by the dual types of complementary probes is always attractive because, in this case, functionalized objects inherit the function of both materials. Porous calcium carbonate microparticles are becoming popular carriers of biomolecules and biosensors, as well as imaging enhancers. We demonstrate here a dual function of these carriers by incorporating both magnetic and silver nanoparticles. Magnetic nanoparticles enable movements and displacements by a magnetic field, while silver nanoparticles provide surface-enhanced Raman signal amplification necessary for the detection of biomolecules. Application of such dual-functional carriers is foreseen beyond the applications of biomedicine and theranostics.

Carrier-inside-carrier: polyelectrolyte microcapsules as reservoir for drug-loaded liposomes

Conventional liposomes have a short life-time in blood, unless they are protected by a polymer envelope, most often polyethylene glycol. However, these stabilizing polymers frequently interfere with cellular uptake, impede liposome-membrane fusion and inhibit escape of liposome content from endosomes. To overcome such drawbacks, polymer-based systems as carriers for liposomes are currently developed. Conforming to this approach, we propose a new and convenient method for embedding small size liposomes, 30–100 nm, inside porous calcium carbonate microparticles. These microparticles served as templates for deposition of various polyelectrolytes to form a protective shell. The carbonate particles were then dissolved to yield hollow polyelectrolyte microcapsules. The main advantage of using this method for liposome encapsulation is that carbonate particles can serve as a sacrificial template for deposition of virtually any polyelectrolyte. By carefully choosing the shell composition, bioavailability of the liposomes and of the encapsulated drug can be modulated to respond to biological requirements and to improve drug delivery to the cytoplasm and avoid endosomal escape.

Drug loading into porous calcium carbonate microparticles by solvent evaporation

Drug loading into porous carriers may improve drug release of poorly water-soluble drugs. However, the widely used impregnation method based on adsorption lacks reproducibility and efficiency for certain compounds. The aim of this study was to evaluate a drug-loading method based on solvent evaporation and crystallization, and to investigate the underlying drug-loading mechanisms. Functionalized calcium carbonate (FCC) microparticles and four drugs with different solubility and permeability properties were selected as model substances to investigate drug loading. Ibuprofen, nifedipine, losartan potassium, and metronidazole benzoate were dissolved in acetone or methanol. After dispersion of FCC, the solvent was removed under reduced pressure. For each model drug, a series of drug loads were produced ranging from 25% to 50% (w/w) in steps of 5% (w/w). Loading efficiency was qualitatively analyzed by scanning electron microscopy (SEM) using the presence of agglomerates and drug crystals as indicators of poor loading efficiency. The particles were further characterized by mercury porosimetry, specific surface area measurements, differential scanning calorimetry, and USP2 dissolution. Drug concentration was determined by HPLC. FCC–drug mixtures containing equivalent drug fractions but without specific loading strategy served as reference samples. SEM analysis revealed high efficiency of pore filling up to a drug load of 40% (w/w). Above this, agglomerates and separate crystals were significantly increased, indicating that the maximum capacity of drug loading was reached. Intraparticle porosity and specific surface area were decreased after drug loading because of pore filling and crystallization on the pore surface. HPLC quantification of drugs taken up by FCC showed only minor drug loss. Dissolution rate of FCC loaded with metronidazole benzoate and nifedipine was faster than the corresponding FCC–drug mixtures, mainly due to surface enlargement, because only small fractions of amorphous drug (12.5%, w/w, and 8.9%, w/w, respectively) were found by thermal analysis. Combination of qualitative SEM analysis and HPLC quantification was sufficient to proof the feasibility of the solvent-evaporation method for the loading of various drugs into FCC. Mechanistic investigation revealed that a high specific surface area of the carrier is required to facilitate heterogeneous nucleation, and large pore sizes (up to 1μm) are beneficial to reduce crystallization pressures and allow drug deposition within the pores. The solvent-evaporation method allows precise drug loading and appears to be suitable for scale-up.

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 μm in diameter. Nitrogen adsorption–desorption 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.

Preparation of DNA capsules cross-linked through NeutrAvidin–biotin interaction

We developed a templating method based on NeutrAvidin–biotin interaction, for the preparation of hollow microcapsules composed of DNA. In this method, porous calcium carbonate microparticles were employed as a sacrificial template and an adsorbent for DNA, and NeutrAvidin was chosen as a cross-linker for biotin-labeled DNA. By using biotin-labeled DNA with a degree of biotinylation high enough to retain a hollow spherical structure, hollow DNA microcapsules were obtained with the same size as the templates after the dissolution of the templates with chelating agents. In addition, the combination biotin-labeled DNA and NeutrAvidin could be applied to layer-by-layer assembled multilayers. Layer-by-layer assembled capsules exhibited the size-dependent permeability of macromolecular solutes. This study suggests that our method would be facile and widely applicable to prepare various polymer capsules.

Cross-linked DNA capsules templated on porous calcium carbonate microparticles

To prepare hollow microcapsules composed of native DNA, we developed a templating method using porous calcium carbonate microparticles as sacrificial templates. At first, DNA was adsorbed onto calcium carbonate microparticles, and then the adsorbed DNA was covalently cross-linked with each other by using ethylene glycol diglycidyl ether. After the dissolution of the templates, the resultant DNA capsules ranged from 1.5 to 8 μm in diameter, according to ionic strength. The low cross-linked and highly cross-linked DNA capsules exhibited enzymatic degradability and permeability that was dependent on the molecular weight of macromolecular solutes, respectively. This method has the potential to be used for the preparation of various single-component polymer capsules.

Protein-Calcium Carbonate Coprecipitation: A Tool for Protein Encapsulation

A new approach of encapsulation of proteins in polyelectrolyte microcapsules has been developed using porous calcium carbonate microparticles as microsupports for layer-by-layer (LbL) polyelectrolyte assembling. Two different ways were used to prepare protein-loaded CaCO3 microparticles: (i) physical adsorption--adsorption of proteins from the solutions onto preformed CaCO3 microparticles, and (ii) coprecipitation--protein capture by CaCO3 microparticles in the process of growth from the mixture of aqueous solutions of CaCl2 and Na2CO3. The latter was found to be about five times more effective than the former (approximately 100 vs approximately 20 mug of captured protein per 1 mg of CaCO3). The procedure is rather mild; the revealed enzymatic activity of alpha-chymotrypsin captured initially by CaCO3 particles during their growth and then recovered after particle dissolution in EDTA was found to be about 85% compared to the native enzyme. Core decomposition and removal after assembly of the required number of polyelectrolyte layers resulted in release of protein into the interior of polyelectrolyte microcapsules (PAH/PSS)5 thus excluding the encapsulated material from direct contact with the surrounding. The advantage of the suggested approach is the possibility to control easily the concentration of protein inside the microcapsules and to minimize the protein immobilization within the capsule walls. Moreover, it is rather universal and may be used for encapsulation of a wide range of macromolecular compounds and bioactive species.

Novel Type of Self-Assembled Polyamide and Polyimide Nanoengineered ShellsFabrication of Microcontainers with Shielding Properties

Two types of microcontainers were prepared by using the adsorption of polyamide on the surface of micrometer-sized inorganic porous calcium carbonate microparticles followed by thermal conversion of the polyamide layers into polyimide coatings. The effect of the preparation conditions on the structure and morphology of the microcontainers was studied by transmission electron microscopy and scanning electron microscopy. The smoothest and defect-free coatings were prepared using polyethylenimine as the supporting polymer. The thickness of the polyamide/polyimide shells was estimated by atomic force microscopy and scanning electron microscopy between 50 and 150 nm depending on the quantity of the layers. The water-soluble antibiotic, doxorubicin hydrochloride, was used as a model compound to demonstrate the efficiency of the microcontainers for encapsulation. The resistance of the novel microcontainers to solvent treatment was visualized by the confocal scanning fluorescence microscopy. It was demonstrated that the combination of the high thermal and chemical resistance of polyamide/polyimide shell and the sorption capacity of the CaCO3 is very useful for development of highly protective microcontainers and thermal detectors for smart fabrics.

Combination of adsorption by porous CaCO 3 microparticles and encapsulation by polyelectrolyte multilayer films for sustained drug delivery

Combination of adsorption by porous CaCO 3 microparticles and encapsulation by polyelectrolyte multilayers via the layer-by-layer (LbL) self-assembly was proposed for sustained drug release. Firstly, porous calcium carbonate microparticles with an average diameter of 5 μm were prepared for loading a model drug, ibuprofen (IBU). Adsorption of IBU into the pores was characterized by ultraviolet (UV), infrared (IR), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) experiment and X-ray diffraction (XRD). The adsorbed IBU amount Γ was 45.1 mg/g for one-time adsorption and increased with increasing adsorption times. Finally, multilayer films of protamine sulfate (PRO) and sodium poly(styrene sulfonate) (PSS) were formed on the IBU-loaded CaCO 3 microparticles by the layer-by-layer self-assembly. Amorphous IBU loaded in the pores of the CaCO 3 microparticles had a rapider release in the gastric fluid and a slower release in the intestinal fluid, compared with the bare IBU crystals. Polyelectrolyte multilayers assembled on the drug-loaded particles by the LbL reduced the release rate in both fluids. In this work, polymer/inorganic hybrid core-shell microcapsules were fabricated for controlled release of poorly water-soluble drugs. The porous inorganic particles are useful to load drugs in amorphous state and the polyelectrolyte multilayer films coated on the particle assuage the initial burst release.

Porous calcium carbonate microparticles as templates for encapsulation of bioactive compounds

The paper describes the preparation and characterisation of porous calcium carbonate microparticles with an average size of 5 µm and their use for encapsulation of biomacromolecules. The average pore size of about 30–50 nm enables size selective and time-dependent permeation of different macromolecules. Layer-by-layer adsorption of polyelectrolytes into these particles followed by core dissolution leads to formation of interconnecting networks (matrix-like structure) made of polyelectrolyte complexes. The structure can be used for accumulation of bio-macromolecules, mainly proteins. Besides the inter-polyelectrolyte structure templated on porous CaCO3 microparticles the microgel particles (“ghost”) can also be made inside by complexing alginate and calcium. The adsorption of biomacromolecules inside the porous calcium carbonate particles is presumably regulated by electrostatic interactions on the microparticle surface within pores and protein–protein interactions. Protein adsorption into CaCO3 microparticle voids together with layer-by-layer assembly of biopolymers provide a way for fabrication of completely biocompatible microcapsules envisaging their use as biomaterials.