Preparation of calcium carbonate microparticles containing organic fluorescent molecules from vaterite

Exploiting Benefits of Vaterite Metastability to Design Degradable Systems for Biomedical Applications

The widespread application of calcium carbonate is determined by its high availability in nature and simplicity of synthesis in laboratory conditions. Moreover, calcium carbonate possesses highly attractive physicochemical properties that make it suitable for a wide range of biomedical applications. This review provides a conclusive analysis of the results on using the tunable vaterite metastability in the development of biodegradable drug delivery systems and therapeutic vehicles with a controlled and sustained release of the incorporated cargo. This manuscript highlights the nuances of vaterite recrystallization to non-porous calcite, dissolution at acidic pH, biodegradation at in vivo conditions and control over these processes. This review outlines the main benefits of vaterite instability for the controlled liberation of the encapsulated molecules for the development of biodegradable natural and synthetic polymeric materials for biomedical purposes.

Radiolabeling Strategies of Micron- and Submicron-Sized Core-Shell Carriers for In Vivo Studies

Core-shell particles made of calcium carbonate and coated with biocompatible polymers using the Layer-by-Layer technique can be considered as a unique drug-delivery platform that enables us to load different therapeutic compounds, exhibits a high biocompatibility, and can integrate several stimuli-responsive mechanisms for drug release. However, before implementation for diagnostic or therapeutic purposes, such core-shell particles require a comprehensive in vivo evaluation in terms of physicochemical and pharmacokinetic properties. Positron emission tomography (PET) is an advanced imaging technique for the evaluation of in vivo biodistribution of drug carriers; nevertheless, an incorporation of positron emitters in these carriers is needed. Here, for the first time, we demonstrate the radiolabeling approaches of calcium carbonate core-shell particles with different sizes (CaCO₃ micron-sized core-shell particles (MicCSPs) and CaCO₃ submicron-sized core-shell particles (SubCSPs)) to precisely determine their in vivo biodistribution after intravenous administration in rats. For this, several methods of radiolabeling have been developed, where the positron emitter (⁶⁸Ga) was incorporated into the particle's core (co-precipitation approach) or onto the surface of the shell (either layer coating or adsorption approaches). According to the obtained data, radiochemical bounding and stability of ⁶⁸Ga strongly depend on the used radiolabeling approach, and the co-precipitation method has shown the best radiochemical stability in human serum (96-98.5% for both types of core-shell particles). Finally, we demonstrate the size-dependent effect of core-shell particles' distribution on the specific organ uptake, using a combination of imaging techniques, PET, and computerized tomography (CT), as well as radiometry of separate organs. Thus, our findings open up new perspectives of CaCO₃-radiolabeled core-shell particles for their further implementation into clinical practice.

Core-Assisted Formation of Porphyrin J-Aggregates in pH-Sensitive Polyelectrolyte Microcapsules Followed by Fluorescence Lifetime Imaging Microscopy

A strategy assisted by an inorganic template was developed to promote the organized self-assembly of meso-(tetrakis)-(p-sulfonatophenyl)porphyrin (TPPS) on pH-sensitive core-shell polyelectrolyte microcapsules (PECs) of poly(styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH). A key feature of this strategy is the use of template CaCO₃ microparticles as a nucleation site endorsing inside-outside directional growth of porphyrin aggregates. Using this approach, TPPS self-assembly in positively charged PECs with CaCO₃ (PAH/PSS)₂PAH as a sequence of layers was successfully achieved using mild pH conditions (pH 3). Evidence for porphyrin aggregation was obtained by UV-vis with the characteristic absorption bands in PECs functionalized with porphyrins. Fluorescence lifetime imaging microscopy (FLIM) of the polyelectrolyte core-shell confirmed the presence of radially distributed needlelike structures sticking out from polyelectrolyte shells. Microscopic images also revealed a sequential process (adsorption, redistribution, and aggregation) for the directional growth (inside/outside) of TPPS aggregates, which highlights the importance of the core in the aggregation induction. Removing the CaCO₃ core alters the porphyrin interaction in the PEC environment, and aggregate growth is no longer favored.

Design of polyelectrolyte core-shells with DNA to control TMPyP binding

The interaction of DNA with 5,10,15,20-tetrakis(4-N-methylpyridiniumyl)porphyrin (TMPyP) in polyelectrolyte core-shells obtained via layer by layer adsorption of poly(sodium 4-styrenesulfonate), PSS, and poly(allylamine hydrochloride), PAH, polyelectrolytes was followed by steady state, time resolved fluorescence and by Fluorescence Lifetime Imaging Microscopy (FLIM). Our results show that DNA adsorption onto polyelectrolyte core-shell changes the TMPyP interaction within PSS/PAH core-shells structure and increase significantly the TMPyP uptake. Specific DNA/TMPyP interactions are also altered by DNA adsorption favouring porphyrin intercalation onto GC pair rich regions. Circular dichroism (CD) spectra reveal that DNA undergoes important conformational changes upon adsorption onto the core-shell surface, which are reverted upon TMPyP encapsulation.

Bioinspired synthesis of fluorescent calcium carbonate/carbon dot hybrid composites

Herein, we report a novel method to synthesise fluorescent calcium carbonate/carbon dots (CaCO3/CDs) by simply mixing CaCl2 and Na2CO3 solutions in the presence of CDs. There are two roles of CDs in this easy and cost-effective biomimetic strategy, that is as the template to direct the formation and assembly of calcite nanocrystals into hierarchical spheres with diameters in the range of 200-300 nm and simultaneously as the phosphor to enable the CaCO3 to emit blue fluorescence under UV (365 nm) irradiation with a quantum yield of 56.2%. The CaCO3/CD hybrid composites possessing unique fluorescence properties are potentially useful in various applications.

Double hydrophilic polyphosphoester containing copolymers as efficient templating agents for calcium carbonate microparticles

The use of calcium carbonate (CaCO₃) microparticles is becoming more and more attractive in many fields especially in biomedical applications in which the fine tuning of the size, morphology and crystalline form of the CaCO₃ particles is crucial. Although some structuring compounds, like hyaluronic acid, give satisfying results, the control of the particle structure still has to be improved. To this end, we evaluated the CaCO₃ structuring capacity of novel well-defined double hydrophilic block copolymers composed of poly(ethylene oxide) and a polyphosphoester segment with an affinity for calcium like poly(phosphotriester)s bearing pendent carboxylic acids or poly(phosphodiester)s with a negatively charged oxygen atom on each repeating monomer unit. These copolymers were synthesized by a combination of organocatalyzed ring opening polymerization, thiol-yne click chemistry and protection/deprotection methods. The formulation of CaCO₃ particles was then performed in the presence of these block copolymers (i) by the classical chemical pathway involving CaCl₂ and Na₂CO₃ and (ii) by a process based on supercritical carbon dioxide (scCO₂) technology in which CO₃ ^2- ions are generated in aqueous media and react with Ca²⁺ ions. Porous CaCO₃ microspheres composed of vaterite nanocrystals were obtained. Moreover, a clear dependence of the particle size on the structure of the templating agent was emphasized. In this work, we show that the use of the supercritical process and the substitution of hyaluronic acid for a carboxylic acid containing copolymer decreases the size of the CaCO₃ particles by a factor of 6 (∼1.5 μm) while preventing their aggregation.