Controlling the Vaterite CaCO₃ Crystal Pores. Design of Tailor-Made Polymer Based Microcapsules by Hard Templating

Abstract

The spherical vaterite CaCO3 microcrystals are nowadays widely used as sacrificial templates for fabrication of various microcarriers made of biopolymers (e.g., proteins, nucleic acids, enzymes) due to porous structure and mild template elimination conditions. Here, we demonstrated for the first time that polymer microcarriers with tuned internal nanoarchitecture can be designed by employing the CaCO3 crystals of controlled porosity. The layer-by-layer deposition has been utilized to assemble shell-like (hollow) and matrix-like (filled) polymer capsules due to restricted and free polymer diffusion through the crystal pores, respectively. The crystal pore size in the range of few tens of nanometers can be adjusted without any additives by variation of the crystal preparation temperature in the range 7-45 °C. The temperature-mediated growth mechanism is explained by the Ostwald ripening of nanocrystallites forming the crystal secondary structure. Various techniques including SEM, AFM, CLSM, Raman microscopy, nitrogen adsorption-desorption, and XRD have been employed for crystal and microcapsule analysis. A three-dimensional model is introduced to describe the crystal internal structure and predict the pore cutoff and available surface for the pore diffusing molecules. Inherent biocompatibility of CaCO3 and a possibility to scale the porosity in the size range of typical biomacromolecules make the CaCO3 crystals extremely attractive tools for template assisted designing tailor-made biopolymer-based architectures in 2D to 3D targeted at drug delivery and other bioapplications.

Design of intelligent chitosan/heparin hollow microcapsules for drug delivery

“…In other words, the PEMs are stiffer if Hep is on the top of the capsules, which is similar to observation published previously where allied phenomenon is extensively studied with PAH/PAA. 36 The measured f-potentials are consistent with the overcompensation model by (PSS/PAH) 5 . 37 This is in agreement with the QCM-D results that the growth of PEMs containing Hep/PAH is linear.…”

“…There were several reports showing the possibilities of CaCO 3 templates‐based drug delivery systems (DDS) . In one of the studies, CaCO 3 templates were directly used as drug depot where insulin was released after dissolution of the template within 20 min.…”

“…There were several reports showing the possibilities of CaCO 3 templates-based drug delivery systems (DDS). [3][4][5] In one of the studies, CaCO 3 templates were directly used as drug depot where insulin was released after dissolution of the template within 20 min. In another study, CaCO 3 were coated with polyelectrolytes and followed by the dissolution of the template, and hollow capsules with proteins inside were formed.…”

The mechanism of catalase loading into porous vaterite CaCO3 crystals by co-synthesis

“…Control over the crystal growth provides one with a simple way to adjust the crystal porosity even without any additives. 25,26 The surface of the nanocrystallites can be coated with different materials, for example, lipids, for protection. 27 Some recent efforts have been made in the size reduction of calcium carbonate crystals that open new perspectives to employ the crystals for a wide range of administration routes in modern drug delivery.…”

Release from Polyelectrolyte Multilayer Capsules in Solution and on Polymeric Surfaces

“…Template size control [21] as well as their porosity [35] are of high interest for biological applications and stimulates further works towards synthesis of the calcium carbonate templates.…”