A sustainable one-pot method to transform seashell waste calcium carbonate to osteoinductive hydroxyapatite micro-nanoparticles

We have developed a straightforward, one-pot, low-temperature hydrothermal method to transform oyster shell waste particles (bCCP) from the species Crassostrea gigas (Mg-calcite, 5 wt% Mg) into hydroxyapatite (HA) micro/nanoparticles. The influence of the P reagents (H3PO4, KH2PO4, and K2HPO4), P/bCCP molar ratios (0.24, 0.6, and 0.96), digestion temperatures (25-200 & DEG;C), and digestion times (1 week-2 months) on the transformation process was thoroughly investigated. At 1 week, the minimum temperature to yield the full transformation significantly reduced from 160 & DEG;C to 120 & DEG;C when using K2HPO4 instead of KH2PO4 at a P/bCCP ratio of 0.6, and even to 80 & DEG;C at a P/bCCP ratio of 0.96. The transformation took place via a dissolution-reprecipitation mechanism driven by the favorable balance between HA precipitation and bCCP dissolution, due to the lower solubility product of HA than that of calcite at any of the tested temperatures. Both the bCCP and the derived HA particles were cytocompatible for MG-63 human osteosarcoma cells and m17.ASC murine mesenchymal stem cells, and additionally, they promoted the osteogenic differentiation of m17.ASC, especially the HA particles. Because of their physicochemical features and biological compatibility, both particles could be useful osteoinductive platforms for translational applications in bone tissue engineering

Bioinspired Calcium Phosphate Coated Mica Sheets by Vapor Diffusion and Its Effects on Lysozyme Assembly and Crystallization

We propose for the first time the vapor diffusion method to deposit bioinspired calcium phosphate films on mineral substrates, that is, delaminated mica muscovite sheets and to assess the capability of these films to affect the nucleation and growth of lysozyme crystals. Deposited calcium phosphate layers were composed of octacalcium phosphate (OCP) and apatite (Ap) nanocrystals, with increased amount of OCP at higher crystallization times. In the presence of poly­(acrylic acid) (PAA) deposited layers were composed of amorphous calcium phosphate (ACP). Results of lysozyme crystallization showed that OCP/Ap-coated mica sheets slowed down the nucleation process without altering significantly the number of nucleated crystals per droplet respect to the uncoated control. ACP-coated mica sheets acted as an inhibitor, thus delaying the nucleation and reducing in addition the number of crystals. These results contrasted with the nucleation induction effect observed when calcium phosphate nanopowders were added to the crystallization drops. All coated-substrates promoted the formation of flat lysozyme crystals at the substrate–solution interface, and some of them retained its laminar morphology. Unexpectedly, the ACP coatings templated the 2D assembly of lysozyme producing thin films. The observation of the lysozyme thin films was possible only in those ACP-coated supports prepared in the presence of 0.015 and 0.02 wt % PAA

pH-Responsive Delivery of Doxorubicin from Citrate–Apatite Nanocrystals with Tailored Carbonate Content

In this work, the efficiency of bioinspired citrate-functionalized nanocrystalline apatites as nanocarriers for delivery of doxorubicin (DOXO) has been assessed. The nanoparticles were synthesized by thermal decomplexing of metastable calcium/citrate/phosphate solutions both in the absence (Ap) and in the presence (cAp) of carbonate ions. The presence of citrate and carbonate ions in the solution allowed us to tailor the size, shape, carbonate content, and surface chemistry of the nanoparticles. The drug-loading efficiency of the two types of apatite was evaluated by means of the adsorption isotherms, which were found to fit a Langmuir–Freundlich behavior. A model describing the interaction between apatite surface and DOXO is proposed from adsorption isotherms and ζ-potential measurements. DOXO is adsorbed as a dimer by means of a positively charged amino group that electrostatically interacts with negatively charged surface groups of nanoparticles. The drug-release profiles were explored at pHs 7.4 and 5.0, mimicking the physiological pH in the blood circulation and the more acidic pH in the endosome-lysosome intracellular compartment, respectively. After 7 days at pH 7.4, cAp-DOXO released around 42% less drug than Ap-DOXO. However, at acidic pH, both nanoassemblies released similar amounts of DOXO. <i>In vitro</i> assays analyzed by confocal microscopy showed that both drug-loaded apatites were internalized within GTL-16 human carcinoma cells and could release DOXO, which accumulated in the nucleus in short times and exerted cytotoxic activity with the same efficiency. cAp are thus expected to be a more promising nanocarrier for experiments <i>in vivo</i>, in situations where intravenous injection of nanoparticles are required to reach the targeted tumor, after circulating in the bloodstream

Transient Calcium Carbonate Hexahydrate (Ikaite) Nucleated and Stabilized in Confined Nano- and Picovolumes

Calcium carbonate precipitation at different values of the nominal ionic activity product (IAP) is studied in nanoliter and picoliter droplets at (20 ± 2 °C). Experiments are carried out through direct mixing of equimolar reactant solutions using two different setups: first, droplet-based microfluidics using Teflon capillaries (nanoliter experiments) and second, the microinjection technique under oil (picoliter droplets). Instantaneous precipitation of a metastable CaCO₃ phase is initially observed. This phase is stabilized in time by reducing the initial volume of the experiments from the nano- to picoliters range and when the CaCl₂/Na₂CO₃ ratio approaches 1. Further analysis by X-ray diffraction, transmission electron microscopy, and selected area electron diffraction confirms the first nucleated phase is CaCO₃·6H₂O (ikaite) and in few droplets ikaite plus CaCO₃·H₂O (monohydrocalcite). No evidence of amorphous calcium carbonate (ACC) is found even in conditions where the IAP exceeds the solubility product of this phase. The in vitro finding of ikaite formation and stabilization due to volume confinement is an unexpected result since it is the first time that this hydrous phase is stabilized at room temperature (it is normally found at near 0 °C) in the absence of additives. This result can be of interest for those biomineralization processes occurring in the confined volumes of intracellular vesicles and for biomimetic materials science in general