A Comparative Study of Ultrasmall Calcium Carbonate Nanoparticles for Targeting and Imaging Atherosclerotic Plaque.

Atherosclerosis is a complex disease that can lead to life-threatening events, such as myocardial infarction and ischemic stroke. Despite the severity of this disease, diagnosing plaque vulnerability remains challenging due to the lack of effective diagnostic tools. Conventional diagnostic protocols lack specificity and fail to predict the type of atherosclerotic lesion and the risk of plaque rupture. To address this issue, technologies are emerging, such as noninvasive medical imaging of atherosclerotic plaque with customized nanotechnological solutions. Modulating the biological interactions and contrast of nanoparticles in various imaging techniques, including magnetic resonance imaging, is possible through the careful design of their physicochemical properties. However, few examples of comparative studies between nanoparticles targeting different hallmarks of atherosclerosis exist to provide information about the plaque development stage. Our work demonstrates that Gd (III)-doped amorphous calcium carbonate nanoparticles are an effective tool for these comparative studies due to their high magnetic resonance contrast and physicochemical properties. In an animal model of atherosclerosis, we compare the imaging performance of three types of nanoparticles: bare amorphous calcium carbonate and those functionalized with the ligands alendronate (for microcalcification targeting) and trimannose (for inflammation targeting). Our study provides useful insights into ligand-mediated targeted imaging of atherosclerosis through a combination of in vivo imaging, ex vivo tissue analysis, and in vitro targeting experiments.

Calcareous deposit formation under cathodic polarization and marine biocalcifying bacterial activity.

CaCO3 precipitation can occur through bacterial activity (biomineralization) but can also take place in abiotic conditions in seawater at a steel surface under cathodic polarization. In this work, we used two biocalcifying bacterial strains: Pseudoalteromonas sp. and Virgibacillus halodenitrificans isolated in a previous work from marine environment for their ability to induce CaCO3 precipitation. Motility experiments were performed to evaluate the bacterial behaviour in the absence or presence of an applied electric current of -600 µA/cm2 in a solid medium. As no alteration of bacterial growth or CaCO3 crystal formation were observed, we studied both strains in liquid cultures at different applied currents densities: -100, -200 and -600 µA/cm2. The deposits formed on the cathode surface were characterized by µ-Raman spectroscopy and X-ray diffraction. The strain ability to biocalcify in the presence of electric current, in the liquid medium, was evaluated by monitoring bacterial growth, pH evolution, CaCO3 production and metabolic characterization for 7 days. Our results show that neither bacterial growth, enzymatic pathways or CaCO3 production were altered by the electric current. Moreover, bacterial activity modified drastically the nature of the compounds formed on the cathode surface. It favoured Mg-containing calcite, hindering the formation of both aragonite and brucite.

Study of Overprotective-Polarization of Steel Subjected to Cathodic Protection in Unsaturated Soil.

Various electrochemical methods were used to understand the behavior of steel buried in unsaturated artificial soil in the presence of cathodic protection (CP) applied at polarization levels corresponding to correct CP or overprotection. Carbon steel coupons were buried for 90 days, and the steel/electrolyte interface was studied at various exposure times. The coupons remained at open circuit potential (OCP) for the first seven days before CP was applied at potentials of -1.0 and -1.2 V vs. Cu/CuSO4 for the remaining 83 days. Voltammetry revealed that the corrosion rate decreased from ~330 µm yr-1 at OCP to ~7 µm yr-1 for an applied potential of -1.0 V vs. Cu/CuSO4. CP effectiveness increased with time due to the formation of a protective layer on the steel surface. Raman spectroscopy revealed that this layer mainly consisted of magnetite. EIS confirmed the progressive increase of the protective ability of the magnetite-rich layer. At -1.2 V vs. Cu/CuSO4, the residual corrosion rate of steel fluctuated between 8 and 15 µm yr-1. EIS indicated that the protective ability of the magnetite-rich layer deteriorated after day 63. As water reduction proved significant at this potential, it is proposed that the released H2 bubbles damage the protective layer.

New Biocalcifying Marine Bacterial Strains Isolated from Calcareous Deposits and Immediate Surroundings.

Marine bacterial biomineralisation by CaCO3 precipitation provides natural limestone structures, like beachrocks and stromatolites. Calcareous deposits can also be abiotically formed in seawater at the surface of steel grids under cathodic polarisation. In this work, we showed that this mineral-rich alkaline environment harbours bacteria belonging to different genera able to induce CaCO3 precipitation. We previously isolated 14 biocalcifying marine bacteria from electrochemically formed calcareous deposits and their immediate environment. By microscopy and µ-Raman spectroscopy, these bacterial strains were shown to produce calcite-type CaCO3. Identification by 16S rDNA sequencing provided between 98.5 and 100% identity with genera Pseudoalteromonas, Pseudidiomarina, Epibacterium, Virgibacillus, Planococcus, and Bhargavaea. All 14 strains produced carbonic anhydrase, and six were urease positive. Both proteins are major enzymes involved in the biocalcification process. However, this does not preclude that one or more other metabolisms could also be involved in the process. In the presence of urea, Virgibacillus halodenitrificans CD6 exhibited the most efficient precipitation of CaCO3. However, the urease pathway has the disadvantage of producing ammonia, a toxic molecule. We showed herein that different marine bacteria could induce CaCO3 precipitation without urea. These bacteria could then be used for eco-friendly applications, e.g., the formation of bio-cements to strengthen dikes and delay coastal erosion.

Formation of Iron Sulfides on Carbon Steel in a Specific Cement Grout Designed for Radioactive Waste Repository and Associated Corrosion Mechanisms.

Carbon steel coupons were buried in a specific low-pH cement grout designed for radioactive waste disposal and left 6 months in anoxic conditions at 80 °C. The corrosion product layers were analyzed by µ-Raman spectroscopy, XRD, and SEM. They proved to be mainly composed of iron sulfides, with magnetite as a minor phase, mixed with components of the grout. Average corrosion rates were estimated by weight loss measurements between 3 and 6 µm yr-1. Corrosion profiles revealed local degradations with a depth up to 10 µm. It is assumed that the heterogeneity of the corrosion product layer, mainly composed of conductive compounds (FeS, Fe3S4, and Fe3O4), promotes the persistence of corrosion cells that may lead to locally aggravated degradations of the metal. New cement grouts, characterized by a slightly higher pH and a lower sulfide concentration, should then be designed for the considered application.

Laboratory and in-situ investigations for trapping Pb and Ni with an unusual electrochemical device, the calcareous deposit in seawater.

In seawater, the application of a cathodic current in a metallic structure induces the formation of a calcareous deposit formed by co-precipitation of CaCO3 and Mg(OH)2 on the metal surface. A previous study proved that this electrochemical technique is convincing as a remediation tool for dissolved nickel in seawater and that it is trapped as nickel hydroxide in the deposit. Here, the precipitation of a carbonate form with lead is studied. Pb2+ precipitation in calcareous deposit was investigated with a galvanized steel electrode by doping artificial seawater with PbCl2. Results show for the first time the presence of Pb incorporated in its carbonate form in the calcareous deposit. Trapped Pb content increased with initial Pb content in seawater. Simultaneous doping with Ni and Pb revealed that Ni trapping was favoured by higher current densities while Pb trapping was favoured by lower current densities. Finally, preliminary in situ experiments were performed in an industrial bay and validated the incorporation in real conditions of contaminants by precipitation with the calcareous deposit The present work demonstrates that co-precipitation of contaminants under their hydroxide or carbonate form in a calcareous deposit is a promising clean-up device for remediation of contaminated seawater.