Calcium Carbonate

Calcium carbonate exerts its hemostatic effect through two complementary mechanisms: calcium ion release and platelet concentration. In citrated blood where calcium-dependent coagulation is disrupted, calcium carbonate polymorphs including coral-derived aragonite and synthetic calcite reduce coagulation time by up to two-fold. Prothrombin time and partial thromboplastin time decrease by 13 percent and 24 percent respectively following calcite treatment. Calcite particles reduce circulating platelet counts by 13 percent through direct platelet binding, indicating effective recruitment of platelets to the site of injury. Simultaneously, calcite raises free calcium levels in plasma by 2.6-fold compared to untreated controls, overcoming the calcium chelation effect of citrate. These dual actions address both the cellular and ionic components of coagulation that are impaired in citrate-induced coagulopathy. The smaller particle size of calcite (average 11 micrometers) compared to aragonite contributes to its enhanced efficacy, with calcite grains smaller than 40 micrometers reducing coagulation time to 6.4 minutes.

Calcium carbonate nanoparticles exhibit excellent biocompatibility and biodegradability due to their chemical similarity to bone minerals, with by-products limited to calcium ions and carbonate that already exist in blood. The nanoparticles remain stable under normal blood pH of 7.4 but decompose rapidly in the acidic tumor microenvironment (pH 6.5-6.8), enabling targeted drug release. Preparation methods include solution precipitation, microemulsion and gas diffusion. Biomedical applications encompass diagnosis (fluorescence imaging, MRI and ultrasound), treatment (chemotherapy, gene therapy, photothermal/photodynamic therapy) and theranostics. CaCO₃ nanoparticles serve both as drug carriers and as calcium ion generators that induce immunogenic cell death and autophagy for cancer immunotherapy.

Fig. 2 Schematic illustration of the prepared CaCO3 NPs for MRI. (Zhao P.; et al. 2022)