Functionalized Calcium Carbonate-Based Microparticles as a Versatile Tool for Targeted Drug Delivery and Cancer...

Nano- and microparticles are increasingly widely used in biomedical research and applications, particularly as specific labels and targeted delivery vehicles. Silica has long been considered the best material for such vehicles, but it has some disadvantages limiting its potential, such as the proneness of silica-based carriers to spontaneous drug release. Calcium carbonate (CaCO₃) is an emerging alternative, being an easily available, cost-effective, and biocompatible material with high porosity and surface reactivity, which makes it an attractive choice for targeted drug delivery. CaCO₃ particles are used in this field in the form of either bare CaCO₃ microbeads or core/shell microparticles representing polymer-coated CaCO₃ cores. In addition, they serve as removable templates for obtaining hollow polymer microcapsules. Each of these types of particles has its specific advantages in terms of biomedical applications. CaCO₃ microbeads are primarily used due to their capacity for carrying pharmaceutics, whereas core/shell systems ensure better protection of the drug-loaded core from the environment. Hollow polymer capsules are particularly attractive because they can encapsulate large amounts of pharmaceutical agents and can be so designed as to release their contents in the target site in response to specific stimuli. This review focuses first on the chemistry of the CaCO₃ cores, core/shell microbeads, and polymer microcapsules. Then, systems using these structures for the delivery of therapeutic agents, including drugs, proteins, and DNA, are outlined. The results of the systematic analysis of available data are presented. They show that the encapsulation of various therapeutic agents in CaCO₃-based microbeads or polymer microcapsules is a promising technique of drug delivery, especially in cancer therapy, enhancing drug bioavailability and specific targeting of cancer cells while reducing side effects. To date, research in CaCO₃-based microparticles and polymer microcapsules assembled on CaCO₃ templates has mainly dealt with their properties in vitro, whereas their in vivo behavior still remains poorly studied. However, the enormous potential of these highly biocompatible carriers for in vivo applications is undoubted. This last issue is addressed in depth in the Conclusions and Outlook sections of the review.