# Synthesis of High-Precision Sub-Micron CaCO\({}_{3}\) Anticancer Drug Carriers from Coral Remains
## 4 Conclusions  
Compared to other calcium-rich biogenic wastes such as oyster and clam shells, coral remains at present to be a cleaner and more easily collected alternative. This study, initiated from a circular economy perspective, investigated the potential of repurposing coral remains, a topic typically associated with environmental challenges, into a valuable raw material for better use. The major composition of coral remains is CaCO\({}_{3}\), a common raw material in industrial and pharmaceutical products. In this study, coral remains could meet the industrial standards for CaCO\({}_{3}\) undergoing a series of purification and modification processes. Vaterite, one of the crystal phases of CaCO\({}_{3}\), demonstrated excellent physicochemical properties, making it a promising material for anticancer drug carriers. The conclusions drawn from the experiments are as follows:  
1. The composition analysis of coral remains showed the absence of heavy metals such as Pd and Cd, both of which are of most concern in food and pharmaceutical products, indicating their suitability as raw materials for these industries. 2. The efficient conversion of CaCO\({}_{3}\) to CaO in an N\({}_{2}\) atmosphere at 800 \({}^{\circ}\)C within just 5 min demonstrates a significant enhancement in process efficiency, potentially reducing both time and cost. 3. The whiteness level of purified CaCO\({}_{3}\) reached 95%, surpassing many industrial standards (93%), making it suitable for industrial applications. Figure 9: Loading result of TRITC-Dextran: (**a**) synthesized calcium carbonate (CaCO\({}_{3}\)) only; (**b**) with the fluorescently labeled (red signals on the particles) drug TRITC-Dextran; (**c**) the fluorescence spectrum of the supernatant. 4. The synthesized vaterite possesses several desirable drug carrier properties such as spherical morphology, small particle size, high porosity, pH sensitivity, and biocompatibility. Given its widespread use in the food and pharmaceutical industries, CaCO\({}_{3}\) has shown to be a superior option for anticancer drug delivery compared to other drug carriers such as mesoporous silica nanoparticles and gold nanoparticles. 5. The effective utilization of the EPR effect for targeting cancer cell necessitates particle sizes below 600 nm. Smaller particles are more efficient in penetrating cell membranes and also positively impact the drug loading capacity, a crucial factor of the efficiency of CaCO\({}_{3}\) as a drug carrier. While typical reproducibility of vaterite particle size range from 4 to 6 \(\mu\)m [40; 50; 51], our study successfully synthesized drug carriers with an average size of 344 nm, and some even smaller than 200 nm. 6. During CaCO\({}_{3}\) synthesis, the involvement of EG necessitated sufficient time to form a complete vaterite crystal. Insufficient time resulted in the formation of either amorphous phases or incomplete calcite crystals. 7. Given the high costs associated with cancer drug production and the expensive, intricately synthesized carriers typically used for their delivery, the overall price of anticancer drug carriers remains notably high. CaCO\({}_{3}\), in contrast, is a widely available, cost-effective, and stable material. Its application as a drug carrier could significantly reduce costs while maintaining excellent biocompatibility and precision in drug delivery. This approach not only provides a solution to the high expenses involved in synthesizing drug carriers, but also tackles environmental concerns related to coral remains, offering a dual advantage. Conceptualization, S.-A.C. and W.-S.C.; methodology, W.-C.C. ; software, S.-A.C.; validation, S.-A.C. and W.-C.C. ; formal analysis, S.-A.C.; investigation, S.-A.C.; resources, S.-A.C.; data curation, S.-A.C.; writing--original draft preparation, P.-H.C.; writing--review and editing, P.-H.C.; visualization, P.-H.C.; supervision, W.-S.C.; project administration, S.-A.C.; funding acquisition, S.-A.C. All authors have read and agreed to the published version of the manuscript.