Morphology-Dependent Transformation of Dicalcium Phosphate Dihydrate (DCPD) to Octacalcium Phosphate (OCP) and Its Stability in Simulated Physiological Fluids

Calcium phosphate (CaP) materials are biocompatible and non-toxic to the body. However, they lack biointegration, exhibit a low resorption rate and can cause fibrous encapsulation throughout the implant material. A promising approach for dental or orthopedic regeneration is the use of dicalcium phosphate dihydrate (DCPD) and octacalcium phosphate (OCP), as they are well-suited to bone components. From a novel perspective, these apatites can be used as drug carriers for individuals with low tolerance to common excipients. In this study, the transformation of DCPD into different morphologies in DMEM was investigated using an induced dissolution and reprecipitation reaction solution. The DCPD transformation time was observed to be morphology-dependent and can occur between 48 and 168 h. In the interaction with simulated body fluid (SBF), simulated gastric fluid (SGF) and a combination of both (BFS/SGF), a higher mass loss was observed in SGF (~80%) than in the other fluids (~35%). The structural changes presented in DCPD and OCP before and after immersion in physiological fluids were analyzed by ATR-FTIR, SEM, XRD and EDS. The obtained OCP showed low stability in SGF compared to SBF and SBF/SGF, which indicates that it may be a suitable candidate for drug delivery in the digestive tract.