The aim of this review is to investigate the possibility of fabricating coatings functionalized with bioactive molecules. These coatings are interesting when applied to biomedical devices, particularly in the orthopedic field. In fact, the application of calcium phosphate-based coatings on the surface of implanted devices is an effective strategy to increase their osteoinductive and osseointegrative properties. Several coating fabrication technologies are presented, including chemical deposition and physical methods. The application of bioactive molecules in combination with calcium phosphate coatings may improve their osteointegrative, antibacterial, and antitumor properties, therefore increasing the performance of implantable devices.

Strontium, cobalt, and manganese ions are present in the composition of bone and useful for bone metabolism, even when combined with calcium phosphate in the composition of biomaterials. Herein we explored the possibility to include these ions in the composition of apatitic materials prepared through the cementitious reaction between ion-substituted calcium phosphate dibasic dihydrate, CaHPO₄·2H₂O (DCPD) and tetracalcium phosphate, Ca₄(PO₄)₂O (TTCP). The results of the chemical, structural, morphological and mechanical characterization indicate that cobalt and manganese exhibit a greater delaying effect than strontium (about 15 at.%) on the cementitious reaction, even though they are present in smaller amounts within the materials (about 0.8 and 4.5 at.%, respectively). Furthermore, the presence of the foreign ions in the apatitic materials leads to a slight reduction of porosity and to enhancement of compressive strength. The results of biological tests show that the presence of strontium and manganese, as well as calcium, in the apatitic materials cultured in direct contact with human mesenchymal stem cells (hMSCs) stimulates their viability and activity. In contrast, the apatitic material containing cobalt exhibits a lower metabolic activity. All the materials have a positive effect on the expression of Vascular Endothelial Growth Factor (VEGF) and Von Willebrand Factor (vWF). Moreover, the apatitic material containing strontium induces the most significant reduction in the differentiation of preosteoclasts into osteoclasts, demonstrating not only osteogenic and angiogenic properties, but also ability to regulate bone resorption.

Brushite (dicalcium phosphate dihydrate, DCPD) is considered one of the possible precursors of the apatitic phase that constitutes the mineral component of bones, and it is often utilized in the preparation of biomaterials for hard tissue repair. In this work, we investigated the influence of ionic substitution on the synthesis, structure, and morphology of this calcium phosphate, as well as on its hydrolysis process. The results of structural refinements indicate that the range of possible substitution can reach values up to about 38 atom % for the big Sr ion, whereas it is quite limited for Zn, Co, and Mn. In particular, DCPD cannot be obtained as a single phase in the presence of zinc ions in solution. The kind and amount of substituent ions significantly influence the morphology of DCPD, promoting aggregation and crystal shape modifications, as well as its hydrolysis in solution. The results provide useful information for the understanding of the mineralization processes and for the design of new biomaterials.