The effect of chemical composition and morphology on the drug delivery properties of hydroxyapatite-based biomaterials

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In the case of orthopedic and dental interventions, local antibiotic therapy reduces significantly the risk associated with the intervention. The aim of this study was the preparation and characterization of pure hydroxyapatite (HA), Si- and Mg-doped HA, which ensures the sustained release of doxycycline, and the investigation of the parameters, which were crucial for the drug release. The carriers were synthesized using the precipitation method. In order to achieve different morphologies, traditional drying and spray drying methods were used: Si-doped HA was prepared using two different sources of Si, Na2SiO3 and Ludox AS-40, while (Mg(NO3)2)*6H2O was used for substitution with Mg. The carriers were characterized by XRD, SEM, EDX and TG/DTA methods, and the ion incorporation was also confirmed by lattice parameters calculations. Doxy was bound on the carriers by physical adsorption, the adsorption capacity increased proportionally by increasing the concentration of the initial Doxy solutions (10, 15, 20, 25 g/L). The investigated systems showed different releases with the change of the dissolution medium (in the case of HA microspheres, the release in PBS was twice as high as in SBF), chemical composition and morphology of the carriers. The retard effect of the carriers was improved by the spherical morphology, and the reduced release by ion substitution in both SBF and PBS increased as follows: HA < HASi1<HAMg < HASi2. The release mechanism of Doxy was discussed through five different release kinetics models.