Hydroxyapatite (HAp, Ca$_{10}$(PO$_4$)$_6$(OH)$_2$) is the main inorganic component of bone tissue, accounting for approximately 65% of bone mass. Synthetic HAp is biocompatible, osteoconductive, and widely used in bone tissue engineering; however, it has limited potential for bone tissue regeneration and for promoting the differentiation of human mesenchymal stem cells (hMSC). Doping HAp with bioactive ions has been shown to improve its bioactivity and capacity to induce osteogenic differentiation.
Multi-doped hydroxyapatites (mHAp), containing several different ions, enable a synergistic effect in which individual ions contribute to different phases of bone regeneration. Strontium (Sr$^{2+}$) and gallium (Ga$^{3+}$) ions act as antiresorptive agents and inhibit osteoclast activity, magnesium (Mg$^{2+}$) and zinc (Zn$^{2+}$) ions participate in mineralization and maintenance of bone density, while silicon (Si$^{4+}$) ions support angiogenesis and contribute to preserving the quality of the bone matrix and the mechanical properties of bone. Multi-doped HAp thus acts as a system for the gradual release of doped ions during bioresorption, enabling long-term stimulation of natural bone regeneration. Furthermore, the presence of Ga$^{3+}$ ions provides antimicrobial protection, which is essential for preventing infections in bone implants.
The aim of this master's thesis was to synthesize and characterize hydroxyapatite co-doped with Mg$^{2+}$, Zn$^{2+}$, Ga$^{3+}$, Sr$^{2+}$ and Si$^{4+}$ ions, and to evaluate the effect of doping on the properties of the synthesized material. The main research objectives are: (i) synthesis of mHAp doped with optimal concentrations of Mg$^{2+}$, Zn$^{2+}$, Ga$^{3+}$, Sr$^{2+}$ and Si$^{4+}$ ions; (ii) characterization of the structural, morphological, and surface properties of the synthesized material, which are critical for its bioactivity and osseointegration; and (iii) preparation of mHAp samples for the evaluation of osteogenic bioactivity and antimicrobial activity.
In the experimental part of the master's thesis, the wet chemical precipitation method in the presence of urea as a precipitating agent was used for the preparation of multi-doped hydroxyapatite. The synthesized material was characterized by structural (XRD, FTIR), morphological (SEM, EDS), thermal (TGA-DSC), and surface (BET) analyses, as well as elemental analysis (ICP-MS). The results of this research contribute to the understanding of the effect of multi-doping on the structure and functionality of hydroxyapatite and provide a foundation for the development of a novel biomaterial with improved regenerative and antimicrobial properties for use in regenerative medicine and bone tissue engineering.
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