## 4 Conclusions and Future Perspectives  
Hydroxypatite (HA) has proven to be an invaluable material for bone synthesis and repair, owing to its osteoinductive, osteoconductive, and biocompatible properties. However, the limited mechanical strength of pure HA has driven researchers to develop various modifications to enhance its performance. Structural and chemical alterations, including ion doping, have enabled HA's properties to be tailored to meet specific clinical needs in orthopaedics, dentistry, and other medical fields. Ion doping modifies the microstructure of HA, reducing its fragility and enhancing its fracture resistance, thus making it more suitable for use in high-stress areas, such as the spine.  
Doping with ions such as cerium and carbonate (CO\({}_{3}\)\({}^{2-}\)) can reduce the crystallinity of HA, increasing its solubility in biological environments, which is beneficial for bone regeneration. Additionally, doping with magnesium, strontium, or zinc enhances the biological and mechanical properties of HA, promoting angiogenesis, bone tissue regeneration, and antibacterial activity. For example, the incorporation of silver, zinc, or copper ions imparts antibacterial properties to HA, thereby reducing the risk of infection around implants or during the wound healing process. Moreover, combining HA with natural compounds like curcumin has shown promising results not only in bone cancer treatment but also in enhancing bone regeneration in patients with type II diabetes.  
While modified hydroxyapatite demonstrates significant potential in bone healing and regeneration, the synthesis methods and optimal concentrations of ion doping still need further refinement. The future of HA-based materials depends on a deeper understanding of bone regeneration processes and the creation of suitable microenvironments for effective healing. Additionally, impurities in synthetic bone graft materials, including HA, can adversely affect biocompatibility, bioactivity, and mechanical strength, leading to complications such as inflammation or material rejection. Therefore, standardizing production processes and exploring additional doping agents is essential to improve the purity and effectiveness of these biomaterials.  
Future research should focus on developing more durable and effective HA-based materials, and long-term clinical trials are necessary to ensure optimal patient outcomes. Enhanced materials and improved understanding of bone regeneration mechanisms will pave the way for more advanced and personalized therapeutic approaches.  
Conceptualization, Z.K.-M. and J.H.; methodology, Z.K.-M. and T.G.; validation, LN.-H., M.D., J.M. and J.H.; formal analysis, M.D., T.G. and J.H.; investigation, Z.K.-M.; data curation, [PERSON]-M., A.B., A.P. and J.M.; writing--original draft preparation, [PERSON]-M. and A.B.; writing--review and editing, [PERSON], A.P., M.D., J.M., A.K. and I.N.-H.; supervision, T.G. and J.H. All authors have read and agreed to the published version of the manuscript.  
This research was funded and supported by the Wroclaw Medical University, grant no. SUBZ.B040.24.008.  
Not applicable.  
Data Availability Statement: Data can be made available on request.  
The authors declare no conflicts of interest.