Estudo do efeito de parâmetros de reação na síntese de hidroxiapatita: caracterização e comparação entre metodologias

Abstract

The evolution and application of biomaterials are fundamental for addressing clinical challenges related to the restoration of lost or damaged tissues, whether due to trauma, disease, or congenital anomalies. Although bone tissue has the capacity for self-repair and continuous remodeling, in many cases, large injuries or critical defects can exceed the body’s ability to regenerate, requiring external interventions. Among the most widely used biomaterials in tissue engineering is hydroxyapatite (HA). Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) is a bioceramic material whose chemical composition closely resembles that of bone tissue, which accounts for its excellent biocompatibility. Due to these properties, HA has been extensively used in biomedicine, especially when combined with composites for bone regeneration. The present study proposes to evaluate two wet-chemical synthesis methods, using different calcium precursors and varying the aging time of the samples (1, 6, and 24 hours). The main objective was to determine which of the evaluated routes produces hydroxyapatite with chemical composition and crystallinity most similar to those of biological apatite. Part of the data used derives from a previous work by the author, based on the synthesis parameters of the sample named EXP06, which employed CaO as a Ca²⁺ source, a temperature of 60 °C, a concentrated H₃PO₄ feed rate of 6 mL/min, and an aging time of 1 hour, resulting in an HA/β-TCP ratio of 1.38. The other samples in this study were synthesized using Ca(OH)₂ and H₃PO₄ solutions as precursors, keeping all other parameters constant except for the aging time. After the dripping process, the pH of the reaction systems was adjusted to values around 12, which favors the formation of the HA phase. Once the aging periods were completed, the samples were dried at 100 °C for 24 hours, subsequently calcined at 800 °C for two hours, and subjected to the following characterization techniques: X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and high-resolution field-emission scanning electron microscopy (FEG-SEM). In addition, the antimicrobial potential was evaluated using the agar disk diffusion test against Escherichia coli and Salmonella. The diffractograms revealed that Method 2 resulted in HA as the major phase, with peaks at 2θ = 25.9°, 31.8°, 33.0°, and 39.9°, along with a β-TCP peak at 34.14°. Method 1, in contrast, showed phase overlap, with several intense peaks that could be attributed to both HA and β-TCP. The FTIR spectra confirmed characteristic bands of phosphate (PO₄³⁻) and hydroxyl (OH⁻) groups, supporting the formation of the apatite phase, in addition to secondary phases indicated by additional or shifted bands. SEM images showed marked morphological differences, such as needle-like particles in Method 1 and rod-like structures in Method 2, the latter resembling biological apatite and making it ideal for implant applications. Finally, none of the samples exhibited antimicrobial activity against the tested strains.