The effect of temperature on the physical-chemical properties of bovine hydroxyapatite biomimetic scaffolds for bone tissue engineering

This work focuses on the changes in hydroxyapatite (HAp) scaffolds obtained from bovine trabecular bone after heat treatments ranging from 400 to 1100 °C. The main objective is to gain a comprehensive understanding of the thermal behavior and structural modifications of these HAp scaffolds and evaluate their suitability for specific applications. Thermal analysis using thermogravimetry and differential scanning calorimetry revealed distinct thermal events associated with HAp crystallite coalescence, carbonate elimination, and Mg out-diffusion. Fourier transform infrared spectroscopy demonstrates the presence of organics in samples annealed at temperatures below 500 °C and the elimination of carbonates in samples annealed at temperatures above 700 °C. Raman spectroscopy indicated a transition from nano-to-micro-sized HAp crystallites in both the raw and samples annealed at 400 and 500 °C. X-ray diffraction analysis shows changes in the full width at half maximum (FWHM) of the (002) peak for the annealed samples. Crystalline parameters were determined using Rietveld refinement. Scanning electron microscopy images revealed the phenomenon of HAp crystallite coalescence during heat treatment. The growth of the crystallites and the transition from nano to micro size occurred at approximately 600 °C. Importantly, the macroporosity of the HAp scaffolds remained unchanged regardless of the calcination temperature, while mesoporosity was observed only in scaffolds calcined at lower temperatures (400, 500, and 600 °C). Furthermore, the raw, 400, and 500 °C scaffolds retained organic materials, resulting in improved mechanical properties. These findings provide valuable insights into the thermal behavior and structural changes of HAp scaffolds derived from bovine trabecular bone. The study suggests that scaffolds calcined at 600 °C exhibit suitable properties for bone tissue engineering applications, predominantly consisting of carbonated HAp nanocrystals, featuring three types of porosity, and are free of organic material.