Miodrag J. Lukić

Synthetical bone-like and biological hydroxyapatites: a comparative study of crystal structure and morphology

Phase composition, crystal structure and morphology of biological hydroxyapatite (BHAp) extracted from human mandible bone, and carbonated hydroxyapatite (CHAp), synthesized by the chemical precipitation method, were studied by x-ray powder diffraction (XRD), Fourier transform infrared (FTIR) and Raman (R) spectroscopy techniques, combined with transmission electron microscopy (TEM). Structural and microstructural parameters were determined through Rietveld refinement of recorded XRD data, performed using the FullProf computing program, and TEM. Microstructural analysis shows anisotropic extension along the [00l] crystallographic direction (i.e. elongated crystallites shape) of both investigated samples. The average crystallite sizes of 10 and 8 nm were estimated for BHAp and CHAp, respectively. The FTIR and R spectroscopy studies show that carbonate ions substitute both phosphate and hydroxyl ions in the crystal structure of BHAp as well as in CHAp, indicating that both of them are mixed AB-type of CHAp. The thermal behaviour and carbonate content were analysed using thermogravimetric and differential thermal analysis. The carbonate content of about 1 wt.% and phase transition, at near 790 °C, from HAp to β-tricalcium phosphate were determined in both samples. The quality of synthesized CHAp powder, particularly, the particle size distribution and uniformity of morphology, was analysed by a particle size analyser based on laser diffraction and field emission scanning electron microscopy, respectively. These data were used to discuss similarity between natural and synthetic CHAp. Good correlation between the unit cell parameters, average crystallite size, morphology, carbonate content and crystallographic positions of carbonate ions in natural and synthetic HAp samples was found.

45S5Bioglass®-based scaffolds coated with selenium nanoparticles or with poly(lactide-co-glycolide)/selenium particles: Processing, evaluation and antibacterial activity

In the bone tissue engineering field, there is a growing interest in the application of bioactive glass scaffolds (45S5Bioglass(®)) due to their bone bonding ability, osteoconductivity and osteoinductivity. However, such scaffolds still lack some of the required functionalities to enable the successful formation of new bone, e.g. effective antibacterial properties. A large number of studies suggest that selenium (Se) has significant role in antioxidant protection, enhanced immune surveillance and modulation of cell proliferation. Selenium nanoparticles (SeNp) have also been reported to possess antibacterial as well as antiviral activities. In this investigation, uniform, stable, amorphous SeNp have been synthesized and additionally immobilized within spherical PLGA particles (PLGA/SeNp). These particles were used to coat bioactive glass-based scaffolds synthesized by the foam replica method. Samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). SeNp, 45S5Bioglass(®)/SeNp and 45S5Bioglass(®)/PLGA/SeNp showed a considerable antibacterial activity against Gram positive bacteria, Staphylococcus aureus and Staphylococcus epidermidis, one of the main causative agents of orthopedic infections. The functionalized Se-coated bioactive glass scaffolds represent a new family of bioactive, antibacterial scaffolds for bone tissue engineering applications.