Synthesis of a new potassium-substituted lead fluorapatite and its structural characterization.

Prismatic crystals of partially potassium substituted lead fluorapatite Pb5.09Ca3.78K1.13(PO4)6F0.87 were grown through a solid-state reaction. The structural study conducted by single-crystal X-ray diffraction revealed that the compound crystallizes in the hexagonal P63/m space group, with unit cell parameters a = b = 9.7190(5) Å, c = 7.1700(6) Å and V = 587.37(7) Å3(Z = 1), as well as final values amounting to R and wR of 0.0309 and 0.0546, respectively. The structural refinement demonstrated that Pb occupies both the (6h) and (4f) structural sites of hexagonal fluorapatite, K occupies the (6h) site, and Ca is placed on the (4f) site. Powder X-ray diffraction study indicated the absence of additional phases or impurities. Chemical analysis using atomic absorption spectrometry and energy-dispersive X-ray spectroscopy confirmed the expected chemical formula. The electrical conductivity measured over a wide temperature range was found to be governed by the ion mobility mechanism in the tunnel along the c axis (probably attributed to the fluorine ion located there). We, therefore, could infer from the analysis of the complex impedance spectra that the electrical conductivity of our apatite depends essentially on the temperature and frequency, which produces a relaxation phenomenon and semiconductor-like behavior. Moreover, the strong absorption in the UV-Visible region was substantiated through studies of the optical properties of the developed sample. Fluorescence spectra exhibited emissions in the orange regions when excited at 375 nm. The findings of the phenomena resulting from the emission and conduction of the apatite in question suggest its potential for application in various technological fields such as photovoltaic cells, optoelectronics, photonics, LED applications, catalysis and batteries.

The impact of orthopedic device associated with carbonated hydroxyapatite on the oxidative balance: experimental study of bone healing rabbit model.

Orthopedic devices are used in pathologic disorder as an adjunct to bone grafts to provide immediate structural stability. Unfortunately, the use of metallic devices has some complications. This study aimed to characterize the oxidative stress biomarker and the antioxidant enzyme profiles during bone regeneration. New Zealand White rabbits were divided into 4 groups: Group (I) was used as control (T), Groups II, III, and IV were used, respectively, as implanted tissue with carbonated hydroxyapatite (CHA), carbonated hydroxyapatite associated with external fixator (CHA + EF), and presenting empty defects (ED). Grafted bone tissues were carefully removed to measure malondialdehyde (MDA) concentration, superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase activities (GPx). Our results showed that 4 weeks after operation, treatment of rabbits with CHA + EF showed a significantly higher malondialdehyde (MDA) concentration when compared to that of control group. The SOD, CAT, and GPx in CHA + EF group showed significantly lower activities when compared to those in control group. Eight weeks after surgery, the CHA + EF group presented a lower concentration of MDA as compared to those seen after the first 4 weeks after surgery. On the other hand, the SOD, CAT, and GPx showed a higher activity when compared with the same group. Consequently, MDA concentration and the antioxidant enzyme activities were not significant (p > 0.05) when compared to those in control group rabbits. Histologic sampling has demonstrated successful time-patterned resorption accompanied by bone replacement and remodeling. These results suggest that there was a temporary increase in the oxidative marker level in CHA + EF healing bone and the 8-week period was sufficient to re-establish oxidant-antioxidant balance accompanied by bone repair in the tibia rabbit model.

Biologic response to carbonated hydroxyapatite associated with orthopedic device: experimental study in a rabbit model.

BACKGROUND: Carbonated hydroxyapatite (CHA) and related calcium phosphates have been studied for many years as implant materials due to their similarity with the mineral phase of bone. The main limitation of CHA ceramics as well as other bioactive materials is that they have poor mechanical proprieties. It is thought that the mechanical device can cause an increase in metabolic activity and bone healing. In this study we investigated the reactivity and tissue behaviour of implanted CHA biomaterial reinforced by mini external fixator. METHODS: The evaluation of biomaterial biocompatibility and osteogenesis was performed on a rabbit model over a period of 6 weeks by radiological, histological and scanning electron microscopy (SEM) coupled with energy dispersive X-ray SEM-energy-dispersive X-ray (EDX) analysis. RESULTS: While rabbits treated with CHA exhibited more bone formation, and fibrous tissue was observed when empty bone defects were observed. EDX analysis detected little calcium and phosphorus on the surface of the bone that was not implanted, while high content of calcium (62.7%) and phosphorus (38%) was found on the interface bone cement. CONCLUSIONS: Bone repairing showed that the mini external fixator stimulated the ossification which was pushed when grafted by CHA. This effect may play an important role in the prevention of implant loosening.

Lead bismuth calcium sodium phosphate: Pb4.6Bi0.4Ca2.6Na2.4(PO4)6.

The title compound, lead bismuth calcium sodium phosphate, Pb(4.6)Bi(0.4)Ca(2.6)Na(2.4)(PO(4))(6) crystallizes in the apatite structure type, with vacancies in sites 2a or 2b that are normally occupied by anions. The fact that the Bi and Pb ions are mainly localized in the 6h sites confirms the electron lone-pair influence on the apatite structure.