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Abstract: The hydroxyapatite (Ca10(PO4)6 (OH)2–HAP) is the main mineral constituent of teeth and bones with excellent biocompatibility with hard and muscle tissues. This material exhibits several problems of handling and preparation, which can be minimized by mixing the HAP with a suitable binder. In order to improve the phase structure, morphology and the dielectric properties, nanocrystalline hydroxyapatite was prepared by a microwave assisted solid-state reaction technique from Ca(OH)2 and CaHPO4 powders. After milling the mixture was submitted to microwave radiation in a domestic microwave oven (ƒ=2.45GHz−1kW) during 15 and 30min at 1000, 1100 and 1200°C. The samples were analyzed by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), EDS (energy dispersive spectroscopy), FT-IR spectroscopy. The dielectric properties were measured in the frequency range 1Hz–30MHz at several temperatures (250–350K). The dielectric study in function of frequency, at 300K, was made using the Modulus formalism (M*=1/ε*) and a distribution of relaxation times was observed. [Copyright &y& Elsevier]

Calcium phosphate-based bioceramics, mainly in the form of hydroxyapatite, Ca10(PO4)6(OH)2—HAP, is the main mineral constituent of teeth and bones with excellent biocompatibility with hard and muscle tissues. These materials exhibit several problems of handling and fabrication, which can be overcome by mixing them with a suitable binder. The dry milling process of fabrication of HAP presents the advantage that melting is not necessary and the powder obtained is nanocrystalline. The high efficiency of the dry milling process opens a new way to produce commercial amount of nanocrystalline HAP and others bioceramic. In this work dry mechanical alloying has been used to produce nanocrystalline powders of HAP using three different experimental procedures (HAPA: Ca(H2PO4)2 + Ca(OH)2; HAPB: Ca(H2PO4)2 + CaCO3; and HAPC: CaHPO4 + CaCO3). HAP was obtained after 5, 10 and 15 h of milling in the reactions HAPA and HAPB, but it is necessary 15 h of milling in the reaction HAPC to obtain HAP. In order to improve the mechanical properties of HAP calcium phosphate ceramics, with titanium (CaP-Ti) and zirconium (CaP-Zr), have been prepared by dry ball milling using two different experimental procedures: CaP-Ti1: Ca(H2PO4)2 + TiO2; CaP-Ti2: CaHPO4 + TiO2; and CaP-Zr1: Ca(H2PO4)2 + ZrO2, CaP-Zr2: CaHPO4 + ZrO2. The calcium titanium phosphate phase, CaTi4P6O24, was obtained in the reaction CaP-Ti1. In the reactions CaP-Ti2, CaP-Zr1 and CaP-Zr2, it was not observed the formation of any calcium phosphate phase even after 15 h of dry mechanical alloying. The milled HAP and the ceramics systems obtained were characterized by X-ray powder diffraction, infrared and Raman scattering spectroscopy. [Copyright &y& Elsevier]

Mechanical alloying has been used successfully to produce nanocrystalline powders of hydroxyapatite (HA) using three different procedures. The milled HA was studied by X-ray diffraction, Infrared, Raman scattering spectroscopy and Scanning Electron Microscopy (SEM). We obtained HA with different degrees of crystallinity and time of milling. The grain size analysis through SEM and XRD shows particles with dimensions of 36.9, 14.3 and 35.5 nm (for (R1), (R2) and (R3), respectively) forming bigger units with dimensions given by 117.2, 110.8 and 154.4 nm (for (R1), (R2) and (R3), respectively). The Energy-Dispersive Spectroscopy (EDS) analysis showed that an atomic ratio of Ca/P=1.67, 1.83 and 1.50 for reactions (R1), (R2) and (R3), respectively. These results suggest that the R1 nanocrystalline ceramic is closer to the expected value for the ratio Ca/P for hydroxyapatite, which is 5/31.67. The bioactivity analysis shows that all the samples implanted into the rabbits can be considered biocompatible, since they had been considered not toxic, had not caused inflammation and reject on the part of the organisms of the animals, during the period of implantation. The samples implanted in rabbits had presented new osseous tissue formation with the presence of osteoblasts cells. [Copyright &y& Elsevier]

Calcium phosphate based bioceramics, mainly in the form of hydroxyapatite (HA), have been in use in medicine and dentistry for the last 20 years. Applications include coatings of orthopaedic and dental implants, alveolar ridge augmentation, maxillofacial surgery, otolaryngology, and scaffolds for bone growth and as powders in total hip and knee surgery. These materials exhibit several problems of handling and fabrication, which can be overcome by mixing with a suitable binder. In this paper, mechanical alloying has been used successfully to produce nanocrystalline powders of HA using five different experimental procedures. The milled HA were studied by X-ray powder diffraction, infrared and Raman scattering spectroscopy. For four different procedures, HA was obtained after a couple of hours of milling (on an average, 20 h of milling depending on the reaction procedure). The XRD patterns indicate that the grain size is within the range of 29–103 nm. This milling process, used to produce HA, presents the advantage that melting is not necessary and the powder obtained is nanocrystalline with extraordinary mechanical properties. The material can be compacted and transformed in solid ceramic samples. The high efficiency of the process opens a way to produce commercial amount of nanocrystalline HA. Due to the nanocrystalline character of this powder, their mechanical properties have changed and for this reason a pressure of 1 GPa is enough to shape the sample into any geometry. [Copyright &y& Elsevier]

Abstract: Hydroxyapatite (HAP), Ca10(PO4)6(OH)2, has a wide range of biomedical applications because it is excellent biocompatibility and similar to natural bone tissue. The synthesis of the nanocrystalline powders of hydroxyapatite (HAP) was developed by the high energy method of dry mechanical alloying. The Ca(OH)2 and CaHPO4 were used in the preparation. Galactomannans are polysaccharides that occur in the endosperm of the seeds of leguminous plants as cell wall storage components was obtained from seeds of Adenanthera pavonina L. family Leguminosae (Fabaceae) and subfamily Mimosoideae. The nanocrystalline powders of hydroxyapatite were mixed with 10% (Gal 90), 20% (Gal 80) and 30% (Gal 70) of galactomannan. The aim of the study was to investigate influence of the galactomannan on the electrical characterization of bioceramic materials based on hydroxyapatite. The samples were studied by X-ray diffraction (XRD) was recorded to confirm the formation of a single phase solid solution and comportment this phase through the Rietveld analysis, scanning electron microscopy (SEM) and Dielectric measurements in the 10Hz–100MHz frequency range, at room temperature, have been performed. The presence of nanocrystals was confirmed by X-ray diffraction of HAP with size crystallite of 110nm. [Copyright &y& Elsevier]