Estudo das propriedades ópticas, elétricas e térmicas da hidroxiapatita obtida por moagem de alta energia, seus compósitos e filmes espessos

Abstract

Mechanical alIoying has been used successfulIy to produce nanocrystalIine powders of hydroxyapatite (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 hours of milling (15, 30, 45 and 60 hours). For one of the procedures we do not had the HA formation. This milling process, used to produce HA, - presents the advantage that melting is not necessary and the powder obtained is nanocrystalIine. 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 nanocrystalIine HA. We did a study of the structural and electrical properties of bioceramic hydroxiapatite (HA) thick films prepared by the screen printing technique. The films were prepared in two layers using the screen printing technique on Al203 substrates. Mechanical alIoying has been used successfulIy to produce nanocrystalIine powders of hydroxyapatite (HA) to be used in the films. We also look for the effect ofthe grain size of the HA in the final properties of the filmo The samples were studied using X-Ray diffraction, scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), infrared and Raman scattering spectroscopy and electric measurements. We did a study of the dielectric permittivity and the loss of the films in the radio-frequency of the spectra. One can notice that, for all the films there is a decrease of the De with the increase of the frequency. The values of the dielectric constant of the films are in between 4 and 9 (at 1KHz), as a function of the fuse concentration. The loss is decreasing as we increase the frequency for all the films. The X-ray diffraction (XRD) pattems of the films indicate that all the peaks associated to HA phase i present in the films. These results strongly suggests that the screen-printing HA thick films are good candidates for applications in biocompatible coatings of implant materials but also for the insulating materials of electronic circuits and dielectric layer in bio-sensors. We also did a study of the biocompatibility of the nanocrystalIine HA. HA with different degrees of crystallinity and time of milling (HA2/60, HA4/15 and HA5/15) were used in the tests. The bioactivity analysis shows that all the samples implanted in rabbits can be considered biocompatible, since they had been considered non toxic, had not caused inflammation and reject on the part of organisms of the animals, during the period of implantation. The samples implanted in rabbits had presented new osseous tissue formation with the presence of osteoblastics cells. The physicochemical, optical, dielectric and piezoelectric properties of the anionic collagen (Col), collagen-nanocrystalline hydroxyapatite (Col-HAN) and collagencommercial hydroxyapatite (Col-HACOM) composite was studied in view of the development of new biomaterials which have potential applications in support for cellular growth and m systems for controlled drug delivery. The piezoelectric strain tensor element d14, the elastic constant S55, and the dielectric permittivity Ell were measured for the anionic collagen film, with value of 0,102 pC/N, which is in good agreement compared with values reported in the literature obtained with other techniques. For the collagen-HAN composite membranes, a slight decrease of the value of the piezoelectricity (0,041 pC/N ) and 0,012 pC/N for the Col-HACOM was observed. The thermal analysis shows two denaturation endothermic for the collagen sample, Col-HAN and Col-HACOM composite films. The Col-HAN composite film shows a better thermo stability, if compared with Col-HACOM sample. The X-ray diffraction pattem of the collagen film shows a broad diffraction pattem characteristic of amorphous material. The main peaks associated to the crystalline HA are present in the sample of Col-HAN and Col-HACOM. In the Col-HAN composite, one can also notice the presence of other peaks with low intensities which is an indicator of the formation of other crystalline phases of apatite.