J.C. Góes

Structural properties of hydroxyapatite obtained by mechanosynthesis

In this paper mechanical alloying has been used successfully to produce nanocrystalline powders of hydroxyapatite (HA) using five different experimental procedures in a pure dry process. 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 (in average 60 hours of milling, depending in the reaction procedure). This milling process, used to produce HA, presents the advantage that melting is not necessary and the powder obtained is nanocrystalline with crystallite size in the range of 22 nm to 39 nm.

Structural properties of CaCu3Ti4O12 obtained by mechanical alloying

Mechanical alloying has been used successfully to produce nanocrystalline powders of CaCu3Ti4O12 (CCTO), for the first time, using two different experimental procedures. The milled CCTO were studied by X-ray powder diffraction, infrared and Raman scattering spectroscopy. For two different milling procedures, CCTO was obtained after a couple of hours of milling (in average 30 h of milling, depending on the reaction procedure). The X-ray diffraction (XRD) patterns indicate that the crystallite size is within the range of 20 � /35 nm. After 100 h of milling the formation of CCTO was confirmed by X-ray powder diffraction in both procedures, with good stability. We also prepare the CCTO ceramic using the traditional procedure described in the literature and compared the physical properties of these samples with those ones obtained by milling process and good agreement was observed. The infrared and Raman scattering spectroscopy results suggest that the increase of the milling time leads to the formation of nanocrystalline CCTO, as seen by XRD analysis. These materials are attractive for capacitor applications and certainly for microelectronics, microwav ed evices (cell mobile phones for example), where the decrease of the size of the devices are crucial. This milling process 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 or used in others procedures of film preparation. The high efficiency of the process opens a way to produce commercial amount of nanocrystalline powders. 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. # 2002 Elsevier Science B.V. All rights reserved.

Polyanionic collagen membranes for guided tissue regeneration: Effect of progressive glutaraldehyde cross-linking on biocompatibility and degradation.

The ultimate goal of periodontal therapy is to control periodontal tissue inflammation and to produce predictable regeneration of that part of the periodontium which has been lost as a result of periodontal disease. In guided tissue regeneration membranes function as mechanical barriers, excluding the epithelium and gingival corium from the root surface and allowing regeneration by periodontal ligament cells. This report aims to study the effect of glutaraldehyde (GA) cross-linking on mineralized polyanionic collagen (PAC) membranes by conducting a histological evaluation of the tissue response (biocompatibility) and by assessing the biodegradation of subcutaneous membrane implants in rats. We studied six different samples: a PAC, a PAC mineralized by alternate soaking processes for either 25 or 75 cycles (PAC 25 and PAC 75, respectively) and these films cross-linked by GA. Inflammatory infiltrate, cytokine dosage, fibrosis capsule thickness, metalloproteinase immunohistochemistry and membrane biodegradation after 1, 7, 15 and 30 days were measured. The inflammatory response was found to be more intense in membranes without cross-linking, while the fibrosis capsules became thicker in cross-linked membranes after 30 days. The membranes without cross-linking suffered intense biodegradation, while the membranes with cross-linking remained intact after 30 days. The cross-linking with GA reduced the inflammatory response and prevented degradation of the membranes over the entire course of the observation period. These membranes are thus an attractive option when the production of new bone depends on the prolonged presence of a mechanical barrier.

Piezoelectric properties of collagen-nanocrystalline hydroxyapatite composites

In this paper we did a study of the physicochemical, dielectric and piezoelectric properties of anionic collagen and collagen-hydroxyapatite (HA) composites, considering the development of new biomaterials which have potential applications in support for cellular growth and in systems for bone regeneration. The piezoelectric strain tensor element d14, the elastic constant s55, and the dielectric permittivity ɛ11 were measured for the anionic collagen and collagen-HA films. For the collagen-HA composite film (Col-HACOM) the main peaks associated to the crystalline HA is present. For the nanocrystalline composite, nanometric HA powder (103 nm particle size) (HAN), obtained by mechanical milling were used. For the composite film (Col-HAN) the HA and CaH(PO4)2H2O phases were detected. One can see that the HA powder (HAN) present the main peaks associated to crystalline HA. The IR spectroscopy measurements on HA-COM and HAN powders, Col-HACOM and Col-HAN composite films and collagen film (Col) presents the main resonances associated to the modes of (PO4)3−, (CO3)2−. The IR spectra of Collagen Film (Col) shows the bands associated to amide I (C=O), amide II (N–H) and amide III (C–N) vibrational modes. The scanning electron photomicrography of the Col-HACOM and Col-HAN films, respectively, shows deposits of HA on the surface of collagen. It also shows that HACOM crystals has a dense feature, whereas the HAN crystals has soft porous surface. Energy-dispersive spectroscopy (EDS) analysis showed that the main elements of the hybrid sponge were carbon, oxygen, calcium, and phosphorus. The EDS of HACOM crystal, present in the Col-HACOM composite showed a molar ratio Ca/P = 1.71, whereas the Col-HAN composite the molar ratio of calcium and phosphorus (Ca/P = 2.14) and the amount of carbon were greater. The piezoelectric strain tensor element d14 obtained for the anionic collagen was around 0.102 pC/N. The collagen composite with nanocrystalline HA crystals (Col-HAN) present a better result (d14 = 0.040 pC/N) compared to the composite with the commercial ceramic (d14 = 0.012 pC/N). This is an indication that the nanometric particles of HA present little disturbance on the organization of the collagen fibers in the composite. In this situation the nanometric HA are the best candidates in future applications of these composites.

Yttrium Iron Garnet: Properties and Applications Review

Due to a fast progress in the development of communication systems, the dielectric and magnetic ceramics (ferrites) have become attractive to be used in devices. Although the ferrites of the spinel type were the first material to be used in the microwave range, garnets have smaller dielectric losses and, therefore, are chosen for many applications. High demands for modern electric applications in magnetic materials results in new techniques and products being permanently studied and researched, with a consequent appearance of new solutions for a wide applications series. This work presents the study of the ferrimagnetic composite, constituted by Y3Fe5O12 (YIG) and Gd3Fe5O12 (GdIG) phases, through solid state synthetic route and submitted to high-energy mechanical milling. Additionally, experiments were made in order to evaluate the electric and magnetic behavior of the composites at radio frequency and microwave range and then later suggest an adequate technological application. The composites were efficient as ferrite resonator antennas (FRAs) and microstrip antennas (thick films deposited on metalized surface alumina substrate by screen-printing technique), in the microwave frequency range. The experiments with FRAs showed satisfactory results due to the control of the antennas radiation characteristics and their tuning by the use of an external magnetic field. The composite resonators studied in this work can be important to the development of a third generation (3G) wideband antennas to cell phones and other wireless products.

Dielectric permittivity and loss of hydroxyapatite screen-printed thick films

In this paper we did a study on the structural and electrical properties of bioceramic hydroxiapatite (HA) thick films. The films were prepared in two layers using the screen printing technique on Al2O3substrates. Mechanical alloying has been used successfully to produce nanocrystalline powders of hydroxyapatite (HA) to be used in the films. We also look for the effect of the grain size of the HA in the final properties of the film. The samples were studied using X-ray diffraction, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and electric measurements. We did a study of the dielectric permittivity and the loss of the films in the radio-frequency of the spectra. The X-ray diffraction (XRD) patterns of the films indicates that all the peaks associated to HA phase is present in the films. One can notice that, for all the films there is a decrease of the DC with the increase of the frequency. The values of the dielectric constant of the films are in between 4 and 9 (at 1 KHz), as a function of the flux material concentration. The loss is decreasing as we increase the frequency for all 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.

Effect of the pH on the piezoelectric properties of collagen films

Abstract In this paper, we did a study of the physicochemical, dielectric and piezoelectric properties of collagen films, considering the development of new biomaterials which have potential applications in coating of cardiovascular prostheses, support for cellular growth and in systems for controlled drug delivery. The piezoelectric strain tensor element d 14 , the elastic constant S 55 , and the dielectric permittivity e 11 were measured for collagen films. It was observed that the collagen samples submitted to different pH treatment lead to different electrical behavior. For sample S2 (pH=5.2 ) one has a higher denaturation temperature ( T d =80.55°C), lowest density ( ρ =909.6 kg m −3 ), highest dielectric function, lowest frequency constant product ( f × L =320.33 kHz.m) and higher piezoelectricity ( d 14 =0.122 pC/N) which is our major interest in this study. The loss factor Q −1 measured for all the samples shows that for all the electrodes dimensions sample S2 present the highest loss factor which is between 0.68 and 0.76. We believe that the different pH treatment is critical to the final level of organization of the microscopic structure of the sample, which could result in an increase of the piezoelectricity.

Piezoelectric and Dielectric Properties of Collagen Films

In this paper we studied the piezoelectric and dielectric properties of collagen films, considering the development of new biomaterials which have potential applications in coating of cardiovascular prostheses, support of cellular growth and in systems for controlled drug delivery. The resonance technique was used to measure the piezoelectric strain tensor element d 14 , the elastic constant S 55 , and the dielectric permittivity e 11 , for collagen films. The resonance measurement of the piezoelectric strain constant d 14 of collagen gives 0.096 pC/N, which is in good agreement with values reported in the literature measured using other experimental techniques. We believe that the use of the resonance technique is very efficient in the study of piezoelectricity in films of biological materials.

Study of the piezoelectricity in iron-doped collagen films

In this paper a study was carried out of collagen membranes prepared with iron as an impurity. In this study the function of the iron in the collagen structure was examined with the aim of increasing the value of the piezoelectric strain tensor element d14. We prepared different samples with different iron doping levels. Doped samples by immersion in solutions of FeCl2 (0.1 M and 0.2 M), FeCl3 (0.1 M) and FeNH4SO4 (0.1 M) and iron doped directly in solution with Fe2O3 at 5% and 15% were examined. Mössbauer spectroscopy, the piezoelectric strain tensor element d14 the elastic constant s55, and the dielectric function ɛ11 of the samples were examined. The loss factor Q−1 of the samples was also measured using the admittance resonance method. The role played by the iron in the different situations and the consequences for the transport properties are discussed.