Anselmo Ortega Boschi

Influence of polymeric additives on the mechanical properties of α-tricalcium phosphate cement

Abstract Recently, great attention has been paid to calcium phosphate cements, because of their advantages in comparison with conventional calcium phosphate bioceramics employed for bone repairing, regarding in situ handling, and shaping abilities. Nevertheless, the calcium phosphate cements exhibit relatively low mechanical strength. The aim of this work was the improvement of the compressive strength of α-tricalcium phosphate-based cement. The hydraulic setting reaction of this system produces a calcium-deficient hydroxyapatite phase suitable for bone repairing: α-Ca 3 (PO 4 ) 2 + H 2 O → Ca 9 (HPO 4 )(PO 4 ) 5 OH. Mechanical strength can be improved using technological solutions developed for other applications, such as Portland cement and dual-setting glass-ionomers, by using polymeric additives. The additives used in this work were sodium alginate, sodium polyacrylate, and an in situ polymerization system resulting in a polyacrylamide crosslinked hydrogel. Parameters evaluated were setting time, compressive strength before and after immersion in simulated body fluid, density, porosity, crystalline phases, and microstructure. Sodium alginate and sodium polyacrylate were deleterious to both setting time and mechanical strength. When the in situ polymerization system was added, two setting reactions progressed in parallel: the conventional hydraulic reaction and the copolymerization of acrylamide and crosslinking water-soluble monomers. The initial and final setting times of the “dual-setting” cement were 9 and 35 min, respectively, and they can be regulated varying the initiator, catalyst, and monomers concentrations. The initial compressive strength of the dual- setting cement (6.8 MPa at 0 h, and 15.2 MPa at 24 h) is higher than that of unmodified cement. The major crystalline phase after setting is hydroxyapatite. The dual-setting cement seems to be suitable for clinical applications in bone repairing and remodeling.

α-Tricalcium phosphate cement: “in vitro” cytotoxicity

Calcium phosphate-based bioceramics have revolutionized orthopedic and dental repair of damaged parts of the bone system. Among these materials, calcium phosphate-based cements, with hydraulic setting, stand out due to their biocompatibility and in situ hardening, which allow easy manipulation and adaptation to the shape and dimensions of bone defects. An investigation was made of the in vitro cytotoxic effect of calcium phosphate cement based on a-tricalcium phosphate, immersed for different lengths of time in simulated body fluid (SBF), based on the ISO-10993 ‘‘Biological Evaluation of Medical Devices’’ standard. The culture medium was Chinese hamster ovary (CHO) cells in contact with diluted cement extracts. The results revealed that the calcium phosphate cement used was cytotoxic and that the material’s cytotoxicity decreased the longer the cement was immersed in SBF. r 2002 Elsevier Science Ltd. All rights reserved.

Colour development of red perovskite pigment Y(Al, Cr)O3 in various ceramic applications

Abstract Ceramic pigments based on the perovskite structure develop a promising red hue and furthermore present no environmental or health problems. Pigment colouring efficiency was tested in different ceramic applications, both in the body and in glazes. Final products, with variations in both maximum firing temperature and soaking time, were characterised by colorimetry. The investigation focused on the factors and mechanism influencing perovskite dissolution by calculating phase compositions of different ceramic matrices and observing pigment microstructure. Pigment powders were also characterised by structural analysis and spectroscopy. Pigment dissolution was only slightly affected by the firing cycle, mostly being governed by the amount and chemical composition of the liquid phase. In particular, the larger the content of chemically aggressive components such as calcium, magnesium, zinc and lead oxides, the stronger and faster the pigment dissolution.

Um método simples de caracterização de argilominerais por difração de raios X

The X-ray diffraction technique has been widely used for the determination of crystalline phases in ceramic materials. The large content and high degree of orientation of quartz in clays pose a problem to the identification and characterization of the remaining phases. A simple and reliable method for the determination of clay minerals in clay materials, based on the sedimentation principle, is presented.

Bonelike Apatite Coating on Ti6A4V: Novel Nucleation Process Using Sodium Silicate Solution

Despite the well known biocompatibility and bioactivity of synthetic hydroxyapatite (HA), its use, as structural biomaterial has been limited because of intrinsic low mechanical properties. In order to avoid this problem, metallic implants are commonly coated with a thin HA layers. Among the various techniques used to produce coatings on metals, the biomimetic process has gained increasing attention in the last years. In this work, a metallic substrate (Ti6A14V) was coated using a variation of the traditional biomimetic method. The HA coatings were characterised by diffused reflectance spectroscopy (DRIFT) and scanning electron microscopy (SEM).

Biomimetic Method for Obtaining Hydroxyapatite

Coating of bioinerts or biotolerable materials with a bioactive layer, generally composed of hydroxyapatite (HA), has been currently used when one wishes to combine bioactivity and material properties. Coating methods include: plasma and flame spray, sputtering, electrophoresis and electrolysis. Except the electrolytic one, all other methods involve high working temperatures. Therefore, the physical and chemical characteristics of hydroxyapatite can be affected, with possible consequences on the behavior of the implanted material. A recently proposed method named biomimetic, can be employed to coat several types of substrates through precipitation of a hydroxyapatite layer. This approach imitates the biological natural conditions of hydroxyapatite formation, through control of temperature, pH and concentration of ionic species. In this work, barium titanate substracts were coated with hydroxyapatite and characterized by X-ray diffraction, infrared spectroscopy and scanning electron microscopy.

Comparative Evaluation of the Performance of Commercial Inks Used in Digital Decoration of Ceramic Tiles

The decoration technique of inkjet digital printing, because of its numerous advantages, has revolutionized the ceramic tile industry in recent years. Because of the peculiarities of this technique, there is no methodology to thoroughly evaluate the performance of commercial inks, in order to assist the industry in the selection of the inks. Thus, ceramic tile producers cannot predict the ink yield, the image definition, or the color gamut provided by the inks and inks from different manufacturers may differ significantly in these aspects. This work proposes a methodology for comparative evaluation of the performance of industrial inks for digital printing, based on the colorimetric evaluation of the dots produced by the inks and their spreading behavior on the surface of ceramic substrates. The results revealed important differences in the performance of commercial inks, confirming the need of a methodology to evaluate the inks.

Influência da distribuição granulométrica de argilas para via seca sobre o rendimento de moagem em moinho de martelos

A method to evaluate the hardness and milling yield of raw materials to dry route ceramic tiles industry was the goal of this work. Evaluation of the potential of a clayish raw material to dry route ceramic tiles industry does not cover characteristics such as hardness and milling yield, but these characteristics also affect, besides durability and performance of hammer and pendular industrial mills, the productive process. Six industrial samples were characterized to grain size distribution before and after being milled in a laboratorial hammer mill, under two initial size distributions. The evaluations considered the changes in distribution coefficient modulus n and in the fractions smaller than sieve 45 (355 µm). Proposed methodology proved to be useful to characterize raw materials according to its hardness and milling yield.

Production Speed and its Influence on Hue Variation on Tiles Decoration Based on Silicon Cylinder Technique Laser Engraving Method

On the ceramic tile production there are plenty of different possible origins inside the process that can lead to hue variation. Many tile producers use to increase the speed of production and the machinery industry follow this tendency to please their costumers; and so this scenario creates a need of a study on the influence of the speed production on hue variation. In this work this influence was verified using the silicon laser engraving method, one of the most methods worldwide used.

Searching for the Causes for the Differences in Performance of Commercial Inks Used in Digital Decoration of Ceramic Tiles

The inkjet digital printing has revolutionized the ceramic tile sector in recent years. In a previous work, the colorimetric behavior of commercial inks and their spreading behavior on the ceramic substrate were evaluated. The inks present significant differences in theses aspects, which, in practice, result in differences in the provided color gamut, the resolution of the printed images and their yield. This work aimed to identify the causes of the differences observed in the performances of some of the studied inks. It was found that inks from different manufacturers supposed to provide the same color, contained different pigments, which explain their colorimetric differences. It was also found that the viscosity of the inks varies considerably, which probably is partially responsible for the observed variation of the spreading ratio.