الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 187 |  |  |
| | | from | 187 | | |
Abstract
The aim of this work is to study the structure and physical properties of some bioactive glasses. For this purpose, two types of glasses were prepared and investigated. One of the them has the formula 50 mol% SiO2 26 mol% Na2O21 mol% CaO3 mol% P2O5 while the other glass contains 1 mol% TiO2 over it<U+2019>s components [50 mol% SiO2 26 mol% Na2O 21 mol% CaO3 mol% P2O5]. Addition of a small concentration of TiO2 improves the biological response of the material to be become suitable in the field of biomedical applications. Xray and IR spectra were used to confirm the amorphous nature of the glass. The IR spectral analysis was used to characterize various functional groups such as the hydroxyl and phosphate groups. The surface modifications and microstructure of bioglass samples were examined using a scanning electron microscope (SEM). The SEM micrographs were used to distinguish the type and nature of the different precipitations on the surfaces of the glass specimens after soaking them in a simulated body fluid (SBF), which has an ion concentration similar to that of the human plasma. Glass solidified directly from the melt is known to have an amorphous nonsoluble phases (apatite) as a minor phase. Formation of this phase delays or inhibits the precipitation processes of hydroxyapatite layer (HA) on the surface of the glass during the reaction between the surface and body fluid (SBF). To overcome these problems, a technique of coating the surface of sample with an artificial crystalline soluble apatite was applied. But the coating process needs extremely high temperature to be fixed on the surface (greater than 1000 (R@(BC). The high temperature causes diffusion of the bioactive elements (Ca2+, P+5) from the layer to the bulk of the sample, leaving the surface as a poor bioactive. In this work we tried to overcome all these difficulties through treating the bioactive glass (base) thermally at a favorable temperature. Treating the glass thermally may cause separation of some phases in addition to nucleation and then crystallization. The separated phases can interact together at high temperature to yield a crystalline apatite phase precipitated on the surface. This phase well enhance the bioactivity of the material. Moreover, development of the precipitative process of hydroxyapatite (HA) is found to increase with addition of an activator agent such as (TiO2). The bioactivity of the studied material was enhanced by the effect of the different mechanisms, which are: 1. Prompt precipitation of Ca2+ and P5+ ions from body fluid (SBF). 2. Dissolution of wollastonite crystal, which increases the precipitated layer. 3. Addition of a small amount of an activation agent (1 mol% TiO2). The bioactivity and biocompatibility enhancement through formation of active layer of hydroxyapatite was discussed in terms of an electrostatic interaction model. Assessments of bioactivity lend support that this glass can be used as an implant (or a bone substitution material). It is evident from the results of SEM, Xray and IR spectroscopy that: 1 The solidified glass from the melt contains an amorphousapatite phase. When the sample soaked in the body fluid, this phase delays or inhibit the interaction between the glass and SBF. Consequently the glass in this case is considered as nonbioactive glass. 2 Treating the glass thermally at different temperatures at variable times, results in transforming the amorphous, nonsoluble (in SBF) phase into a crystalline apatitewollastonite one. The later can easily dissolve in SBF. As a result a hydroxyapatite like bone layer precipitated on the glass surfaces would be formed. The formation of this layer enhances the activity of the bioactive glass. 3 Ca2+andP5+inSBFaretheessentialcomponents of hydroxyapatite (HA) layer. Density and electrical conductivity measurements were studied. It is evident that neither the temperature nor heat treatment time dose affect the density of glass. The constancy of molar volume of both types of glass (with and without TiO2) indicates that it is not affected by the heat treatment. The structural changes that take place during heat treatment are due to the rearrangement of the ions without changing the overall packing of the structure. In the studied glasses, Na+ and Ca2+ ions are assumed to be the charge carriers. Because the mobility of Ca2+ ions is less than that of Na+ ,then they (Ca2+) block the passes of Na+ ions. The conductivity would then depend on the concentration and mobility of both Na+ and Ca2+ ions in the conductivity species. Similar trends are observed for the activation energy (E) of the electric conduction of these glasses free from TiO2. The electric conductivity of samples containing TiO2 differs from that of samples free from it. The dependence of activation energy of samples containing TiO2 on the heat treatment time is similar to that samples free from TiO2, except the samples which are treated at 560 (R@(BC. The differences in behaviour between glasses containing TiO2 and that free of it are certainly related to effects connected to TiO2 as a nucleating agent.