الفهرس 
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Abstract
Glasses in tellurate, borate and mixed former borotellurate systems have been prepared and characterized from the view point of their biological activity. Comprehensive structural techniques, including X-ray diffraction (XRD), high resolution scanning electron microscopy (SEM) equipped with an energy dispersive X-ray analyzer (EDX) and Fourier transform infrared (FTIR) spectroscopy were used to provide experimental evidences of the effect of both short and long range order on bioactivity of the studied glass. The effect of glass composition, mixing two different glass formers, thermal treatment and fluorine substitution on the properties of crystallized biophases including solubility, crystallinity, chemical composition, crystal size and their morphologies have been studied.
The concentration of network former (TeO2) was found to have an effective influence on the crystallization of the apatite, even if it changed with a limited value (3 mol%). Depending on the content of TeO2, one of the studied glasses is highly crystallized to homogenous tellurate and phosphate phases. This is limited to composition with 50 mol% TeO2. whereas, other glass with lower TeO2 concentration (47 mol% TeO2) showed a great difference, since only inhomogeneous distribution of few crystals in the network of the sample is observed.
It was concluded that, two effective parameters influence the solubility of crystalline tellurate phases and formation of HA bioactive layer under physiological conditions. These parameters are: crystallinity of biophases and the addition of (CaF2) to the modified glass network. Presence of F- ions can substitute for atoms present in the apatite structure to make the apatite chemically similar to natural bone mineral. In fact, the properties of hydroxyapatite (HA) including bioactivity, biocompatibility, and solubility can be tailored by modifying its composition through anionic substitution. In considering anionic substitute, F- is quantitavely one of the most important ions associated with biological apatite. This is because, enamel, dentin and bone contain specific portion of F-. Addition of 5 mol% CaF2 at expense of CaO inhibited the crystallization of biophases in both tellurate and borate glasses. An opposite behavior was found in the mixed former borotellurate glass, since crystallization process could be activated by the presence of CaF2. The obtained crystalline phases are assigned to CaF2, NaF and Ca-fluoroborate which may play a limited role in bioactivity. Further enhancement in crystallinity could be achieved in both single and mixed former glasses by the effect of thermal treatment processes. Therefore, specific heat treatment process was applied to the glass to activate the separation of extra bioactive phases which are finally crystallized in form of fluoroapatite phase. The latter is the most bioactive phase and has a good ability to react with simulated body fluid (SBF) to yield fluorohydroxyapatite (mineral phase of bone). Moreover, different crystallized phases containing Ca and P with appropriate Ca/P molar ratio are reconstructed by the effect of thermal treatment processes.
In addition, the effect of soaking time of glass samples containing apatite in simulated body fluid (SBF) on the final phase has been studied. The results indicated that, soaking for appropriate time resulted in transformation of the composition of the crystalline apatite and fluoroapatite into mixture from hydroxyfluoroapatite and hydroxyapatite phases. Assessments of bioactivity through the in vitro test lend support that the fluoridated glasses can be recommended as biomaterials valuable in branches of biomedical applications such as bone repair or bone substitution. This was supported by in vitro test which carried out on samples that contained crystalline apatite phases, since their chemical composition and crystalline structure are evidenced to closely resemble that of bone materials. However, the results indicated that the Ca/P ratio after the reaction with SBF agrees to great extend with the corresponding ratio in natural bone. Moreover, the concentration of the HA in some of the treated glasses was found to exceed 95 % of the standard HA. In addition the high quality HA showed angular position of XRD similar to induced by human terabecular bone.
Then the high quantity and quality of the HA in the prepared tellurate and borotellurate glasses can recommend them as important (new) raw materials that can be used as implant materials responsible for the repair of bone defects.