Inspection of copper and stronsium added bioactive glass samples' crystallization kinetic

In medical applications, materials which require specific property and functions are needed and these materials are named as biomaterials. In order to use biomaterials in an effective way they should have consistent mechanical properties depending on where they are used and should prevent any toxic/cancer effects or reactions to occur (bioavailability), apart from these they should resist against corrosion in body fluid (bioinert). Biomaterials are grouped as metals, ceramics, polymers and composite materials. Ceramics which used for the repair, restructuring and replacing of damaged or lost functioned parts are called "bioceramics". Bioceramics may be prepared as polycrystalline ceramics (alumina and hydroxyapatite), bioactive glass, bioactive glass ceramics and bioactive composites (polietilenhidroksiapatit) form. The bioactive glasses are silicate glasses made of sodium, calcium and phosphate. The bioactive glass ceramics as multi crystallized biomaterials, designed to be used for medical purposes which react with tissues and / or bones for forming strong bonds with privatized end usages, are produced with controlled crystallization of appropriate glasses. Strength in the glass structure is removed by controlled crystallization. One of the disadvantages of bioactive glass is amorphous structure. Crystal structure is the most important feature for improving mechanical properties. Mechanical weakness originating from two way web and broken toughness can be developed by this way. Aim of glass-ceramic production is to determine the suitable composition and process, afterwards to perform stable glass and converting this glass to microcrystalline ceramic which has better properties than original form. Improving mechanical strength is the most important purpose. Micro structure with fine particle generates for developing the mechanical strength. Most important parameters of constituting of glass ceramic are thermal process variables. Heating rate, time, temperature effect to average crystal size, crystal volume fraction, glass phase and type of crystal. Because of this reason determining the thermal operation process is the most important stage for production of glass-ceramic. DTA is very common and fast way for examining the crystallization of glass. The base of DTA is recording the differences of temperature with thermal inert material and sample during the controlly heating and colding process. Various ions are added to bioactive glass for improving bone-activated features. At this study strontium and copper ions' crystallization kinetic was examined and bioactivity was determined because of increasing bone-cell constituting and having similar weight and ion radius like calcium in order to involve in glass composition. In this study, by using DTA (Differential Thermal Analysis) method bioactive glass samples in weight percentages of 45% SiO2, 24.5% Na2O, 6% P2O5, 2% SrO ve 22.5% CaO ile 45% SiO2, 24.5% Na2O, 6% P2O5, 0.5% CuO were examined by isothermal and non-isothermal methods. At isothermal method, glass samples are heated fast and waited above the glass transition temperature. Crystallization occurs at stable temperature. At non-isothermal method glass samples are heated at stable heating rate, nucleation and crystallization occur during the thermal analyse. Strontium and copper ions effect to activation energy and crystallization mechanism were determined with isothermal and non-isothermal method. Optimum nucleation temperature and time of bioactive glass samples were determined with DTA method. Biaoctive glass production happened with thermal process that occured at optimum nucleation time and temperature. Kissinger, Matusita-Sakka and Ozawa methods are used at non-isothermal method. For this reason stronsitum and copper added bioactive glass samples were grinded and eliminated. End of this process 1-1.4 mm sized particles are obtained. Almost 4 mg glass samples were weighed and DTA analysis is done with 10, 15, 20, 25, 30 K/min heating rate for strontium added bioactive glass and 10, 15, 20, 25, 30 K/min heating rate for copper added bioactive glass. Glass sample's crystallization activation energy and crystallization mechanism are determined with JMA at isothermal method. At this method, glass samples were heated to optimum nucleation temperature with 20 K/min heating rate and were waited at this temperature as nucleation time. The glass sample that nucleation process is completed, was heated with 20 k/min heating rate to between nucleation and crystallization peak temperature. Also thermal process was applied as 15, 30, 60 min. After that, temperaure was increased to crystallization temperature and the samples were removed from DTA. From Kissinger Matusita-Sakka and the Ozawa equations, the activation energy of bioactive glass samples and value of n were calculated with the aid of DTA results. For Strontium-added bioactive glass sample n value was around 2, whereas value for the copper-added bioactive glass sample was found around 3. According to the obtained values of n, volume crystallization was occurred for both of bioactive glasses, but two-dimensional crystal growth was performed in strontium-added bioactive glass whereas three-dimensional crystal growth occurred in copper-added bioactive glass. The activation energy of bioactive glass that strontium-added is calculated as 327.7 kJ/mol from Matusita-Sakka equaiton and 304. 1 kJ/mol from Kissenger equation. . The activation energy of bioactive glass that copper-added is calculated as 236.3.7 kJ/mol from Matusita-Sakka equation and 263.2 kJ/mol from Kissenger equation. The results that evaluated from the Matusita-Sakka ve Kissinger equations support each other. Nucleated feature of strontium-added bioactive glass is more than copper-added one. This situation shows that crystallization occur with lower energy so activation energy of bioactive glass that copper-added is lower than strontium-added bioactive glass. Avrami constant values that evaluated with isothermal and non-isothermal methods are close to each other and in the limits of experimental errors. This result shows that accuracy both of the methods. Optimum nucleation temperature, time and crystallization temperature were determined with result of these operations for strontium and copper added glasses. Base on optimum nucleation time, temperature and crystallization temperature at all the thermal processes for providing nucleation, crystal growing and heat-treat of glass. Heat-treatment is applied during the process for removing internal strength. At this study samples were waited at 673 K and 2 hours in the oven. Crystallization temperature is determined as over 10 K than the temperature that is defined from DTA for completing the crystallization. Strontium added bioactive glass samples were waited in muffle type oven at 833 K and 120 min for crystallization, at 1059 K and 30 min for growing the crystal. After that bioactive glass samples were allowed to cool. Same process is occured for copper added bioactive glass at 808 K and 150 min for crystallization, 991 K and 30 min for growing crystal. Also bioactive glass ceramic is produced with optimum thermal operations and its crystal structure is examined with XRD (X-Ray Diffraction) whereas micro structure is examined with scanning electron microscope (SEM). At the same time bioactivitiy properties are determined with examining of bioactive glass behaviour in the simulated body fluid. Strontium doped and copper doped bioactive glass-ceramic samples' XRD results that belong to before simulated body fluid. and after simulated body fluid as 1, 7, 14, 28 days were examined. Both of samples' crystalline structure included combeite phase. Combeite phase occured at bioactive ceramic because thermal process of bioactive glass. This result shows that addition of strontium and addition of copper don't change the crystalline structure of bioactive glass ceramic. Hydroxyapatite crystalline structure weren't determined at XRD results of strontium doped and copper doped bioactive glasses. It was concluded that peak to show the presence of hydroxyapatite layer, dissappeared in combeite peak. Bioactive glass ceramics microstructures were examined with SEM. Strontium doped and copper doped bioactive glass ceramic samples had crystalline structure before waiting simulated body fluid. After waiting 28 days in simulated body fluid, identified that their surfaces were covered by white, homogenous hysroxyapatite layer. This study clearly shows that: Bioactive glasses produced during the experiment are suitable for crystallaziation. These bioactive glasses have convenient properties to be used in tissue engineering because of their biaoctivity features, optimum Sr2+ and Cu2+ ion emiting.