Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 7Citation - Scopus: 8Compositional, Microstructural and Mechanical Effects of Nacl Porogens in Brushite Cement Scaffolds(Elsevier, 2021) Şahin, Erdem; Çiftçioğlu, MuhsinModification of the setting process of brushite cements by varying the concentration of ions that alter calcium phosphate crystallization kinetics, is known to enable control on the monetite conversion extent and the accompanying microporosity. This is useful because monetite serves as a suitable matrix in macroporous scaffolds due to its higher phase stability and finer crystal morphology compared to its hydrous counterpart brushite. In this study the synergistic effect of NaCl and citric acid on the microstructural evolution of brushite cement was demonstrated and microporosity of macroporous monetite-rich cement blocks was minimized by a variable NaCl porogen size distribution approach. Initially, maximum packing ratio of various combinations of NaCl size groups in PEG were determined by their rheological analysis in a range between 57% and 69%. Statistical analysis revealed a positive correlation between the amounts of NaCl particles under 38 mu m and 212 mu m and the maximum packing ratio. Further broadening the size distributions of NaCl porogens with fine cement precursors was effective in increasing the solids packing ratio of cement blocks more than the maximum packing ratio for the porogens. This improvement in packing was accompanied by a reduction in microporosity despite the increase in micropore volume with ion induced monetite formation. The detrimental effect of the microporosity introduced to the structure during monetite formation was balanced for some size distributions and not so much for others, thereby resulting in a wide range of porosities and mechanical properties. Thus, the exponential dependence of mechanical properties on porosity and the mechanical properties of monetite-rich macroporous blocks at the theoretical zero-porosity were determined according to Rice's model. Zero-porosity extrapolations were much higher than those predicted for brushite cement, contrary to the common assumption that brushite is mechanically stronger than monetite.Article Citation - WoS: 13Citation - Scopus: 14Monetite Promoting Effect of Citric Acid on Brushite Cement Setting Kinetics(Maney Publishing, 2014) Şahin, Erdem; Çiftçioğlu, MuhsinBrushite forming calcium phosphate cements receive growing interest in hard tissue scaffold applications due to their high surface area and high bioresorbability. The finer microstructure of monetite, the dehydrated form of brushite, has attracted attention for bone tissue engineering applications. The reduction in brushite content of the b-tricalcium phosphate-monocalcium phosphate monohydrate cement system by selective inhibition of growth upon addition of citric acid to excess setting liquid was investigated. The relaxation period during cement setting was monitored by pH stat titration and free drift runs. Spectrometric analysis revealed that the change in solubility of calcium phosphates upon addition of citric acid caused the inhibition of brushite formation and promotion of monetite precipitation. Dissolution of monetite crystals was insensitive to citrate adsorption despite their lower surface area compared to brushite. Overall brushite/ monetite ratio decreased consistently with increasing citric acid concentration in the of 0?1-0?5M range.Article Citation - WoS: 6Citation - Scopus: 7Preparation and Characterization of Flexible Poly(vinyl Chloride) Foam Films(John Wiley and Sons Inc., 2012) Şahin, Erdem; Yaşar Mahlıçlı, Filiz; Yetgin, Senem; Balköse, DevrimIn this study, the effect of activator ZnO and heating time at 190°C on foaming, gelation, and dehydrochlorination of poly(vinyl chloride) (PVC) plastisol was investigated. For this purpose, a PVC plastisol was prepared by mixing PVC, dioctyl phthalate (DOP), azodicarbonamide (ADC), ZnO, and the heat stabilizers calcium stearate (CaSt 2) and zinc stearate(ZnSt 2). PVC plastisol films were heated for 3, 6, 12, and 24 min periods at 190°C to see the effect of heating time on the gelation and foaming processes of the PVC foam. The time of 12 min was determined to be optimum for the completion of gelation and foaming processes without thermal degradation of PVC. No foaming was observed under the same conditions for the samples without ZnO. ZnO had a significant catalytic effect on ADC decomposition, accelerating the foaming of the films. Average porosity measurement showed a consistent increase in porosity with heating time up to 76% and the average density decreased from 1.17 to 0.29 g/cm 3 on foaming. Tensile tests showed that the tensile strength and tensile strain both increased considerably up to 0.98 MPa and 207%, respectively, with heating time and the elastic modulus was seen to gradually decrease from 4.7 to 0.7 MPa with heating time. Films without ZnO had higher tensile strength since there were no pores. PVC thermomat tests showed that ZnO lowered the stability time of plastigel film with azodicarbonamide.