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Natural and Synthetic Silica Incorporated Chitosan Composite Scaffolds for Bone Tissue Engineering Applications
(İzmir Institute of Technology, 2016) Tamburacı, Sedef; Tıhmınlıoğlu, Funda; Tıhmınlıoğlu, Funda; Havıtçıoğlu, Hasan
Recently bone tissue engineering studies have focused on the development of 3D scaffolds that can organize the tissue regeneration in natural way with appropriate porosity and reinforced the structure. Natural polymer-based composites have been focused with more attention than synthetic polymer composites for bone tissue engineering applications because of their biocompatibility and biodegradability. In this work, the goal was to combine the useful biomaterial properties of both chitosan and silica to design biocomposite organic/inorganic biomaterials for bone tissue engineering applications. The composite scaffolds were fabricated by freeze drying method bu using two different silicas; natural silica; Diatomite and synthetic silica, octa (tetramethylammonium) polyhedral oligomeric silsesquioxanes (OctaTMA-POSS). The effects of silica type and loading on the mechanical, morphological, chemical, surface properties, wettability and biocompatibility of composite scaffolds were investigated and characterized by using SEM, AFM, contact angle analysis, swelling study, protein adsorption assay, biodegradation and biomineralization tests. WST-1 cytotoxicity, cell proliferation with rezasurin and alkaline phosphatase activity assays were performed to determine biological activity of the composite scaffolds. In vitro biomineralization on scaffolds was determined by Von Kossa and Alizarin red staining. POSS and diatomite incorporation increased the surface roughness. Chitosansilica composites exhibited 82-90% porosity. Wet chitosan-silica composite scaffolds exhibited higher compression moduli compared to pure chitosan scaffold in 67.3- 81.4kPa and 78.1 to 107.6kPa range respectively. Average pore size range of chitosandiatomite and chitosan-POSS composite scaffolds was obtained as 15-180μm and 220- 300μm, respectively. Results indicated that chitosan-silica composites did not show any cytotoxic effect on 3T3, MG-63 and Saos-2 cell lines. Chitosan-silica composites were found to be favorable for osteoblast proliferation. Diatomite and POSS incorporation showed promising effects with enhancing ALP activity on hFob cells. Therefore, these composite scaffolds could be used for bone tissue engineering applications.
Use of Silica-Based Sorbents for Separation and Preconcentration of V (iv) and V (v)
(Izmir Institute of Technology, 2010) Erdem, Aslı; Eroğlu, Ahmet Emin
Vanadium is one of the essential trace elements for plants and animals. While it is beneficial for normal cell growth, it becomes toxic at high concentrations. In the present study, silica-based sorbents were prepared and used for sorption/speciation of vanadium from waters prior to inductively coupled plasma mass spectrometric (ICP-MS) determination. Among the sorbents developed, 3-APTES-modified silica, has been shown to be an efficient material for the speciation of vanadium. Solution pH of 2.0 and 3.0 can be used for the respective sorption of V(V) and the total vanadium, namely, V(IV) and V(V). The concentration of V(IV) can then be calculated from the difference. Desorption from the sorbent was realized with 0.5 M thiourea prepared in 0.2 M HCl. The validity of the method was checked via spike recovery experiments with four different types of water; namely, ultra pure, bottled drinking, tap, and sea water. The method works efficiently (>85% recovery) for ultra pure, bottled drinking, and tap water; and a relatively high recovery (>70%) was obtained even for sea water which has a very heavy matrix. For trypsin-immobilized silica, the sorption percentage towards V(IV) and V(V) is almost constant (>90%) within the pH range 4.0-8.0 which demonstrates the possibility of using this sorbent for the sorption of both vanadium species. The sorption of vanadate ion was investigated both from a kinetic perspective and also in terms of Freundlich, Dubinin-Radushkevich and Langmuir isotherm models; and Langmuir model was found to describe the sorption better for both of the functionalized silicas.
Dna Adsorption on Silica, Alumina and Hydroxyapatite and Imaging of Dna by Atomic Force Microscopy
(Izmir Institute of Technology, 2013) Yetgin, Senem; Balköse, Devrim; Balköse, Devrim
The scope of the study is to investigate calf thymus DNA adsorption process on solid powders such as silica, alumina and hydroxyapatite (HAP) to improve DNA solid phase extraction efficiency and to visiulize DNA adsorption by atomic force microscopy (AFM). The equilibrium and kinetics of the DNA adsorption were investigated in batch adsorption on a commercial silica gel and a synthesized silica aerogel, commercial alumina and HAP powders from aqueous DNA solution. Commercial DNA extraction kit adsorbents were also characterized and used for adsorption. Adsorbed DNA was imaged in ambient air on flat surfaces of mica, silica and alumina wafers and HAP particles coated glass surfaces and a HAP pellet surface by AFM. Effects of ambient air, nitrogen flow and freeze drying methods on DNA morphology on the releted surfaces were also investigated. Adsorption of DNA on silica, alumina and HAP increased with the decrease of pH from 9.0 to 2.0. Enhancements of the adsorption capacities of adsorbents were obtained with the addition of MgCl2. It was found that the Van der Waals and the hydrogen bonds rather than the surface charge were the cause of the adsorption. The adsorption isotherms of DNA on silica, alumina and HAP were fitted to Langmuir model in pH range 2-9. The adsorption kinetics obeyed pseudo second order model. The sharpest image of DNA by AFM was obtained by freeze drying method on alumina surface. Dispersed DNA in water was adsorbed on the surfaces not as single molecules but as supercoils consisting of many molecules.

Phd Degree / Doktora

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