Burcu Oktay

Polydimethylsiloxane (PDMS)-based antibacterial organic–inorganic hybrid coatings

UV-curable antibacterial organic–inorganic hybrid coatings were prepared by sol–gel method. Triethoxysilane-terminated poly(dimethylsiloxane) (TESi-PDMS) as a new coupling agent to improve the compatibility between organic and inorganic phases was synthesized. PDMS-based urethane methacrylate oligomer was obtained by reacting isophorone diisocyanate with hydroxyethyl methacrylate and hydroxyl-terminated PDMS. The formulations were applied onto polycarbonate panels and then cured by UV radiation. Physical properties of UV-cured free films such as gel content, stress–strain, and conversion of acrylate double bond were examined. In addition, the antibacterial effects of the coatings were investigated. Nanosilver-containing formulations exhibited high antibacterial effect against Escherichia coli and Staphylococcus aureus. Thermogravimetric analysis indicated that thermal stability of the hybrids was significantly higher than the organic polymer. Contact angle measurement showed that addition of silane precursor increased the contact angle from 95° to 110°.

Chitosan-co-Hyaluronic acid porous cryogels and their application in tissue engineering

In this work, the usability of chitosan-co-hyaluronic acid cryogels as a tissue-engineering scaffold was investigated. Chitosan-co-hyaluronic acid cryogels were synthesized at subzero temperature. Cryogels which were composed of various compositions of chitosan and hyaluronic acid (0, 10, 20, 30 and 50wt% hyaluronic acid) was prepared. Morphological studies showed that the macroporous cryogels have been developed with 90-95% porosity. Particularly, the mechanical and biomaterial property of pure chitosan was improved by making copolymer with hyaluronic acid in different concentration. The MTT cell viability results demonstrated that the cryogels have no significant cytotoxicity effect on 3T3 fibroblast and SAOS-2 cells.

Immobilization of α-amylase onto poly(glycidyl methacrylate) grafted electrospun fibers by ATRP

In this study, novel α-amylase immobilized poly(vinyl alcohol) (PVA) nanofibers were prepared. The PVA nanofiber surfaces were functionalized with 2-bromoisobutyryl bromide (BiBBr) and followed by surface initiated atom transfer radical polymerization (SI-ATRP) of glycidyl methacrylate (GMA). The morphology of the poly(glycidyl methacrylate) (PGMA) grafted PVA nanofibers was characterized by scanning electron microscopy (SEM). Also PGMA brushes were confirmed by X-ray photo electron microscopy (XPS). α-Amylase was immobilized in a one step process onto the PGMA grafted PVA nanofiber. The characteristic properties of the immobilized and free enzymes were examined. The thermal stability of the enzyme was improved and showed maximum activity at 37 °C by immobilization. pH values of the maximum activity of the free and immobilized enzymes were also found at 6.0 and 6.5, respectively. Free enzyme lost its activity completely within 15 days. The immobilized enzyme lost only 23.8% of its activity within 30 days.

Dual-crosslinked thiol-ene/sol gel hybrid electrospun nanowires: preparation and characterization

In this report, we describe the preparation and characterization of cross-linked electrospun membranes by using a reactive electrospinning. A novel methacrylate functional poly(vinyl alcohol) (M-PVA) was synthesized by reacting PVA and isocyanatoethyl methacrylate (2-ICEMA). The crosslinked membranes were achieved in a simple process at a single step using thiol-ene reaction between M-PVA and 3-mercaptopropyl trimethoxysilane (MPTMS) during the electrospinning process. In order to improve theirs the stability, the crosslinked membranes were also thermally treated. The morphology was characterized by scanning electron microscopy (SEM). The structure of M-PVA was characterized by attenuated total reflectance FT-IR. Morphological investigations show that the resulting membranes have nanowires morphology. The thermal analysis of the electrospun membranes was also investigated. Thermal stability of the membranes was improved with the incorporation of the sol gel precursor. The described method provides novel route for organic–inorganic hybrid membranes.

Fabrication of nanofiber mats from electrospinning of functionalized polymers

Electrospinning technique enabled us to prepare nanofibers from synthetic and natural polymers. In this study, it was aimed to fabricate electrospun poly(vinyl alcohol) (PVA) based nanofibers by reactive electrospinning process. To improve endurance of fiber toward to many solvents, PVA was functionalized with photo-crosslinkable groups before spinning. Afterward PVA was crosslinked by UV radiation during electrospinning process. The nanofiber mats were characterized by scanning electron microscopy (SEM). The results showed that homogenous, uniform and crosslinked PVA nanofibers in diameters of about 200 nm were obtained. Thermal stability of the nanofiber mat was investigated with thermal gravimetric analysis (TGA). Also the potential use of this nanofiber mats for tissue engineering was examined. Osteosarcoma (Saos) cells were cultured on the nanofiber mats.

Zwitterionic phosphorylcholine grafted chitosan nanofiber: Preparation, characterization and in-vitro cell adhesion behavior

In this study, zwitterionic phosphorylcholine grafted electrospun chitosan fiber was accomplished in three steps: (1) Azide groups on the chitosan were regioselectively replaced with hydroxyl side group and then the product was electrospun. (2) Chitosan based macroinitiator was prepared using an azide-alkyne click reaction from azide-functionalized electrospun chitosan fiber. (3) Poly(2-methacryloyloxyethyl phosphorylcholine) (MPC) was grafted onto the electrospun chitosan fiber by atom transfer radical polymerization (ATRP) in order to enhance cellular viability and proliferation of 3T3, ECV and Saos. The structure of surface modified chitosan was characterized by Fourier transform infrared spectrometer (FT-IR) and 1H nuclear magnetic resonance (1H NMR). The surface morphology of the nanofibers was investigated by scanning electron microscope (SEM). In-vitro cellular attachment and spreading experiments of 3T3, ECV304 and Saos were performed on electrospun chitosan fibers in the presence and the absence of MPC grafting. Poly(MPC) grafted electrospun fiber showed an excellent performance due to phosphorylcholine groups mimicking the natural phospholipid.

Multi-Walled Carbon Nanotube Reinforced Polyimide Composites

Polyimides have a wide range of uses such as aerospace industry fuel cell applications, optic and electronic materials industry due to their outstanding thermal, mechanical and chemical properties. In this study, it was aimed to prepare composite polyimide films with amine tethered multi-walled-carbon nanotube (MWCNT). Firstly, to produce amine functional groups onto the surface of MWNCTs, MWCNTs were reacted with H 2 SO 4 /HNO 3 , thionyl chloride and ethylenediamine, respectively. Then polyamicacid solution was prepared from BTDA and ODA. The functionalized carbon nanotube was added to the PAA solutions with a certain amounts (1%, 3%, 4%, 5% and 6%wt.) and followed by stepwise thermal imidization. The thermal stability of the composite polyimide films were enhanced with addition of modified-carbon nanotube since covalent interaction between polyimide based matrix and modified-carbon nanotube happened by imidization reaction. In addition, the mechanical properties of the films were improved.