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The study consists of three parts. In the first part, synthesis and characterization of core-shell magnetic composite beads based on chitosan and containing two different magnetic nanoparticles were carried out. The beads were formed from CoFe 2 O 4 /chitosan and MnFe 2 O 4 /chitosan. TGA and SEM were used for the characterization of core-shell materials. In the second part, swelling experiments of magnetic beads were performed. In the third part, 5-Fluorouracil was encapsulated at different rates in two different magnetic materials, release experiments were carried out at pH 7.4, pH 6.8, and pH 1.2, and the model of drug release was determined. Korsmeyer-Peppas, Higuchi, first-order, and zero-order models were used for mathematical modeling. Both prepared systems were found to be suitable for controlled release for 5-Fluorouracil.

Electrospun polyvinyl alcohol (PVA)/Chitosan nanofibers were successfully prepared and were used as carriers for the first time in urease immobilization. Also, urease immobilized electrospun PVA/Chitosan nanofibers were applied for the removal of urea from artificial blood serum by recycled reactor. The nanofibers were optimized and synthesized by electrospinning technique according to the operational parameters. The morphology and structure of the nanofibers were characterized by scanning electron microscopy (SEM), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and thermogravimetric analysis (TGA). Urease was immobilized on the nanofibers by adsorption and crosslinking methods. According to immobilization results, nanofiber enhanced urease stability properties like thermal stability, pH stability, and reusability. Urease immobilized electrospun PVA/Chitosan nanofiber protected its activity by 85% after 10 uses and 45% after 20 uses. Urea removal rates of artificial blood serum were as follows: 100% at 1st cycle, 95% at 2nd, 3rd and 4th cycles; 85% at the 5th cycle; 76% at the 6th cycle, and 65% at the last three cycles.

Polyvinyl alcohol (PVA)/Zn 2+ electrospun nanofibers that were a kind of polymer/ionic metal composite was successfully embedded in the hybrid fibers for the first time in the literature, due to chemical interactions between PVA and Zn 2+ . Also, the nanofibers were used as carriers for the first time in enzyme immobilization. The nanofibers were optimized and synthesized by electrospinning technique according to the operational parameters like as PVA concentration (%), Zn 2+ concentration (%), voltage (kV), needle tip-collector distance (cm) and injection speed (ml/h). The morphology and structure of the nanofibers were characterized by SEM, XRD, ATR-FTIR and TGA. Lipase was immobilized on the nanofibers by adsorption and crosslinking methods. According to immobilization results, nanofiber enhanced enzyme stability properties like as thermal stability, pH stability and reusability. Lipase immobilized nanofiber protected 90% of its activity after 14 reuses., (Copyright © 2019. Published by Elsevier B.V.)

In this study, lipase was successfully immobilized on polyvinyl alcohol/alginate and polyethylene oxide/alginate nanofibers that were prepared by electrospinning. Results showed that nanofibers (especially polyvinyl alcohol/alginate) enhanced the stability properties of lipase. When the free lipase lost its all activity after 40-60min at high temperatures, both lipase immobilized nanofibers kept almost 65-70% activity at the same time. The lipase immobilized poly vinyl alcohol/alginate and polyethylene oxide/alginate nanofibers protected approximately all of their activities until pH 9. Lipase immobilized polyvinyl alcohol/alginate and polyethylene oxide/alginate nanofibers maintained 60% of their activities after 14 and 7 reuses, respectively. The morphology of nanofibers was characterized by Scanning Electron Microscope, Fourier Transform Infrared Spectroscopy and Thermal Gravimetric Analyzer. As a result, this nanofiber production method, electrospinning, is simple, versatile and economical for preparing appropriate carrier to immobilize the enzymes., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The aim of the present study is to synthesize TiO2 beads for urease immobilization. Two different strategies were used to immobilize the urease on TiO2 beads. In the first method (A), urease enzyme was immobilized onto TiO2 beads by adsorption and then crosslinking. In the second method (B), TiO2 beads were coated with chitosan-urease mixture. To determine optimum conditions of immobilization, different parameters were investigated. The parameters of optimization were initial enzyme concentration (0.5; 1; 1.5; 2mg/ml), alginate concentration (1; 2; 3%), glutaraldehyde concentration (1; 2; 3% v/v) and chitosan concentration (2; 3; 4 mg/ml). The optimum enzyme concentrations were determined as 1.5mg/ml for A and 1.0mg/ml for B. The other optimum conditions were found 2.0% (w/v) for alginate concentration (both A and B); 3.0mg/ml for chitosan concentration (B) and 2.0% (v/v) for glutaraldehyde concentration (A). The optimum temperature (20-60°C), optimum pH (3.0-10.0), kinetic parameters, thermal stability (4-70°C), pH stability (4.0-9.0), operational stability (0-230 min) and reusability (20 times) were investigated for characterization. The optimum temperatures were 30°C (A), 40°C (B) and 35°C (soluble). The temperature profiles of the immobilized ureases were spread over a large area. The optimum pH values for the soluble urease and immobilized urease prepared by using methods (A) and (B) were found to be 7.5, 7.0, 7.0, respectively. The thermal stabilities of immobilized enzyme sets were studied and they maintained 50% activity at 65°C. However, at this temperature free urease protected only 15% activity., (Copyright © 2014 Elsevier B.V. All rights reserved.)