Eda Ayse Aksoy

Synthesis and surface modification of polyurethanes with chitosan for antibacterial properties

Surface modification and providing antibacterial properties to the materials or devices are getting great attention especially in the last decades. In this study, polyurethane (PU) films were prepared by synthesizing them in medical purity from toluene diisocyanate and polypropylene ethylene glycol without using any other ingredients and then the film surfaces were modified by covalent immobilization of chitosan (CH) which has antibacterial activity. CH immobilized PU films (PU-CH) were found to be more hydrophilic than control PU films. Electron Spectroscopy for Chemical Analysis (ESCA) and Atomic Force Microscopy (AFM) analyses showed higher nitrogen contents and rougher surface topography for PU-CH compared to PU films. Modification with CH significantly increased antibacterial activity against Gram positive (Staphylococcus aureus) and Gram negative (Pseudomonas aeruginosa) bacteria. It was observed that the number of bacteria colonies were less about 10(2)-10(5) CFU/mL and number of attached viable bacteria decreased significantly after CH modification of PU films.

Plasma Protein Adsorption and Platelet Adhesion on Heparin-Immobilized Polyurethane Films

Polyurethane surfaces were modified by covalent immobilization of different molecular weight heparins (fractionated Mw ~3000 Da, and unfractionated Mw ~17,000—19,000 Da) and examined by ESCA, AFM, and contact angle goniometer. The effect of these different surface-immobilized heparins on blood protein adsorption and on platelet adhesion, were examined after incubating the samples with platelet-poor and platelet-rich plasma. Protein adsorption kinetics was studied by electrophoresis and the platelets adhered on the surfaces were examined by SEM after incubation. The two heparin types clearly showed different behavior with respect to protein adsorption, especially in the early stages of blood plasma interaction. After a 5-min incubation in plasma, low molecular weight heparin-immobilized polyurethanes (PU-LMWH) showed three times less protein adsorption compared to unfractionated heparin-immobilized polyurethanes (PU-UFH). The total amount of adhered protein became more similar as the incubation time was extended. The morphology of adhered platelets on material surfaces demonstrated differences: PU-UFH had clusters with some pseudopodia extensions, while PU-LMWH surfaces had round-shaped platelets with little clustering. For contact times >15 min, the amount of adsorbed proteins and adhered platelets on the heparinized PU surfaces decreased.

Silver nanoparticle containing silk fibroin bionanotextiles

Development of new generation bionanotextiles is an important growing field, and they have found applications as wound dressings, bandages, tissue scaffolds, etc. In this study, silver nanoparticle (AgNP) containing silk-based bionanotextiles were fabricated by electrospinning, and processing parameters were optimized and discussed in detail. AgNPs were in situ synthesized within fibroin nanofibers by UV reduction of silver ions to metallic silver. The influence of post-treatments via methanol treatment and glutaraldehyde (GA) vapor exhibited changes in the secondary structure of silk. Methanol treatment increased the tensile properties of fibers due to supported crystalline silk structure, while GA vapor promoted amorphous secondary structure. AgNP containing silk fibroin bionanotextiles had strong antibacterial activity against gram-positive Staphylococcus aureus and gram-negative Pseudomonas aeruginosa.

Immobilization of heparin on chitosan-grafted polyurethane films to enhance anti-adhesive and antibacterial properties

Infections caused by bacteria adhering to implant surfaces are one of the main reasons for the failure of the implants. In this study, polyurethane (PU), which is the most commonly used polymer in the production of medical devices, was synthesized and surfaces of polyurethane films were modified by chitosan (CH) grafting and heparin (Hep) immobilization in order to enhance anti-adhesiveness and antibacterial properties. Functional groups present on the surface, topographical shapes, and free energies of the polyurethane films were determined. Pristine polyurethane, chitosan-grafted polyurethane (PU–CH), and heparin immobilized polyurethane (PU–CH–Hep) films demonstrated high anti-adhesive efficacy against bacteria in the given order, where PU–CH–Hep was the most effective one. When PU–CH–Hep samples were incubated with different bacteria, complete death was observed for Pseudomonas aeruginosa (Gram negative), Staphylococcus aureus (Gram positive), and Staphylococcus epidermidis (Gram positive). Some living Escherichia coli (Gram negative) were observed after 24 h of incubation. Pristine and modified polyurethane samples demonstrated no adverse effect on proliferation of L929 fibroblast cells and were found to be biocompatible according to MTT cytotoxicity tests.