Yumuşak kısım yapısı ve sert kısım miktarının poliüretanürelerin yüzey ve yığın özellikleri üzerindeki etkisi

Due to their interesting combination of bulk and surface properties segmented thermoplastic polyurethanes (TPU), polyureas and polyurethaneureas (TPUU) find wide range of applications in many diverse fields. One of the emerging applications of TPUUs include their usage as biomaterials in blood contacting applications. This is mainly due to the possibility of designing and synthesizing TPUUs with controlled bulk and surface properties that possess very good blood and tissue compatibility. [1] The main goals of this study were the investigation of the influence of; (i) soft segment (SS) structure, (ii) SS molecular weight and (iii) hard segment (HS) content on the morphology and bulk and surface properties of TPUUs. In addition, another aim was to investigate the relationship between the surface energies of copolymers and their resistance to biofilm formation. A large number of segmented thermoplastic poly(urethaneurea)s (TPUU), polyurethanes (TPU) and polyureas (PU) based on five different SS were synthesized by using the conventional two step "prepolymer" polymerization method (or in one step if the polymer was non-chain extended) and characterized. Bis(4-isocyanatocyclohexyl)methane (HMDI) was used as the diisocyanate and 2-methyl-1,5-diaminopentane (MDAP) or 1,4 butanediol (BD) was used as the chain extender. Five different SS which were used in this study included poly(ethylene oxide) glycol (PEO), poly(propylene oxide) glycol (PPO), poly(tetramethylene oxide) glycol (PTMO), aminopropyl and hydroxyhexyl terminated polydimethylsiloxane (PDMS) and a hydroxy terminated polyfluoroether (PFE) oligomer (Fluorolink E10-H®). HS contents of the copolymers were generally kept constant at 20 and 30% by weight with a few exception. To investigate the influence of the molecular weight, SS oligomers with two different molecular weights of 1,000 and 2,000 g/mol were used during the synthesis. The bulk and surface properties of all polymers were characterized by using a large number of techniques, which included; ATR-FTIR (Attenuated Total Reflection Fourier Transform Infrared), DSC (Differential Scanning Calorimetry), SAXS (Small Angle X-ray Scattering) and stress strain analysis, AFM (Atomic Force Microscopy), XPS (X-ray Photoelectron Spectroscopy) and static water contact angle measurements. Selected copolymers with different surface energies were also tested for biofilm formation. Results obtained indicated extensive biofilm formation on all samples regardless of their surface properties. Characterization results showed that polyether based copolymers, especially those with PEO SS, displayed poor microphase separation when compared with PDMS and PFE based copolymers. This is expected since the polyethers used in this study have higher solubility parameters and ether groups can form hydrogen bonding with urethane and urea groups, which is not possible in case of PDMS and PFE. Surface characterization by contact angle measurements showed dramatic differences depending on the SS structure and molecular weight. As indicated by XPS studies, in general the soft segments tend to migrate to the polymer surface and affect the hydrophobicity and hydrophilicity of the copolymer depending on their solubility parameters. The extent of biofilm formation was not affected by the surface energy differences within the copolymers. Many alternatives for the bacterium sticking mechanism on surfaces have been proposed in the literature. [2] Some studies suggest that bacterium tend to stick on hydrophilic surfaces[3], while other studies suggest that bacterium tend to stick on hydrophobic surfaces [2]. It should also be noted that the sticking mechanism of every strain of bacterium is different [4], which makes this concept even more challenging to explain. Therefore our study is a contribution to the literature on this topic and suggests that the sticking mechanism of Staphylococcus aureus 700698 strain of bacterium is not affected by the surface of the polymer being hydrophilic or hydrophobic.