Poliüretan filmlerde yüzey pürüzlülüğü ve kristalinitenin protein adsorpsiyonuna etkilerinin incelenmesi

Accelerating developments for human health care necessitate need for biocompatible devices to be used inside the body and for outside applications. There has been an increasing trend to use biocompatible polymeric materials in biomedical field. Among biopolymers, polyurethanes are widely used in many fields such as prosthesis, implants and in controlled drug delivery systems due to their excellent chemical and mechanical properties. The most important factor in determining and developing a biomaterial is to examine the relationship between polymeric structures with blood proteins. Thus, a clear understanding of protein adsorption is crucial to design new biomaterials. It is known that protein structure, protein solution and surface properties are major components that determine adsorption kinetics. In this point of view, important surface properties such as crystallinity, hydrophilicity and roughness were investigated in the context of thisstudy using both experimental and computational approaches. In this study, six different polyurethane films were synthesized by using castor oil (CO), hexamethlyene diisocyanate (HDI) and 1,4-butandiol (BDO). Among these polyurethanes, poly(ethylene glycol) (PEG) was also used as polyol in the synthesis of three polyurethane samples. Polymers were synthesized at different CO/PEG weight ratios (50/50, 60/40, 70/30, 100/0) by bulk polymerization. In order to obtain chemically identical surfaces with different roughness, tetra hydrofuran (THF) or dimethylacetamide (DMAc) were used during the polymer sythesis for two PEG free samples. Structural characterization of films was carried by Fourier transform spectroscopy (FT-IR).Thermal and mechanical characterization were performed by thermal gravimetric analyses (TGA), differential scanning calorimeter (DSC) and dynamic mechanical analyses (DMA). Crystallinity of films was determined by x-ray diffraction (XRD), hydrophilicty of films was calculated by contact angle measurements and surface properties were analyzed by atomic force microscopy (AFM). Effect of each surface property on protein adsorption kinetics was investigated using Brownian dynamics simulations for albumin-polyurethane system. Brownian dynamics enabled the simulation of the coarse-grained polymer-protein system in three-dimension comparable with experimental findings. For this purpose, polymeric film was modeled as lattice surface with protein binding regions predetermined according to the experimental results on crystallinity. Furthermore, the polymeric film was modeled as a flat or rough surface, which actually depended on the solvent evaporation rate employed in the experiments. Bovine serum albumin proteins were described as uniform spheres interacting with the polymeric surface. Various protein concentrations were considered in order to reveal the effect of macromolecular crowding on protein adsorption rate. The model system represented quarter of one-micrometer square polymer film interacting with proteins at real molar levels, which provided an effective comparison with experimental observations. Considering the effect of surface roughness, hydrophilicity, crystallinity and protein adsorption results together, computational results indicated that the molecular crowding, i.e. high concentrations had the biggest impact on protein adsorption, then degree of surface crystallinity and finally roughness. Observation from simulations suggested the roughness had an implicit effect on protein adsorption by providing higher surface area compared to smooth surfaces. In other words, if high surface area revealed more crysttaline regions, more proteins adsorbed on the surface. In contrary, if high surface area revealed more amorphous regions, protein adsorption rate diminished.