| As a membrane material used in plasmapheresis, polysulfone (PSF) has advantages in aspects of biocompatibility, chemo stability, mechanical strength, which make it popular in the field of biomedical materials. But the hydrophobic of PSF would cause serious fouling during the process of plasmapheresis, resulting in the irreversible adsorption of proteins on membranes, and reducing their permeability at least 30%. Once the conformation of the absorbed proteins changed, severe injuries would take place, such as blood coagulation and activation of immunosystem. In order to prevent the fouling of proteins, most efforts of current researches are focused on hydrophilic modification of membrane surfaces. Through the hydrophilic modification, researchers expect to obtain biocompatible surfaces and maintain the intrinsic bulk properties of the material. Among these researches, physisorption and covalent attachment of poly(ethylene glycol) on surface of various materials has long been studied widely and there're a lot of papers and patents being published in the past three decades. In 1990's, it was found that the capability of mono-layered PEG brush to resist protein fouling was much greater than that of multi-layered PEG. In this paper, spin coated PSF films were used as the material to be surface-modified by grafting brush-like PEG with 4-azidobenzoic acid photocoupler. Achievement of UV irradiation grafting of MPEG on polysulfone films may provide the foundation for further advancement in tethering brush-like PEG on ultrafiltration Psf membrane.By using potassium naphthalene as catalyst, MPEG-OTs was synthesized from MPEG and 4- tolylsulfonyl chloride. According to Gabriel's method, MPEG-NH2was synthesized from MPEG-OTs and potassium phthalimide, and purified by means of recrystallization in dichloromethane//ether mixture at least three times until crystal pure product obtained. And analyses of Aldrich's MPEGs used in this study show that these polymers contain only undetectable amounts of bifunctional PEG.On the other hand, the glass coverslips are spin-coated with a 3%(w:w) solution of polysulfone in 1,2-dichlorobenzene( 1 Os at 1000 rpm and consecutively for 50s at 3000 rpm). Then we measured the relative spectral energy distribution of self-designed 365nm UV-radiation apparatus, the radiation intensity distribution with light filter and temperature.4-azidobenzoic acid (AzBA) which was prepared by the addition of sodium azide to the acidic diazonium chloride from 4-aminobenzoic acid was purified in ethanol water solution (ethanol: H2O= 6(v): 4(v)), and got crystal pure. Furthermore, AzBA was grafted to the polysulfone films under the following conditions: in the darkroom, adjust the concentration of AzBA to 25.8g/l, with the amount was lml; keep Psf films wet during UV irradiation for lOmin. By the results of XPS and AFM analysis, AzBA has been grafted on polysulfone successfully. Then used l,3-(3-dimethylaminopropyl)ethylcarbodiimide(EDC) as photocoupler, MPEG-NH2 through its amino group reacted with the -COOH of AzBA forming amide bond and grafted on.From water contact angle and protein absorption measurements, there was a improvement of hydrophilicity of the PSF films grafted with MPEG . Efficiency of reacting of AzBA and MPEG-NH2 by X-ray photoelectron spectroscopy was 72%. With atomic force microscope (AFM), very low roughness of the grafting layer indicates the high density of MPEG . The presence of a PEO-brush was demonstrated using ellipsomtry. |
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