| Summary: | 博士 === 國立陽明大學 === 醫學工程研究所 === 99 === Abstract
Due to its hydrophilic and biocompatible properties, nonionic surfactants have been widely used as a stabilizer for colloids or suspend particles in various emulsion processes. Recently, nonionic surfactants with poly-ethylene oxide (PEO) segment are found useful in reducing protein adsorption of a biomaterial by physisorption or chemical bonding to material surfaces. The PEO modified surfaces can increase the selectivity of a biosensor and improve the biocompatibility of a biomaterial or a drug carrier. In this study, surface modifications through physic-sorption of a triblock copolymer, PEO-PPO-PEO (Pluronic), and chemical bonding of PEG groups are studied to delineate the adsorbed film structure and its effects in protein adsorption. Ellipsomery and surface plasma resonance methods are applied to measure the thickness and concentration of the adsorbed film. The results for the adsorption of Pluronics on a gold surface indicate that its behavior is similar to the adsorption on a hydrophobic surface. By increasing solution concentration, the adsorption amount increases accordingly and the adsorption of PEO chains change from an extended form at the interface to a brush-like form of being expelled into the bulk solution. The saturation surface concentration of Pluronics at critical micellization concentration is about 0.4 μg/cm2. This value does not changes with the change of molecular weight and the EO/PO ratio of the Pluronics. Desorption tests indicate that The adsorption of Pluronics is partially reversible. For the adsorption of Pluronics with 80% PEO, the adsorption becomes irreversible when σ* <2. While, for Pluronic with PPO > PEO, the adsorption behavior tends to be dominated by the PPO group and the criterion of σ* < 2 is no longer to be able to be used to determine whether the adsorption is reversible or not. The adsorption of Pluronics on a –CH3 terminated SAM surface is relatively unstable. The adsorbed film can be desorbed completely under prolong desorption in water suggesting the adsorption on –CH3 terminated SAM surface is reversible. The thickness of PEG films chemically grafted on a SAM surfaces can be controlled by the solvent property used in the surface modification process. By using a series of alcohol solvents with various carbon chain lengths, the results show that the resulting surface PEG chain density reaches maximum value when the solubility parameter of the solvent, i.e. dodecanol, is closest to the solubility parameter of the polymer. This PEG film exhibits Brush form structure. The experiments of protein adsorption show that the amount of albumin adsorbed on a Au/Pluronic surface decreases with the increase of PEO chain length. However, the adsorption of albumin on a CH3 SAM/Pluronic surface does not reveal similar tendency. In general, surface modified by the physisorption of pluronic molecules can only reduce the adsorption of albumin to about 50%. By properly choosing a solvent for the surface modification by chemical grafting of PEG molecule, one can effectively raising the surface density of PEG to a level of σ* > 2. A surface PEG film with brush-like structure can effectively block the nonspecific adsorption of albumin, IgG, fibrinogen and lysozyme.
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