Investigation Of The Nonfouling Mechanism And Property Of The Nonfouling Materails

Nonfouling materials could effectively prevent nonspecific protein adsorption on the surface and thus improve the biocompatibility. Polyethylene glycol (PEG) is a well-known nonfouling materials in biomedical applications. However, its long-term effectiveness and stability is very limited especially in biological applications due to the extremely complicated internal environment. It is observed that certain people could generate immunoresponse to PEG and the PEG modification would dramatically decrease the activity of protein. Nowadays, zwitterionic materials, poly(2-methacryloyloxyethyl phosphorylcholine)(pMPC), poly(sulfobetaine methacylate)(pSBMA) and poly(carboxybetaine methacylate)(pCBMA), have demonstrated excellent resistance to nonspecific protein adsorption and long-term biocompatibility over PEG. A comprehansive understanding of the difference of nonspecific protein adsorption mechanism between PEG and zwitterionic materials will not only help us to provide the insight of the protein resistance and also select and design more appropriate materials to resist nonspecific protein adsorption. This paper mainly focuses on two typical nonfouling materials through comparatively investigating the hydration water layer of PEG and the representive of zwitterionic polymer pSBMA, as well as the binding behavior of PEG and pSBMA with protein, and last the diffusion behavior of the protein in PEG, PEG-pSBMA mixed and pSBMA hydrogels. The main contents and conclusions of this dissertation include the following six parts:1. The strong interaction between water molecules and PEG was investigated through each T2component in water/PEG mixtures using multi-exponential inversion of T2relaxation time measured by the Can—Purcell—Meiboom—Gill (CPMG) sequence of low-field nuclear magnetic resonance (LF-NMR). Results show that about one water molecule is tightly bound with one ethylene glycol (EG) unit. This result was also supported by the endothermic behavior of water/PEG mixtures measured by differential scanning calorimetry (DSC).2. Eight water molecules are tightly bound with one sulfobetaine (SB) unit, and additional water molecules over8:1ratio mainly swell the pSBMA matrix, which is obtained through the measurement of T2relaxation time by LF-NMR. This result was also supported by the endothermic behavior of water/pSBMA mixtures measured by DSC. Furthermore, by comparing both results of pSBMA and PEG, it is found that (1) the hydrated water molecules on the SB unit are more tightly bound than on the ethylene glycol (EG) unit before saturation, and (2) the additional water molecules after forming the hydration layer in pSBMA solutions show higher freedom than those in PEG.3. The interactions of bovine serum albumin (BSA) and lysozyme (LYZ) with different molecular weight (MW) PEGs was investigated through the T2relaxation time of PEGs measured by LF-NMR. The results show that a large number of PEG molecules could associate with protein molecules with association constants in the range～104to105M-1.4. The interactions between PEG and proteins in aqueous solution were investigated using fluorescence spectroscopy, atomic force microscopy (AFM), and nuclear magnetic resonance (NMR). The molecular weight effect of each on PEG-protein interactions as well as binding characteristics were examined. In contrast to too long and too short PEG chains, collective results indicated that the PEG with optimal MW exhibits the highest interacting with proteins.5. The interactions between two model proteins (BSA and LYZ) and two typical antifouling polymers of PEG and pSBMA in aqueous solution were investigated using fluorescence spectroscopy, AFM and NMR. Collective data clearly demonstrate the existence of medium interactions between PEG and proteins through multiple weak hydrophobic interaction, while there are no detectable interactions between pSBMA and proteins.6. The protein-polymer interaction was investigated through the diffusion behavior of the labeled protein in the PEG, PEG-pSBMA mixed and pSBMA hydrogel. It was observed that the protein diffusion rate through PEG hydrogel is much smaller than pSBMA hydrogel, indicating the interaction between the protein-PEG is stronger than protein-pSBMA.