Investigation Of Antifouling Polypeptides:Synthesis,Characterization And In Vitro Enzymatic Degradation

The inherent difference between the biomaterials and common materials is their biocompatibility. Biocompatibility includes not only organ compatibility, but also blood compatibility. Organ compatibility means that biomaterials doesn’t cause inflammation immunogenicity for the organ, and blood compatibility means that biomaterials doesn’t cause coagulation or thrombosis. PEG is one of the few biomaterials approved by the Food and Drug Adiministration (FDA) for clinical use, but researchers demonstrated that it can be easily oxidized, becoming failure or causing thrombosis under long exposure to the blood. Traditional zwitterionic materials, such as poly(2-methacryloyloxyethyl phosphorylcholine)(pMPC), poly(sulfobetaine methacylate)(pSBMA) and poly(carboxybetaine methacylate)(pCBMA) are ideal candidates for nonfouling materials due to their excellent anti-nonspecific protein adsorption property and biocompatibility. But their methacrylic backbones cannot biodegrade, which hinders their further applications. Herein, we developed several polypeptide-based antifouling biomaterials and intensive investigations were done for their properties especially for their enzymatic degradation property. The main contents and conclusions of the dissertation are presented as follows:1. Using H-Lys(Z)-O\Bu.HCl and Boc-Glu(Z)-OH as starting materials, antifouling polypeptide with alternative uniform charges (poly(EK), its corresponding dimer is designated as dimer1) were synthesized by polycondesation. We have resolved the dilemma of ununiformity or local defects caused by the random ring opening polymerzation(ROP) of glutamic acid and lysine N-carboxyanhydrate (NCA) and the unbiodegradability of poly(ethylene glycol)(PEG) or methacrylic materials. Results from Nuclear Magnetic Resonance (1HNMR) and Gel Permeation Chromatography (GPC) demonstrated successful synthesis of the target polymer. Typical yield of the polypeptide is about45%from the dimer1. Successful formation of self-assembly monolayers (SAMs) on gold chips were demonstrated by ATR-FTIR, XPS and ELL. The thicknesses of the SAMs determined by ELL are several nanometers and the thicknesses don’t linearly increase with the molecular weights (MWs) increase. The lowest relative nonspecific adsorption of the polypeptide SAMs for anti-IgG and Fg is5.1±1.6%and7.3±1.8%, respectively, when tissue cultural polystyrene (TCPS) surface adsorption is set as control. No obvious cell attachment or bacterium adhesion were observed on the SAMs surfaces. When the feeding concentration of the polypeptide is about5mg/mL, no toxicity or hemolytic activity were detected for the polypeptide.2. Using H-Lys(Z)-OBzl.HCl and BOC-Glu-O’Bu as starting materials, polypeptide of poly(glutamic acid) backbone with lysine side chains (poly(E)-K, its corresponding dimer is designated as dimer2) were synthesized. Results from1HNMR and GPC show that poly(E)-K with different molecular weights(MWs) were obtained. Typical yield of the polypeptide is about40%from the dimer2. Results from ATR-FTIR, XPS and ELL demonstrate the formation of the polypeptide SAMs on gold surface. The lowest relative protein adsorption for anti-IgG and Fg were observed for the3.5kDa polypeptide SAMs, for which the values are3.3±1.8%and4.4±1.6%, respectively, indicating this kind of polypeptide owns better antifouling property than poly(EK). No toxicity and no hemolytic activity were detected for the polypeptide. In hemolytic assay, the absorbance of polypeptide is even lower than the negative control PBS, indicating the low interactions between the polypeptide and the cell membranes or even the protection of the polypeptide for the cells.3. In preparatory enzymatic degradation experiments, we found that poly(EK) can degrade while poly(E)-K can’t. Thus, we synthesized several copolypeptide by adjusting the ratios of dimer1to dimer2. Results from1HNMR demonstrate that we have successfully synthesized the co-polypeptides with different ingredients. The enzymatic degradation results indicate that the enzymatic degradation time of the copolypeptide become longer when the ratios of the poly(E)-K increase. Consequently, the enzymatic degradation speed and time of the copolypeptide can be easily manipulated by adjusting the proportions of the two dimmers. We are sure to believe that this kind of technology will have a wide range of applications in drug/gene controlled release or tissue engineering in future.