The Preparation And Application Of Hydrophilic Branched Polymer-Based Antifouling Coating

The performance of the materials can be compromised by the non-specific attachment of biomolecular (protein, platelet and cell) on its surfaces (biofouling). Coating the surface with a thin layer of anti-biofouling polymer is one universal strategy for minimizing problems arising from biomolecular adsorption. It has been shown that the surface polymer chain density is one of the most important parameters which determine biomolecular adsorption on surfaces. Furthermore, some evidences also suggested that the branched polymers on surface can provide enhanced resistance to biomolecular adsorption, due to the increased surface coverage offered by the branched polymers for a given grafting density compared to that of linear polymers. Thus, this work mainly focuses on the preparation and application of hydrophilic branched polymer-based antifouling coating and also the relationship between polymer architecture and properties. The dissertation involved following aspects:(1) We have synthesized a set of well-defined hydrophilic multiarm star copolymers, hyperbranched poly(ethylenimine)-graft-poly(ethylene glycol) (PEI-g-PEG) with different PEG grafting ratios and amine terminated linear poly(ethylene glycol) (PEG2000-NH2). The linear/star PEG-based coatings were prepared by immobilizing the corresponding polymers onto PDA-coated substrates. The surface PEG chain densities of coatings were evaluated quantitative. Our results demonstrate that the surface copolymer grafting densities of star PEG-based coatings decreased with increasing PEG grafting ratios. However, the surface PEG chain density of the star PEG-based coating increased with increasing PEG grafting ratios and became higher than that of linear ones at PEG grafting ratios> 10. The amount of protein adsorbed onto surfaces, determined by SPR, was found to depend on the surface PEG chain density. Generally, the surface with higher surface PEG chain density possessed better protein resistant property than that with lower surface PEG chain density. At last, the star PEG-based coating was successfully applied to coat the fused-silica capillary inner wall for the separation of protein mixture (lysozyme, cytochrome c, ribonuclease A, and a-chymotrypsinogen A) by capillary electrophoresis (CE).(2) As a polyether, PEG can undergo oxidative degradation, leading to chain scission as well as oxidation of chain termini, which is the major limitation for its long-term applications. Previous research has shown that poly(2-methyl-2-oxazoline) (PMOXA) and its derivatives have been identified as highly potent candidates of PEG, due to their excellent biocompatible, promising antifouling properties, and much better physiologic stability. Therefore, a set of well-defined multiarm star copolymers hyperbranched poly(ethylenimine)-graft-poly(2-methyl-2-oxazoline) (PEI-g-PMOXA) with different PMOXA grafting ratios and chain lengths were synthesized. The cytotoxicity assay revealed that the linear PMOXA-OH did not show any cytotoxicity to HUVECs, and the cell viability increased with increasing PMOXA grafting ratios and arm lengths for copolymer PEI-g-PMOXA. Furthermore, the PMOXA-based film was successfully prepared rapidly via a simple one-step dopamine-assisted codeposition method. The results showed that the star PMOXA can produce films with a higher surface PMOXA chain density, more uniform surface structures, and better antifouling properties compared to the linear ones. Besides, our results demonstrated that the surface antifouling properties of PMOXA-based films were found to be dependent on the surface PMOXA chain densities, which were controlled by the PMOXA grafting ratios and chain lengths. With increasing PMOXA grafting ratios and chain lengths, the surface PMOXA chain densities of star PMOXA-based films increased and also the antifouling properties. At last, the PMOXA-based films showed superior stability in long-term applications than PEG-based films with similar structure under identical conditions.(3) Our previous work has focused on hyperbranched PEI-based multiarm star copolymers. It is noteworthy that the DBs (degree of branching) and molecular weights of commercially PEI were relatively single, and the PEI molecular will also adsorb large amounts of protein at physiological buffer (PBS, pH 7.4). Thus, we want to get the hyperbranched copolymers that the DBs can be adjusted to study the effect of branched architectures on the coating surface composition and antifouling properties. We have first synthesized the functional RAFT agent S-(4-Vinyl) benzyl S’-propyltrithiocarbonate (VBPT). Then, the poly(2-methyl-2-oxazoline) acrylate macromonomers (PMeOxA) was polymerizated with VBPT by RAFT-SCVP to get the hyperbranched copolymer poly(PMeOxA-co-VBPT). By adjusting the molar ratios of monomers, a set of hyperbranched copolymers poly(PMeOxA-co-VBPT) with different DBs were synthesized. Furthermore, the poly(PMeOxA-co-VBPT)-based films were successfully prepared via dopamine-assisted codeposition method. The effect of incubation conditions and polymer architectures (linear, hyperbranched copolymers with different DBs) on deposited films with respect to their surface composition, wettability and antifouling properties were investigated in detail. The results showed that the surface PMeOx chain densities were controlled by DBs and the PMeOx content in the copolymers. With decreasing DBs, the surface PMeOx chain densities increased and reached the maximum value at PMeOxA(3)-co-VBPT(1)/PDA coating. However, as DBs kept decreasing, the surface PMeOx chain densities decreased, due to the lower DBs. Bseides, the surface PMeOx chain densities of hyperbranched PMeOx-based cotings were all higher than that of linear ones. The antifouling studies showed that the surface antifouling properties of hyperbranched PMeOx-based films depend on the surface PMeOx chain densities. With increasing surface PMOXA chain densities, the antifouling properties increased. Among the hyperbranched copolymers, PMeOxA(3)-co-VBPT(1)/PDA deposited films showed the highest resistance to protein adsorption (-98.7% relative to the bare gold surface), cell attachment (-99.0% relative to the bare glass surface), and platelet adhesion (-98.5% relative to the bare silicon).