The Protein-resistant Performance Of Amphiphilic V-shaped Polymer Brushes And The Associated Mechanism

Biofilm formation by the adsorption and growth of microorganisms on material surfaces in aqueous environments can lead to various adverse effects and has become a serious problem.Understanding and controlling the interaction between proteins and material surfaces is accordingly of great significance in designing protein-resistant materials.Since proteins are inherently amphiphilic,either completely hydrophilic or hydrophobic surfaces can form a certain degree of interaction with the protein moleculars.Thus,homogeneous surface is not believed to be the best candidate for achieving the optimal protein-resistant performance.According to structural characteristics of protein,the great interest in the development of materials with antifouling and fouling-release properties was recently focused on the amphiphilic coatings,containing with both hydrophobic and hydrophilic components.Actually,the molecular structure and morphology of amphiphilic surface is much more complex,owing to the chemical incompatibility of hydrophilic and hydrophobic domains,usually leading to obvious microphase separation.So far,scientists have started to realize that nanometer-scale phase separated surface could prevent biofouling efficiently.However,the underlying mechanism why the amphiphilic surface would effectively reduce the protein-surface interaction remain unclear,especially from a molecular level perspective.Systematic studies are needed to fully elucidate the mechanism of protein adhesion.In this thesis,the amphiphilic V-shaped polymer brushes with two highly incompatible arms of mPEG110 and PMMAn-PFMA5 were prepared by the “grafting to” method.The surface structure and phase separated behavior for amphiphilic V-shaped polymer brushes were well controlled by altering the number of PMMA units(n).The protein-resistant performance of this kind of V-shaped polymer brushes was investigated and the mechanism of protein adhesion was elucidated.(1)The surface structures of the amphiphilic V-shaped polymer brushes were studied.It was found that fluorinated species of the V-shaped polymer brush surface increased with increasing of DP(n)of PMMA,and the well-ordered structure of perfluorinated alkyl was formed as n > 64.The degree of phase segregation increased with the increase of DP(n)of PMMA.The V-shaped polymer brushes with n = 82 or 109 exhibited an alternating phase separation structure,in which one domain was water-soluble PEG and the other was ultralow surface energy domain with a crystalline fluorinated side group.The domain size of V-shaped brush with n = 82 was 27 nm,and the domain size of the V-shaped brush with n = 109 was 81 nm.(2)The protein-resistant performance of the amphiphilic V-shaped brushes were investigated.It was found that all the V-shaped polymer brushes exhibited more better protein-resistance performance compared with pure PEG brush.In particular,the V-shaped polymer brush with n = 82 exhibited the lowest bovine serum albumin(BSA)adsorption and the V-shaped brush surface with n = 109 exhibited the lowest Human fibrinogen(HFg)adsorption.Combining with the surface structures of the V-shaped polymer brushes,when the brush surfaces showed an obvious alternating phase separation structure and domain sizes were twice longer than protein sizes,the V-shaped brush surfaces presented optimal protein repellence.(3)The mechanism of protein-resistant performance of amphiphilic V-Shaped polymer brushes was investigated.It was found that the amount of absorbed protein drops linearly with the adhesion force and the friction force of protein on the V-shaped polymer brush surfaces.The reason was that protein adsorption onto highly flexible PEG brushes compressed the polymer chains(??S),and protein adsorption on hydrophobic component surface with ultralow surface energy increased the enthalpy of the system(??H).Therefore,the adsorption of proteins on amphiphilic V-Shaped brush surfaces was not a spontaneous process.In particular,when the polymer brush surfaces showed an alternating phase separation structure,the stimuli-responsive PEG domain stretched out at the interface in water and the low-surface-free-energy PFMA domain remained relatively stable.The synergistic effect of the surface hydrophilic and hydrophobic components was enhanced.Furthermore,the micro-phase structures of V-shaped polymer brush surfaces furthest disrupted the protein-surface interaction,when the size of the micro domain doubled that of the protein.(4)The relationship between surface structures and protein-resistant properties of amphiphilic V-shaped polymer brushes(mPEGx-V-PSy)were studied.It was also found that polymer brushes exhibited alternating ordered arrangement of hydrophilic and hydrophobic micro domains has good protein resistant ability.Best protein resistance was obtained when the size of the micro domain doubled that of the protein.The amount of absorbed protein drops linearly with the adhesion force and the friction force of protein on the V-shaped polymer brush surfaces,which further approves the protein-resistant mechanism of amphiphilic polymer brushes.