(499f) Long-Term Resistance of Novel Zwitterionic Surfaces to Biofilm Formation

Microbial adhesion onto surfaces and subsequent formation of biofilm are critical issues for many biomedical and engineering applications. One of the most effective methods to prevent the formation of biofilm is to avoid or reduce the initial adhesion of bacteria to a surface. In order to suppress the attachment of microorganisms onto the surfaces and delay biofilm formation, the most commonly used method is to graft surfaces with hydrophilic polymers, such as poly(ethylene glycol) (PEG) derivatives and more recently zwitterionic polymers. In our previous work, we demonstrated that poly(sulfurbetaine methacrylate) p(SBMA) is highly resistant to nonspecific protein adsorption, and can dramatically reduce bacterial adhesion and biofilm formation, and a more recent study show that the two novel zwitterionic surfaces poly(carboxybetaine methacrylate) (pCBMA) and poly(carboxybetaine acrylic amide) (pCBAA) can resist nonspecific protein adsorption from 100% plasma and serum. The outstanding performance of zwitterionic polymers and PEG derivatives to resist protein adsorption and bacterial attachment is attributed to their intrinsically strong hydration via electrostatic interactions for pSBMA or hydrogen bonding interactions for PEG derivatives. Our hypothesis is that the water structures in the hydration may influence the long-term non-fouling performance of these hydrophilic polymers.

There are three objectives of this study. The first one is to understand the correlation between water structures in the hydration layer of PEG and zwitterionic polymers and the capacity of these polymers to resist biofilm formation. The second objective is to understand the effect of film thickness and surface density on the performance of zwitterionic surfaces to resist biofilm formation. The third objective is to identify the key factors which lead to the eventual fail of the non-fouling surfaces in the long-term biofilm formation study. In this work, pCBAA, pCBMA and poly(oligo(ethylene glycol) methyl ether methacrylate) (pOEGMA) were grafted from glass surfaces via atom transfer radical polymerization (ATRP) to achieve the highest efficiency to resist biofilm formation on top of these surfaces. The long-term accumulation (5 days) of Gram-negative Pseudomonas aeruginosa on these surfaces was studied using a laminar flow chamber, and the biofilm formation on these surfaces were observed and recorded in situ using a Nikon epifluorescent microscope at different time points. The result showed that pCBAA and pCBMA can efficiently delay the biofilm formation up to five days comparing to untreated glass. The effect of film thickness and density on the performance of zwitterionic surfaces to resist biofilm formation was studied by using the polymer brushes with different precisely controlled thickness. The stability of the polymer brushes in the complex medium is one of the key factors affecting the performance of polymer surface. After 5 days, biofilm was removed and the surfaces were analyzed by XPS. The effect of the stability of ester or amide bond on the performance of non-fouling polymer brushes is obtained by comparing pCBMA with pCBAA, and the contribution of functional group stability to non-fouling performance is obtained by comparing pOEGMA and pCBMA.