Zeng Guanghong, Ogaki Ryosuke, Meyer Rikke L
Interdisciplinary Nanoscience Center (iNANO), Faculty of Science and Technology, Aarhus University, Aarhus 8000, Denmark.
Interdisciplinary Nanoscience Center (iNANO), Faculty of Science and Technology, Aarhus University, Aarhus 8000, Denmark.
Acta Biomater. 2015 Sep;24:64-73. doi: 10.1016/j.actbio.2015.05.037. Epub 2015 Jun 17.
Polymer brushes of poly(ethylene glycol) have long been considered the gold standard for antifouling surfaces that resist adsorption of biomolecules and attachment of microorganisms. However, despite displaying excellent resistance to protein adsorption, the polymer brush coatings cannot entirely avoid colonization by bacteria. Here we investigate and identify which non-proteinaceous bacterial adhesins challenge the antifouling properties of polymer brush coatings and how these challenges might be overcome. We quantified biofilm formation on a well-known polymer brush coating of poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) on titanium. The coating successfully resisted colonization by Staphylococcus aureus and Pseudomonas aeruginosa, but not Staphylococcus epidermidis. This colonization pattern was also reflected on the adhesion forces measured on single bacterial cells. The biofilm produced from S. epidermidis on PLL-g-PEG were found to be rich in polysaccharides and extracellular DNA, and quantification of DNA, polysaccharides and proteins on PLL-g-PEG surfaces revealed that although the coating almost fully resisted protein adsorption, polysaccharides could adsorb, and exposure to DNA led to desorption of the polymer from the titanium surface. We hypothesized that this problem could be overcome by increasing the polymer brush density to better resist the penetration of DNA and polysaccharides into the polymer layer. Indeed, high density PLL-g-PEG brushes prepared by the recently discovered temperature-induced polyelectrolyte (TIP) grafting method resisted the interaction with DNA and polysaccharides, and therefore also the colonization by S. epidermidis. The TIP grafting is a simple improvement of PLL-g-PEG brush formation, and our results suggest that it provides an important advancement to the bacterial resistance by polymer brush coatings.
The antifouling properties of poly(ethylene glycol) brush coatings against protein adsorption are well documented, but it is not well understood why these coatings do not perform as well against bacterial colonization when tested against a wide range of species and over periods of days. Here we investigated bacterial colonization on poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) grafted on Ti, and revealed that bacteria relying mostly on polysaccharides and extracellular DNA for adhesion and biofilm formation could successfully colonize PLL-g-PEG coated surfaces. The coatings could not resist adsorption of polysaccharides, and DNA could even desorb the coatings from the Ti surface. Fortunately, the shortcomings of conventional PLL-g-PEG could be overcome by increasing the graft density, using the recently discovered and very simple grafting method, 'temperature-induced polyelectrolyte (TIP) grafting'. Our study highlights that it is of utmost importance to develop coatings which resist adsoprtion of non-proteinaceous bacterial adhesins such as polysaccharides and DNA, and we demonstrated that TIP grafted high density PLL-g-PEG coatings are promising materials to achieve diverse bacterial resistance.
长期以来，聚乙二醇聚合物刷一直被视为抗污表面的金标准，这种表面能够抵抗生物分子的吸附和微生物的附着。然而，尽管聚合物刷涂层对蛋白质吸附表现出优异的抗性，但仍无法完全避免细菌的定植。在此，我们研究并确定了哪些非蛋白质类细菌粘附素对聚合物刷涂层的抗污性能构成挑战，以及如何克服这些挑战。我们对钛表面一种著名的聚（L-赖氨酸）-接枝-聚乙二醇（PLL-g-PEG）聚合物刷涂层上的生物膜形成进行了定量分析。该涂层成功抵抗了金黄色葡萄球菌和铜绿假单胞菌的定植，但对表皮葡萄球菌无效。这种定植模式也反映在单个细菌细胞上测得的粘附力上。发现表皮葡萄球菌在PLL-g-PEG上形成的生物膜富含多糖和细胞外DNA，对PLL-g-PEG表面的DNA、多糖和蛋白质进行定量分析表明，尽管该涂层几乎完全抵抗蛋白质吸附，但多糖可以吸附，并且暴露于DNA会导致聚合物从钛表面解吸。我们推测，通过增加聚合物刷的密度以更好地抵抗DNA和多糖渗透到聚合物层中，可以克服这个问题。事实上，通过最近发现的温度诱导聚电解质（TIP）接枝方法制备的高密度PLL-g-PEG刷抵抗了与DNA和多糖的相互作用，因此也抵抗了表皮葡萄球菌的定植。TIP接枝是PLL-g-PEG刷形成的一种简单改进，我们的结果表明它为聚合物刷涂层的抗菌性能提供了重要进展。
聚乙二醇刷涂层对蛋白质吸附的抗污性能已有充分记录，但当针对多种物种进行数天测试时，为何这些涂层在抵抗细菌定植方面表现不佳，目前尚不清楚。在此，我们研究了接枝在钛上的聚（L-赖氨酸）-接枝-聚乙二醇（PLL-g-PEG）上的细菌定植情况，发现主要依赖多糖和细胞外DNA进行粘附和生物膜形成的细菌能够成功定植在PLL-g-PEG涂层表面。该涂层无法抵抗多糖的吸附，DNA甚至能使涂层从钛表面解吸。幸运的是，通过使用最近发现的非常简单的接枝方法“温度诱导聚电解质（TIP）接枝”增加接枝密度，可以克服传统PLL-g-PEG的缺点。我们的研究强调，开发能够抵抗多糖和DNA等非蛋白质类细菌粘附素吸附的涂层至关重要，并且我们证明TIP接枝的高密度PLL-g-PEG涂层是实现多种抗菌性能的有前途的材料。
