Department of Chemistry and Chemical Engineering, Chalmers University of Technology, 41296 Gothenburg, Sweden.
Institute of Applied Physics, Group of Applied Interface Physics, Vienna University of Technology, 1040 Vienna, Austria.
Langmuir. 2021 Apr 27;37(16):4943-4952. doi: 10.1021/acs.langmuir.1c00271. Epub 2021 Apr 14.
Polymer brushes are widely used to alter the properties of interfaces. In particular, poly(ethylene glycol) (PEG) and similar polymers can make surfaces inert toward biomolecular adsorption. Neutral hydrophilic brushes are normally considered to have static properties at a given temperature. As an example, PEG is not responsive to pH or ionic strength. Here we show that, by simply introducing a polymeric acid such as poly(methacrylic acid) (PMAA), the highly hydrated brush barrier can change its properties entirely. This is caused by multivalent hydrogen bonds in an extremely pH-sensitive process. Remarkably, it is sufficient to reduce the pH to 5 for complexation to occur at the interface, which is two units higher than in the corresponding bulk systems. Below this critical pH, PMAA starts to bind to PEG in large amounts (comparable to the PEG amount), causing the brush to gradually compact and dehydrate. The brush also undergoes major rheology changes, from viscoelastic to rigid. Furthermore, the protein repelling ability of PEG is lost after reaching a threshold in the amount of PMAA bound. The changes in brush properties are tunable and become more pronounced when more PMAA is bound. The initial brush state is fully recovered when releasing PMAA by returning to physiological pH. Our findings are relevant for many applications involving functional interfaces, such as capture-release of biomolecules.
聚合物刷广泛用于改变界面的性质。特别是聚乙二醇（PEG）和类似的聚合物可以使表面对生物分子吸附表现惰性。中性亲水性刷通常被认为在给定温度下具有静态性质。例如，PEG 对 pH 值或离子强度没有响应。在这里，我们表明，只需引入一种聚合物酸，如聚（甲基丙烯酸）（PMAA），高度水合的刷状屏障就可以完全改变其性质。这是由于在极其敏感的 pH 值过程中形成多价氢键。值得注意的是，界面处的络合反应仅需将 pH 值降低到 5，这比相应的体相系统高两个单位。在这个临界 pH 值以下，PMAA 开始大量（与 PEG 量相当）与 PEG 结合，导致刷逐渐变紧凑和脱水。刷还经历了主要的流变学变化，从粘弹性变为刚性。此外，在结合的 PMAA 达到一定量后，PEG 的蛋白质排斥能力丧失。刷的性质变化是可调的，当结合更多的 PMAA 时，变化更加明显。当通过回到生理 pH 值释放 PMAA 时，初始刷状态可以完全恢复。我们的发现与涉及功能界面的许多应用相关，例如生物分子的捕获和释放。
