Dipartimento di Fisica, Università della Calabria, Cubo 31/C, Rende, CS 87036, Italy.
Department of Mechanical Engineering, Technical University of Denmark, DK-2800, Kgs. Lyngby, Denmark.
Soft Matter. 2017 Jan 18;13(3):590-599. doi: 10.1039/c6sm01801g.
Lubrication of soft polydimethylsiloxane (PDMS) elastomer interfaces was studied in aqueous mixtures of porcine gastric mucin (PGM) and branched polyethyleneimine (b-PEI) at neutral pH and various ionic strengths (0.1-1.0 M). While neither PGM nor b-PEI improved lubrication compared to polymer-free buffer solution, their mixtures produced a synergistic lubricating effect by reducing friction coefficients by nearly two orders of magnitude, especially at slow sliding speed in the boundary lubrication regime. An array of spectroscopic studies revealed that small cationic b-PEI molecules were able to strongly bind and penetrate into large anionic PGM molecules, producing an overall contraction of the randomly coiled PGM conformation. The interaction also affected the structure of the folded PGM protein terminals, decreased the surface potential and increased light absorbance in PGM:b-PEI mixtures. Adding an electrolyte (NaCl) weakened the aggregation between PGM and b-PEI, and degraded the lubrication synergy, indicating that electrostatic interactions drive PGM:b-PEI complexation.
在中性 pH 值和不同离子强度（0.1-1.0 M）的猪胃粘蛋白（PGM）和支化聚乙烯亚胺（b-PEI）的水溶液混合物中研究了软聚二甲基硅氧烷（PDMS）弹性体界面的润滑。虽然与无聚合物缓冲溶液相比，PGM 或 b-PEI 都不能改善润滑，但它们的混合物通过将摩擦系数降低近两个数量级产生了协同润滑效果，特别是在边界润滑区的低速滑动速度下。一系列光谱研究表明，小分子的阳离子 b-PEI 分子能够强烈结合并穿透到大的阴离子 PGM 分子中，使随机卷曲的 PGM 构象整体收缩。这种相互作用还影响了折叠的 PGM 蛋白末端的结构，降低了表面电位并增加了 PGM:b-PEI 混合物的光吸收。添加电解质（NaCl）会削弱 PGM 和 b-PEI 之间的聚集，并降低润滑协同作用，表明静电相互作用驱动 PGM:b-PEI 络合。
