Reversible Swelling of Chitosan and Quaternary Ammonium Modified Chitosan Brush Layers: Effect of pH and Counter Anion Size and Functionality.

Hyun-Su Lee, Michael Q Yee, Yonaton Y Eckmann, Noreen J Hickok, David M Eckmann, Russell J Composto
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Abstract

This study investigates the swelling of grafted polycationic brushes as a function of pH and anion type. The brushes are chitosan (CH) and chitosans with 27% and 51% degree of substitution (DS) of quaternary ammonium salt, denoted as CH-Q(25) and CH-Q(50), respectively. The water content and swelling behaviors are monitored using in situ quartz-crystal microbalance with dissipation (QCM-D). The pH varies from ~3.5 to 8.5, and the counter anion types include chloride, acetate, and citrate. At fixed pH, the water content and brush swelling increase as the DS increases. Whereas the CH-Q(50) brush layer shows symmetric swelling with a minimum near pH = 4.5, the swelling of CH and CH-Q(25) is relatively constant as pH decreases from 8.2 to 5.5, and then begins to increase near pH 4. These studies indicate that the symmetric swelling of CH-Q(50) is likely attributed to increasing protonation of primary amines for pH values below pH 6.5 and the quaternary ammonium salts above pH 6.5. At pH 4, the swelling of the CH brush increases upon exchanging the smaller chloridewith a bulkier acetate anion, which is less effective at screening intra/inter molecular repulsion. In contrast, upon exchanging the acetate with trifunctional citrate, CH and CH-Q(25) brushes collapse by 53 and 42%, respectively, because the citrate forms ionic cross-links. To test antibacterial properties, silicon oxide, CH and CH-Q(50) brush layers are exposed to 10(7)-10(8) cfu/ml of S. aureus for two days at 37 °C and exposed to stepped shear stresses in 2 min intervals. Whereas an S. aureus biofilm adheres strongly to silicon oxide and CH for stresses up to 12 dyne/cm(2), biofilms on CH-Q(50) detach at a relatively low shear stress, 1.5 dyne/cm(2). Due to their high degree of swelling that can be tuned via pH, counterion size and type, chitosan and quaternary modified chitosans have potential as responsive coatings for applications including MEMS/NEMS devices and drug eluting implants.

壳聚糖和季铵改性壳聚糖刷层的可逆膨胀:pH 值及阴离子大小和功能性的影响
本研究探讨了接枝聚阳离子刷的溶胀与 pH 值和阴离子类型的关系。这些刷子是壳聚糖(CH)和季铵盐取代度(DS)分别为 27% 和 51% 的壳聚糖,分别称为 CH-Q(25) 和 CH-Q(50)。使用带耗散的原位石英晶体微天平(QCM-D)对含水量和溶胀行为进行了监测。pH 值从 ~3.5 到 8.5 不等,反阴离子类型包括氯化物、醋酸盐和柠檬酸盐。在固定的 pH 值下,随着 DS 的增加,含水量和刷肿胀也随之增加。这些研究表明,CH-Q(50) 刷层的对称溶胀可能是由于在 pH 值低于 6.5 时,伯胺的质子化作用增强,而在 pH 值高于 6.5 时,季铵盐的质子化作用增强。在 pH 值为 4 时,当较小的氯离子与体积较大的醋酸阴离子交换时,CH 刷的膨胀会增加,因为醋酸阴离子在分子内/分子间排斥的屏蔽作用较弱。相反,当用三官能团柠檬酸盐交换醋酸盐时,CH 和 CH-Q(25)刷分别塌陷 53% 和 42%,这是因为柠檬酸盐形成了离子交联。为了测试抗菌性能,氧化硅、CH 和 CH-Q(50)刷层在 37 °C、10(7)-10(8) cfu/ml 金黄色葡萄球菌的作用下暴露两天,并每隔 2 分钟暴露于阶梯剪切应力下。金黄色葡萄球菌生物膜可在高达 12 dyne/cm(2) 的应力下牢固地粘附在氧化硅和 CH 上,而 CH-Q(50)上的生物膜则会在相对较低的剪切应力(1.5 dyne/cm(2))下脱离。壳聚糖和季化合物修饰壳聚糖具有很高的溶胀度,可通过 pH 值、反离子大小和类型进行调节,因此具有作为响应涂层的潜力,可应用于 MEMS/NEMS 设备和药物洗脱植入物。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Journal of Materials Chemistry
Journal of Materials Chemistry 工程技术-材料科学:综合
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1.5 months
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