Giubertoni Giulia, Burla Federica, Bakker Huib J, Koenderink Gijsje H
AMOLF, Science Park 104, Amsterdam 1098 XG, The Netherlands.
Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, Van der Maasweg 9, Delft 2629 HZ, The Netherlands.
Macromolecules. 2020 Dec 8;53(23):10503-10513. doi: 10.1021/acs.macromol.0c01742. Epub 2020 Nov 18.
Many biopolymer hydrogels are environmentally responsive because they are held together by physical associations that depend on pH and temperature. Here, we investigate how the pH and temperature responses of the rheology of hyaluronan hydrogels are connected to the underlying molecular interactions. Hyaluronan is an essential structural biopolymer in the human body with many applications in biomedicine. Using two-dimensional infrared spectroscopy, we show that hyaluronan chains become connected by hydrogen bonds when the pH is changed from 7.0 to 2.5 and that the bond density at pH 2.5 is independent of temperature. Temperature-dependent rheology measurements show that because of this hydrogen bonding the stress relaxation at pH 2.5 is strongly slowed down in comparison to pH 7.0, consistent with the sticky reptation model of associative polymers. From the flow activation energy, we conclude that each polymer is cross-linked by multiple (5-15) hydrogen bonds to others, causing slow macroscopic stress relaxation, despite the short time scale of breaking and reformation of each individual hydrogen bond. Our findings can aid the design of stimuli-responsive hydrogels with tailored viscoelastic properties for biomedical applications.
许多生物聚合物水凝胶对环境敏感，因为它们是通过依赖于pH值和温度的物理缔合作用聚集在一起的。在此，我们研究透明质酸水凝胶流变学的pH值和温度响应是如何与潜在的分子相互作用相关联的。透明质酸是人体中一种重要的结构生物聚合物，在生物医学中有许多应用。通过二维红外光谱，我们发现当pH值从7.0变为2.5时，透明质酸链通过氢键连接，并且在pH 2.5时的键密度与温度无关。温度依赖性流变学测量表明，由于这种氢键作用，与pH 7.0相比，pH 2.5时的应力松弛显著减慢，这与缔合聚合物的粘性爬行模型一致。从流动活化能来看，我们得出结论，尽管每个氢键的断裂和重新形成时间尺度很短，但每个聚合物都通过多个（5 - 15个）氢键与其他聚合物交联，导致宏观应力松弛缓慢。我们的研究结果有助于设计具有定制粘弹性特性的刺激响应水凝胶，用于生物医学应用。
