Abstract
Hydrogels find application in many areas of technology and research due to their ability to combine responsiveness and robustness. A detailed understanding of their molecular structure and dynamics (which ultimately underpin their functional properties) is needed for their design to be optimized and these hydrogels to be exploited effectively. In this review, we shed light on the unique capabilities of solid-state NMR spectroscopy to reveal this information in molecular detail. We review recent literature on the advancements in solid-state NMR techniques in resolving the structure, degree of grafting, molecular organization, water-biopolymer interactions and internal dynamical behavior of hydrogels. Among various solid-state NMR techniques, 13C cross polarization (CP) magic angle spinning (MAS) NMR is examined for its ability to probe the hydrogel and its trapped solvent. Although widely applicable to many types of polymeric and supramolecular hydrogels, the current review focuses on polysaccharide-based hydrogels.
Highlights
Hydrogels are conventionally considered three-dimensional nanofibrous materials consisting of cross-linked hydrophilic polymer networks (Chai, Jiao, & Yu, 2017)
It can be used to provide distinctive information on the molecular structure, and on the molecular interactions, polymorphism, and chemical compositions of the hydrogel. This will be examined in more detail in the papers discussed in this review, which we focus primarily on illustrative recent alginate and chitosan hydrogels
Based on a combination of practical applications in biomedicine and the illustrative use of incisive ssNMR studies, we focus this review on recent cross polarization (CP) magic angle spinning (MAS) ssNMR studies of alginate and chitosan hydrogels
Summary
Hydrogels are conventionally considered three-dimensional nanofibrous materials consisting of cross-linked hydrophilic polymer networks (Chai, Jiao, & Yu, 2017). MAS is often combined with a complementary line-narrowing technique based on the “decoupling” of line-broadening (dipolar) interactions with strong radio-frequency (RF) pulses These decoupling sequences can cause substantial sample heating, which is counteracted by additional sample cooling and improved probe designs (Gor’kov et al, 2007; Stringer et al, 2005). The cross-linked nanofibrous network traps water, which in turn expands throughout its spacious volume, forming an insoluble non-fluid gel These particular properties of a hydrogel make it suitable for use as a decent drug delivery system, allowing an encapsulation (and subsequent release) of target molecules in the trapped water phase. Based on a combination of practical applications in biomedicine and the illustrative use of incisive ssNMR studies, we focus this review on recent CP MAS ssNMR studies of alginate and chitosan hydrogels
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