Abstract
Supramolecular hydrogels that are based on inclusion complexes between α-cyclodextrin and (co)polymers have gained significant attention over the last decade. They are formed via dynamic noncovalent bonds, such as host–guest interactions and hydrogen bonds, between various building blocks. In contrast to typical chemical crosslinking (covalent linkages), supramolecular crosslinking is a type of physical interaction that is characterized by great flexibility and it can be used with ease to create a variety of “smart” hydrogels. Supramolecular hydrogels based on the self-assembly of polypseudorotaxanes formed by a polymer chain “guest” and α-cyclodextrin “host” are promising materials for a wide range of applications. α-cyclodextrin-based polypseudorotaxane hydrogels are an attractive platform for engineering novel functional materials due to their excellent biocompatibility, thixotropic nature, and reversible and stimuli-responsiveness properties. The aim of this review is to provide an overview of the current progress in the chemistry and methods of designing and creating α-cyclodextrin-based supramolecular polypseudorotaxane hydrogels. In the described systems, the guests are (co)polymer chains with various architectures or polymeric nanoparticles. The potential applications of such supramolecular hydrogels are also described.
Highlights
The conditions of supramolecular hydrogel formation that are based on α-CD–polymer chain polypseudorotaxanes are a basic consideration in the design of novel hydrogels
The formation of supramolecular PPR hydrogel that is based on α-CD/polymeric chain occurs in two main stages: (i) first, host–guest interactions allow for the polymeric chain to penetrate into the CD cavity with the formation of polypseudorotaxane; (ii) hydrogen bonding occurs between neighboring α-cyclodextrin molecules, and these CDs aggregate into crystalline complexes, which act as knots of the physically crosslinked polymer network (Figure 2)
The results revealed that the incorporation of methacrylic acid (MA) groups as grafted chains increased and temperature-responsive sol–gel transition of a supramolecular hydrogel
Summary
Supramolecular chemistry, as defined by Nobel Prize laureate Jean-Marie Lehn, refers to non-binding interactions that play the same role as covalent bonds in classic organic chemistry. Noncovalent interactions force molecules to associate into highly organized structures, which are characterized by lower bond energy than the typical energy of covalent bonds [1,2]. These supramolecular systems are based on physical interactions, such as van der Waals interactions, hydrogen bonding, π–π dipolar interactions, hydrophobic effects, and host–guest interactions [3,4]. Supramolecular systems are able to freely self-assemble or disassemble because of their noncovalent interactions. These dynamic interactions impart such systems with thixotropic and self-healing properties. The application of polymers with desired features (e.g., biocompatibility, biodegradability, stimuli responsivity, defined mechanical, and rheological properties) for the preparation of supramolecular systems is an efficient strategy in biotechnology, chemistry, materials engineering, and biomedicine [9,10,11,12,13,14]
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