A hydrogel is a network of polymer chains featuring chemically or physically cross-linked that can swell in water and hold a large amount of water. It has the advantages of good chemical modification, high permeability, and good biocompatibility, allowing it broad application prospects in industry, agriculture, biomedicine, skin care and other fields.
Cyclodextrin (CD) can be incorporated into hydrogels to form a cross-linked network, and CD-containing hydrogels not only have good mechanical properties, but also can give the hydrogel more functions, such as stimulus responsiveness, self-healing, shape memory, and injectability, exhibiting great research value and broad application potential [1].
According to cross-linking methods, CD-containing hydrogels are divided into the following types: (a) covalently cross-linked hydrogels, (b) non-covalently cross-linked hydrogels, (c) cross-linked double-network (DN) hydrogels and (d) slide-ring hydrogels. Their structure diagrams are shown in Fig. 1.
Fig. 1 The four different structure diagrams of hydrogel based on CDs [2].
CD-Containing Covalently Cross-Linked Hydrogel
Covalently cross-linked hydrogel, also known as chemically cross-linked hydrogel, refers to a CD-based hydrogel formed by polymerizing CD molecules through some small molecule cross-linkers, such as epichlorohydrin, diisocyanate, and acid anhydride.
Due to the presence of CD molecules in this structure, the cross-linked network of the hydrogel is more regular and tight, resulting in better mechanical strength. The application field of this CD-containing covalently cross-linked hydrogel has gradually expanded from separation to drug controlled release.
CD-Containing Non-Covalently Cross-Linked Hydrogel
Non-covalent cross-linked hydrogel, also known as physically cross-linked hydrogel, refers to a hydrogel material prepared by physical cross-linking with CD. There are two main ways of cross-linking: (a) the cross-linking of CD with polymer chains of different lengths through hydrogen bonds; (b) the cavity of the CD acts as a host to allow the cross-linking of hydrophobic guest molecules like adamantane, dioxane, ferrocene derivatives, n-butyl acrylate, and benzene through a host-guest interaction.
CD-based non-covalently cross-linked hydrogels are mostly responsive and have good self-healing ability, and have wide applications in biomaterial science.
CD-Containing Cross-Linked DN Hydrogel
The strength and recoverability of traditional cross-linked hydrogel are low due to its high water content, which seriously limits its application. The proposal of CD-containing cross-linked DN hydrogel provides a new idea to enhance its mechanical properties. It consists of two polymer networks and exhibits unique mechanical strength and toughness.
The preparation includes two steps: (a) CD and guest molecules first form a physically cross-linked structure through host-guest coupling; (b) On the basis of the physical network, a second layer of highly cross-linked rigid structure is formed through chemical covalent bonds.
CD-Containing Slide-Ring Hydrogel
Unlike the three CD-containing hydrogels discussed above, slide-ring hydrogels are not cross-linked using traditional physical or chemical methods. Due to the unique toroid cone structure and cavity hydrophobicity, CD can be innovatively connected in series to the polymer chains to construct a candied-haws-like structure, forming slide-ring hydrogels.
Various CD-containing slide-ring hydrogels have been synthesized, whose cross-linking mechanism is to construct a topological structure of CD by figure-of-eight cross-links. Material viscoelastic and swelling properties can be effectively enhanced by these slide-ring hydrogels.
Alfa Chemistry is dedicated to the manufacture of CDs. We offer high-quality native CDs, CD derivatives, and CD inclusion complexes. We have strong supply capabilities and can provide products at the kilogram level. Please feel free to contact us and we will serve you wholeheartedly.
References
- Liu, J.; et al. Cyclodextrin-containing hydrogels: a review of preparation method, drug delivery, and degradation behavior. Int J Mol Sci. 2021, 22(24): 13516.
- Wang, Z.; et al. Advances in hydrogel materials based on cyclodextrin derivatives. China Academic Journal Electronic Publishing House. 2018, 32(10): 3456.
It should be noted that our our products and services are for research use only, not for clinical use.
