Hydrogels are desirable for use as 3D scaffolds in cell and tissue culture due to their tunable mechanical properties and high water content that facilitates rapid gas and nutrient exchange. A challenge with existing hydrogels is that, though the natural extracellular matrix of tissues may be ordered, there are limited biocompatible ways to incorporate anisotropy within a hydrogel. This work investigates the generation of liquid crystalline (LC) phases within a hydrogel, and the ability of LC phases to affect behavior of mesenchymal stem cells. Liquid crystalline networks (LCNs) combine microstructural ordering and elasticity, which permits LCNs to reversibly extend and contract through a process called actuation. The application of LCNs as culture substrates has focused on exploiting actuation in two-dimensional (2D) culture on films or in three-dimensional (3D) culture on scaffolds. Although LCNs have shown good biocompatibility, ordered microstructure, and tunable mechanical properties, the hydrophobic nature of LC mesogens has hindered their use in hydrogels that permit 3D cell encapsulation.<br/><br/>To overcome the challenges to generate biocompatible LC hydrogels, we report on the synthesis and characterization of thermotropic water-soluble main-chain LC polymers using alkyne-azide cycloaddition (AAC). A new alkyne-terminated mesogen (5yHBP) was polymerized with azide-terminated poly(ethylene glycol) (PEG) to impart flexibility and increase the hydrophilicity of the polymers. The strong hydrophobic core of 5yHBP results in LC phase formation in these polymers, while enough hydrophilic PEG content imparts aqueous solubility. The LC polymers can be cross-linked in aqueous media using a tetrafunctional dibenzocyclooctyne molecule via catalyst-free strain-promoted AAC, selected for its high efficiency and cytocompatibility. The resulting networks maintain LC phases in both the dry and hydrated states. Human mesenchymal stem cells were encapsulated in the LC hydrogels successfully by cross-linking the LC polymers in culture medium while in the presence of the cells. The results show excellent cell viability and proliferation, suggesting potential for thermotropic LC hydrogels for applications in tissue regeneration.

Main-chain liquid crystalline networks for biomaterialsapplications

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ACS Fall 2022

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