Methylcellulose (MC) is a water-soluble cellulose derivative with a thermogelling property which allows it form physically crosslinked hydrogels as it undergoes sol-gel transition, driven by the aggregation of hydrophobic methoxy groups with increasing temperature. This property makes MC an appealing material for biomedical applications that require a sol-gel transition initiated at ≤ 37°C, enabling ease of injection as a liquid followed by gel formation post-injection within the body. However, physical crosslinking of MC alone does not result in adequate mechanical stability for most biomedical applications. To overcome this, we have added methacrylates to MC to enable chemical crosslinking via free-radical polymerization to form robust, stable hydrogels. The following study characterizes the influence of methacrylates on the thermoresponsiveness of MC. Methacrylated MC (mMC) was synthesized by reacting MC with methacrylic anhydride. Degree of methacrylation was quantified via <sup>1</sup>H NMR (7.55%). Rheological analysis of mMC and unmodified MC (uMC) (3% w/v) showed that the thermoresponsiveness of MC (characterized by a sharp increase in G’ at the thermogelation onset temperature) was preserved in mMC (n=3). Both uMC and mMC showed characteristic “salt-out” responses of lower gelation temperature when dissolved in PBS vs H<sub>2</sub>O. The presence of methacrylate groups on the mMC significantly lowered the thermogelation temperature (~14°C) compared to uMC in both solutes. In addition, the rate of increase in G’ was lower in mMC than uMC, indicating the potential role of steric interactions of the methacrylate group on the kinetics of MC aggregation. Thermogelation onset was at or below 37°C only in the mMC dissolved in PBS. The combined effect of thermogelation onset at or below physiologic temperatures with free-radical crosslinking results in a physiologically relevant injectable hydrogel with a wide variety of biomedical applications.

Effect of methacrylation on the thermoresponsive sol-gel transition of methylcellulose

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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