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Water added to a solution of microcrystalline cellulose (MCC) in 1-allyl-3-methylimidazolium chloride (AmimCl) reduces the solvent quality and causes significant changes in the flow properties and microstructure due to restructuring and aggregation of cellulose molecules. We report an experimental investigation by means of polarization optical microscopy (POM) and rheology of the distinct phases formed in 5-20 wt% MCC/AmimCl solutions due to the addition of water. With increase in the cellulose concentration, the MCC/AmimCl/water mixtures showed different morphologies such as the non-aligned cholesteric liquid crystalline (LC) domain, the coexistence of spherulite-like structures within the LC domain and a space-spanning network of spherulite-like structures at high concentrations of water. In situ microscopy during shear and POM observations pre and post shear revealed a significant increase in the size of the birefringent domains as the shear rate is increased, which continued to exist even after the cessation of shear. With an increase in the concentration of water, the zero shear viscosity of the MCC/AmimCl/water mixtures was found to go through a minimum, beyond which the aggregation of cellulose commenced. The corresponding oscillatory shear response showed a sol-gel transition with an increase in water concentration. Moreover, at high cellulose concentrations (12-20 wt%), the MCC/AmimCl/water gels exhibited self-similarity and followed the Chambon-Winter (CW) criterion. The similar phase behavior and rheological response observed for MCC dissolved in 1-butyl-3 methylimidazolium chloride (BmimCl) indicated the generality of the presented results.

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Hyaluronic acid is a native extra-cellular matrix derivative that promises unique properties, such as anti-inflammatory response and cell-signaling with tissue-specific applications under its bioactive properties. Here, we investigate the importance of the duration of synthesis to obtain photocrosslinkable methacrylated hyaluronic acid (MeHA) with high degree of substitution. MeHA with high degree of substitution can result in rapid photocrosslinking and can be used as a bioink for stereolithographic (SLA) three dimensional 3D bioprinting. Increased degree of substitution results Our findings show that a ten-day synthesis results in an 88% degree of methacrylation (DM), whereas three-day and five-day syntheses result in 32% and 42% DM, respectively. The rheological characterization revealed an increased rate of photopolymerization with increasing DM. Further, we developed a hybrid bioink to overcome the non-cell-adhesive nature of MeHA by combining it with gelatin methacryloyl (GelMA) to fabricate 3D cell-laden hydrogel scaffolds. The hybrid bioink exhibited a 55% enhancement in stiffness compared to MeHA only and enabled cell-adhesion while maintaining high cell viability. Investigations also revealed that the hybrid bioink was a more suitable candidate for stereolithography (SLA) 3D bioprinting than MeHA because of its mechanical strength, printability, and cell-adhesive nature. This research lays out a firm foundation for the development of a stable hybrid bioink with MeHA and GelMA for first-ever use with SLA 3D bioprinting.

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