Thixotropic chitosan hydrogels for biomedical applications: Unravelling the effect of chitosan concentration on the mechanical behaviour

Chitosan hydrogels are highly sought after in biomedical applications due to their biocompatibility, non-toxicity, and tunable mechanical properties. Nevertheless, achieving stable hydrogels with the required mechanical strength remains a notable obstacle. In this study, we prepared chitosan hydrogels with enhanced stability using minimal concentrations of glutaraldehyde to mitigate toxicity risks. The resulting hydrogel system is characterized by strong covalent bonds formed through imine and hydrogen bonding, facilitated by the aldehyde groups of glutaraldehyde. Rheological analyses reveal the viscoelastic properties of the hydrogels, showcasing stable gel-like structures with shear-thinning behavior, which are further enhanced with increasing chitosan concentration. Our observation demonstrates that the complex shear moduli of 0.5 - 1.5 w/v % chitosan hydrogel ranged between 3.08 kPa and 8.5 kPa, closely matching the shear moduli of the brain and connective tissues. The shear moduli obtained for the 2w/v% (10.2 kPa) and 2.5w/v% hydrogels (11.34 kPa) conform to the shear moduli of liver, fat, relaxed muscle, and breast gland tissue. Thixotropic studies reveal good structural recovery behaviour in the hydrogels. The swellability of 2w/v% and 2.5w/v% hydrogels (50-70%) suggests their suitability for bone tissue engineering, with moderate porosity required for bone growth (60-75%). Moreover, the yield stress values of 0.5 - 1.5 w/v % hydrogels satisfy the requirements for soft tissue engineering, while those of 2 and 2.5 w/v% match the requirements for bone tissue engineering. Our findings suggest that chitosan hydrogels of varying concentrations (0.5–2.5% w/v) hold promise for a range of biomedical applications, including tissue engineering for brain, nerve, soft, and bone tissues, and wound dressing. This research addresses the pressing need for stable chitosan hydrogels with tailored mechanical properties, potentially offering solutions to challenges in biomedical materials design.