Double crosslinking of chitosan/vanillin hydrogels as a basis for mechanically strong gradient scaffolds for tissue engineering

Polysaccharides, such as chitosan (CS), are widely used in many biomedical applications. However, they require crosslinking agents to achieve chemical stability and appropriate mechanical properties. In this work, chitosan-based hydrogels were crosslinked using vanillin and/or sodium tripolyphosphate, as chemical and physical crosslinking agents, respectively. Microstructural (digital microscope, SEM), structural (FTIR-ATR), mechanical (static compression test), and in vitro biological (chemical stability and swelling ratio in PBS, cytotoxicity) properties of the obtained materials were evaluated to assess materials potential as biomedical scaffolds. The optimal ratio of vanillin to chitosan (DD = 89%) to crosslink the polymer was found to be 1.2:1. Moreover, the double crosslinking with vanillin caused a two-time increase in the compression strength of the samples and led to the slower biodegradability. Cytotoxicity studies showed that the cells prefer double vanillin crosslinked hydrogels over those treated with TPP. Further studies, such as bioactivity are required to determine the specific functionality of the hydrogels and the specific tissue which may be treated with the tested materials. The optimal material was chosen to the next step of the study, which may be obtaining composite hydrogels with hydroxyapatite and/or graphene oxide to tailor or improve properties towards specific tissue regeneration.