Tough polyion complex hydrogel films of natural polysaccharides

The developments of tough hydrogels in recent years have greatly expanded the applications of hydrogels as structural materials.However,most of the tough hydrogels are made of synthetic polymers.To develop biopolymer-based tough hydrogels has both fundamental and practical significances.Here we report a series of polysaccharides-based tough hydrogel films prepared by polyion complexation and solvent evaporation of chondroitin sulfate (CS) and protonated chitosan (CHT) solutions with different weight ratios.The obtained CS/CHT gel films with thickness of 40-80 μm and water content of 66 wt％-81 wt％ possess excellent mechanical properties,with tensile breaking stress and breaking strain being 0.4-3 MPa and 160％-320％,respectively.We found that in the mixture solutions there are large amounts of excess CHT in terms of charges;after swelling the films in water,the acetic acid,which is used to protonate the amino groups of CHT,diffuses out of the gel matrix,enhancing the intermolecular interactions between CHT molecules and thus improving the mechanical properties of gel films,besides the ionic bonds between CS and CHT.Antimicrobial tests also showed that the gel films with low weight ratio of CS to CHT,corresponding to the case with excess CHT,have evident antimicrobial effect.These CS/CHT gel films with good mechanical properties and antimicrobial effect should extend the applications of hydrogels in biomedical fields.