Reversibly Reconfigurable Cross-Linking Induces Fusion of Separate Chitosan Hydrogel Films

Chitosan is an aminopolysaccharide that can be physically cross-linked through two independent, reversible, and pH-switchable mechanisms. At high pH, neutral chitosan chains can self-assemble to form crystalline domains that serve as one type of physical cross-link (such cross-linked hydrogels are designated Chit⁰). At low pH, the chains are cationic and dis-assembled from each other but can be electrostatically cross-linked by multivalent anionic micelles of sodium dodecyl sulfate (such cross-linked hydrogels are designated SDS-Chit-H⁺). Here, we report that the ability to reversibly reconfigure cross-linking mechanisms provides a means to fuse separately prepared chitosan films. Experimentally, neutral Chit⁰ hydrogel films were first prepared by cathodic electrodeposition, and then separately prepared Chit⁰ films were fused by overlapping them in the presence of SDS and acid. Qualitative evidence demonstrates fusion across the interface at both the microscale (e.g., SEM) and macroscale. Mechanical testing (e.g., tear test) demonstrates that fusion leads to strong bonding with failure occurring in the bulk region of the film and not at the joint. Potentially, the ability to fuse separately prepared films may provide new opportunities for additive manufacturing of biobased materials.