Adhesive, Self-Healing, and Antibacterial Chitosan Hydrogels with Tunable Two-Layer Structures

Hydrogels with multifunctional properties such as biocompatibility, adhesion, and self-healing and inherent antibacterial properties are of great significance in biomedical applications, especially for wound dressings and drug release. However, it remains a significant challenge to combine all of these properties in a one-component hydrogel system. Furthermore, most injectable hydrogels are mechanically weak and not self-healing, which limits their applications as wound dressings. Herein, we designed a hydrogel with a tunable two-layer structure that endows the hydrogel with adhesion, self-healing, and antibacterial properties in different layers. First, chitosan (CHI) was oxidized to aldehyde-chitosan (ACHI). The Schiff base reaction was then used to fabricate the CHI/ACHI hydrogel resulting in the first layer. For the second layer, a physical cross-linking process using phytic acid (PA) as a sequential cross-linker was achieved, resulting in a CHI/ACHI/PA hydrogel. The CHI/ACHI hydrogel exhibited good injectable, adhesion, and self-healing properties. After cross-linking with PA, the CHI/ACHI/PA hydrogel showed enhanced mechanical properties, which enabled it to act as a protective layer. Additionally, the antibacterial test and cytotoxicity tests performed on this two-layer structured CHI/ACHI hydrogel exhibited excellent inherent antibacterial activity and good biocompatibility. The biocompatible injectable hydrogel was endowed with more possibilities relying on its self-healing and antibacterial abilities. These properties endorse the CHI/ACHI two-layer hydrogel as an excellent candidate for biological applications, especially wound dressings.