Strong Silk Fibroin/PVA/Chitosan Hydrogels with High Water Content Inspired by Straw Rammed Earth Brick Structures

Poly(vinyl alcohol) (PVA) is a safe high-molecular polymer with good biocompatibility that can be prepared into hydrogels with high tensile strength by salting out. However, inorganic ions will cause PVA chains to form strong crystals through intramolecular H-bond interactions, resulting in dehydration of PVA chains and greatly reducing the water content of hydrogels. Herein, inspired by the structural model of straw rammed earth bricks, a PVA, silk nanofiber (SNF), and chitosan (CS) composite hydrogel (PSC) were prepared with a high Young's modulus (8.85 ± 0.24 MPa), acceptable tensile strength (4 ± 0.28 MPa), and high fatigue threshold (8.09 ± 0.5 kJ/m2). Because SNF plays the role of straw-formed hydrogen bonds (H-bonds) with PVA and CS, the formation of H-bonds between PVA chains was inhibited, leading to more free hydrophilic groups (−OH). Therefore, the water content increased significantly to as high as 87%. By fabricating the structure of straw rammed earth bricks in hydrogels, PSC had both a high Young's modulus and a high water content, even though the crystallinity of PVA decreased. PSC also showed antibacterial properties against Escherichia coli and Staphylococcus aureus due to CS and are expected to be further applied in biomedicine and tissue engineering.