title: Chitosan films with improved tensile strength and toughness from N-acetyl-cysteine mediated disulfide bonds.
abstract: To improve the mechanical properties of chitosan (Ct) materials without the use of cytotoxic crosslinkers, disulfide cross-linkable Ct was synthesized by grafting N-acetyl-cysteine (NAC) to Ct using carbodiimide chemistry. Cast films of NAC-Ct conjugates were prepared with degrees of substitution (DS) of 0%, 6%, 15%, and 20%, and the disulfide bond formation was induced by increasing the reaction media pH to 11. The tensile strength, breaking strain, elastic moduli and toughness of disulfide cross-linked polymers were analyzed by monotonic tensile testing of hydrated NAC-Ct films. Crystallinity was determined via XRD. Results demonstrated that NAC incorporation and crosslinking in chitosan produced tougher polymer films with 4-fold higher tensile strength (10 MPa) and 6-fold greater elongation (365%), but reduced crystallinity, compared to unmodified chitosan. The resilience of NAC-Ct films was evaluated by cyclic testing, and results demonstrate that increasing NAC content produced a more resilient material that dissipated less energy when deformed. These improved mechanical properties broaden chitosan's applicability towards the construction of mechanically robust implantable scaffolds for tissue regeneration.
authors.affiliation: Department of Chemical Engineering and Materials Science, Wayne State University, 5050 Anthony Wayne Drive, Detroit, MI 48202, United States. Electronic address: kbmiles@wayne.edu.
authors.forename: Kevin Barrett
authors.initials: KB
authors.lastname: Miles
authors.affiliation: Department of Chemical Engineering and Materials Science, Wayne State University, 5050 Anthony Wayne Drive, Detroit, MI 48202, United States. Electronic address: rlball@andrew.cmu.edu.
authors.forename: Rebecca Lee
authors.initials: RL
authors.lastname: Ball
authors.affiliation: Department of Chemical Engineering and Materials Science, Wayne State University, 5050 Anthony Wayne Drive, Detroit, MI 48202, United States. Electronic address: hmatthew@wayne.edu.
authors.forename: Howard William Trevor
authors.initials: HW
authors.lastname: Matthew
mesh_terms: D000111:Acetylcysteine / Q000737:chemistry*; D048271:Chitosan / Q000031:analogs & derivatives* / Q000737:chemistry; D003460:Crystallization; D004220:Disulfides / Q000737:chemistry; D055119:Elastic Modulus; D006863:Hydrogen-Ion Concentration; D013718:Tensile Strength; D023822:Tissue Engineering
chemical_list: D004220:Disulfides; C540141:chitosan-N-acetylcysteine conjugate; D048271:Chitosan; D000111:Acetylcysteine
keywords: Biomaterial crystallinity; Biomaterial mechanical properties; Cyclical tensile properties; Disulfide bonds; N-acetyl-cysteine chitosan