Effects of material property and heat treatment on nanomechanical properties of chitosan films

The influence of degree of deacetylation (DDA), molecular weight (MW), and heat treatment on nanomechanical properties of three different chitosan coatings was assessed. Chitosans (2.5 wt % in 2% acetic acid) were solution cast and bonded to glass slides, subjected to 40, 70, or 908C heat treatments for 1 h, and then allowed to air dry. Non-heat treated films were used as controls. The nanomechanical and structural properties were evaluated using quasi-static nanoindentation, X-ray diffraction (XRD), and atomic force microscopy (AFM). Nanoindentation results showed that the coating with the lowest MW and highest DDA (95.6% DDA and MW = 2.43 × 106 Da) had higher reduced modulus of elasticity, (E = 4.02 ± 0.85 GPa) as compared to the other chitosans; 76.1% DDA/MW = 3.20 3 106 Da, E = 3.66 ± 0.68 GPa, and 92.3% DDA/MW = 7.52 × 106 Da, E = 3.56 ± 0.25 GPa; (n 5 75, p \u3c 0.05). Crystallinity index, estimated via XRD, ranged from 36.4% ± 1% to 49.7% ± 6.5%. AFM revealed the presence of different crystalline morphologies such as needle-like crystals, sheetlike crystals, and small spherulites. The heat treatments applied during solution casting of the chitosan coatings did not affect morphology or nanomechanical properties. In conclusion, nanomechanical properties of chitosan coatings varied with DDA and MW and may be important to cell/tissue interactions. © 2008 Wiley Periodicals, Inc