Improvement of mechanical properties and in vitro bioactivity of freeze-dried gelatin/chitosan scaffolds by functionalized carbon nanotubes

Functionalized multiwall carbon nanotubes (f-MWCNTs) were used to reinforce the freeze-dried gelatin (G)/chitosan (Ch) scaffolds for bone graft substitution. Two types of G/Ch scaffolds at a ratio of 2:1 and 3:1 by weight incorporated with 0.025, 0.05, or 0.1 and 0.2 or 0.4 wt% f-MWCNT, respectively, were prepared by freeze drying, and their structure, morphology, and physicochemical and compressive mechanical properties were evaluated. The scaffolds exhibited porous structure with pore size of 80-300 and 120-140 mu m for the reinforced scaffolds of G/Ch 2:1 and 3:1, respectively, and porosity 90-93% which slightly decreased with an increase in f-MWCNTs content for both types. Incorporation of f-MWCNTs led to 11- and 9.6-fold increase in modulus, with respect to their pure biopolymer blend scaffolds at a level of 0.05 wt% for G/Ch 2:1 and 0.2 wt% for G/Ch 3:1, respectively. The higher content of f-MWCNTs resulted in loss of mechanical properties due to agglomeration. The highest value of compressive strength and modulus was obtained for G/Ch 2:1 with 0.05 wt% f-MWCNT as 411 kPa and 18.7 MPa, respectively. Improvement of in vitro bioactivity as a result of f-MWCNTs incorporation was proved by formation of a bone-like apatite layer on the surface of scaffolds upon immersion in simulated body fluid. The findings indicate that the f-MWCNT-reinforced gelatin/chitosan scaffolds may be a suitable candidate for bone tissue engineering.