Characterization of nanocomposite scaffolds composed of collagen and functionalized carbon nanotubes for tissue engineering applications

Covalently-functionalized single-walled carbon nanotubes (SWNTs) have been proposed as a novel means of reinforcing collagen-based scaffolds. In contrast to previous work in which SWNTs were functionalized with carboxylic acids to facilitate hydrophilic dispersion within a collagen matrix and thus enhance interaction with collagen at the fibrillar level, this study implemented a modified process of diimide-activated amidation to covalently functionalize SWNTs for highly-specific binding with collagen at the molecular level. In order to investigate the potential advantages of incorporating functionalized SWNTs into collagen scaffolds, three experimental constructs were developed and characterized: the first construct (COL) consisted of collagen and was used as a control against which the other two constructs were evaluated; the second construct (CXNT-COL) consisted of carboxyl-functionalized SWNTs dispersed within a collagen matrix; the third construct (CFNT-COL) consisted of covalently-functionalized SWNTs embedded in a collagen matrix. The effects of varying SWNT loading were also investigated by preparing CXNT-COL and CFNT-COL constructs with 1, 10, 20, and 30 wt% SWNT loading. Low-vacuum scanning electron microscopy and confocal laser scanning microscopy revealed the biphasic structure of all constructs and the tendency of the nanotubes to aggregate into large bundles at 30-wt% loading. Static stress-strain testing performed in compression did not demonstrate significant reinforcement of the constructs. Creep/recovery testing performed in compression revealed that all constructs exhibited poroelastic behavior as described by the Kelvin-Voigt constitutive model for viscoelastic materials. Cytotoxicity assays indicated that cell viability, in general, was lower on scaffolds containing functionalized SWNTs. It was also found that the degree of surface coverage exhibited by living cells was significantly lower on the CFNT-COL scaffolds with respect to the COL control scaffolds.