Quaternary ammonium-functionalized carbon nanotubes/alginate nanocomposite hydrogels support myoblast growth and differentiation

Carbon nanotube (CNT) composite hydrogels are promising materials for tissue engineering due to the biocompatibility of the matrix and the electrical conductivity of the filler, which is crucial for promoting the growth and functions in electroactive tissues. While pristine CNTs are insoluble, we synthesized and fully characterized a water-soluble CNT derivative (fCNT) bearing quaternary ammonium groups, and we homogeneously dispersed it within alginate-based hydrogels. Through external and internal gelation we obtained two plain and two fCNT-filled hydrogels (HG1 and HG2 and HG1-fCNT and HG2-fCNT, respectively), and we compared the physical properties of the four different materials. A measurement setup and an approach were specifically designed for the electrical characterization of our hydrogel samples, showing that the addition of a low amount (0.1 mg mL^-1) of fCNT enhanced the conductivity of the hydrogel from internal gelation (HG2-fCNT) by more than one order of magnitude, from 5.7 × 10^-10 to 2.8 × 10^-8 S cm^-1. Even more interestingly, HG2-fCNT featured a faster transmission of low frequency signals (with time scales from 1 ms to 100 ms, typical of electroactive biological tissues) than the other samples. Finally, the behavior of the four hydrogels as scaffolds for muscle tissue engineering was compared through studies of myoblast viability, proliferation, and differentiation. A relevant improvement in differentiation (more than doubling the number and area of myotubes and the fusion index) was obtained by adding the fCNT in the case of HG2-fCNT, in line of its superior electrical properties. These outcomes hint at the feasibility of using the fCNT combined with the alginate hydrogel in order to support the myoblast growth and proliferation.