Figure 13. Scanning electron microscope images of C2C12 cells on cellulose acetate (CA) nanofibers (A, C, E) after 14, 21, and 28 days of cell culture, respectively, and cellulose acetate nanofibers with annatto extract (CA@A) (B, D, F) after 14, 21, and 28 days of cell culture, respectively. Scale bars indicate 50 µm.
After 14 days of culture, cells completely covered the CA@A scaffold, while few cells were visible in the CA matrix (Figure 13). By 21 days, the CA scaffold was also entirely covered with cells. Figure 13 suggests that both the CA and CA@A nanofiber substrates can sustain long-term culture of C2C12 cells, up to 28 days. According to Choi et al. [49] and Post et al. [2], production of muscle cells in meat cultivation requires numerous muscle precursor cells, and consequently in vitro expansion of cells is a critical step for such applications. This present study suggests that annatto extract is useful in promoting rapid proliferation and coverage during the initial days of culture, providing sufficient quantities of muscle cells and thus permitting large-scale application for meat production. In addition, as already mentioned, annatto extract can be an important factor for the long-term preservation of the culture, avoiding unwanted contamination during the process. Future studies can be carried out to confirm the protective action of annatto extract as a meat preserver.