After CHO Concanamycin A were seeded and cultured in complete medium for 24 h, the culture medium was replaced with DMEM without serum. The relative cell density on TCPS after an additional 48 h culture in the absence of serum was set as 100%. Higher relative cell densities were observed for those cells grown on the films containing insoluble cyanophycin. As the culture continued, the cells grown on TCPS gradually became apoptotic as the relative cell density dropped to 60%, and then to below 20% after an additional 96 h culture (Fig. 6A). The cell number diminished and the cell shapes became rounded (Fig. 6B1). On the other hand, the cells on the cyanophycin films maintained a healthier state as the relative cell density stayed almost unchanged after an additional culture in the absence of serum for 72 h, and dropped slightly after 96 h (Fig. 6A). For the cells grown on the insoluble cyanophycin films, the changes in confluence over time were less than those on TCPS, and most of the cell shapes remained unchanged (Fig. 6B2–5), especially on the films containing higher concentrations of cyanophycin, suggesting that those films provided a sustained environment for cell growth. The basis of the ability of cyanophycin to support sustained cell growth remains unclear, but might be attributable to the unique comb structure of arginine and lysine side chains along the aspartic backbone; the lysine and arginine could provide a charged environment to which the cells might more readily anchor.