Cellular biocompatibility of cyanophycin substratum prepared with recombinant Escherichia coli

• Purified cyanophycin elicits minimal activation of macrophages.
• Purified cyanophycin can provide an environment for cellular proliferation.
• Purified cyanophycin forms films with a structure of stacking lamellae.

Cyanophycin from recombinant Escherichia coli is composed of aspartic acid as a backbone with arginine and lysine as the side chains. Cyanophycin exists in insoluble and soluble forms based on its solubility in aqueous solution. This study aims to assess the physical properties and cellular biocompatibility of cyanophycin prepared with recombinant E. coli. The decomposition temperature of cyanophycin was around 230 °C for both forms of cyanophycin, as measured by thermogravimetric analysis. Soluble cyanophycin showed no toxicity to Chinese Hamster Ovary (CHO) cells at a concentration of 5 mg/mL as revealed by the thiazolyl blue tetrazolium bromide method. When the insoluble cyanophycin formed thin films, the films exhibited a structure of stacking lamellae. CHO cells grown on the films had a higher relative cell density, or 107–142% that of those grown on tissue culture polystyrene (TCPS), 48 h after seeding. After the removal of serum-containing medium, the CHO cells maintained cell morphology for up to 72 h in Dulbecco’s modified Eagle medium without serum, and the relative cell density was 150–170% that of the cells grown on TCPS 48 h after serum removal, indicating that the cyanophycin substratum could provide sustained cell growth. When RAW 246.7 cells were grown on the films of insoluble cyanophycin for 96 h, nitric oxide concentration released from the macrophages was below 2 mM/mg protein, suggesting that a minimal immune response was elicited. The results showed that cyanophycin might have the potential to serve as a biocompatible, degradable material in biomedical applications, such as tissue engineering and drug delivery.