Optimization of MP:DNA complex formation. (A,B) Effects of serum free medium on MF: (A) transfection efficiency and GFI in hHF-MSCs, and (B) percentage of dead cells following application of the MF293T protocol with two serum free media, DMEM or OPTI-MEM. (C,D) Effects of MP:DNA ratio on transfection efficiency and toxicity of hHF-MSC: (C) percentage of EGFP+ cells and GFI, and (D) percentage of dead cells and total cell count of hHF-MSCs after MF with different ratios of MP:DNA in OPTI-MEM. All values are the mean ± SD of triplicate samples in a representative experiment (n = 3). The symbol * denotes p < 0.05 between DMEM and OPTI-MEM serum free medium. N.S.: not significant (p ≥ 0.05).