Fig. 8. (A) Absorbance at 280 nm of the eluent of PP-DA and PP-DA/PEI with different mass ratios of DA/PEI immersed in 1.0 M HCl or 1.0 M NaOH solutions for 2 h. (B) The deposition density of DA/PEI coatings with different mass ratios of DA/PEI. (C) Absorbance at 280 nm of the eluent of PP-DA and PP-DA/PEI immersed in aqueous solutions with different pH for 2 h, *p < 0.05. (D) Absorbance at 280 nm of the eluent of PP-DA and PP-DA/PEI immersed in 50 mM buffer solutions with different pH for 2 h: citrate buffer (pH = 3, 4, 5), phosphate buffer (pH = 6, 7, 8), Tris buffer (pH = 9) and sodium bicarbonate buffer (pH = 10, 11) solution, *p < 0.05. And the absorbance at 280 nm of the eluent of different molecular weight PEI co-deposited with DA on PP immersed in 1.0 M HCl (E) or 1.0 M NaOH (F) solutions for 2 h. n = 3.