In a 40-mL vial were mixed an aqueous suspension of copolymer nanoparticles and an equal volume of aqueous potassium hydroxide solution (KOH, 5 wt %). The vial was placed in an orbital shaker (IKA KS4000i control, 37℃, 90 rpm) and samples were withdrawn at different intervals, and lyophilized. 2 mL of chloroform was added, followed by three washes with HCl (1 mL, 1 mol.L -1 ). After extraction, the organic phase was filtered with 0. Cell viability assay. In 96-well microtiter plates (TPP, Switzerland), A549 cells were seeded (5 × 10 4 cells mL -1 ) in 100 μL of growth medium and preincubated for 24 h in incubator (37 °C and 5% CO 2 ). After appropriate dilutions, 100 μL of aqueous copolymer nanoparticles in cell culture medium were added over the cells and incubated for 72 h. A MTT solution (5 mg.mL -1 )