2.4. In vitro release study

For determination of drug release, PLHNs containing 100 µg PTX were added to the dialysis bag with molecular weight cutoff 8000–14 000 Da, which was placed in 80 ml HEPES buffer (pH 6.86) containing 0.1% Tween 80 (V/V), and then incubated at a rotation speed of 100 rpm/min in an air-bath oscillator (37.0 ± 0.5 °C). At predetermined time points (0.5, 1, 2, 3, 4, 6, 12, 24 and 48 h), 2 ml release medium was withdrawn for drug content measurement. Meanwhile, fresh medium of equal volume was replenished for further release study. Release profiles differentiation of the tested formulations were evaluated by calculating similarity factor (f₂) using the following equation:

where R_t and R’_t are the cumulative release amount of two independent formulations at time t respectively, and n is the number of time points.