Release of DOX from SELPs 815K, 815K-RS1, and 815K-RS2 as measured across a microdialysis setup in various concentrations of MMP-9: (a) 0 nM, (b) 1 nM, (c) 5 nM, and (d) 50 nM. The DOX sample refers to the passage of free DOX across the microdialysis membrane and into the measured reservoir. Cumulative release totals over 96 hr at different concentrations of MMP-9: (e) 0 nM, (f) 1 nM, (g) 5 nM, and (h) 50 nM. Data plotted as mean ± standard deviation; n = 3. **, p < 0.01; ***, p < 0.001.