Comparison of osteogenic efficacy of rhBMP-2 released from different delivery films—B80 (B), B80G40 (BG), B80L15G40 (BLG), and B80L15G40L15 (BLGL)—(A) Visual inspection of temporal expression patterns for alkaline phosphatase (ALP) signals shows the sustained release of rhBMP-2 from composite films and the effect of barrier layers on modulating rhBMP-2 release. (B) ALP activity normalized to total protein confirms the observed release behaviors for different rhBMP-2 delivery films, and also demonstrates that the bioactivity of rhBMP-2 released from different films is preserved over the course of the study. Culture with uncoated substrates in differentiation medium served as control; its ALP activity was 0.04±0.01. The dotted lines are drawn by eye. *P < 0.05, **P < 0.01, ***P < 0.001, analysis of variance (ANOVA) with a Tukey post hoc test.