Fig. 2.

Effect of polymer M_w [A: Boehringer-Ingelheim Resomer® RG 502H (●), RG 503H (▲), and RG 504H (□)], incubation temperature (B: 37 (Δ), 25 (▲), and 4 (■) °C) and polymer mass/film thickness (C: octreotide sorption at 22 (●), 30 (▲) and 37 (Δ) °C, and leuprolide sorption at 37 °C (■) after 24 h) on peptide sorption to PLGA, and medium on desorption of peptide from PLGA particles or films (D). Sorption of peptides to PLGA was performed at 37 °C in 0.1 M HEPES buffer (pH 7.4) with an initial peptide concentration of 0.4 (A and B) or 1 (C and D) mM. RG 502H polymer was used in sorption and desorption studies unless otherwise specified. Dashed lines represent fits to a biexponential model. Desorption of octreotide from PLGA 50:50 particles (E-M) or films (N) was performed in 5 wt% SDS in water (E); 50 vol% methanol in water (F); 1 mg/mL PEI in 0.1 M acetate buffer, pH 4.0 (G); 0.1 M HEPES, pH 7.4 (H); 0.1% TFA in 0.1 M HEPES, pH 7.0 (I); 0.1 M DEPP, pH 4.0 (J); 0.1 M HEPES, pH 7.4 (K: particles and N: films); 2 M CaCl₂ in HEPES (L); 0.1 M HEPES, pH 7.4 (M). Desorption studies of E to L, and N were performed at 37 °C, except N, which was at 4 °C. PLGA RG502H was used in all cases, except H, which used RG503H. Desorption of octreotide in case of SDS (E) was assessed by recovering sorbed octreotide via two-phase extraction. Symbols represent mean of 3 determinations.