Figure 3.

Representative ex situ SEM images monitoring morphological changes in polymer-coated or uncoated pSi particles at various stages of exposure to eluent solutions of different pH values. In this experiment, particles were sequentially exposed to SGF for 2 h followed by SIF or PBS for 3 h and a 5 μL sample aliquot was taken at specified time point for SEM imaging. Uncoated (as-etched) pSi particles after (a) 2 h incubation in SGF (pH 1.2), (b) 1.5 h incubation in PBS (pH 7.4), or (c) 3 h incubation in PBS (pH 7.4). The uncoated particles are stable at pH 1.2 but show signs of slow dissolution at pH 7.4. Eudragit L100-coated pSi after (d) 2 h in SGF (pH 1.2), (e) 1.5 h in FasSIF (pH 6.8), or (f) 3 h incubation in FasSIF (pH 6.8). The Eudragit L100 coating is stable at pH 1.2 but readily dissolves at pH 6.8 to expose the underlying pSi particles. Eudragit S100-coated pSi particles after (g) 2 h in SGF (pH 1.2), (h) 1.5 h in PBS (pH 7.4), or (i) 3 h in PBS (pH 7.4). The Eudragit S100 coating is stable at pH 1.2 but dissolves at pH 7.4 to expose the underlying pSi particles. Scale bars for all images are 200 nm.