Figure 2.

Size and degradation characteristics of photodegradable microparticles. a. BSA-488 was entrapped within photodegradable microspheres. b. Image analysis was used to quantify the size distribution of the particles synthesized by this method (n = 3130). The particles were formed with a number average diameter of 22 μm and a diameter average diameter of 42 μm, which resulted in a polydispersity index of 1.9. Over 80% of the particles had a diameter less than 50 μm. c. Photodegradable particles swell and, ultimately, erode in response to flood irradiation (λ = 365 nm; I₀ = 13.5 ± 0.5 mW/cm²) over the time course of a minute. d. The swelling was quantified with image analysis and plotted as normalized volume (V/V₀) as a function of irradiation time. Particles were exposed to 365 nm (I₀ = 13.5 ± 0.5 mW/cm²; circles) and 400-500 nm (I₀ = 20.0 ± 0.5 mW/cm²; triangles) irradiation, and the particles eroded at 55 ± 5 s and 300 ± 30 s for the two conditions, respectively (indicated by the dashed gray lines). e. The release of BSA-488 as a function of irradiation time was quantified as the particles swelled and dissolved. Prior to dissolution (indicated by the dashed gray line), BSA-488 began diffusing out as the particles swelled, and after dissolution the majority of the payload was released into solution. Scale bars, 100 μm.