Release profile and biological activity of BDNF-encapsulated PGA particles. (a) Incubating BDNF-encapsulated PGA particles in PBS solution at 37 °C triggered the release of BDNF robustly within the first 3 days (inset), more modestly in the next 20 days and slowly toward the end of incubation period. Data are the mean ± the standard error of three independent release experiments. (b) In the absence of fetal calf serum, differentiated SH-SY5Y neurons underwent apoptosis, as indicated by the presence of darkly stained, TUNEL-positive neurons (arrows), but significantly fewer neurons died when 2 nM of BDNF released from BDNF-encapsulated PGA particles was added (c), demonstrating that BDNF maintained its bioactivity following release from the PGA particles. In four different experiments, BDNF released from BDNF-encapsulated PGA particles or fresh BDNF significantly reduced apoptotic death in serum-deprived differentiated SHSY-5Y neurons (d).