In vitro studies. A, B) Cumulative release of EPO-R76E from the PPS (A) and PLGA (B) MPs into solution over time showing mean ± s.d. C) Quantification of cell viability after exposure to different amounts of empty and loaded MPs showing mean ± s.d. D) Quantification of H2O2 induced ARPE-19 cell death. Cells challenged with cytotoxic levels of H2O2 were treated with PPS, PPS + EPO-R76E, PLGA, or PLGA+EPO-R76E MPs. E, F) Quantification of DHE fluorescence in ARPE-19 cells treated with empty or EPO-R76E loaded PPS (E) or PLGA (F) MPs. For the cell survival and DHE experiments, cells were treated with the appropriate quantity of MPs to provide a 50 ng EPO-R76E dose.