Microparticles were incubated with various concentrations of growth factors in 0.1% BSA in PBS for 16 hours at 4°C; remaining unbound growth factor was measured via ELISA. A) 0.1 mg of heparin microparticles were incubated with 10 ng of FGF-2, VEGF, BMP-2, and TNF-α. Heparin microparticles depleted the majority of positively charged growth factors from solution (FGF-2, VEGF, BMP-2), while the negatively charged growth factor (TNF-α) did not bind. (* = p < 0.05 compared to all other conditions.) B) Different amounts of heparin microparticles were incubated with 20 ng of BMP-2. Percentage of BMP-2 depleted increased with the addition of more microparticles. Conversely, the amount of BMP-2 depleted on a per mg of microparticles basis increased with decreasing microparticle amounts. C) 0.2 μg of heparin microparticles were incubated with increasing amounts of BMP-2. Heparin microparticles depleted significantly more BMP-2 from solution as the loading mass of BMP-2 added was increased. D) 0.2 μg of heparin microparticles were incubated with increasing amounts of BMP-2. Heparin microparticles exhibited maximal BMP-2 binding at approximately 300 μg BMP-2/mg microparticles.