Figure 1.

Study design. After fabrication, microsphere morphology was examined qualitatively by means of scanning electron microscopy. Interleukin-1 receptor antagonist (IL-1ra) release kinetics were quantified. IL-1ra conditioned media were generated by suspending microspheres in CM^- (chemically defined medium without transforming growth factor-beta 3) under gentle agitation. Media containing released IL-1ra were collected at the intervals indicated and used to treat functionally mature nucleus pulposus (NP) constructs that were challenged with IL-1β.