Biodegradable, porous, polymeric implant material provides substantially continuous release of bioactive agent during in vivo use. Bioactive agent is initially released in amounts that are less than degradation rate of polymer, thereby promoting migration of cells into material. Later larger amounts of bioactive agent is released, thereby promoting differentiation of cells. Method of making material includes step of applying vacuum to form pores. Implant material may be adapted for one phase implant (e.g., for bone or cartilage) or for two phase layered implant (e.g., for cartilage layer on top of bone layer).