Microspheres for controlled release of a bioactive agent are disclosed, and in particular, blend, cross-linkable poly(propylene fumarate) for immobilization and controlled drug delivery. The microsphere includes poly(propylene fumarate), a polymeric material other than poly(propylene fumarate) (e.g., poly(lactic-co-glycolic acid)), and a bioactive agent. The bioactive agent is selected depending on the physiological effect desired. For example, in bone regeneration applications, the bioactive agent may be selected from osteoinductive agents, peptides, growth hormones, osteoconductive agents, cytokines and mixtures thereof. The bioactive agent is dispersed in the microsphere, the microsphere has a diameter in the range of 1 to 300 micrometers, the poly(propylene fumarate) and poly(lactic-co-glycolic acid) are distributed in the microsphere, and the microsphere releases the bioactive agent in a sustained manner after an initial burst release. The microspheres may be covalently attached to a poly(propylene fumarate) scaffold for tissue regeneration applications in which the bioactive agent is released from the scaffold.