a system for stabilizing fibroblast - derived growth factors , maintaining their bioactivity over a prolonged period of time and controllably releasing them for use is disclosed . the system uses growth factors bound to biocompatible substrates via heparin or heparin derived compounds to maintain the bioactivity of the growth factors . a growth factor bound to a heparin coated substrate can be used independently as a controlled release device , or can be incorporated into a reservoir or matrix type controlled release devices to further enhance the controlled release properties . the stabilized growth factors can be implanted into a patient , thereby providing a means for producing an in vivo controlled release of a growth factor to the patient .