Growth factors are of great potential in regenerative medicine. However, their clinical applications are largely limited in by short in vivo half-lives and a narrow therapeutic window. Thus, a robust controlled release system remains an unmet medical need for growth-factor-based therapies. A nanoscale controlled release system (degradable protein nanocapsule) is provided via in-situ polymerization on growth factor. The release rate can be finely tuned by engineering the surface polymer composition. Improved therapeutic outcomes are achieved with the growth factor nanocapsules, as illustrated in spinal cord fusion mediated by bone morphogenetic protein-2 (BMP-2) nanocapsules.