Dual-peptide Gene-Activated Scaffolds for Combined Osteogenesis and Angiogenesis Section 1 — Abstract Significance. Critical size bone defects, which are too large to heal on their own, remain one of the hardest problems in orthopaedic surgery. The current treatment, a recombinant protein called BMP-2, is expensive, requires very high doses, and causes side effects including ectopic bone growth, swelling, and inflammation. BMP-2 also only triggers bone formation; it does nothing for blood vessel growth. Without a blood supply, new bone cannot survive, so this gap is one of the main reasons large defects fail to heal.