The regenerative power of tissues and organs in biology has no analog in synthetic materials. Although self-healing of microscopic defects has been demonstrated, the regrowth of material lost through catastrophic damage requires a regenerative-like approach. We demonstrate a vascular synthetic system that restores mechanical performance in response to large-scale damage. Gap-filling scaffolds are created through a two-stage polymer chemistry that initially forms a shape-conforming dynamic gel but later polymerizes to a solid structural polymer with robust mechanical properties. Through the control of reaction kinetics and vascular delivery rate, we filled impacted regions that exceed 35 mm in diameter within 20 min and restored mechanical function within 3 hours. After restoration of impact damage, 62% of the total absorbed energy was recovered in comparison with that in initial impact tests.