When a scaffold matches the geometry of what it replaces, the system rebuilds itself without external instruction. Four domains prove it: a lab-grown organ, a coral reef, a bone graft, and a bombed city. Scientists at University College London and Great Ormond Street Hospital published results in Nature Biotechnology this March that should change how we think about rebuilding broken systems. They took a pig's esophagus, stripped it of every living cell through a process called decellularization, and were left with nothing but the structural scaffold — the collagen and extracellular matrix that gave the organ its shape. They then seeded that scaffold with muscle precursor cells from a different pig and implanted it. All eight recipient animals recovered normal swallowing. Within three to six months, the grafts had developed functioning muscle, nerves, and blood vessels. The engineered tissue grew with the animals. No immunosuppression was needed, because the scaffold carried the recipient's own cells.…