© GEORGE RETSECK

To repair a fractured pig tibia, researchers inserted a collagen scaffold that attracts mesenchymal stem cells (MSCs). Two weeks later, they injected a mix of microbubbles and DNA encoding bone morphogenetic protein (BMP) at the fracture site. Finally, they applied a pulse of ultrasound to encourage the MSCs to take up the DNA, and thus begin producing BMP. Within eight weeks, the bones were healed.

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