Functional muscle recovery with nanoparticle-directed M2 macrophage polarization in mice

Significance Chronic inflammation contributes to the progression of many diseases, including 7 of the 10 leading causes of death. Macrophages play a central role in regulating inflammation because they adopt proinflammatory (M1) and proregenerative (M2) phenotypes. While an initial M1 response is critical, the prolonged presence of M1 macrophages, or the imbalance of M1 over M2 macrophages, can cause tissue damage and inhibit regeneration. We demonstrate that gold nanoparticles can be used to deliver a cytokine to direct M2 macrophage polarization following muscle injury in vivo. The polarization shift promoted regeneration and increased muscle strength. The ability to direct macrophage polarization in an inflammatory microenvironment may be useful in the treatment of many injuries and inflammatory diseases.