Blank NPs (polymer: 6.4 mg·kg−1) treatment were found to inhibit the polarization of Iba1‐positive microglia (activated microglia) toward the CD16/32‐positive M1 phenotype (pro‐inflammatory phenotype) with a 47.8% reduction in the cerebral ischemia penumbra within 24 h when compared to the model group (Figure 8B; Figure S31, Supporting Information). The gene discussed is AIF1; the disease is brain ischemia.