Results demonstrated that RMSN25–PEG-TA(2:1) enabled the blood-brain tumor barrier(BBTB) penetration to achieve subsequent accumulation in the brain.Pericytes are cells tightly wrapped around the ECs, which providethe barrier structural support and are related to the transcellularmechanism.44 The middle image in Figure S3 shows that RMSN25–PEG-TA(2:1)(red, RITC) were partially colocalized with the pericytes (green,anti-CD-140b), clearly revealing that the transcellular diffusionmechanism (transcytosis) might have contributed to MSNs crossing theBBB (yellow arrowhead). Here, PDGFRB is linked to brain neoplasm.