Scheme 1. Schematic illustration showing (a) the preparation process of NanoDOX and (b) the preparation process of NDHM. (c) NDHM is injected and formed in the tumor site of the mouse by a disposal-connected mixing system, and then, NDHM can be degraded by MMP-2 in the tumor microenvironment, leading to NanoDOX spreading in the tumor tissue and further entering into tumor cells. Finally, DOX released from NanoDOX will enter into the nucleus and intercalate on DNA to induce programmed cell death.