(42 %) after 72 h compared to physiological pH (13 %). They also demonstrated significant cytotoxicity on HepG2 cells with 23 % of cell viability at 0.1 mg.mL Inorganic silica nanoparticles have also been decorated with polymers from RDRP in which hydrazone linkages have been incorporated to obtain theranostic systems. Mesoporous silica nanoparticles are considered promising candidates for theranostic applications, 79 particularly as they can both allow the encapsulation of a fluorescent dye in their pores and the grafting of polymers onto their surface. For instance, random copolymerization of OEGMA and methacrylamide tert-butyl carbazate (MABH) was achieved from RAFT agents immobilized at the surface of hollow mesoporous silica nanoparticles (HMSNs). 80 This step was followed by the coupling of Dox to the acylhydrazine groups of MABH (Figure ) and the encapsulation of the IR825 photothermal dye into the hydrophobic hollow cavity of silica. The resulting HMSNshyd-Dox@IR825 polymer prodrug hybrid nanoparticles exhibited an average diameter of 120 nm and showed enhanced Dox release in mild acid conditions (i.e., pH 5 and 6) compared to pH 7.4 (76 %, 69 % and 18 % after 58 h, respectively). In vitro studies on HeLa cells confirmed significant cytotoxicity of such particles even if it was lower than that of free Dox and fast internalization as strong Dox fluorescence was observed in the cell nucleus region after 24 h. The imine group is another Schiff base bond widely used as acid-labile linkage for the design of pH-sensitive polymer prodrugs by RDRP. It is formed by condensation reaction between an aldehyde or a ketone moiety and a primary amine group (Figure ). It usually degrades at pH < 5-6 and remains stable at physiological pH, which facilitates its use for drug delivery applications by enabling a precise control of the drug release under physiopathological conditions.