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Poly(propylene carbonate) (PPC) decomposes at high temperature to release CO 2 . This CO 2 -generation temperature of PPC can be reduced down to less than 80 °C with the aid of a photoacid generator (PAG). In the present work, we demonstrate that using an additional helper component, surface plasmonic gold nanorods (GNRs), the PPC degradation reaction can also be initiated by infrared (IR) irradiation. For this purpose, a PPC-containing nanoparticle formulation was developed in which PPC-based amphiphilic block copolymers (BCPs), poly(poly(ethylene glycol) methacrylate- b-propylene carbonate- b-poly(ethylene glycol) methacrylate) (PPEGMA-PPC-PPEGMA), were self-assembled with GNRs and PAG molecules via solvent exchange. Under IR irradiation, GNRs produce heat that can cause PPC to decompose into CO 2 , and PAG (after UV pretreatment) catalyzes this PPC degradation process. Two PPEGMA-PPC-PPEGMA materials were used for this study: PPEGMA 7.3K -PPC 5.6K -PPEGMA 7.3K ("G7C6G7") and PPEGMA 2.1K -PPC 5.6K -PPEGMA 2.1K ("G2C6G2"). Addition of CTAB-coated GNRs dispersed in water to a G2C6G2 solution in DMF produced individually G2C6G2-encapsulated GNRs, whereas the same solvent exchange procedure resulted in the formation of polymer-coated GNR clusters when G7C6G7 was used as the encapsulating material. GNR/G2C6G2 NPs exhibited a surface plasmon resonance peak at 697 nm. The clustered morphology of G7C6G7-encapsulated GNRs caused a blue shift of the absorbance maximum to 511 nm. As a consequence, GNR/G2C6G2 NPs showed a greater absorbance/heat generation rate under IR irradiation than did GNR/G7C6G7 NPs. The IR-induced CO 2 generation rate was about 4.2 times higher with the GNR/G2C6G2+PAG sample than that with the GNR/G7C6G7+PAG sample. Both GNR/G7C6G7+PAG and GNR/G2C6G2+PAG systems produced ultrasound contrast enhancement effects under continuous exposure to IR light for >20 min; contrast enhancement was more spatially uniform for the GNR/G2C6G2+PAG sample. These results support the potential utility of PPC as a CO 2 -generating contrast agent in ultrasound imaging applications.

Currently, there is great interest in the development of ways to achieve the benefits of radiation treatments with reduced negative effects. The present study demonstrates the utilization of radio-luminescent particles (RLPs) as a means to achieve radio-sensitization and enhancement and their ability to affect head- and neck-cancer-cell cultures (in vitro) and xenografts (in vivo). Our approach utilizes a naturally abundant radio-luminescent mineral, calcium tungstate (CaWO 4 ), in its micro or nanoparticulate form for generating secondary UV-A light by γ ray or X-ray photons. In vitro tests demonstrate that unoptimized RLP materials (uncoated CaWO 4 (CWO) microparticles (MPs) and PEG-PLA-coated CWO nanoparticles (NPs)) induce a significant enhancement of the tumor-suppressive effect of X-rays and γ rays in both radio-sensitive- and radio-resistant-cancer models; uncoated CWO MPs and PEG-PLA-coated CWO NPs demonstrate comparable radio-sensitization efficacies in vitro. Mechanistic studies reveal that concomitant CaWO 4 causes increased mitotic death in radio-resistant cells treated with radiation, whereas CaWO 4 sensitizes radio-sensitive cells to X-ray-induced apoptosis and necrosis. The radio-sensitization efficacy of intratumorally injected CaWO 4 particles (uncoated CWO MPs and PEG-PLA-coated CWO NPs) is also evaluated in vivo in mouse head- and neck-cancer xenografts. Uncoated CWO MPs suppress tumor growth more effectively than PEG-PLA-coated CWO NPs. On the basis of theoretical considerations, an argument is proposed that uncoated CWO MPs release subtoxic levels of tungstate ions, which cause increased photoelectric-electron-emission effects. The effect of folic acid functionalization on the in vitro radio-sensitization behavior produced by PEG-PLA-coated CWO NPs is studied. Surface folic acid results in a significant improvement in the radio-sensitization efficiency of CaWO 4 .