Poly(2-n-propyl-2-oxazoline)/tannic acid nanocapsules with in-situ synthesized gold nanorods for cancer theranostics

Abstract

The concept of hollow polymeric capsules fabricated with thermoresponsive polymers has revealed immense possibilities in the field of nanomedicine due to their tunable temperature and pH responsiveness caused by lower critical solution temperature (LCST) behavior. Herein, we report a new methodology to in-situ synthesize gold nanorods (AuNRs) within the pores of mesoporous silica nanoparticles (NPs) by trapping gold seed crystals and growing them into NRs in the presence of a weak reducing agent. The mesoporous silica NPs with incorporated NRs, i.e., modified silica NPs (SiO2-NRs) were used as sacrificial template for the fabrication of hollow polymeric multilayer capsules via layer-by-layer (LbL) assembly using poly(2-n-propyl-2-oxazoline) (PnPrOx) and tannic acid (TA) as layer components. The NRs of 25 ± 5 nm in size were uniformly distributed in the interior structure of PnPrOx/TA nanocapsules. The photo-thermal conversion efficiency of the PnPrOx/TA nanocapsules was found to be 47.5%. The release of encapsulated doxorubicin was found to be 55%, which increased to 68% when the incubation time was increased from 1 to 2 h. An on-demand burst release of 56% of the drug occurred within 2 min of NIR light exposure, and it reached 72% within 30 min, which inflicted major damage to cancer cells. Notably, the capsule suspension temperature increase from room temperature to 47 °C under laser light exposure, which is not only playing a key role in rupturing the capsules to enhance the drug release but also induces a hyperthermia effect in the tumor environment. Further, the in-vitro cytotoxicity experiments with human epithelial HEp-2 cells and fibrosarcoma HT1080 cells revealed an enhanced anti-cancer activity due to a synergistic chemo-photothermal effect. Hence, the proposed nanocapsule system can provide a unique, cheap, and efficient way of fabricating cancer theranostics for in-vivo applications.