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Acute kidney injury (AKI) is a kind of kidney disease with a high mortality rate, and is predominantly associated with abundant endogenous reactive oxygen/nitrogen species (RONS). However, there are no universal clinical treatment options currently. Development of antioxidants with high kidney enrichment is highly desired to prevent AKI. As a promising new artificial enzyme, nanozymes have attracted extensive attention over the past decade because of their commendable advantages over natural and traditional artificial enzymes. In this study, we reported ultrasmall polyvinylpyrrolidone-coated iridium nanoparticles (denoted as Ir NPs-PVP, 1.5 nm) as multi-enzyme mimetic to scavenge a variety of RONS, offering an efficient RONS-induced cellular protection. Meanwhile, computed tomography and inductively coupled plasma mass spectrometry demonstrated preferential renal uptake of Ir NPs-PVP following intravenous administration, leading to alleviate clinical symptoms in mice subjected to rhabdomyolysis- or cis-platinum-induced AKI. Impressively, ultrasmall Ir NPs-PVP exhibit relatively low systemic side effects in vivo due to rapid renal clearance via urine. Our work presents the clinically translatable potential of ultrasmall nanozymes for AKI management. [Display omitted] [ABSTRACT FROM AUTHOR]

• Ultrasmall platinum nanoparticles are prepared as multienzyme mimetics. • Pt nanozymes exhibit preferential kidneys enrichment and rapid clearance from the body. • Pt nanozymes facilitate effective removal of a variety of RONS. • Pt nanozymes promise PA/CT dual-modal imaging guided treatment of AKI. Acute kidney injury (AKI) is a common kidney disease with high mortality rate, while surprisingly, the supportive treatment and renal replacement are the only available clinical treatment options to date. The onset of AKI is often triggered by excessive toxic reactive oxygen/nitrogen species (RONS), and hence, the development of antioxidants with high renal accumulation and effective renal clearance is highly demanded to consume RONS in the kidneys. In this study, we developed ultrasmall polyvinylpyrrolidone-coated platinum nanoparticles (Pt NPs-PVP, ~3 nm) as multienzyme mimetics (catalase, peroxidase, and superoxide dismutase). Thanks to their excellent RONS scavenging ability, Pt NPs-PVP effectively reduced the hydrogen peroxide induced cellular damage. Analytical (inductively coupled plasma mass spectrometry) as well as imaging (photoacoustic and computed tomography) techniques revealed the preferential renal uptake and high enrichment of ultrasmall Pt NPs-PVP after intravenous administration, offering remarkable relief of the clinical symptoms of glycerol-induced AKI mice without any apparent systemic toxicity in vivo. Importantly, because of their ultrasmall size, Pt NPs-PVP exhibited rapid excretion from healthy mice, presenting relatively low toxicity and side effects. In conclusion, our work demonstrated ultrasmall Pt nanozyme as a state of the art antioxidant for dual-modal imaging guided treatment of AKI with improved treatment efficacy. [ABSTRACT FROM AUTHOR]

• 3D printed PCL/CS scaffolds were developed with excellent bioactive compositions and controllable porous structures. • Alkaline phosphatase (ALP)-responsive scaffolds were developed through the combination of a hemicyanine dye and PCL/CS scaffolds. • The combination of near-infrared (NIR) fluorescence and photoacoustic imaging was achieved. • Non-invasive, real-time visualization of enhanced bone formation was achieved both in vitro and in vivo. Although numerous biomaterials have been fabricated as scaffolds for the application of tissue engineering, real-time non-invasive monitoring of in vivo bone regeneration is still a big challenge. Particularly, the early osteogenesis is difficult to detect using conventional imaging modalities, such as X-ray computed tomography (CT) and magnetic resonance imaging (MRI) due to the limited amount of neo-bone tissue. Herein we report on alkaline phosphatase (ALP)-responsive scaffolds, which are composed of a turn-on hemicyanine dye (LET-3) and a typical three dimensional (3D) printed bone tissue engineering scaffold (polycaprolactone/calcium silicate, PCL/CS), for real-time non-invasive monitoring of in vivo bone regeneration by near-infrared fluorescence (NIR-FL) and photoacoustic (PA) duplex imaging. ALP, an early-stage biomarker of bone formation, turns "on" the NIR-FL/PA signals of LET-3 in scaffolds both in vitro and in vivo. Thus, the osteogenic-associated bioactivity of LET-3 labeled scaffolds could be visualized by NIR-FL/PA dual-modal imaging. Our results provide a promising strategy for detecting neo-bone formation by the combination of ALP prober and bone tissue engineering scaffolds, which holds great potential for traceable tissue engineering. [ABSTRACT FROM AUTHOR]