Polyphosphazene-Based Nanoparticles as Contrast Agents

Advancements in nanotechnology have led to significant changes to what is possible with medical imaging techniques in the past decades; however, there are still enormous incentives to develop novel imaging contrast agents that could facilitate detection of cancer at early stages, have improved renal clearance, have longer circulation half-lives, or otherwise provide complementary information. A vast variety of nanomaterials have been developed to enhance the contrast of medical images. Among them, polymers such as polyphosphazenes (PPPs) have recently gained considerable interest due to their excellent properties such as biocompatibility, biodegradability, synthetic flexibility, high versatility, hydrophilicity, and nontoxicity. Here, we present the synthetic methods, properties, and applications of PPPs. We describe imaging modalities such as computed tomography (CT), magnetic resonance imaging (MRI), photoacoustics (PA) and fluorescence, along with the advantages of using polymeric nanoparticles in these imaging techniques. Moreover, multimodal PPPs-based agents that enhanced the imaging accuracy, renal clearance and cytotoxicity of conventional contrast agents are discussed.