Mechanism of Self-Oxidative Copolymerization and its Application with Polydopamine-pyrrole Nano-copolymers

Currently, the copolymer of dopamine (DA) and pyrrole (PY) via chemical and electrochemical oxidation usually requires additional oxidants, and lacks flexibility in regulating the size and morphology, thereby limiting the broad applications of DA-PY copolymer in biomedicine. Herein, the semiquinone radicals produced by the self-oxidation of DA is ingeniously utilized as the oxidant to initiate the following copolymerization with PY, and a series of quinone-rich polydopamine-pyrrole copolymers (PDAm -nPY) with significantly enhanced absorption in near-infrared (NIR) region without any additional oxidant assistance is obtained. Moreover, the morphology and size of PDAm -nPY can be regulated by changing the concentration of DA and PY, thereby optimizing nanoscale PDA0.05 -0.15PY particles (≈ 150 nm) with excellent NIR absorption and surface modification activity are successfully synthesized. Such PDA0.05 -0.15PY particles show effective photoacoustic (PA) imaging and photothermal therapy (PTT) against 4T1 tumors in vivo. Furthermore, other catechol derivatives can also copolymerize with PY under the same conditions. This work by fully utilizing the semiquinone radical active intermediates produced through the self-oxidation of DA reduces the dependence on external oxidants in the synthesis of composite materials and predigests the preparation procedure, which provides a novel, simple, and green strategy for the synthesis of other newly catechol-based functional copolymers.

Pyrrole-Doped Polydopamine-Pyrrole (PDA-nPY) Nanoparticles with Tunable Size and Improved NIR Absorption for Photothermal Therapy

Polydopamine (PDA) as a melanin-like biomimetic material with excellent biocompatibility, full spectrum light absorption capacity and antioxidation property has been extensively applied in the biomedical field. Based on the high reactivity of dopamine (DA), exploiting new strategies to fabricate novel PDA-based nano-biomaterials with controllable size and improved performance is valuable and desirable. Herein, we reported a facile way to synthesize pyrrole-doped polydopamine-pyrrole nanoparticles (PDA-nPY NPs) with tunable size and enhanced near-infrared (NIR) absorption capacity through self-oxidative polymerization of DA with PY in an alkaline ethanol/H2O/NH4OH solution. The PDA-nPY NPs maintain excellent biocompatibility and surface reactivity as PDA. By regulating the volume of added PY, PDA-150PY NPs with a smaller size (<100 nm) and four-fold higher absorption intensity at 808 nm than that of PDA can be successfully fabricated. In vitro and in vivo experiments effectively further demonstrate that PDA-150PY NPs can effectively inhibit tumor growth and completely thermally ablate a tumor. It is believed that these PY doped PDA-nPY NPs can be a potential photothermal (PT) agent in biomedical application.