Well known for the adhesive property, mussel-inspired polydopamine (PDA) has been shown to enhance performance in a wide range of adsorption-based applications. However, imparting porous nanostructures to PDA materials for enhanced loading capacities has not been demonstrated even when surfactants were present in the synthesis. Herein, we report on the preparation of mesoporous PDA particles (MPDA) based on the assembly of primary PDA particles and Pluronic F127 stabilized emulsion droplets on water/1,3,5-trimethylbenzene (TMB) interfaces. The key to the formation of this new type of the MPDA structure is the full utilization of the π-π stacking interactions between PDA structures and the π-electron-rich TMB molecules. Remarkably, this method presents a facile approach for MPDA particles with an average diameter of ∼90 nm, slit-like pores with a peak size of ∼5.0 nm as well as hollow cavities. When used as the adsorbent for a model dye RhB, the MPDA particles achieved an ultrahigh RhB adsorption capacity of 1100 μg mg, which is significantly higher than that for the PDA-reactive dyes with Eschenmoser structure. Moreover, it was demonstrated that the cavity space in MPDA can facilitate high volumetric uptake in a capillary filling/stacking manner via the π-π interactions. These developments pave a new avenue on the mechanism and the designed synthesis of functional PDA materials by organic-organic composite assembly for advanced adsorption applications.

Theranostic agents for combined chemo-photothermal therapy have attracted intensive interest in the treatment of multi-drug resistance (MDR) in cancer therapy. However, the development of simple theranostic agents as dual hosts for both heat and a high payload of chemotherapeutic agents remains a big challenge. Herein, mesoporous polydopamine nanoparticles (MPDA) were successfully developed with properties of a high payload of DOX (up to 2000 μg mg) and the drug efflux inhibitor TPGS (d-α-tocopheryl polyethylene glycol 1000 succinate), as well as strong near-infrared absorption. Particularly, DOX and TPGS were sequentially loaded in the pore space and on the external particle surface of MPDA via π-π stacking and hydrophobic interactions, resulting in a MPDA-DOX@TPGS complex. The DOX release observably relies on the pH value and glutathione (GSH). Furthermore, it is possible to accelerate the rate of drug release by NIR irradiation. Importantly, the MPDA-DOX@TPGS complex was found to escape from endosomes after cellular uptake and release the loaded drugs into the cytosol. By TPGS mediated MDR reversal, the delivered DOX induced significant cytotoxicity to MCF-7/ADR cells. Besides, MPDA can absorb the NIR light and convert it into fatal heat to kill the cancer cells. As a consequence, the combined therapy in our system yields a synergistic effect with high therapeutic efficacy.

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The translation of mussel‐inspired wet adhesion to biomedical engineering fields have catalyzed the emergence of polydopamine (PDA)‐based nanomaterials with privileged features and properties of conducting multiple interfacial interactions. Recent concerns and progress on the understanding of PDA's hierarchical structure and progressive assembly are inspiring approaches toward novel nanostructures with property and function advantages over simple nanoparticle architectures. Major breakthroughs in this field demonstrated the essential role of π–π stacking and π‐cation interactions in the rational intervention of PDA self‐assembly. In this review, the recently emerging concepts in the preparation and application of PDA nanomaterials, including 3D mesostructures, low‐dimensional nanostructures, micelle/nanoemulsion based nanoclusters, as well as other multicomponent nanohybrids by the segregation and organization of PDA building blocks on nanoscale interfaces are outlined. The contribution of π‐electron interactions on the interfacial loading/release of π electron‐rich molecules (nucleic acids, drugs, photosensitizers) and the exogenous coupling of optical energy, as well as the impact of wet‐adhesion interactions on the nano‐bio interface interplay, are highlighted by discussing the structure‐property relationships in their featured applications including fluorescent biosensing, gene therapy, drug delivery, phototherapy, combined therapy, etc. The limitations of current explorations, and future research directions are also discussed.

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