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.

Study of Chemical Polymerization of Polypyrrole with SDS Soft Template: Physical, Chemical, and Electrical Properties

Polypyrrole (PPy) is a conductive polymer known for its biocompatibility and ease of synthesis. Chemically polymerized PPy was synthesized in the presence of sodium dodecyl sulfate (SDS), showing correlations among chemical properties, physical morphology, and electrical properties. Focused synthesis parameters included the pyrrole (Py) concentration, SDS concentration, and ammonium persulfate (APS)/Py ratio. The addition of SDS during chemical polymerization influenced the physical morphology of PPy by altering the self-assembling process via micelle formation, yielding sheet-like morphologies. However, the phenomenon also relied heavily on other synthesis parameters. Varying SDS concentrations within the 0.01 to 0.30 M window produced PPy sheets with no significant difference in optical band gap or physical size. While using 0.10 M SDS, an increase in Py concentration from 0.10 to 0.30 M yielded a larger size of PPy as the morphology changed from sheet-like to irregular shape. The band gap dropped from 2.35 to 1.10 eV, and the conductivity rose from 6.80 × 10-1 to 9.40 × 10-1 S/m. With an increase in the APS/Py ratio, the PPy product changed from a random to a sheet-like form. The product provided a larger average size, a decreased band gap, and increased electrical conductivity. Py polymerization in the absence of SDS revealed no significant change in shape or size as the Py concentration increased from 0.10 to 0.30 M; only a sphere-like form was observed, with a large band gap and small conductivity. Results from Raman spectral analysis indicated a correlation between optical band gap, physical morphology, and bipolaron/polaron ratio, mainly at the wavelengths associated with C-C stretching and C-H deformation. The increase in average size was associated with a decrease in band gap and resistance as well as an increase in the bipolaron/polaron ratio. This work indicates a strong correlation between size, morphology, electrical properties, and the bipolaron/polaron ratio of PPy in the presence of SDS.

Polypyrrole Nanomaterials: Structure, Preparation and Application

In the past decade, nanostructured polypyrrole (PPy) has been widely studied because of its many specific properties, which have obvious advantages over bulk-structured PPy. This review outlines the main structures, preparation methods, physicochemical properties, potential applications, and future prospects of PPy nanomaterials. The preparation approaches include the soft micellar template method, hard physical template method and templateless method. Due to their excellent electrical conductivity, biocompatibility, environmental stability and reversible redox properties, PPy nanomaterials have potential applications in the fields of energy storage, biomedicine, sensors, adsorption and impurity removal, electromagnetic shielding, and corrosion resistant. Finally, the current difficulties and future opportunities in this research area are discussed.

Fabrication of a pH-responsive core-shell nanosystem with a low-temperature photothermal therapy effect for treating bacterial biofilm infection

Recently, photothermal therapy (PTT) has been recognized as a viable alternative strategy against bacterial biofilm infection. However, the hyperthermia required for PTT to ablate a biofilm usually induces damage in normal tissues/organs nearby. Herein, we developed zeolite-based imidazole framework (ZIF-8)-coated mesoporous polydopamine (MPDA) core-shell nanoparticles and then loaded Pifithrin-μ (PES), a natural inhibitor of heat-shock protein (HSP) that plays an essential role in bacteria resisting heating-induced damage. The ZIF-8 shell of the MPDA@ZIF-8/PES nanoplatform enabled a rapid degradation in response to the acidic environment in bacterial biofilm infection, which triggered the controlled release of PES and Zn ions. As a result, HSP was remarkably suppressed for enhancing PTT efficacy upon mild near-infrared light irradiation. In addition, the release of Zn²⁺ also had an antibacterial/antibiofilm effect. Thus, the fabricated nanosystem was able to induce the effective elimination of the bacterial biofilm, realizing low-temperature PTT (∼45 °C) with excellent antibacterial efficacy. This work presented here not only provides a facile approach to fabricate the MPDA@ZIF-8/PES nanosystem with the responsiveness of the bacterial infection environment, but also proposes a promising low-temperature PTT strategy to treat bacterial biofilm-infection effectively.

Two-dimensional biomaterials: material science, biological effect and biomedical engineering applications

To date, nanotechnology has increasingly been identified as a promising and efficient means to address a number of challenges associated with public health. In the past decade, two-dimensional (2D) biomaterials, as a unique nanoplatform with planar topology, have attracted explosive interest in various fields such as biomedicine due to their unique morphology, physicochemical properties and biological effect. Motivated by the progress of graphene in biomedicine, dozens of types of ultrathin 2D biomaterials have found versatile bio-applications, including biosensing, biomedical imaging, delivery of therapeutic agents, cancer theranostics, tissue engineering, as well as others. The effective utilization of 2D biomaterials stems from the in-depth knowledge of structure-property-bioactivity-biosafety-application-performance relationships. A comprehensive summary of 2D biomaterials for biomedicine is still lacking. In this comprehensive review, we aim to concentrate on the state-of-the-art 2D biomaterials with a particular focus on their versatile biomedical applications. In particular, we discuss the design, fabrication and functionalization of 2D biomaterials used for diverse biomedical applications based on the up-to-date progress. Furthermore, the interactions between 2D biomaterials and biological systems on the spatial-temporal scale are highlighted, which will deepen the understanding of the underlying action mechanism of 2D biomaterials aiding their design with improved functionalities. Finally, taking the bench-to-bedside as a focus, we conclude this review by proposing the current crucial issues/challenges and presenting the future development directions to advance the clinical translation of these emerging 2D biomaterials.

Long-Term Stable Near-Infrared-Short-Wave-Infrared Photodetector Driven by the Photothermal Effect of Polypyrrole Nanostructures

Polypyrrole (PPy) is a conductive polymer and widely applied in different applications owing to its broadband absorption in the UV-visible, near-infrared (NIR), and short-wave-infrared (SWIR) spectrum, excellent conductivity, and strong photothermal effect. In this work, we explored for the first time the photothermal effect of PPy nanoparticles (PPy-NPs) in a photothermal-induced detector structure and developed a new type of air-stable hybrid PPy-NPs/Pt photodetector (PD) with NIR/SWIR sensitivity. By combining PPy-NPs with a platinum (Pt)-resistive pattern, we fabricated PPy-NPs/Pt PDs that are sensitive to illumination in the wavelength range from 800 to 2000 nm. Under the illumination of λ = 1.5 μm, the maximum photoresponsivity was measured to be ∼1.3 A/W with a 131 μs photoresponse rise time. Owing to the excellent material stability from both PPy-NPs and the Pt pattern, the current photodetectors show long-term stable photoresponsivity when they were stored in air without encapsulation. The results suggest that the PPy-NPs/Pt hybrid PDs are promising candidates for a new type of low-cost and broadband due to their multiple advantages such as free of toxic heavy metals, air stability, and solution processing.

Interfacial Engineering of Hybrid Polydopamine/Polypyrrole Nanosheets with Narrow Band Gaps for Fluorescence Sensing of MicroRNA

Nanoquencher-based biosensors have emerged as powerful tools for the detection of tumor markers, where challenges in efficiently docking the π-electron interaction interface toward nucleic acid probes containing π-electron-rich units of bases and fluorescent dyes still remain. Herein, we present hybrid polydopamine/polypyrrole nanosheets (PDA-PPy-NS) with π electron coupling and ultranarrow band gap (0.29 eV) by interfacial engineering of polymer hybrids at the nanoscale. PDA-PPy-NS were first prepared through oxidant-induced polymerization of pyrrole on PDA nanosheets. By utilizing fluorescent-dye-labeled single-stranded DNA as a probe, the hybrid nanoquencher showed ultrahigh fluorescence quenching ability, i.e., a Cy5-ssDNA/nanoquencher mass ratio of 36.9 under the complete quenching condition, which is comparable to that of graphene oxide. It was demonstrated that the energy level coupling of nanosheets and nucleic acid dye (Cy5) was the key factor contributing to the efficient photoinduced electron transfer (PET). Subsequently, the nanoquencher/DNA probe was proved to possess superior sensitivity and selectivity for efficient and reliable detection of miRNA-21 with a detection limit of 23.1 pM. Our work proves that the π-electron-rich biosensor interface can significantly enhance the PET efficiency, providing a theoretical basis for developing novel high-performance sensors.

Intervention of Polydopamine Assembly and Adhesion on Nanoscale Interfaces: State-of-the-Art Designs and Biomedical Applications

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.