Metal-Containing Polydopamine Nanomaterials: Catalysis, Energy, and Theranostics

Preparation and Properties of Antibacterial Polydopamine and Nano-Hydroxyapatite Modified Polyethylene Terephthalate Artificial Ligament

Due to its great biomechanical property, the polyethylene terephthalate (PET) artificial ligament has become one of the most promising allografts for anterior cruciate ligament (ACL) reconstruction. However, because of its chemical and biological inertness, PET is not a favored scaffold material for osteoblast growth, which promotes the ligament-bone healing. Meanwhile, in consideration of prevention of potential infection, the prophylactic injection of antibiotic was used as a post-operative standard procedure but also has the increasing risk of bacterial resistance. To face these two contradictions, in this article we coated a polydopamine (PDA) nano-layer on the PET ligament and used the coating as the adhesion interlayer to introduce nano-hydroxyapatite (nHA) and silver atoms to the surface of PET ligament. Because of the mild self-polymerization reaction of dopamine, the thermogravity analysis (TGA), Raman spectrum, and tensile test results show that the modification procedure have no negative effects on the chemical stability and mechanical properties of the PET. The results of NIH3T3 cell culture show that the PDA and nHA could effectively improve the biocompatibility of PET artificial ligament for fibroblast growth, and staphylococcus aureus antibacterial test results show that the Ag atom provided an antibacterial effect for PET ligament. As shown in this paper, the nano-PDA coating modification procedure could not only preserve the advantages of PET but also introduce new performance characteristics to PET, which opens the door for further functionalization of PET artificial ligament for its advanced development and application.

A moisture balanced antibacterial dressing loaded with lysozyme possesses antibacterial activity and promotes wound healing

Wound moisture management is very important in wound healing. Previous wound management has included dry healing and moist healing, and the theory of wound moisture balance is currently generally accepted. However, current studies have not reported which humidity is suitable for wound healing and how to appropriately use antibacterial compounds when the humidity is suitable. Our study explored the moisture balance of polyurethane foam dressings through a moisture balance test and constructed a safe and effective moisture balanced antibacterial dressing by loading lysozyme onto a polyurethane foam dressing. Wound healing experiments showed that the wound healing speed was the fastest when the humidity was 25%. In vivo and in vitro antibacterial experiments showed the superior antibacterial performance of the dressing after lysozyme loading. We loaded lysozyme on moisture balanced polyurethane dressings by means of dopamine adsorption, and the modified dressings were named PU/DA-LYS (polyurethane/dopamine-lysozyme). Experiments on wound healing in infected mice indicated that PU/DA-LYS helps fight infection while promoting wound healing. Cytotoxicity experiments and in vivo biological safety experiments indicated that PU/DA-LYS was safe for use. Our study found that the lysozyme loaded polyurethane dressing can provide appropriate wound moisture and prevent bacterial infection, which is a future developmental direction for wound dressings.

Tailored-Made Polydopamine Nanoparticles to Induce Ferroptosis in Breast Cancer Cells in Combination with Chemotherapy

Ferroptosis is gaining followers as mechanism of selective killing cancer cells in a non-apoptotic manner, and novel nanosystems capable of inducing this iron-dependent death are being increasingly developed. Among them, polydopamine nanoparticles (PDA NPs) are arousing interest, since they have great capability of chelating iron. In this work, PDA NPs were loaded with Fe3+ at different pH values to assess the importance that the pH may have in determining their therapeutic activity and selectivity. In addition, doxorubicin was also loaded to the nanoparticles to achieve a synergist effect. The in vitro assays that were performed with the BT474 and HS5 cell lines showed that, when Fe3+ was adsorbed in PDA NPs at pH values close to which Fe(OH)3 begins to be formed, these nanoparticles had greater antitumor activity and selectivity despite having chelated a smaller amount of Fe3+. Otherwise, it was demonstrated that Fe3+ could be released in the late endo/lysosomes thanks to their acidic pH and their Ca2+ content, and that when Fe3+ was co-transported with doxorubicin, the therapeutic activity of PDA NPs was enhanced. Thus, reported PDA NPs loaded with both Fe3+ and doxorubicin may constitute a good approach to target breast tumors.

A Gd-doped polydopamine (PDA)-based theranostic nanoplatform as a strong MR/PA dual-modal imaging agent for PTT/PDT synergistic therapy

Based on widely used photoacoustic imaging (PAI) and photothermal properties of polydopamine (PDA), a multifunctional Gd-PDA-Ce6@Gd-MOF (GPCG) nanosystem with a core-shell structure and strong imaging ability was constructed. Benefitting from the metal-organic framework (MOF) structure, GPCG nanoparticles (NPs) showed enhanced magnetic resonance imaging (MRI) ability with high relaxation rates (r1 = 13.72 mM-1 s-1 and r2 = 216.14 mM-1 s-1). The MRI effect of Gd ions combined with the PAI effect of PDA, giving GPCG NPs a dual-modal imaging ability. The core, mainly composed of PDA and photodynamic photosensitizer chlorin e6 (Ce6), achieved photothermal/photodynamic therapy (PTT/PDT) synergistic performance. Besides, to overcome the unexpected release of Ce6, the MOF shell realized pH-sensitive release and a high local concentration. Through in vivo studies, we concluded that GPCG NPs show a good inhibitory effect on tumor growth. In conclusion, we successfully obtained a GPCG theranostic nanoplatform and paved the way for subsequent design of imaging guided therapeutic nanostructures based on metal-doped PDA.

Efficient Iron and ROS Nanoscavengers for Brain Protection after Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) will be accompanied by the overload of iron and reactive oxygen species (ROS) following hematoma clearance. Although deferoxamine (DFO) has been widely utilized as a clinical first-line siderophore to remove the iron overload, the ROS-inducing damage still greatly limits the therapeutic effect of DFO. To address this issue, we designed and fabricated a series of dual-functional macromolecular nanoscavengers featuring high-density DFO units and catechol moieties. Note that the former units could effectively remove the iron overload, while the latter ones could efficiently deplete the ROS. The resulting nanoscavengers efficiently down-regulate the iron and ROS levels as well as significantly reduce the cell death in both iron-overloaded RAW 264.7 cells and the ICH mice model. This work suggests a novel clue for the ICH-ameliorated iron-depleting interventional therapeutic regimen.

A Mussel-Inspired Polydopamine-Filled Cellulose Aerogel for Solar-Enabled Water Remediation

A solar steam generation method has been widely investigated as a sustainable method to achieve seawater desalination and sewage treatment. However, oil pollutants are usually emitted in real seawater or wastewaters, which can cause serious fouling problems to disturb the solar evaporation performance. In this work, a mussel-inspired, low-cost, polydopamine-filled cellulose aerogel (PDA-CA) has been rationally designed and fabricated with both superhydrophilicity and underwater superoleophobicity. The resulting PDA-CA device could also achieve a high solar evaporation rate of 1.36 kg m^-1 h^-1 with an 86% solar energy utilize efficiency under 1 sun illumination. In addition, the PDA-CA not only exhibited promising antifouling capacity for long-term water evaporation but also engaged in the effective adsorption of organic dye contaminants. These promising features of PDA-CA may offer new opportunities for developing multifunctional photothermal devices for solar-driven water remediation.

Melanins as Sustainable Resources for Advanced Biotechnological Applications

Melanins are a class of biopolymers that are widespread in nature and have diverse origins, chemical compositions, and functions. Their chemical, electrical, optical, and paramagnetic properties offer opportunities for applications in materials science, particularly for medical and technical uses. This review focuses on the application of analytical techniques to study melanins in multidisciplinary contexts with a view to their use as sustainable resources for advanced biotechnological applications, and how these may facilitate the achievement of the United Nations Sustainable Development Goals.

PSMA-targeted melanin-like nanoparticles as a multifunctional nanoplatform for prostate cancer theranostics

Prostate-specific membrane antigen (PSMA) is highly expressed on the surface of most prostate tumor cells and is considered a promising target for prostate cancer imaging and treatment. It is possible to establish a PSMA-targeted theranostic probe to achieve early diagnosis and treatment of this cancer type. In this contribution, we prepared a multifunctional melanin-like polydopamine (PDA) nanocarrier decorated with a small-molecule PSMA inhibitor, N-[N-[(S)-1,3-dicarboxypropyl]carbamoyl]-(S)-l-lysine (DCL). PDA-DCL was then functionalized with perfluoropentane (PFP) and loaded with the photosensitizer chlorin e6 (Ce6) to give Ce6@PDA-DCL-PFP, which was successfully used for ultrasound-guided combined photodynamic/photothermal therapy (PDT/PTT) of prostate cancer. Compared with the corresponding non-targeted probe (Ce6@PDA-PEG-PFP), our targeted probe induced higher cellular uptake in vitro (6.5-fold) and more tumor accumulation in vivo (4.6-fold), suggesting strong active targeting capacity. Meanwhile, this new nanoplatform significantly enhanced the ultrasound contrast signal at the tumor site in vivo, thus facilitating precise and real-time detection of the tumor. In addition, this Ce6-loaded PDA nanoplatform produced a synergistic effect of PDT and PTT under 660 nm and 808 nm irradiation, inducing a more efficient killing effect compared with the individual therapy in vitro and in vivo. Furthermore, the tumor in the targeted group was more effectively suppressed than that in the non-targeted group under the same irradiation condition. This multifunctional probe may hold great potential for precise and early theranostics of prostate cancer.

Core–shell ZIF-8@polydopamine nanoparticles obtained by mitigating the polydopamine coating induced self-etching of MOFs: prototypical metal ion reservoirs for sticking to and killing bacteria

ZIF-8@PDA nanoparticles can work as metal ion reservoirs that locally release metal ions to kill bacteria after sticking to them.

Stimuli-responsive polydopamine-based smart materials

This review provides in-depth insight into the structural engineering of PDA-based materials to enhance their responsive feature and the use of them in construction of PDA-based stimuli-responsive smart materials.

Polyphenol scaffolds in tissue engineering

Polyphenols are a class of ubiquitous compounds distributed in nature, with fascinating inherent biocompatible, bioadhesive, antioxidant, and antibacterial properties. The unique polyphenolic structures based on catechol or pyrogallol moieties allow for strong non-covalent interactions (e.g., multiple hydrogen bonding, electrostatic, and cation-π interactions) as well as covalent interactions (e.g., Michael addition/Schiff-base reaction, radical coupling reaction, and dynamic coordination interactions with boronate or metal ions). This review article provides an overview of the polyphenol-based scaffolds including the hydrogels, films, and nanofibers that have emerged from chemical and functional signatures during the past years. A full description of the structure-function relationships in terms of their utilization in wound healing, bone regeneration, and electroactive tissue engineering is also carefully discussed, which may pave the path towards the rational design and facile preparation of next-generation polyphenol scaffolds for tissue engineering applications.

The mechanisms of HSA@PDA/Fe nanocomposites with enhanced nanozyme activity and their application in intracellular H2O2 detection

Nanozymes have drawn increasing attention with their broad applications but most nanozymes lack enzyme-like molecular structures, resulting in weak selectivity and low activity. Bioinspired molecular assembly provides an extremely promising strategy to mimic natural enzyme processes and develop function enhanced architectures. Herein, a new bioinspired molecular assembly strategy based on human serum albumin@polydopamine/Fe nanocomposites (HSA@PDA/Fe NCs) was proposed, in which Fe(iii)/Fe(ii) were anchored on HSA supported on PDA. HSA@PDA/Fe NCs with iron as the active center and HSA@PDA as the skeleton showed excellent peroxidase-like activity, which was nearly 1000 times higher than that of free Fe(iii). This may be attributed to the phenomenon that the cycle of quinones and the hydroxyl group on the nanocomposite surface greatly accelerate the conversion of Fe(iii)/Fe(ii) in acidic microenvironments. Systematic experimental studies illustrated that its activity was mainly affected by the metal active center, followed by the polymeric ligand, while the protein framework has little effect on its activity. Meanwhile, even after freeze-thaw and thermal cycle tests, it also showed excellent catalytic stability. Besides, a colorimetric assay based on HSA@PDA/Fe NCs was developed for detection of H₂O₂in vitro and in situ detection of H₂O₂ generated from live cells. This work will facilitate the developments on theoretical analysis, rational design and practical applications of nanozymes based on bioinspired molecular assemblies.

Bio-Applications of Multifunctional Melanin Nanoparticles: From Nanomedicine to Nanocosmetics

Bioinspired nanomaterials are ideal components for nanomedicine, by virtue of their expected biocompatibility or even complete lack of toxicity. Natural and artificial melanin-based nanoparticles (MNP), including polydopamine nanoparticles (PDA NP), excel for their extraordinary combination of additional optical, electronic, chemical, photophysical, and photochemical properties. Thanks to these features, melanin plays an important multifunctional role in the design of new platforms for nanomedicine where this material works not only as a mechanical support or scaffold, but as an active component for imaging, even multimodal, and simple or synergistic therapy. The number of examples of bio-applications of MNP increased dramatically in the last decade. Here, we review the most recent ones, focusing on the multiplicity of functions that melanin performs in theranostics platforms with increasing complexity. For the sake of clarity, we start analyzing briefly the main properties of melanin and its derivative as well as main natural sources and synthetic methods, moving to imaging application from mono-modal (fluorescence, photoacoustic, and magnetic resonance) to multi-modal, and then to mono-therapy (drug delivery, anti-oxidant, photothermal, and photodynamic), and finally to theranostics and synergistic therapies, including gene- and immuno- in combination to photothermal and photodynamic. Nanomedicine aims not only at the treatment of diseases, but also to their prevention, and melanin in nature performs a protective action, in the form of nanopigment, against UV-Vis radiations and oxidants. With these functions being at the border between nanomedicine and cosmetics nanotechnology, recently examples of applications of artificial MNP in cosmetics are increasing, paving the road to the birth of the new science of nanocosmetics. In the last part of this review, we summarize and discuss these important recent results that establish evidence of the interconnection between nanomedicine and cosmetics nanotechnology.

Facile and Controllable Growth of β-FeOOH Nanostructures on Polydopamine Spheres

Polydopamine (PDA) has a wide range of applications in biomedicine due to its high biocompatibility and surface chemistry and because of the presence of many functional groups in it, enabling further modification. As a catechol-like material, it has chelation properties for various types of metal ions, including iron. Here, we developed a procedure that uses PDA as a template to grow iron structures β-FeOOH directly on its surface. The innovative approach of this work relies on that these structures can be obtained in neutral conditions and selective iron-ion source. The influence of iron-ion source, environment, and solution concentration on the structure and amount of resulting material is presented. The growth has been characterized over time, taking into account their photothermal, magnetic, and colloidal stability properties. Moreover, we shed new light on understanding the interaction of PDA with iron ions for the growth of iron-based nanostructure on polydopamine particles. Finally, we predict that PDA@β-FeOOH nanoparticles could be a promising material in dual therapy merging photothermal therapy (PTT) treatment and magnetic resonance imaging (MRI) contrast agents.

Antibacterial Hybrid Hydrogels

Bacterial infectious diseases and bacterial-infected environments have been threatening the health of human beings all over the world. In view of the increased bacteria resistance caused by overuse or improper use of antibiotics, antibacterial biomaterials are developed as the substitutes for antibiotics in some cases. Among them, antibacterial hydrogels are attracting more and more attention due to easy preparation process and diversity of structures by changing their chemical cross-linkers via covalent bonds or noncovalent physical interactions, which can endow them with various specific functions such as high toughness and stretchability, injectability, self-healing, tissue adhesiveness and rapid hemostasis, easy loading and controlled drug release, superior biocompatibility and antioxidation as well as good conductivity. In this review, the recent progress of antibacterial hydrogel including the fabrication methodologies, interior structures, performances, antibacterial mechanisms, and applications of various antibacterial hydrogels is summarized. According to the bacteria-killing modes of hydrogels, several representative hydrogels such as silver nanoparticles-based hydrogel, photoresponsive hydrogel including photothermal and photocatalytic, self-bacteria-killing hydrogel such as inherent antibacterial peptides and cationic polymers, and antibiotics-loading hydrogel are focused on. Furthermore, current challenges of antibacterial hydrogels are discussed and future perspectives in this field are also proposed.

Regulating the absorption spectrum of polydopamine

Polydopamine (PDA) has been increasingly exploited as an advanced functional material, and its emergent light absorption property plays a crucial role in determining various utilizations. However, the rational design and efficient regulation of PDA absorption property remain a challenge due to the complex structure within PDA. In this work, we propose a facile method to regulate the light absorption behaviors of PDA by constructing donor-acceptor pairs within the microstructures through the chemical connections between indoledihydroxy/indolequinone and their oligomers with 2,2,6,6-tetramethylpiperidine-1-oxyl moiety. The detailed structural and spectral analysis, as well as the density functional theory simulation, further confirms the existence of donor-acceptor molecular pair structures, which could decrease the energy bandgap and increase the electron delocalization for enhancing light absorption across a broad spectrum. These rationally designed PDA nanoparticles with tunable absorption properties also show improved total photothermal effect and demonstrate excellent performances in solar desalination.

Integrated POSS-dendrimer nanohybrid materials: current status and future perspective

Polyhedral oligomeric silsesquioxane (POSS)-dendrimer hybrid materials have attracted great interest in the past ten years. The integration of inorganic POSS and organic dendrimer blocks in a single-phase material offers numerous possibilities to access desirable mechanical, optical, and biomedical properties for various applications. In this review article, we describe several kinds of POSS-dendrimer hybrid materials (POSS as the core, surface functionality, repeating unit of dendrimers and the POSS-dendron conjugates) with an emphasis on their synthetic strategies, tunable macroscopic properties, and potential applications. Moreover, the current trends, challenges and future directions of POSS-dendrimer hybrid materials are elaborated.

Antioxidant shape amphiphiles for accelerated wound healing

We reported a series of POSS-based antioxidant shape amphiphiles for preventing cell oxidative damage and promoting wound healing.

“Blackness” is an index of redox complexity in melanin polymers

Blackness as an emergent property associated with redox disorder and π-electron complexity in melanin polymers.

Polydopamine free radical scavengers

This feature article summarizes the recent progress, challenges and future directions of free radical scavengers based on polydopamine, including the integrated mechanism, current regulating strategies, and kinds of biomedical applications.