Self-Assembled Metal-Phenolic Networks on Emulsions as Low-Fouling and pH-Responsive Particles

Fabrication of soy protein nanoparticles based on metal-phenolic networks for stabilization of nano-emulsions delivery system

The use of soy protein isolate (SPI) nanoparticles as a stabilizer in nano-emulsion systems has garnered significant interest. While metal-phenolic networks (MPNs) have been explored for their multifunctional surface modification capabilities, their integration with food protein-based delivery systems remains less explored. In this study, we attempt to develop a novel strategy to encapsulate cinnamaldehyde using MPNs (EGCG-Fe3+) with self-assembling soy protein nanoparticles (SE-Fe NPs) as a stabilizer for nano-emulsions. UV, Raman, and X-ray photoelectron spectroscopy analyses demonstrated that SE-Fe NPs were generated through metal-phenolic coordination and covalent interactions. SE-Fe NPs had a narrower particle size distribution and enhanced radical scavenging (up to 3.35-fold), as well as thermal stability. Furthermore, the smaller droplet size, higher modulus, higher cinnamaldehyde encapsulation efficiency (from 63.5% to 84.2%), and improved bio-accessibility of SE-Fe NPs stabilized nano-emulsions delivery system demonstrated in this study shows promising future applications in the food industry.

Oxidative Coupling and Self-Assembly of Polyphenols for the Development of Novel Biomaterials

In recent years, the development of biomaterials from green organic sources with nontoxicity and hyposensitivity has been explored for a wide array of biotherapeutic applications. Polyphenolic compounds have unique structural features, and self-assembly by oxidative coupling allows molecular species to rearrange into complex biomaterial that can be used for multiple applications. Self-assembled polyphenolic structures, such as hollow spheres, can be designed to respond to various chemical and physical stimuli that can release therapeutic drugs smartly. The self-assembled metallic-phenol network (MPN) has been used for modulating interfacial properties and designing biomaterials, and there are several advantages and challenges associated with such biomaterials. This review comprehensively summarizes current challenges and prospects of self-assembled polyphenolic hollow spheres and MPN coatings and self-assembly for biomedical applications.

Phenolic Ligand-Metal Charge Transfer Induced Copper Nanozyme with Reactive Oxygen Species-Scavenging Ability for Chronic Wound Healing

Chronic wounds frequently arise as a complication in diabetic patients, and their management remains a significant clinical hurdle due to their nonhealing nature featured by heightened oxidative stress and impaired healing cells at the wound site. Herein, we present a 2D copper antioxidant nanozyme induced by phenolic ligand-metal charge transfer (LMCT) to eliminate reactive oxygen species (ROS) and facilitate the healing of chronic diabetic wounds. We found that polyphenol ligands coordinated on the Cu3(PO4)2 nanosheets led to a strong charge transfer at the interface and regulated the valence states of Cu. The obtained Cu nanozyme exhibited efficient scavenging ability toward different oxidative species and protected human cells from oxidative damage. The nanozyme enhanced the healing of diabetic wounds by promoting re-epithelialization, collagen deposition, angiogenesis, and immunoregulation. This work demonstrates the LMCT-induced ROS scavenging ability on a nanointerface, providing an alternative strategy of constructing metal-based nanozymes for the treatment of diabetic wounds as well as other diseases.

Engineering poly(ethylene glycol) particles for targeted drug delivery

Poly(ethylene glycol) (PEG) is considered to be the "gold standard" among the stealth polymers employed for drug delivery. Using PEG to modify or engineer particles has thus gained increasing interest because of the ability to prolong blood circulation time and reduce nonspecific biodistribution of particles in vivo, owing to the low fouling and stealth properties of PEG. In addition, endowing PEG-based particles with targeting and drug-loading properties is essential to achieve enhanced drug accumulation at target sites in vivo. In this feature article, we focus on recent work on the synthesis of PEG particles, in which PEG is the main component in the particles. We highlight different synthesis methods used to generate PEG particles, the influence of the physiochemical properties of PEG particles on their stealth and targeting properties, and the application of PEG particles in targeted drug delivery.

Assembly of Metal-Phenolic Networks onto Microbubbles for One-Step Generation of Functional Microcapsules

The one-step assembly of metal-phenolic networks (MPNs) onto particle templates can enable the facile, rapid, and robust construction of hollow microcapsules. However, the required template removal step may affect the refilling of functional species in the hollow interior space or the in situ encapsulation of guest molecules during the formation of the shells. Herein, a simple strategy for the one-step generation of functional MPNs microcapsules is proposed. This method uses bovine serum albumin microbubbles (BSA MBs) as soft templates and carriers, enabling the efficient pre-encapsulation of guest species by leveraging the coordination assembly of tannic acid (TA) and FeIII ions. The addition of TA and FeIII induces a change in the protein conformation of BSA MBs and produces semipermeable capsule shells, which allow gas to escape from the MBs without template removal. The MBs-templated strategy can produce highly biocompatible capsules with controllable structure and size, and it is applicable to produce other MPNs systems like BSA-TA-CuII and BSA-TA-NiII . Finally, those MBs-templated MPNs capsules can be further functionalized or modified for the loading of magnetic nanoparticles and the pre-encapsulation of model molecules through covalence or physical adsorption, exhibiting great promise in biomedical applications.

Recent Advances of Metal-Polyphenol Coordination Polymers for Biomedical Applications

Nanomedicine has provided cutting-edge technologies and innovative methods for modern biomedical research, offering unprecedented opportunities to tackle crucial biomedical issues. Nanomaterials with unique structures and properties can integrate multiple functions to achieve more precise diagnosis and treatment, making up for the shortcomings of traditional treatment methods. Among them, metal-polyphenol coordination polymers (MPCPs), composed of metal ions and phenolic ligands, are considered as ideal nanoplatforms for disease diagnosis and treatment. Recently, MPCPs have been extensively investigated in the field of biomedicine due to their facile synthesis, adjustable structures, and excellent biocompatibility, as well as pH-responsiveness. In this review, the classification of various MPCPs and their fabrication strategies are firstly summarized. Then, their significant achievements in the biomedical field such as biosensing, drug delivery, bioimaging, tumor therapy, and antibacterial applications are highlighted. Finally, the main limitations and outlooks regarding MPCPs are discussed.

Recent Advances of Fe(III)/Fe(II)-MPNs in Biomedical Applications

Metal-phenolic networks (MPNs) are a new type of nanomaterial self-assembled by metal ions and polyphenols that have been developed rapidly in recent decades. They have been widely investigated, in the biomedical field, for their environmental friendliness, high quality, good bio-adhesiveness, and bio-compatibility, playing a crucial role in tumor treatment. As the most common subclass of the MPNs family, Fe-based MPNs are most frequently used in chemodynamic therapy (CDT) and phototherapy (PTT), where they are often used as nanocoatings to encapsulate drugs, as well as good Fenton reagents and photosensitizers to improve tumor therapeutic efficiency substantially. In this review, strategies for preparing various types of Fe-based MPNs are first summarized. We highlight the advantages of Fe-based MPNs under the different species of polyphenol ligands for their application in tumor treatments. Finally, some current problems and challenges of Fe-based MPNs, along with a future perspective on biomedical applications, are discussed.

Pickering emulsions stabilized by homogenized ball-milled eggshell particles in combination with sodium alginate

Eggshells, by-products of egg processing, were ball-milled and homogenized into particles (eggshell particles, ESPs) and then were used as the stabilizer with a two-step oil addition method to produce Pickering emulsions. Meanwhile, sodium alginate (SA) was used to modify the emulsifying ability of ESPs. The results indicated that SA addition helped to improve the dispersion performance and increase the negative charge of ESPs. Pickering emulsions stabilized by ESPs/SA showed much smaller particle size than those stabilized by ESPs. The maximum oil fraction in the ESPs/SA-stabilized emulsions reached up to 0.8, while that was only 0.75 in ESPs-stabilized emulsions. The presence of SA significantly enhanced the freeze-thaw, thermal, dilution, and centrifuge stability of ESPs-stabilized Pickering emulsions. The findings demonstrate the potential of eggshell particles as a kind of natural Pickering stabilizer, which will increase the high value-added utilization of poultry egg industry by-products.

Zinc-Epigallocatechin-3-gallate Network-Coated Nanocomposites against the Pathogenesis of Amyloid-Beta

The aggregation of amyloid beta (Aβ) is a hallmark of Alzheimer's disease (AD), a major cause of dementia and an unmet challenge in modern medicine. In this study, we constructed a biocompatible metal-phenolic network (MPN) comprising a polyphenol epigallocatechin gallate (EGCG) scaffold coordinated by physiological Zn(II). Upon adsorption onto gold nanoparticles, the MPN@AuNP nanoconstruct elicited a remarkable potency against the amyloid aggregation and toxicity of Aβ in vitro. The superior performance of MPN@AuNP over EGCG@AuNP was attributed to the porosity and hence larger surface area of the MPN in comparison with that of EGCG alone. The atomic detail of Zn(II)-EGCG coordination was unraveled by density functional theory calculations and the structure and dynamics of Aβ aggregation modulated by the MPN were further examined by discrete molecular dynamics simulations. As MPN@AuNP also displayed a robust capacity to cross a blood-brain barrier model through the paracellular pathway, and given the EGCG's function as an anti-amyloidosis and antioxidation agent, this MPN-based strategy may find application in regulating the broad AD pathology beyond protein aggregation inhibition.

Novel Strategy of Polymers in Combination with Silica Particles for Reversible Control of Oil-Water Interface

Hybrid smart emulsification systems are highly applicable in manipulating oil-in-water (O/W) droplets. Herein, novel switchable block polymers containing both zwitterionic and tertiary amine pendent groups were designed and synthesized to combine with charged silica particles to stabilize the O/W emulsion responsive to pH. This study was carried out in O/W emulsions stabilized with the polymer and silica particles under different pH conditions. The emulsion system was also simulated using molecular dynamics simulation to reveal the mechanism at molecular levels, thus gaining insight into the relationships between the emulsifying properties and the molecular interaction of the mixed system. Upon acidification of the continuous aqueous phase, protonated polymers with excellent hydrophilicity were induced by charged silica particles to cause rapid emulsion coalescence. In alkaline media, the mixed system conversely stabilized the O/W emulsions, cutting polymer consumption by over three-quarters. The emulsification and demulsification can be switched alternately by tuning the pH conditions. The applications exhibited excellent efficiency in separating heavy oil/water emulsions and proved the high conversion rate in emulsion polymerization. Overall, with this novel strategy to relieve tedious modifications on particle surfaces and massive consumption of polymers, the designed responsive emulsification systems can impart intelligent and controllable chemical reactivity to emulsions on demand in a more affordable and sustainable way.

Self-Assembled Integrative Nutrient Carrier Platform Containing Green Tea Catechin for Short Bowel Syndrome Treatment

Extensive resection of the small intestine leads to the development of short bowel syndrome (SBS), which reduces the effective absorptive surface area of the intestine and predisposes patients to emaciation, malnutrition, and other severe symptoms. Herein, green tea catechin (-)-epigallocatechin gallate (EGCG) and ferrous ions (Fe²⁺ ) are utilized to construct a nutrient carrier platform that self-assembles with nutrients to form phenolic-based nutrient complexes (PNCs). PNCs effectively prolong the residence and absorption time of nutrients in the intestine. Further this platform is applied to integrate full nutrient formula, an enteral nutrition (EN) preparation containing a range of full nutrient components. In an SBS rat model, the prepared phenolic-based integrative nutrient complexes (PINCs) enhance nutritional status, improve anemia and immune function, as well as facilitate the growth of remaining intestinal villi and crypts, and maintain the integrity of the intestinal barrier. In addition, PINCs enable the modulation of gut microbial dysbiosis, enrich the abundance of beneficial bacteria, and have no toxic effects after the long-term ingestion. These results provide a proof of principle for the use of polyphenol-based nanocomplexes as EN preparation, offering a feasible strategy for both nutritional support and therapeutic perspectives for SBS treatment.

Metal-phenolic networks acted as a novel bio-filler of a barrier membrane to improve guided bone regeneration via manipulating osteoimmunomodulation

A guided bone tissue regeneration membrane (GBRM) is traditionally viewed as an inert physical barrier to isolate soft tissue from the bone defect area. However, as a "foreign body", the implantation of a GBRM would inevitably modulate immune response and subsequently affect bone dynamics. Herein, we developed strontium ion (Sr²⁺)-based metal-phenolic network complexes (MPNs) as a novel type of bio-filler to manipulate the osteoimmunomodulation of the advanced GBRM. For controllable delivery of Sr²⁺ depending on the difference in affinity between phenolic ligands and Sr²⁺, tannic acid (TA), epigallocatechin gallate (EGCG), and epigallocatechin (EGC) were selected to chelate with Sr²⁺. The formed MPNs were incorporated into PCL nanofibrous membranes by blending electrospinning. Among them, TA/Sr based MPN particles displayed the most sustainable release profile of phenolic ligands and Sr²⁺. Further investigations demonstrated that Sr²⁺ could not only directly promote osteogenic differentiation of BMSCs, but also manipulate an anti-inflammatory osteoimmune microenvironment in a synergistic manner with TA, thus enhancing osteogenesis and inhibiting bone resorption. The rat alveolar bone defect model also confirmed that the TA/Sr nanoparticle modified membrane displayed better bone regeneration performance than the pure PCL membrane via inhibiting bone resorption. This work provides a new platform for controllable delivery of bioactive nutrient elements, and holds great promise for advancing multi-functional biocomposites.

Engineering metal‐phenolic networks for enhancing cancer therapy by tumor microenvironment modulation

The complicated tumor microenvironment (TME) is featured by low pH values, high redox status, and hypoxia, which greatly supports the genesis, development, and metastasis of tumors, leading to drug resistance and clinical failure. Moreover, a lot of immunosuppressive cells infiltrate in such TME, resulting in depressing immunotherapy. Therefore, the development of TME-responsive nanoplatforms has shown great significance in enhancing cancer therapeutics. Metal-phenolic networks (MPNs)-based nanosystems, which self-assemble via coordination of phenolic materials and metal ions, have emerged as excellent TME theranostic nanoplatforms. MPNs have unique properties including fast preparation, tunable morphologies, pH response, and biocompatibility. Besides, functionalization and surface modification can endow MPNs with specific functions for application requirements. Here, the representative engineering strategies of various polyphenols are first introduced, followed by the introduction of the engineering mechanisms of polyphenolic nanosystems, fabrication, and distinct properties of MPNs. Then, their advances in TME modulation are highlighted, such as antiangiogenesis, hypoxia relief, combination therapy sensitization, and immunosuppressive TME reversion. Finally, we will discuss the challenges and future perspectives of MPNs-based nanosystems for enhancing cancer therapy. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Microencapsulation of Ionic Liquid by Interfacial Self-Assembly of Metal-Phenolic Network for Efficient Gastric Absorption of Oral Drug Delivery

Improving bioavailability of orally delivered drugs is still challenging, as conventional drug delivery systems suffer from non-specific drug delivery in the gastrointestinal (GI) tract and limited drug absorption efficiency. Gastric drug delivery is even more difficult due to the harsh microenvironment, short retention time, and physiologic barriers in the stomach. Here, an oral drug delivery microcapsule system was developed for gastric drug delivery, which consists of ionic liquid (IL) as the inner carrier and metal-phenolic network (MPN) as the microcapsule shell. The IL@MPN microcapsules are prepared by interfacial self-assembly of Fe^III and quercetin at the interface of hydrophobic IL ([EMIM][NTf₂]) and water. The formation of MPN shell could improve the stability of IL droplets in water and endow the system with pH-response drug release properties, while the encapsulated IL core could efficiently load the drug and enhance the drug tissue permeability. The IL@MPN microcapsules showed enhanced drug absorption in the stomach after oral administration in a rat model, where the microcapsules are disassembled in gastric acid, and the released IL could reduce the viscosity of mucus gel and increase the drug transport rate across endothelial cells. This work presents a simple yet efficient strategy for oral drug delivery to the stomach. Given the diversity and versatility of both MPN and IL, the proposed self-assembled microcapsules could expand the toolbox of drug delivery systems with enhanced oral drug bioavailability.

Combined Chemo-Immuno-Photothermal Therapy for Effective Cancer Treatment via an All-in-One and One-for-All Nanoplatform

Tumor metastasis and recurrence are recognized to be the main causes of failure in cancer treatment. To address these issues, an "all in one" and "one for all" nanoplatform was established for combined "chemo-immuno-photothermal" therapy with the expectation to improve the antitumor efficacy. Herein, Docetaxel (DTX, a chemo-agent) and cynomorium songaricum polysaccharide (CSP, an immunomodulator) were loaded into zein nanoparticles coated by a green tea polyphenols/iron coordination complex (GTP/Fe^III, a photothermal agent). From the result, the obtained nanoplatform denoted as DTX-loaded Zein/CSP-GTP/Fe^III NPs was spherical in morphology with an average particle size of 274 nm, and achieved pH-responsive drug release. Moreover, the nanoplatform exhibited excellent photothermal effect both in vitro and in vivo. It was also observed that the nanoparticles could be effectively up take by tumor cells and inhibited their migration. From the results of the in vivo experiment, this nanoplatform could completely eliminate the primary tumors, prevent tumor relapses on LLC (Lewis lung cancer) tumor models, and significantly inhibit metastasis on 4T1 (murine breast cancer) tumor models. The underlying mechanism was also explored. It was discovered that this nanoplatform could induce a strong ICD effect and promote the release of damage-associated molecular patterns (DAMPs) including CRT, ATP, and HMGB1 by the dying tumor cells. And the CSP could assist the DAMPs in inducing the maturation of dendritic cells (DCs) and facilitate the intratumoral infiltration of T lymphocytes to clear up the residual or disseminated tumor cells. In summary, this study demonstrated that the DTX-loaded Zein/CSP-GTP/Fe^III is a promising nanoplatform to completely inhibit tumor metastasis and recurrence.

Applications of metal-phenolic networks in nanomedicine: a review

The exploration of nanomaterials is beneficial for the development of nanomedicine and human medical treatment. Metal-phenolic networks (MPNs) have been introduced as a nanoplatform for versatile functional hybrid nanomaterials and have attracted extensive attention due to their simple preparation, excellent properties and promising medical application prospects. This review presents an overview of recent synthesis methods for MPNs, their unique biomedical properties and the research progress in their application in disease detection and treatment. First, the synthesis methods of MPNs are summarised, and then the advantages and applicability of each assembly method are emphasised. The various functions exhibited by MPNs in biomedical applications are then introduced. Finally, the latest research progress in MPN-based nanoplatforms in the biomedical field is discussed, and their future research and application are investigated.

Metal Ion-Directed Functional Metal-Phenolic Materials

Metal ions are ubiquitous in nature and play significant roles in assembling functional materials in fields spanning chemistry, biology, and materials science. Metal-phenolic materials are assembled from phenolic components in the presence of metal ions through the formation of metal-organic complexes. Alkali, alkali-earth, transition, and noble metal ions as well as metalloids interacting with phenolic building blocks have been widely exploited to generate diverse hybrid materials. Despite extensive studies on the synthesis of metal-phenolic materials, a comprehensive summary of how metal ions guide the assembly of phenolic compounds is lacking. A fundamental understanding of the roles of metal ions in metal-phenolic materials engineering will facilitate the assembly of materials with specific and functional properties. In this review, we focus on the diversity and function of metal ions in metal-phenolic material engineering and emerging applications. Specifically, we discuss the range of underlying interactions, including (i) cation-π, (ii) coordination, (iii) redox, and (iv) dynamic covalent interactions, and highlight the wide range of material properties resulting from these interactions. Applications (e.g., biological, catalytic, and environmental) and perspectives of metal-phenolic materials are also highlighted.

Nanostructured particles assembled from natural building blocks for advanced therapies

Advanced treatments based on immune system manipulation, gene transcription and regulation, specific organ and cell targeting, and/or photon energy conversion have emerged as promising therapeutic strategies against a range of challenging diseases. Naturally derived macromolecules (e.g., proteins, lipids, polysaccharides, and polyphenols) have increasingly found use as fundamental building blocks for nanostructured particles as their advantageous properties, including biocompatibility, biodegradability, inherent bioactivity, and diverse chemical properties make them suitable for advanced therapeutic applications. This review provides a timely and comprehensive summary of the use of a broad range of natural building blocks in the rapidly developing field of advanced therapeutics with insights specific to nanostructured particles. We focus on an up-to-date overview of the assembly of nanostructured particles using natural building blocks and summarize their key scientific and preclinical milestones for advanced therapies, including adoptive cell therapy, immunotherapy, gene therapy, active targeted drug delivery, photoacoustic therapy and imaging, photothermal therapy, and combinational therapy. A cross-comparison of the advantages and disadvantages of different natural building blocks are highlighted to elucidate the key design principles for such bio-derived nanoparticles toward improving their performance and adoption. Current challenges and future research directions are also discussed, which will accelerate our understanding of designing, engineering, and applying nanostructured particles for advanced therapies.

Dialysis-derived urchin-like supramolecular assembly of tannic acid and paclitaxel with high porosity

Co-crystallization of active pharmaceutical ingredients (APIs) with pharmaceutically acceptable additives has emerged as an alternative to current drug delivery systems for hydrophobic drugs, due to their high drug loading efficiency. During this process, we herein report that tannic acid (TA) can be used as an amphiphilic stabilizer for the model drug, paclitaxel (PTX), that results in the shape and morphology variations of the synthesized microstructures, depending on the synthetic environment. We observed that rapid co-precipitation of PTX and TA via dialysis in water resulted in unprecedented urchin-like supramolecular microstructures with high porosity. On the other hand, slow co-precipitation for several hours under static conditions without dialysis exhibited bundles of straight TA-coated PTX fibers without any pores. This was plausibly due to the dynamic change of both the building block concentration and the solvent composition occurring during the transition of the kinetic product to the thermodynamic product. Interestingly, the synthesized urchin-like porous structure further rapidly transformed into a spherical shape through the interaction with serum proteins by remodeling of the non-covalent interactions, which contributed to the overall therapeutic efficacy tested in vitro. Our results provide knowledge on the self-assembly behavior of the hydrophobic drug and amphiphilic stabilizer under dynamic conditions, and contribute to the development of novel strategies in designing drug formulations.

Pickering Emulsion Stabilized by Metal-Phenolic Architectures: A Straightforward In Situ Assembly Strategy

Interfacial self-assembly has been a powerful driving force for fabricating functional and therapeutic carriers in emulsion systems. Herein, we reported a straightforward metal-phenolic supramolecular architecture, directly absorbed and cross-linked at the surfaces of oil drops and acted as the regulator between the oil and water interface to stabilize the emulsion systems. The results showed that the diverse interfacial properties and emulsion stability were tuned by the kinds and concentrations of polyphenols as well as the ratios of polyphenols to metal ions. Concretely, the TA-Fe³⁺ (coordinated by tannin acid and Fe³⁺)- or EGCG-Fe³⁺ (coordinated by EGCG and Fe³⁺)-based solid particles exhibited an increasing amount of interfacial adsorption with an increase in both polyphenol and metal ion concentrations or ratios of Fe³⁺ to polyphenols, and as a consequence of which, the prepared corresponding emulsions displayed enhanced emulsion stability and diverse interfacial characteristics. The rheological measurement results also exhibited that there was an increasing trend in both G' and G″, with enhanced concentrations or ratios of Fe³⁺ to polyphenols. Generally, our study not only highlighted a straightforward strategy for the directly interfacial fabrication of emulsions to improve their stability but also advanced the understanding of broadening the application scope of the metal-phenolic networks.

Recent Advances in Metal-Phenolic Networks for Cancer Theranostics

Nanomedicine integrates different functional materials to realize the customization of carriers, aiming at increasing the cancer therapeutic efficacy and reducing the off-target toxicity. However, efforts on developing new drug carriers that combine precise diagnosis and accurate treatment have met challenges of uneasy synthesis, poor stability, difficult metabolism, and high cytotoxicity. Metal-phenolic networks (MPNs), making use of the coordination between phenolic ligands and metal ions, have emerged as promising candidates for nanomedicine, most notably through the service as multifunctional theranostic nanoplatforms. MPNs present unique properties, such as rapid preparation, negligible cytotoxicity, and pH responsiveness. Additionally, MPNs can be further modified and functionalized to meet specific application requirements. Here, the classification of polyphenols is first summarized, followed by the introduction of the properties and preparation strategies of MPNs. Then, their recent advances in biomedical sciences including bioimaging and anti-tumor therapies are highlighted. Finally, the main limitations, challenges, and outlooks regarding MPNs are raised and discussed.

Encapsulation of Enzymes in Metal-Phenolic Network Capsules for the Trigger of Intracellular Cascade Reactions

Nanoengineered capsules encapsulated with functional cargos (e.g., enzymes) are of interest for various applications including catalysis, bioreactions, sensing, and drug delivery. Herein, we report a facile strategy to engineer enzyme-encapsulated metal-phenolic network (MPN) capsules using enzyme-loaded zeolitic imidazolate framework nanoparticles (ZIF-8 NPs) as templates, which can be removed in a mild condition (e.g., ethylenediaminetetraacetic acid (EDTA) solution). The capsule size (from 250 nm to 1 μm) and thickness (from 9.8 to 33.7 nm) are well controlled via varying the template size and coating time, respectively. Importantly, MPN capsules encapsulated with enzymes (i.e., glucose oxidase) can trigger the intracellular cascade reaction via the exhaustion of glucose to produce H₂O₂ and subsequently generate toxic hydroxyl radicals (^•OH) based on the Fenton reaction via the reaction between H₂O₂ and iron ions in MPN coatings. The intracellular cascade reaction for the generation of ^•OH is efficient to inhibit cancer cell viability, which is promising for the application in chemodynamic therapy.

Quantitatively Tracking Bio-Nano Interactions of Metal-Phenolic Nanocapsules by Mass Cytometry

Polymer nanocapsules, with a hollow structure, are increasingly finding widespread use as drug delivery carriers; however, quantitatively evaluating the bio-nano interactions of nanocapsules remains challenging. Herein, poly(ethylene glycol) (PEG)-based metal-phenolic network (MPN) nanocapsules of three sizes (50, 100, and 150 nm) are engineered via supramolecular template-assisted assembly and the effect of the nanocapsule size on bio-nano interactions is investigated using in vitro cell experiments, ex vivo whole blood assays, and in vivo rat models. To track the nanocapsules by mass cytometry, a preformed gold nanoparticle (14 nm) is encapsulated into each PEG-MPN nanocapsule. The results reveal that decreasing the size of the PEG-MPN nanocapsules from 150 to 50 nm leads to reduced association (up to 70%) with phagocytic blood cells in human blood and prolongs in vivo systemic exposure in rat models. The findings provide insights into MPN-based nanocapsules and represent a platform for studying bio-nano interactions.

Metal-Coordinated Supramolecular Self-Assemblies for Cancer Theranostics

Metal-coordinated supramolecular nanoassemblies have recently attracted extensive attention as materials for cancer theranostics. Owing to their unique physicochemical properties, metal-coordinated supramolecular self-assemblies can bridge the boundary between traditional inorganic and organic materials. By tailoring the structural components of the metal ions and binding ligands, numerous multifunctional theranostic nanomedicines can be constructed. Metal-coordinated supramolecular nanoassemblies can modulate the tumor microenvironment (TME), thus facilitating the development of TME-responsive nanomedicines. More importantly, TME-responsive organic-inorganic hybrid nanomaterials can be constructed in vivo by exploiting the metal-coordinated self-assembly of a variety of functional ligands, which is a promising strategy for enhancing the tumor accumulation of theranostic molecules. In this review, recent advancements in the design and fabrication of metal-coordinated supramolecular nanomedicines for cancer theranostics are highlighted. These supramolecular compounds are classified according to the order in which the coordinated metal ions appear in the periodic table. Furthermore, the prospects and challenges of metal-coordinated supramolecular self-assemblies for both technical advances and clinical translation are discussed. In particular, the superiority of TME-responsive nanomedicines for in vivo coordinated self-assembly is elaborated, with an emphasis on strategies that enhance the accumulation of functional components in tumors for an ideal theranostic outcome.

Metal-phenolic network coatings for engineering bioactive interfaces

The surface modification of biomaterials is crucial for constructing bioactive interfaces capable of interacting with specific biomolecules, controlling cell behavior and regulating biological processes. Because of their excellent biocompatibility, facile preparation, pH-responsiveness and universal adhesion, surface coatings made from metal-phenolic network (MPN) have attracted extensive attention for handling interfacial properties and designing biomaterials in recent years. Different methods and technologies for assembling MPN coatings are summarized and compared in this paper, followed by highlighting the advantages of MPN coatings as bioactive interfaces for controlling biological process at the molecular, cellular, and tissue levels. Current challenges and prospects of MPN coatings for biomedical applications are also discussed.

Phenolic-enabled nanotechnology: versatile particle engineering for biomedicine

Phenolics are ubiquitous in nature and have gained immense research attention because of their unique physiochemical properties and widespread industrial use. In recent decades, their accessibility, versatile reactivity, and relative biocompatibility have catalysed research in phenolic-enabled nanotechnology (PEN) particularly for biomedical applications which have been a major benefactor of this emergence, as largely demonstrated by polydopamine and polyphenols. Therefore, it is imperative to overveiw the fundamental mechanisms and synthetic strategies of PEN for state-of-the-art biomedical applications and provide a timely and comprehensive summary. In this review, we will focus on the principles and strategies involved in PEN and summarize the use of the PEN synthetic toolkit for particle engineering and the bottom-up synthesis of nanohybrid materials. Specifically, we will discuss the attractive forces between phenolics and complementary structural motifs in confined particle systems to synthesize high-quality products with controllable size, shape, composition, as well as surface chemistry and function. Additionally, phenolic's numerous applications in biosensing, bioimaging, and disease treatment will be highlighted. This review aims to provide guidelines for new scientists in the field and serve as an up-to-date compilation of what has been achieved in this area, while offering expert perspectives on PEN's use in translational research.

Surface Coatings via the Assembly of Metal-Monophenolic Networks

Mussel-inspired surface modification has received significant interest in recent years because of its simplicity and versatility. The deposition systems are still mainly limited to molecules with catechol chemical structures. In this paper, we report a novel deposition system based on a monophenol, vanillic acid (4-hydroxy-3-methoxybenzoic acid), to fabricate metal-phenolic network coatings on various substrates. The results of the water contact angle and zeta potential reveal that the modified polypropylene microfiltration membrane is underwater superhydrophobic and positively charged, showing applications in oil/water separation and dye removal. Furthermore, the single-face modified Janus membrane is promising in switchable oil/water separation. The results demonstrate a novel example of the metal-monophenolic deposition system, which expands the toolbox of surface coatings and facilitates the understanding of the deposition of phenols.

Microemulsion-Assisted Templating of Metal-Stabilized Poly(ethylene glycol) Nanoparticles

Poly(ethylene glycol) (PEG) is well known to endow nanoparticles (NPs) with low-fouling and stealth-like properties that can reduce immune system clearance in vivo, making PEG-based NPs (particularly sub-100 nm) of interest for diverse biomedical applications. However, the preparation of sub-100 nm PEG NPs with controllable size and morphology is challenging. Herein, we report a strategy based on the noncovalent coordination between PEG-polyphenolic ligands (PEG-gallol) and transition metal ions using a water-in-oil microemulsion phase to synthesize sub-100 nm PEG NPs with tunable size and morphology. The metal-phenolic coordination drives the self-assembly of the PEG-gallol/metal NPs: complexation between Mn^II and PEG-gallol within the microemulsions yields a series of metal-stabilized PEG NPs, including 30-50 nm solid and hollow NPs, depending on the Mn^II/gallol feed ratio. Variations in size and morphology are attributed to the changes in hydrophobicity of the PEG-gallol/Mn^II complexes at varying Mn^II/gallol ratios based on contact angle measurements. Small-angle X-ray scattering analysis, which is used to monitor the particle size and intermolecular interactions during NP evolution, reveals that ionic interactions are the dominant driving force in the formation of the PEG-gallol/Mn^II NPs. pH and cytotoxicity studies, and the low-fouling properties of the PEG-gallol/Mn^II NPs confirm their high biocompatibility and functionality, suggesting that PEG polyphenol-metal NPs are promising systems for biomedical applications.

Metal-Phenolic Network Covering on Zein Nanoparticles as a Regulator on the Oil/Water Interface

Interfacial self-assembly has become a powerful force for regulating the amphipathy of Pickering emulsions on the oil/water interface. Herein, metal-phenolic supramolecular coatings, acting as a regulator on the oil/water interface, were fabricated on the surface of zein nanoparticles (NPs), as a consequence of which the prepared Pickering emulsions stabilized by the decorated zein NPs exhibited diverse properties, decided by different concentrations of zein, tannic acid (TA), and metal ions (Fe³⁺). Metal-phenolic network-decorated zein NPs named ZTFex NPs (ZTFe NPs represented zein/TA/Fe³⁺ NPs, and x represented different concentrations of compounds) exhibited increasing diameters of 100-110 nm. Three-phase contact angles also showed that the strong hydrophobicity of zein NPs could be decreased as a result of the formation of metal-phenolic networks. As for corresponding Pickering emulsions, the covering of TA-Fe³⁺ networks on zein NPs could enhance the stability of zein NP-based emulsion obviously, which might be due to the fact that ZTFex NPs revealed the ability to form strong films on the oil/water interfaces. ZTFe4 was selected as an optimal concentration because of its minimum size and excellent storage stability. Besides, it was also found that the diameter of ZTFe4-based emulsion enhanced with the increase in the oil phase. The rheological measurement results showed that both G' and G″ increased with the increase of x and the oil phase. In general, our paper not only highlighted a straightforward method for the interfacial nanofabrication of solid particles but also provided a novel and potential strategy in Pickering emulsion applications.

Layered self-assemblies for controlled drug delivery: A translational overview

Self-assembly is a prominent phenomenon observed in nature. Inspired by this thermodynamically favorable approach, several natural and synthetic materials have been investigated to develop functional systems for various biomedical applications, including drug delivery. Furthermore, layered self-assembled systems provide added advantages of tunability and multifunctionality which are crucial for controlled and targeted drug release. Layer-by-layer (LbL) deposition has emerged as one of the most popular, well-established techniques for tailoring such layered self-assemblies. This review aims to provide a brief overview of drug delivery applications using LbL deposition, along with a discussion of associated scalability challenges, technological innovations to overcome them, and prospects for commercial translation of this versatile technique. Additionally, alternative self-assembly techniques such as metal-phenolic networks (MPNs) and Liesegang rings are also reviewed in the context of their recent utilization for controlled drug delivery. Blending the sophistication of these self-assembly phenomena with material science and technological advances can provide a powerful tool to develop smart drug carriers in a scalable manner.

Metal-Phenolic Network-Coated Hyaluronic Acid Nanoparticles for pH-Responsive Drug Delivery

Although self-assembled nanoparticles (SNPs) have been used extensively for targeted drug delivery, their clinical applications have been limited since most of the drugs are released into the blood before they reach their target site. In this study, metal-phenolic network (MPN)-coated SNPs (MPN-SNPs), which consist of an amphiphilic hyaluronic acid derivative, were prepared to be a pH-responsive nanocarrier to facilitate drug release in tumor microenvironments (TME). Due to their amphiphilic nature, SNPs were capable of encapsulating doxorubicin (DOX), chosen as the model anticancer drug. Tannic acid and FeCl₃ were added to the surface of the DOX-SNPs, which allowed them to be readily coated with MPNs as the diffusion barrier. The pH-sensitive MPN corona allowed for a rapid release of DOX and effective cellular SNP uptake in the mildly acidic condition (pH 6.5) mimicking TME, to which the hyaluronic acid was exposed to facilitate receptor-mediated endocytosis. The DOX-loaded MPN-SNPs exhibited a higher cytotoxicity for the cancer cells, suggesting their potential use as a drug carrier in targeted cancer therapy.

One-Step Generation of Multistimuli-Responsive Microcapsules via the Multilevel Interfacial Assembly of Polymeric Complexes

Efforts to develop microcapsules that respond to different stimuli derive from the incorporation of multiple dynamic assemblies of diverse functional species to the capsule shells. However, this usually involves complicated preparation processes that ultimately hinder the integration of multiple functionalities in a single material. This is addressed in the present work by proposing a multilevel interfacial assembly approach involving polymeric complexes that facilitate the fabrication of multistimuli-responsive microcapsules based on one-step Pickering emulsification using oppositely charged polycation-graphene oxide (GO) and polyanion-surfactant complexes prepared in immiscible liquid solutions. The complexes initially stabilize the emulsion based on electrostatic interactions. Subsequently, the highly dynamic bonding between the polymeric complexes facilitates the rearrangement of components at the oil/water interface to form a continuous interfacial shell membrane. The integrity of the microcapsule shells is sensitive to near-infrared irradiation owing to the GO component and is also sensitive to NaCl content because the assemblies between nanoparticles and polyelectrolytes are bonded through electrostatic interactions. The generality of the proposed strategy is demonstrated by the interfacial assembly of polycation-Fe₃O₄ complexes and polyanion-surfactant complexes. The resulting microcapsules exhibit salt responsiveness, pH responsiveness, and the ability to be positioned controllably by the application of an external magnetic field. This work provides a promising approach for the preparation of multistimuli-responsive microcapsules.

Polyphenol and self-assembly: metal polyphenol nanonetwork for drug delivery and pharmaceutical applications

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Selective Metal-Phenolic Assembly from Complex Multicomponent Mixtures

Selective self-assembly in multicomponent mixtures offers a method for isolating desired components from complex systems for the rapid production of functional materials. Developing approaches capable of selective assembly of "target" components into intended three-dimensional structures is challenging because of the intrinsically high complexity of multicomponent systems. Herein, we report the selective coordination-driven self-assembly of metal-phenolic networks (MPNs) from a series of complex multicomponent systems (including crude plant extracts) into thin films via metal chelation with phenolic ligands. The metal (Fe^III) selectively assembles low abundant phenolic components (e.g., myricetrin and quercetrin) from plant extracts into thin films. This selective metal-phenolic assembly is independent of the substrate properties (e.g., size, surface charge, and shape). Moreover, the high selectivity is consistent across different target phenolic ligands in model mixtures, even though each individual component can form thin films from single-component systems. A computational simulation of film formation suggests that the driving force for the selective behavior stems from differences in the number of chelating sites in the phenolic structures. The MPN films are shown to demonstrate improved antioxidant properties compared with the corresponding phenolic compounds in their free form, therefore exhibiting potential as free-standing antioxidant films.

Iron Gall Ink Revisited: In Situ Oxidation of Fe(II)-Tannin Complex for Fluidic-Interface Engineering

The ancient wisdom found in iron gall ink guides this work to a simple but advanced solution to the molecular engineering of fluidic interfaces. The Fe(II)-tannin coordination complex, a precursor of the iron gall ink, transforms into interface-active Fe(III)-tannin species, by oxygen molecules, which form a self-assembled layer at the fluidic interface spontaneously but still controllably. Kinetic studies show that the oxidation rate is directed by the counteranion of Fe(II) precursor salts, and FeCl₂ is found to be more effective than FeSO₄ -an ingredient of iron gall ink-in the interfacial-film fabrication. The optimized protocol leads to the formation of micrometer-thick, free-standing films at the air-water interface by continuously generating Fe(III)-tannic acid complexes in situ. The durable films formed are transferable, self-healable, pliable, and postfunctionalizable, and are hardened further by transfer to the basic buffer. This O₂ -instructed film formation can be applied to other fluidic interfaces that have high O₂ level, demonstrated by emulsion stabilization and concurrent capsule formation at the oil-water interface with no aid of surfactants. The system, inspired by the iron gall ink, provides new vistas on interface engineering and related materials science.