Metal-phenolic networks as tuneable spore coat mimetics

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.

Oral delivery of probiotics using single-cell encapsulation

Adequate intake of live probiotics is beneficial to human health and wellbeing because they can help treat or prevent a variety of health conditions. However, the viability of probiotics is reduced by the harsh environments they experience during passage through the human gastrointestinal tract (GIT). Consequently, the oral delivery of viable probiotics is a significant challenge. Probiotic encapsulation provides a potential solution to this problem. However, the production methods used to create conventional encapsulation technologies often damage probiotics. Moreover, the delivery systems produced often do not have the required physicochemical attributes or robustness for food applications. Single-cell encapsulation is based on forming a protective coating around a single probiotic cell. These coatings may be biofilms or biopolymer layers designed to protect the probiotic from the harsh gastrointestinal environment, enhance their colonization, and introduce additional beneficial functions. This article reviews the factors affecting the oral delivery of probiotics, analyses the shortcomings of existing encapsulation technologies, and highlights the potential advantages of single-cell encapsulation. It also reviews the various approaches available for single-cell encapsulation of probiotics, including their implementation and the characteristics of the delivery systems they produce. In addition, the mechanisms by which single-cell encapsulation can improve the oral bioavailability and health benefits of probiotics are described. Moreover, the benefits, limitations, and safety issues of probiotic single-cell encapsulation technology for applications in food and beverages are analyzed. Finally, future directions and potential challenges to the widespread adoption of single-cell encapsulation of probiotics are highlighted.

Functional metal-phenolic cortical cytoskeleton for artificial cells

Cortex-like cytoskeleton, a thin layer of cross-linked cytoplasmic proteins underlying the cell membrane, plays an essential role in modulating membrane behavior and cell surface properties. However, bottom-up construction of functional cortex-like cytoskeleton in artificial cells remains a challenge. Here, we present metal-phenolic networks as artificial cortical cytoskeletons in liposome-based artificial cells. The metal-phenolic cytoskeleton-reinforced artificial cells exhibit long-term stability, enhanced resistance to a variety of harsh environments, tunable permeability, and well-controlled morphologies. We anticipate that our stable artificial cell models will stride forward to practical applications of liposome-based microsystem.

Novel delivery systems for controlled release of bacterial therapeutics

As more is learned about the benefits of microbes, their potential to prevent and treat disease is expanding. Microbial therapeutics are less burdensome and costly to produce than traditional molecular drugs, often with superior efficacy. Yet, as with most medicines, controlled dosing and delivery to the area of need remain key challenges for microbes. Advances in materials to control small-molecule delivery are expected to translate to microbes, enabling similar control with equivalent benefits. In this perspective, recent advances in living biotherapeutics are discussed within the context of new methods for their controlled release. The integration of these advances provides a roadmap for the design, synthesis, and analysis of controlled microbial therapeutic delivery systems.

Structured soft particulate matters for delivery of bioactive compounds in foods and functioning in the colon

The present review discusses challenges, perspectives, and current needs of delivering bioactive compounds (BCs) using soft particulate matters (SPMs) for gut health. SPMs can entrap BCs for incorporation in foods, preserve their bioactivities during processing, storage, and gastrointestinal digestion, and deliver BCs to functioning sites in the colon. To enable these functions, physical, chemical, and biological properties of BCs are integrated in designing various types of SPMs to overcome environmental factors reducing the bioavailability and bioactivity of BCs. The design principles are applied using food grade molecules with the desired properties to produce SPMs by additionally considering the cost, sustainability, and scalability of manufacturing processes. Lastly, to make delivery systems practical, impacts of SPMs on food quality are to be evaluated case by case, and health benefits of functional foods incorporated with delivery systems are to be confirmed and must outweigh the cost of preparing SPMs.

Cytoprotective Metal-Phenolic Network Sporulation to Modulate Microalgal Mobility and Division

Synthetic cell exoskeletons created from abiotic materials have attracted interest in materials science and biotechnology, as they can regulate cell behavior and create new functionalities. Here, a facile strategy is reported to mimic microalgal sporulation with on-demand germination and locomotion via responsive metal-phenolic networks (MPNs). Specifically, MPNs with tunable thickness and composition are deposited on the surface of microalgae cells via one-step coordination, without any loss of cell viability or intrinsic cell photosynthetic properties. The MPN coating keeps the cells in a dormant state, but can be disassembled on-demand in response to environmental pH or chemical stimulus, thereby reviving the microalgae within 1 min. Moreover, the artificial sporulation of microalgae resulted in resistance to environmental stresses (e.g., metal ions and antibiotics) akin to the function of natural sporulation. This strategy can regulate the life cycle of complex cells, providing a synthetic strategy for designing hybrid microorganisms.

Drying of probiotics to enhance the viability during preparation, storage, food application, and digestion: A review

Functional food products containing viable probiotics have become increasingly popular and demand for probiotic ingredients that maintain viability and stability during processing, storage, and gastrointestinal digestions. This has resulted in heightened research and development of powdered probiotic ingredients. The aim of this review is to overview the development of dried probiotics from upstream identification to downstream applications in food. Free probiotic bacteria are susceptible to various environmental stresses during food processing, storage, and after ingestion, necessitating additional materials and processes to preserve their activity for delivery to the colon. Various classic and emerging thermal and nonthermal drying technologies are discussed for their efficiency in preparing dehydrated probiotics, and strategies for enhancing probiotic survival after dehydration are highlighted. Both the formulation and drying technology can influence the microbiological and physical properties of powdered probiotics that are to be characterized comprehensively with various techniques. Furthermore, quality control during probiotic manufacturing and strategies of incorporating powdered probiotics into liquid and solid food products are discussed. As emerging technologies, structure-design principles to encapsulate probiotics in engineered structures and protective materials with improved survivability are highlighted. Overall, this review provides insights into formulations and drying technologies required to supplement viable and stable probiotics into functional foods, ensuring the retention of their health benefits upon consumption.

Self-Assembled Nanocoatings Protect Microbial Fertilizers for Climate-Resilient Agriculture

Chemical fertilizers have been crucial for sustaining the current global population by supplementing overused farmland to support consistent food production, but their use is unsustainable. Pseudomonas chlororaphis is a nitrogen-fixing bacterium that could be used as a fertilizer replacement, but this microbe is delicate. It is sensitive to stressors, such as freeze-drying and high temperatures. Here, we demonstrate protection of P. chlororaphis from freeze-drying, high temperatures (50 oC), and high humidity using self-assembling metal-phenolic network (MPN) coatings. The composition of the MPN is found to significantly impact its protective efficacy, and with optimized compositions, no viability loss is observed for MPN-coated microbes under conditions where uncoated cells do not survive. Further, we demonstrate that MPN-coated microbes improve germination of seeds by 150% as compared to those treated with fresh P. chlororaphis. Taken together, these results demonstrate the protective capabilities of MPNs against environmental stressors and represent a critical step towards enabling the production and storage of delicate microbes under nonideal conditions.

Synthetic engineered bacteria for cancer therapy

INTRODUCTION

Cancer mortality worldwide highlights the urgency for advanced therapeutic methods to fill the gaps in conventional cancer therapies. Bacteriotherapy is showing great potential in tumor regression due to the motility and colonization tendencies of bacteria. However, the complicated in vivo environment and tumor pathogenesis hamper the therapeutic outcomes. Synthetic engineering methods endow bacteria with flexible abilities both at the extracellular and intracellular levels to meet treatment requirements. In this review, we introduce synthetic engineering methods for bacterial modifications. We highlight the recent progress in engineered bacteria and explore how these synthetic methods endow bacteria with superior abilities in cancer therapy. The current clinical translations are further discussed. Overall, this review may shed light on the advancement of engineered bacteria for cancer therapy.

AREAS COVERED

Recent progress in synthetic methods for bacterial engineering and specific examples of their applications in cancer therapy are discussed in this review.

EXPERT OPINION

Bacteriotherapy bridges the gaps of conventional cancer therapies through the natural motility and colonization tendency of bacteria, as well as their synthetic engineering. Nevertheless, to fulfill the bacteriotherapy potential and move into clinical trials, more research focusing on its safety concerns should be conducted.

Vortex-assisted, nanoarchitectonic manipulation of microparticles with flavonoid-Fe3+ complex in biphasic water-oil systems

Coordination-driven self-assembly of metal-ligand complexes is a powerful nanoarchitectonic tool for particle engineering, but its usability is limited when using two immiscible coating components. This paper reports that simple vortexing of a biphasic system of Fe³⁺ ions in water and flavonoids in oil forms nanoshells on individual particles, thereby enabling the utilization of water-insoluble ligands as coating materials. Mechanistic studies suggest that the biphasic mass-transfer equilibrium of flavonoid-Fe³⁺ species controls the shell formation, with the oil phase acting as a reservoir of coating precursors for continuous coating. The versatility and convenience of our method expand the chemical toolbox for modulating particle-material interfaces.

Versatile Assembly of Metal-Phenolic Network Foams Enabled by Tannin-Cellulose Nanofibers

Metal-phenolic network (MPN) foams are prepared using colloidal suspensions of tannin-containing cellulose nanofibers (CNFs) that are ice-templated and thawed in ethanolic media in the presence of metal nitrates. The MPN facilitates the formation of solid foams by air drying, given the strength and self-supporting nature of the obtained tannin-cellulose nanohybrid structures. The porous characteristics and (dry and wet) compression strength of the foams are rationalized by the development of secondary, cohesive metal-phenolic layers combined with a hydrogen bonding network involving the CNF. The shrinkage of the MPN foams is as low as 6% for samples prepared with 2.5-10% tannic acid (or condensed tannin at 2.5%) with respect to CNF content. The strength of the MPN foams reaches a maximum at 10% tannic acid (using Fe^(III) ions), equivalent to a compressive strength 70% higher than that produced with tannin-free CNF foams. Overall, a straightforward framework is introduced to synthesize MPN foams whose physical and mechanical properties are tailored by the presence of tannins as well as the metal ion species that enable the metal-phenolic networking. Depending on the metal ion, the foams are amenable to modification according to the desired application.

Binding to Iron Quercetin Complexes Increases the Antioxidant Capacity of the Major Birch Pollen Allergen Bet v 1 and Reduces Its Allergenicity

Bet v 1 is the major allergen in birch pollen to which up to 95% of patients sensitized to birch respond. As a member of the pathogenesis-related PR 10 family, its natural function is implicated in plant defense, with a member of the PR10 family being reported to be upregulated under iron deficiency. As such, we assessed the function of Bet v 1 to sequester iron and its immunomodulatory properties on human immune cells. Binding of Bet v 1 to iron quercetin complexes FeQ2 was determined in docking calculations and by spectroscopy. Serum IgE-binding to Bet v 1 with (holoBet v1) and without ligands (apoBet v 1) were assessed by ELISA, blocking experiments and Western Blot. Crosslinking-capacity of apo/holoBet v 1 were assessed on human mast cells and Arylhydrocarbon receptor (AhR) activation with the human reporter cellline AZ-AHR. Human PBMCs were stimulated and assessed for labile iron and phenotypic changes by flow cytometry. Bet v 1 bound to FeQ2 strongly with calculated Kd values of 1 nm surpassing affinities to quercetin alone nearly by a factor of 1000. Binding to FeQ2 masked IgE epitopes and decreased IgE binding up to 80% and impaired degranulation of sensitized human mast cells. Bet v 1 facilitated the shuttling of quercetin, which activated the anti-inflammatory AhR pathway and increased the labile iron pool of human monocytic cells. The increase of labile iron was associated with an anti-inflammatory phenotype in CD14+monocytes and downregulation of HLADR. To summarize, we reveal for the first time that FeQ2 binding reduces the allergenicity of Bet v 1 due to ligand masking, but also actively contributes anti-inflammatory stimuli to human monocytes, thereby fostering tolerance. Nourishing immune cells with complex iron may thus represent a promising antigen-independent immunotherapeutic approach to improve efficacy in allergen immunotherapy.