Single-Cell Nanoencapsulation: From Passive to Active Shells

Biphasic water-oil systems for functional augmentation of probiotic Lactobacillus acidophilus nanoencapsulated in luteolin-Fe3+ shells

Single-cell nanoencapsulation (SCNE) has great potential in the enhancement of therapeutic effects of probiotic microbes. However, the material scope has been limited to water-soluble compounds to avoid non-biocompatible organic solvents that are harmful to living cells. In this work, the SCNE of probiotic Lactobacillus acidophilus with water-insoluble luteolin and Fe3+ ions is achieved by the vortex-assisted, biphasic water-oil system. The process creates L. acidophilus nanoencapsulated in the luteolin-Fe3+ shells that empower the cells with extrinsic properties, such as resistance to lysozyme attack, anti-ROS ability, and α-amylase-inhibition activity, as well as sustaining viability under acidic conditions. The proposed protocol, embracing water-insoluble flavonoids as shell components in SCNE, will be an advanced add-on to the chemical toolbox for the manipulation of living cells at the single-cell level.

Berberis integerrima bioactive molecules loaded in chitosan-based electrospun nanofibers for soybean oil oxidative protection

Natural bioactive molecules such as phenolic acids and alkaloids play a crucial role in preserving the quality and safety of food products, particularly oils, by preventing oxidation. Berberis integerrima, a rich source of such antioxidants, has been explored in this study for its potential application in soybean oil preservation. Electrospun nanofibers, composed of polyvinyl alcohol and chitosan, were fabricated and loaded with an alcoholic extract of Berberis integerrima. The antioxidant activity of Berberis integerrima was evaluated, and the phenolic compounds contributing to its efficacy were identified and quantified. The physicochemical properties of the polyvinyl alcohol /chitosan/Berberis integerrima nanofibers, including morphology, crystallinity, functional groups, and thermal stability, were characterized. The results revealed that the polyvinyl alcohol/chitosan/Berberis integerrima nanofibers exhibited high antioxidant capacity and improved the stability of Berberis integerrima, indicating their potential as effective and biodegradable materials for food preservation. This study underscores the potential of harnessing natural antioxidants from Berberis integerrima in nanofibers to enhance the quality and safety of soybean oil.

Organismal Function Enhancement through Biomaterial Intervention

Living organisms in nature, such as magnetotactic bacteria and eggs, generate various organic-inorganic hybrid materials, providing unique functionalities. Inspired by such natural hybrid materials, researchers can reasonably integrate biomaterials with living organisms either internally or externally to enhance their inherent capabilities and generate new functionalities. Currently, the approaches to enhancing organismal function through biomaterial intervention have undergone rapid development, progressing from the cellular level to the subcellular or multicellular level. In this review, we will concentrate on three key strategies related to biomaterial-guided bioenhancement, including biointerface engineering, artificial organelles, and 3D multicellular immune niches. For biointerface engineering, excess of amino acid residues on the surfaces of cells or viruses enables the assembly of materials to form versatile artificial shells, facilitating vaccine engineering and biological camouflage. Artificial organelles refer to artificial subcellular reactors made of biomaterials that persist in the cytoplasm, which imparts cells with on-demand regulatory ability. Moreover, macroscale biomaterials with spatiotemporal regulation characters enable the local recruitment and aggregation of cells, denoting multicellular niche to enhance crosstalk between cells and antigens. Collectively, harnessing the programmable chemical and biological attributes of biomaterials for organismal function enhancement shows significant potential in forthcoming biomedical applications.

Nanoarmor: cytoprotection for single living cells

Single cell modification or hybridization technology has become a popular direction in bioengineering in recent years, with applications in clean energy, environmental stewardship, and sustainable human development. Here, we draw attention to nanoarmor, a representative achievement of cytoprotection and functionalization technology. The fundamental principles of nanoarmor need to be studied with input from multiple disciplines, including biology, chemistry, and material science. In this review, we explain the role of nanoarmor and review progress in its applications. We also discuss three main challenges associated with its development: self-driving ability, heterojunction characteristics, and mineralization formation. Finally, we propose a preliminary classification system for nanoarmor.

A Micrometric Transformer: Compositional Nanoshell Transformation of Fe3+ -Trimesic-Acid Complex with Concomitant Payload Release in Cell-in-Catalytic-Shell Nanobiohybrids

Nanoencapsulation of living cells within artificial shells is a powerful approach for augmenting the inherent capacity of cells and enabling the acquisition of extrinsic functions. However, the current state of the field requires the development of nanoshells that can dynamically sense and adapt to environmental changes by undergoing transformations in form and composition. This paper reports the compositional transformation of an enzyme-embedded nanoshell of Fe3+ -trimesic acid complex to an iron phosphate shell in phosphate-containing media. The cytocompatible transformation allows the nanoshells to release functional molecules without loss of activities and biorecognition, while preserving the initial shell properties, such as cytoprotection. Demonstrations include the lysis and killing of Escherichia coli by lysozyme, and the secretion of interleukin-2 by Jurkat T cells in response to paracrine stimulation by antibodies. This work on micrometric Transformers will benefit the creation of cell-in-shell nanobiohybrids that can interact with their surroundings in active and adaptive ways.

Nano-Osmolyte Conjugation: Tailoring the Osmolyte-Protein Interactions at the Nanoscale

Osmolytes are small organic compounds accumulated at higher concentrations in the cell under various stress conditions like high temperature, high salt, high pressure, etc. Osmolytes mainly include four major classes of compounds including sugars, polyols, methylamines, and amino acids and their derivatives. In addition to their ability to maintain protein stability and folding, these osmolytes, also termed as chemical chaperones, can prevent protein misfolding and aggregation. Although being efficient protein folders and stabilizers, these osmolytes exhibit certain unavoidable limitations such as nearly molar concentrations of osmolytes being required for their effect, which is quite difficult to achieve inside a cell or in the extracellular matrix due to nonspecificity and limited permeability of the blood-brain barrier system and reduced bioavailability. These limitations can be overcome to a certain extent by using smart delivery platforms for the targeted delivery of osmolytes to the site of action. In this context, osmolyte-functionalized nanoparticles, termed nano-osmolytes, enhance the protein stabilization and chaperone efficiency of osmolytes up to 105 times in certain cases. For example, sugars, polyols, and amino acid functionalized based nano-osmolytes have shown tremendous potential in preventing protein aggregation. The enhanced potential of nano-osmolytes can be attributed to their high specificity at low concentrations, high tunability, amphiphilicity, multivalent complex formation, and efficient drug delivery system. Keeping in view the promising potential of nano-osmolytes conjugation in tailoring the osmolyte-protein interactions, as compared to their molecular forms, the present review summarizes the recent advancements of the nano-osmolytes that enhance the protein stability/folding efficiency and ability to act as artificial chaperones with increased potential to prevent protein misfolding disorders. Some of the potential nano-osmolyte aggregation inhibitors have been highlighted for large-scale screening with future applications in aggregation disorders. The synthesis of nano-osmolytes by numerous approaches and future perspectives are also highlighted.

Self-decorating cells via surface-initiated enzymatic controlled radical polymerization

Through the innovative use of surface-displayed horseradish peroxidase, this work explores the enzymatic catalysis of both bioRAFT polymerization and bioATRP to prompt polymer synthesis on the surface of Saccharomyces cerevisiae cells, with bioATRP outperforming bioRAFT polymerization. The resulting surface modification of living yeast cells with synthetic polymers allows for a significant change in yeast phenotype, including growth profile, aggregation characteristics, and conjugation of non-native enzymes to the clickable polymers on the cell surface, opening new avenues in bioorthogonal cell-surface engineering.

Cell Surface Engineering Tools for Programming Living Assemblies

Breakthroughs in precision cell surface engineering tools are supporting the rapid development of programmable living assemblies with valuable features for tackling complex biological problems. Herein, the authors overview the most recent technological advances in chemically- and biologically-driven toolboxes for engineering mammalian cell surfaces and triggering their assembly into living architectures. A particular focus is given to surface engineering technologies for enabling biomimetic cell-cell social interactions and multicellular cell-sorting events. Further advancements in cell surface modification technologies may expand the currently available bioengineering toolset and unlock a new generation of personalized cell therapeutics with clinically relevant biofunctionalities. The combination of state-of-the-art cell surface modifications with advanced biofabrication technologies is envisioned to contribute toward generating living materials with increasing tissue/organ-mimetic bioactivities and therapeutic potential.

Tandem-biocatalysis reactors constructed by topological evolution of CaCO3 particles into hollow metal hydroxide spheres

Despite remarkable advances in the design and synthesis of hollow inorganic spheres (HISs), the harsh synthetic conditions have precluded the applications of HISs to biochemical and biological fields. Herein we report a biocompatible strategy for synthesizing metal hydroxide HISs (MH-HISs) by simply mixing CaCO3 particles with metal ions in water. The ion-exchange reaction between Ca2+ and metal ions leads to the structural and chemical evolution from solid CaCO3 particles to hollow MH-HISs via core-shell and yolk-shell structures, while enabling the encapsulation of enzymes to the shells without loss of catalytic activities. The biocompatible protocol makes multienzymatic cascade reactions achievable, with great recyclability due to mechanical durability of MH-HISs.

Fugetaxis of Cell-in-Catalytic-Coat Nanobiohybrids in Glucose Gradients

Manipulation and control of cell chemotaxis remain an underexplored territory despite vast potential in various fields, such as cytotherapeutics, sensors, and even cell robots. Herein is achieved the chemical control over chemotactic movement and direction of Jurkat T cells, as a representative model, by the construction of cell-in-catalytic-coat structures in single-cell nanoencapsulation. Armed with the catalytic power of glucose oxidase (GOx) in the artificial coat, the nanobiohybrid cytostructures, denoted as Jurkat[Lipo_GOx] , exhibit controllable, redirected chemotactic movement in response to d-glucose gradients, in the opposite direction to the positive-chemotaxis direction of naïve, uncoated Jurkat cells in the same gradients. The chemically endowed, reaction-based fugetaxis of Jurkat[Lipo_GOx] operates orthogonally and complementarily to the endogenous, binding/recognition-based chemotaxis that remains intact after the formation of a GOx coat. For instance, the chemotactic velocity of Jurkat[Lipo_GOx] can be adjusted by varying the combination of d-glucose and natural chemokines (CXCL12 and CCL19) in the gradient. This work offers an innovative chemical tool for bioaugmenting living cells at the single-cell level through the use of catalytic cell-in-coat structures.

Catalytic metal-nucleotide coordinative cytoskeleton on algae cell towards photosynthetic hydrogen production under air

A metal-nucleotide coordinative cytoskeleton with ascorbate oxidase-like catalytic behavior was constructed on an individual algae cell wall, which endows the engineered cells with the capability of self-generating a localized hypoxic microenvironment around the cell surface, and thus allows the functionality switching from photosynthetic oxygen production to efficient hydrogen evolution for over one month.

DNA-Guided Extracellular-Vesicle Metallization with High Catalytic Activity for Accurate Diagnosis of Pulmonary Nodules

Sensitive and specific analysis of extracellular vesicles (EVs) offers a promising minimally invasive way to identify malignant pulmonary nodules from benign lesions. However, accurate analysis of EVs is subject to free target proteins in blood samples, which compromises the clinical diagnosis value of EVs. Here a DNA-guided extracellular-vesicle metallization (DEVM) strategy is described for ultrasensitive and specific analysis of EV protein biomarkers and classification of pulmonary nodules. The facile DEVM process mainly includes the incorporation of DNA labeled with cholesterol and thiol groups into EV membranes and subsequent deposition of Au3+ and Pt4+ to allow the DNA-functionalized EVs to be encapsulated with AuPt nanoshells. It is found that the synthesized AuPt-metallized EVs possess extrinsic peroxidase-like activity. Utilizing the feature of the catalytic metal nanoshells just growth on the EV membranes, the DEVM method enables multiparametric recognition of target proteins and EV membranes and can produce an amplified colorimetric signal, avoiding the interference of free proteins. By profiling four surface proteins of EVs from 48 patients with pulmonary nodules, the highest area under the receiver operating characteristic curve (0.9983) is obtained. Therefore, this work provides a feasible EVs analysis tool for accurate pulmonary nodules management.

Nanoparticle-Decorated Biomimetic Extracellular Matrix for Cell Nanoencapsulation and Regulation

Cell encapsulation has been studied for various applications ranging from cell transplantation to biological production. However, current encapsulation technologies focus on cell protection rather than cell regulation that is essential to most if not all cell-based applications. Here we report a method for cell nanoencapsulation and regulation using an ultrathin biomimetic extracellular matrix as a cell nanocapsule to carry nanoparticles (CN2 ). This method allows high-capacity nanoparticle retention at the vicinity of cell surfaces. The encapsulated cells maintain high viability and normal metabolism. When gold nanoparticles (AuNPs) are used as a model to decorate the nanocapsule, light irradiation transiently increases the temperature, leading to the activation of the heat shock protein 70 (HSP70) promoter and the regulation of reporter gene expression. As the biomimetic nanocapsule can be decorated with any or multiple NPs, CN2 is a promising platform for advancing cell-based applications.

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.

Engineered Living Materials For Sustainability

Recent advances in synthetic biology and materials science have given rise to a new form of materials, namely engineered living materials (ELMs), which are composed of living matter or cell communities embedded in self-regenerating matrices of their own or artificial scaffolds. Like natural materials such as bone, wood, and skin, ELMs, which possess the functional capabilities of living organisms, can grow, self-organize, and self-repair when needed. They also spontaneously perform programmed biological functions upon sensing external cues. Currently, ELMs show promise for green energy production, bioremediation, disease treatment, and fabricating advanced smart materials. This review first introduces the dynamic features of natural living systems and their potential for developing novel materials. We then summarize the recent research progress on living materials and emerging design strategies from both synthetic biology and materials science perspectives. Finally, we discuss the positive impacts of living materials on promoting sustainability and key future research directions.

Synthesis of a Healthy Sweetener d-Tagatose from Starch Catalyzed by Semiartificial Cell Factories

d-Tagatose is one of the several healthy sweeteners that can be a substitute for sucrose and fructose in our daily life. Whole cell-catalyzed phosphorylation and dephosphorylation previously reported by our group afford a thermodynamic-driven strategy to achieve tagatose production directly from starch with high product yields. Nonetheless, the poor structural stability of cells and difficulty in biocatalyst recycling restrict its practical application. Herein, an efficient and stable semiartificial cell factory (SACF) was developed by constructing an organosilica network (OSN) artificial shell on the cells bearing five thermophilic enzymes to produce tagatose. The OSN artificial shell, the thickness of which can be regulated by changing the tetraethyl silicate concentration, exhibited tunable permeability and superior mechanical strength. In contrast with cells, SACFs showed a relative activity of 99.5% and an extended half-life from 33.3 to 57.8 h. Over 50% of initial activity was retained after 20 reuses. The SACFs can catalyze seven consecutive reactions with tagatose yields of over 40.7% in field applications.

Cytoprotection of Probiotic Lactobacillus acidophilus with Artificial Nanoshells of Nature-Derived Eggshell Membrane Hydrolysates and Coffee Melanoidins in Single-Cell Nanoencapsulation

One-step fabrication method for thin films and shells is developed with nature-derived eggshell membrane hydrolysates (ESMHs) and coffee melanoidins (CMs) that have been discarded as food waste. The nature-derived polymeric materials, ESMHs and CMs, prove highly biocompatible with living cells, and the one-step method enables cytocompatible construction of cell-in-shell nanobiohybrid structures. Nanometric ESMH-CM shells are formed on individual probiotic Lactobacillus acidophilus, without any noticeable decrease in viability, and the ESMH-CM shells effectively protected L. acidophilus in the simulated gastric fluid (SGF). The cytoprotection power is further enhanced by Fe³⁺-mediated shell augmentation. For example, after 2 h of incubation in SGF, the viability of native L. acidophilus is 30%, whereas nanoencapsulated L. acidophilus, armed with the Fe³⁺-fortified ESMH-CM shells, show 79% in viability. The simple, time-efficient, and easy-to-process method developed in this work would contribute to many technological developments, including microbial biotherapeutics, as well as waste upcycling.

Chemical reaction-mediated covalent localization of bacteria

Methods capable of manipulating bacterial colonization are of great significance for modulating host-microbiota relationships. Here, we describe a strategy of in-situ chemical reaction-mediated covalent localization of bacteria. Through a simple one-step imidoester reaction, primary amino groups on bacterial surface can be converted to free thiols under cytocompatible conditions. Surface thiolation is applicable to modify diverse strains and the number of introduced thiols per bacterium can be easily tuned by varying feed ratios. These chemically reactive bacteria are able to spontaneously bond with mucous layer by catalyst-free thiol-disulfide exchange between mucin-associated disulfides and newly converted thiols on bacterial surface and show thiolation level-dependent attachment. Bacteria optimized with 9.3 × 10⁷ thiols per cell achieve 170-fold higher attachment in mucin-enriched jejunum, a challenging location for gut microbiota to colonize. As a proof-of-concept application for microbiota transplantation, covalent bonding-assisted localization of an oral probiotic in the jejunum generates an improved remission of jejunal mucositis. Our findings demonstrate that transforming bacteria with a reactive surface provides an approach to chemically control bacterial localization, which is highly desirable for developing next-generation bacterial living bioagents.

Antifouling Surface Coating on Various Substrates by Inducing Tyrosinase-Mediated Oxidation of a Tyrosine-Conjugated Sulfobetaine Derivative

Inspired by the melanogenesis occurring in nature, we report tyrosinase-mediated antifouling surface coating by synthesizing a tyrosine-conjugated sulfobetaine derivative (Tyr-SB). Synthetic Tyr-SB contains zwitterionic sulfobetaine and tyrosine, whose phenolic amine group acts as a dormant coating precursor. In contrast to catecholamine derivatives, tyrosine derivatives are stable against auto-oxidation and are enzymatically oxidized only in the presence of tyrosinase to initiate melanin-like oxidation. When the surface of interest was applied during the course of Tyr-SB oxidation, a superhydrophilic poly(Tyr-SB) film was coated on the surfaces, thereby showing antifouling performance against proteins or adherent cells. Because the oxidation of Tyr-SB occurred under mild aqueous conditions (pH 6-7) without the use of any chemical oxidants, such as sodium periodate or ammonium persulfate, we anticipate that the coating method described herein will serve as a biocompatible tool in the field of biosensors, cell surface engineering, and medical devices, whose interfaces differ in chemistry.

Decorated bacteria and the application in drug delivery

The use of living bacteria either as therapeutic agents or drug carriers has shown great potential in treating a multitude of intractable diseases. However, cells are often fragile to unfriendly environmental stressors and limited by inadequately therapeutic responses, leading to unwanted cell death and a decline in treatment efficacy. Surface decoration of bacteria has emerged as a simple yet useful strategy that not only confers bacteria with extra capacity to resist environmental threats but also endows them with exogenous characteristics that are neither inherent nor naturally achievable. In this review, we systematically introduce the advancements of physicochemical and biological technologies for surface modification of bacteria, especially the single-cell surface decoration strategies of individual bacteria. We highlight the recent progress on surface decoration that aims to improve the bioavailability and efficacy of therapeutic bacterial agents and also to achieve enhanced and targeted delivery of conventional drugs. The promises along with challenges of surface-decorated bacteria as drug delivery systems for applications in cancer therapy, intestinal disease treatment, bioimaging, and diagnosis are further discussed with respect to future clinical translation. This review offers an overview of the advances of decorated bacteria for drug delivery applications and would contribute to the development of the next generation of advanced bacterial-based therapies.

Cell-in-Catalytic-Shell Nanoarchitectonics: Catalytic Empowerment of Individual Living Cells by Single-Cell Nanoencapsulation

Cell-in-shell biohybrid structures, synthesized by encapsulating individual living cells with exogenous materials, have emerged as exciting functional entities for engineered living materials, with emergent properties outside the scope of biochemical modifications. Artificial exoskeletons have, to date, provided physicochemical shelters to the cells inside in the first stage of technological development, and further advances in the field demand catalytically empowered, cellular hybrid systems that augment the biological functions of cells and even introduce completely new functions to the cells. This work describes a facile and generalizable strategy for empowering living cells with extrinsic catalytic capability through nanoencapsulation of living cells with a supramolecular metal-organic complex of Fe³⁺ and benzene-1,3,5-tricarboxylic acid (BTC). A series of enzymes are embedded in situ, without loss of catalytic activity, in the Fe³⁺ -BTC shells, not to mention the superior characteristics of cytocompatible and rapid shell-forming processes. The nanoshell enhances the catalytic efficiency of multienzymatic cascade reactions by confining reaction intermediates to its internal voids and the nanoencapsulated cells acquire exogenous biochemical functions, including enzymatic cleavage of lethal octyl-β-d-glucopyranoside into d-glucose, with autonomous cytoprotection. The system will provide a versatile, nanoarchitectonic tool for interfacing biological cells with functional materials, especially for catalytic bioempowerment of living cells.

Molecular Trade-Offs between Lattice Oxygen and Oxygen Vacancy Drive Organic Pollutant Degradation in Fungal Biomineralized Exoskeletons

Fungal-mineral interactions can effectively alleviate cellular stress from organic pollutants, the production of which are expected to rapidly increase owing to the Earth moving into an unprecedented geological epoch, the Anthropocene. The underlying mechanisms that may enable fungi to combat organic pollution during fungal-mineral interactions remain unclear. Inspired by the natural fungal sporulation process, we demonstrate for the first time that fungal biomineralization triggers the formation of an ultrathin (hundreds of nanometers thick) exoskeleton, enriched in nanosized iron (oxyhydr)oxides and biomolecules, on the hyphae. Mapped biochemical composition of this coating at a subcellular scale via high spatial resolution (down to 50 nm) synchrotron radiation-based techniques confirmed aromatic C, C-N bonds, amide carbonyl, and iron (oxyhydr)oxides as the major components of the coatings. This nanobiohybrid system appeared to impart a strong (×2) biofunctionality for fungal degradation of bisphenol A through altering molecular-level trade-offs between lattice oxygen and oxygen vacancy. Together, fungal coatings could act as "artificial spores", which enable fungi to combat physical and chemical stresses in natural environments, providing crucial insights into fungal biomineralization and coevolution of the Earth's lithosphere and biosphere.

Metal-phenolic networks as tuneable spore coat mimetics

Bacillus subtilis are important probiotic microbes currently formulated for delivery as spores, but their ability to germinate in the gut remains debatable. To optimize their application, cells should be delivered in their vegetative state, but the sensitivity of B. subtilis prevents this. Through the application of self-assembled metal-phenolic network (MPN) cellular coatings, B. subtilis are protected from lyophilization stresses. These MPNs are an important class of self-assembled materials comprised of polyphenols and metal ions, and the efficacy of MPN protection was found to be dependent on the MPN components used for assembly. Both the size of the polyphenol and stability of the metal-phenol coordination were important factors that influenced their cellular protection; the smallest polyphenol, gallic acid, and the most stable chelated ion, Fe^III, were found to provide the highest level of protection. Further, delivery to the gut involves exposure to acidic conditions in the form of stomach acid and intestinal fluid. MPN coatings rapidly disassemble upon mild acid treatment but were found to protect B. subtilis from the negative impacts of the acid. Overall, optimized MPNs were found to protect vegetative B. subtilis cells from lyophilization stress and enable a more complete understanding of the role of each component in MPNs.

Metal-Phenolic Networks as Versatile Coating Materials for Biomedical Applications

Polyphenols are naturally derived organic compounds that have long been used as food additives, antioxidants, and adhesives owing to their intrinsic physicochemical properties. Recently, there has been growing interest in the fabrication of coordination networks based on the self-assembly of polyphenols and metal ions, termed metal-phenolic networks (MPNs), for multiple biological applications including bioimaging, drug delivery, and cell encapsulation. The as-synthesized MPN complexes feature pH responsiveness, controllable size and rigidity, and tunable permeability based on the choice of polyphenol-metal ion pairs. The aim of this Review is to introduce the physicochemical properties of MPNs, highlight their recent biological applications in cancer theranostics and single-cell encapsulation, and discuss the future utility of MPNs for biomedical applications.

Killing Two Birds with One Stone: Biomineralized Bacteria Tolerate Adverse Environments and Absorb Hexavalent Chromium

Heavy metal ions in contaminated water, such as hexavalent chromium, are harmful to humans. Bacterial biosorption is an ideal method for the treatment of hexavalent chromium. However, hexavalent chromium in solution causes bacteria to produce reactive oxygen species, which leads to bacterial death and affects biosorption. We developed a microfluidics-based biomimetic mineralization method to encapsulate bacteria (e.g., Escherichia coli and Bacillus subtilis) with zeolitic imidazolate framework-8 (ZIF-8), thus allowing the bacteria to form a continuous and homogeneous shell. The artificial shells endowed bacteria with the ability to tolerate harsh environments, which was significant during the treatment of contaminated water. The adsorption of hexavalent chromium was a two-step process: first the fast physical adsorption of ZIF-8 and biosorption by bacteria (up to 30-50% adsorption in 1 day), followed by secondary biosorption after decomposition of the system. The maximum adsorption of hexavalent chromium by the encapsulated bacteria reached 90%. The microfluidic device developed in this study provides a simple method to encapsulate bacteria mildly and enable cell survival in extreme environments, offering the possibility of future microbial applications in environmental and other fields.

Cell-Selective Encapsulation within Metal-Organic Framework Shells via Precursor-Functionalized Aptamer Identification for Whole-Cell Cancer Vaccine

Single-cell encapsulation is an emerging technology to endow cells with various functions, of which developing new applications in vivo is in high demand. Currently, metal-organic frameworks (MOFs) that are used as nanometric shells to coat living cells, however, have not realized cell-selective encapsulation. Here, a biocompatible and selective cell encapsulation strategy based on precursor-functionalized nucleolin aptamer and in situ MOF mineralization on the aptamer-identified cancer cell surface are developed. After MOF coating, the encapsulated cancer cells undergo immunogenic cell death, which is found associated with the changed cell stiffness (indicated by Young's modulus). The immunogenic dead cancer cells are used as whole-cell cancer vaccines (WCCVs), forming the integral WCCV-in-shell structure with enhanced immunogenicity ascribing from the surface-exposed calreticulin to promote dendritic cell recruitment, antigen presentation, and T-cell activation. The major activation pathways in the immune response are identified including tumor necrosis factor signaling pathway, cytokine-cytokine receptor interaction, and Toll-like receptor signaling pathway, suggesting the potential adjuvant effect of the MOF shells. After vaccination, WCCV-in-shell shows much better tumor immunoprophylaxis than either the imperfectly coated cancer cells or the traditional WCCV. This strategy is promising for the universal and facile development of novel whole-cell vaccines.

Preparation and Characterization of Mg-Doped Calcium Phosphate-Coated Phycocyanin Nanoparticles for Improving the Thermal Stability of Phycocyanin

Phycocyanin (PC) is a blue-colored, pigment-protein complex with unique fluorescence characteristics. However, heat leads to PC fading and fluorescence decay, hampering its widespread application. To improve the thermal stability of PC, we induced the in situ mineralization of calcium phosphate (CaP) on the PC surface to prepare PC@Mg-CaP. The nanoparticles were characterized using transmission electron microscopy, energy dispersive spectrometry, fourier transform infrared spectroscopy, and X-ray diffraction. The results showed that PC@Mg-CaP was spherical, and the nanoparticle size was less than 200 nm. The shell of PC@Mg-CaP was composed of amorphous calcium phosphate (ACP). The study suggested that CaP mineralization significantly improved the thermal stability of PC. After heating at 70 °C for 30 min, the relative concentration of PC@Mg-CaP with a Ca/P ratio = 2 was 5.31 times higher than that of PC. Furthermore, the Ca/P ratio was a critical factor for the thermal stability of PC@Mg-CaP. With decreasing Ca/P, the particle size and thermal stability of PC@Mg-CaP significantly increased. This work could provide a feasible approach for the application of PC and other thermal-sensitive biomolecules in functional foods requiring heat treatment.

Fungal-Mineral Interactions Modulating Intrinsic Peroxidase-like Activity of Iron Nanoparticles: Implications for the Biogeochemical Cycles of Nutrient Elements and Attenuation of Contaminants

Fungal-mediated extracellular reactive oxygen species (ROS) are essential for biogeochemical cycles of carbon, nitrogen, and contaminants in terrestrial environments. These ROS levels may be modulated by iron nanoparticles that possess intrinsic peroxidase (POD)-like activity (nanozymes). However, it remains largely undescribed how fungi modulate the POD-like activity of the iron nanoparticles with various crystallinities and crystal facets. Using well-controlled fungal-mineral cultivation experiments, here, we showed that fungi possessed a robust defect engineering strategy to modulate the POD-like activity of the attached iron minerals by decreasing the catalytic activity of poorly ordered ferrihydrite but enhancing that of well-crystallized hematite. The dynamics of POD-like activity were found to reside in molecular trade-offs between lattice oxygen and oxygen vacancies in the iron nanoparticles, which may be located in a cytoprotective fungal exoskeleton. Together, our findings unveil coupled POD-like activity and oxygen redox dynamics during fungal-mineral interactions, which increase the understanding of the catalytic mechanisms of POD-like nanozymes and microbial-mediated biogeochemical cycles of nutrient elements as well as the attenuation of contaminants in terrestrial environments.

Multi-layered ZIF-coated cells for the release of bioactive molecules in hostile environments

Metal-organic framework (MOF) coatings on cells enhance viability in cytotoxic environments. Here, we show how protective multi-layered MOF bio-composite shells on a model cell system (yeast) enhance the proliferation of...

Single-Conidium Encapsulation in Oil-in-Water Pickering Emulsions at High Encapsulation Yield

This study presents an individual encapsulation of fungal conidia in an oil-in-water Pickering emulsion at a single-conidium encapsulation yield of 44%. The single-conidium encapsulation yield was characterized by analysis of confocal microscopy micrographs. Mineral oil-in-water emulsions stabilized by amine-functionalized titania dioxide (TiO₂-NH₂ or titania-NH₂) particles were prepared. The structure and the stability of the emulsions were investigated at different compositions by confocal microscopy and a LUMiSizer^® respectively. The most stable emulsions with a droplet size suitable for single-conidium encapsulation were further studied for their individual encapsulation capabilities. The yields of individual encapsulation in the emulsions; i.e., the number of conidia that were individually encapsulated out of the total number of conidia, were characterized by confocal microscopy assay. This rapid, easy to use approach to single-conidium encapsulation, which generates a significantly high yield with eco-friendly titania-based emulsions, only requires commonly used emulsification and agitation methods.

Manipulation of Multiple Cell-Cell Interactions by Tunable DNA Scaffold Networks

Manipulation of cell-cell interactions via cell surface engineering has potential biomedical applications in tissue engineering and cell therapy. However, manipulation of the comprehensive and multiple intercellular interactions remains a challenge and missing elements. Herein, utilizing a DNA triangular prism (TP) and a branched polymer (BP) as functional modules, we fabricate tunable DNA scaffold networks on the cell surface. The responsiveness of cell-cell recognition, aggregation and dissociation could be modulated by aptamer-functionalized DNA scaffold networks with high accuracy and specificity. By regulating the DNA scaffold networks coated on the cell surface, controlled intercellular molecular transportation is achieved. Our tunable network provides a simple and extendible strategy which addresses a current need in cell surface engineering to precisely manipulate cell-cell interactions and shows promise as a general tool for controllable cell behavior.

Enzyme-Mediated Kinetic Control of Fe3+-Tannic Acid Complexation for Interface Engineering

Supramolecular self-assembly of Fe3+ and tannic acid (TA) has received great attention in the fields of materials science and interface engineering because of its exceptional surface coating properties. Although advances in coating strategies often suggest that kinetics in the generation of interface-active Fe3+-TA species is deeply involved in the film formation, there is no acceptable elucidation for the coating process. In this work, we developed the enzyme-mediated kinetic control of Fe2+ oxidation to Fe3+ in a Fe2+-TA complex in the iron-gall-ink-revisited coating method. Specifically, hydrogen peroxide, produced in the glucose oxidase (GOx)-catalyzed reaction of d-glucose, accelerated Fe2+ oxidation, and the optimized kinetics profoundly facilitated the film formation to be about 9 times thicker. We also proposed a perspective considering the coating process as nucleation and growth. From this viewpoint, the kinetics in the generation of interface-active Fe3+-TA species should be optimized because it determines whether the interface-active species forms a film on the substrate (i.e., heterogeneous nucleation and film growth) or flocculates in solution (i.e., homogeneous nucleation and particle growth). Moreover, GOx was concomitantly embedded into the Fe3+-TA films with sustained catalytic activities, and the GOx-mediated coating system was delightfully adapted to catalytic single-cell nanoencapsulation.

Exploiting the Structural Metamorphosis of Polymers to 'Wrap' Micron-Sized Spherical Objects

There is growing interest in developing methods to 'wrap' nano- and micron-sized biological objects within films that may offer protection, enhance their stability or improve performance. We describe the successful 'wrapping' of lectin-decorated microspheres, which serve as appealing model micron-sized objects, within cross-linked polymer film. This approach utilizes polymer chains able to undergo a structural metamorphosis, from being intramolecularly cross-linked to intermolecularly cross-linked, a process that is triggered by polymer concentration upon the particle surface. Experiments demonstrate that both complementary molecular recognition and the dynamic covalent nature of the crosslinker are required for successful 'wrapping' to occur. This work is significant as it suggests that nano- and micron-sized biological objects such as virus-like particles, bacteria or mammalian cells-all of which may benefit from additional environmental protection or stabilization in emerging applications-may also be 'wrapped' by this approach.

Decorating Bacteria with a Therapeutic Nanocoating for Synergistically Enhanced Biotherapy

Disorders in the gut microbiota have been implicated in various diseases, such as inflammatory bowel diseases, diabetes, and cancers. Oral microecologics are of great importance due to their ability to directly intervene the gut microbiome as well as their noninvasiveness and low side effects, while have suffered from low bioavailability and a single therapeutic effect. Here, probiotics are coated with a therapeutic nanocoating for synergistically enhanced biotherapy, a method inspired by the robust protective and therapeutic effectiveness of silkworm cocoon. With its transition from a random coil to β-sheet conformation, silk fibroin can self-assemble onto the surface of bacteria. By a simple layer-by-layer procedure, an entire nanocoating can be formed along with a near quantitative coating ratio and almost uninfluenced bacterial viability. Thanks to its protective barrier role and innate pharmaceutical activity, silk fibroin nanocoating endows the coated bacteria with a markedly improved survival against gastric insults and a synergistically enhanced therapeutic effect in a murine model of intestinal mucositis. This work demonstrates how therapeutic elements can be combined with probiotics via a simple coating strategy and proposes an alternative to enhance bioavailability and treatment efficacy of oral microecologics.

An Overview of Engineered Hydrogel-Based Biomaterials for Improved β-Cell Survival and Insulin Secretion

Islet transplantation provides a promising strategy in treating type 1 diabetes as an autoimmune disease, in which damaged β-cells are replaced with new islets in a minimally invasive procedure. Although islet transplantation avoids the complications associated with whole pancreas transplantations, its clinical applications maintain significant drawbacks, including long-term immunosuppression, a lack of compatible donors, and blood-mediated inflammatory responses. Biomaterial-assisted islet transplantation is an emerging technology that embeds desired cells into biomaterials, which are then directly transplanted into the patient, overcoming the aforementioned challenges. Among various biomaterials, hydrogels are the preferred biomaterial of choice in these transplants due to their ECM-like structure and tunable properties. This review aims to present a comprehensive overview of hydrogel-based biomaterials that are engineered for encapsulation of insulin-secreting cells, focusing on new hydrogel design and modification strategies to improve β-cell viability, decrease inflammatory responses, and enhance insulin secretion. We will discuss the current status of clinical studies using therapeutic bioengineering hydrogels in insulin release and prospective approaches.

Polymer-Assisted Metallization of Mammalian Cells

Developing biotemplating techniques to translate microorganisms and cultured mammalian cells into metallic biocomposites is of great interest for biosensors, electronics, and energy. The metallization of viruses and microbial cells is successfully demonstrated via a genetic engineering strategy or electroless deposition. However, it is difficult to transform mammalian cells into metallic biocomposites because of the complicated genes and the delicate morphological features. Herein, "polymer-assisted cell metallization" (PACM) is reported as a general method for the transformation of mammalian cells into metallic biocomposites. PACM includes a first step of in situ polymerization of functional polymer on the surface and in the interior of the mammalian cells, and a subsequent electroless deposition of metal to convert the polymer-functionalized cells into metallic biocomposites, which retain the micro- and nanostructures of the mammalian cells. This new biotemplating method is compatible with different cell types and metals to yield a wide variety of metallic biocomposites with controlled structures and properties.

A Decade of Advances in Single-Cell Nanocoating for Mammalian Cells

Strategic advances in the single-cell nanocoating of mammalian cells have noticeably been made during the last decade, and many potential applications have been demonstrated. Various cell-coating strategies have been proposed via adaptation of reported methods in the surface sciences and/or materials identification that ensure the sustainability of labile mammalian cells during chemical manipulation. Here an overview of the methodological development and potential applications to the healthcare sector in the nanocoating of mammalian cells made during the last decade is provided. The materials used for the nanocoating are categorized into polymers, hydrogels, polyphenolic compounds, nanoparticles, and minerals, and the corresponding strategies are described under the given set of materials. It also suggests, as a future direction, the creation of the cytospace system that is hierarchically composed of the physically separated but mutually interacting cellular hybrids.

Bioinspired Cell Silicification: From Extracellular to Intracellular

In nature, biosilicification directs the formation of elaborate amorphous silica exoskeletons that provide diatoms mechanically strong, chemically inert, non-decomposable silica armor conferring chemical and thermal stability as well as resistance to microbial attack, without changing the optical transparency or adversely effecting nutrient and waste exchange required for growth. These extraordinary silica/cell biocomposites have inspired decades of biomimetic research aimed at replication of diatoms' hierarchically organized exoskeletons, immobilization of cells or living organisms within silica matrices and coatings to protect them against harmful external stresses, genetic re-programming of cellular functions by virtue of physico-chemical confinement within silica, cellular integration into devices, and endowment of cells with non-native, abiotic properties through facile silica functionalization. In this Perspective, we focus our discussions on the development and concomitant challenges of bioinspired cell silicification ranging from "cells encapsulated within 3D silica matrices" and "cells encapsulated within 2D silica shells" to extra- and intracellular silica replication, wherein all biomolecular interfaces are encased within nanoscopic layers of amorphous silica. We highlight notable examples of advances in the science and technology of biosilicification and consider challenges to advancing the field, where we propose cellular "mineralization" with arbitrary nanoparticle exoskeletons as a generalizable means to impart limitless abiotic properties and functions to cells, and, based on the interchangeability of water and silicic acid and analogies between amorphous ice and amorphous silica, we consider "freezing" cells within amorphous silica as an alternative to cryo-preservation.

Polymerization-Mediated Multifunctionalization of Living Cells for Enhanced Cell-Based Therapy

Surface decoration of living cells by exogenous substances offers a unique tool for understanding and tuning cell behaviors, which plays a critical role in cell-based therapy. Here, a facile yet versatile approach for decorating individual living cells with multimodal coatings is reported. By simply co-depositing with dopamine under a cytocompatible condition, various functional small molecules and polymers can be encoded to form a multifunctional coating on a cell's surface. The accessibility and versatility of this method to decorate diverse cells, including bacteria, fungi, and mammalian cells is demonstrated. With the ability to tune surface functions, ligand co-deposited gut microbiota is prepared as oral therapeutics for targeted treatment of colitis. Given the dual cytoprotective and targeting effects of the coating, decorated cells show more than 30-times higher bioavailability in the gut and fourfold higher accumulation in the inflamed tissue in comparison with those of uncoated bacteria. Multimodal therapeutic cells further validate strikingly increased treatment efficacy over clinical aminosalicylic acid in colitis mice. Decorating with multifunctional coatings proposes a robust platform for developing multimodal cells for enhanced cell-based therapy.

Novel nanomaterial-organism hybrids with biomedical potential

Instinctive hierarchically biomineralized structures of various organisms, such as eggs, algae, and magnetotactic bacteria, afford extra protection and distinct performance, which endow fragile organisms with a tenacious ability to adapt and survive. However, spontaneous formation of hybrid materials is difficult for most organisms in nature. Rapid development of chemistry and materials science successfully obtained the combinations of organisms with nanomaterials by biomimetic mineralization thus demonstrating the reproduction of the structures and functions and generation of novel functions that organisms do not possess. The rational design of biomaterial-organism hybridization can control biological recognition, interactions, and metabolism of the organisms. Thus, nanomaterial-organism hybrids represent a next generation of organism engineering with great potential biomedical applications. This review summarizes recent advances in material-directed organism engineering and is mainly focused on biomimetic mineralization technologies and their outstanding biomedical applications. Three representative types of biomimetic mineralization are systematically introduced, including external mineralization, internal mineralization, and genetic engineering mineralization. The methods involving hybridization of nanomaterials and organisms based on biomimetic mineralization strategies are described. These strategies resulted in applications of various nanomaterial-organism hybrids with multiplex functions in cell engineering, cancer treatment, and vaccine improvement. Unlike classical biological approaches, this material-based bioregulation is universal, effective, and inexpensive. In particular, instead of traditional medical solutions, the integration of nanomaterials and organisms may exploit novel strategies to solve current biomedical problems. This article is categorized under: Implantable Materials and Surgical Technologies > Nanomaterials and Implants Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

Reversed Anionic Hofmeister Effect in Metal-Phenolic-Based Film Formation

Although metal-phenolic species have emerged as one of the versatile material-independent-coating materials, providing attractive tools for interface engineering, mechanistic understanding of their film formation and growth still remains largely unexplored. Especially, the anions have been overlooked despite their high concentration in the coating solution. Considering that the anions are critical in the reactivity of metal-organic complex and the formation and/or property of functional materials, we investigated the anionic effects on the characteristics of film formation, such as film thickness and properties, in the Fe³⁺-tannic acid coating. We found that the film characteristics were strongly dictated by the counteranions (e.g., SO₄^2-, Cl^-, and Br^-) of the Fe³⁺ ion. Specifically, the film thickness and properties (i.e., mechanical modulus, permeability, and stability) followed the reversed anionic Hofmeister series (Br^- > Cl^- > SO₄^2-). Mechanistic studies suggested that more chaotropic anions, such as Br^-, might induce a more widely extended structure of the Fe³⁺-TA complexes in the coating solution, leading to thicker, harder, but more porous films. The reversed anionic Hofmeister effect was further confirmed by the additive effects of various sodium salts (NaF, NaCl, NaBr, and NaClO₄).

Bioinspired cell-in-shell systems in biomedical engineering and beyond: Comparative overview and prospects

With the development in tissue engineering, cell transplantation, and genetic technologies, living cells have become an important therapeutic tool in clinical medical care. For various cell-based technologies including cell therapy and cell-based sensors in addition to fundamental studies on single-cell biology, the cytoprotection of individual living cells is a prerequisite to extend cell storage life or deliver cells from one place to another, resisting various external stresses. Nature has evolved a biological defense mechanism to preserve their species under unfavorable conditions by forming a hard and protective armor. Particularly, plant seeds covered with seed coat turn into a dormant state against stressful environments, due to mechanical and water/gas constraints imposed by hard seed coat. However, when the environmental conditions become hospitable to seeds, seed coat is ruptured, initiating seed germination. This seed dormancy and germination mechanism has inspired various approaches that artificially induce cell sporulation via chemically encapsulating individual living cells within a thin but tough shell forming a 3D "cell-in-shell" structure. Herein, the recent advance of cell encapsulation strategies along with the potential advantages of the 3D "cell-in-shell" system is reviewed. Diverse coating materials including polymeric shells and hybrid shells on different types of cells ranging from microbes to mammalian cells will be discussed in terms of enhanced cytoprotective ability, control of division, chemical functionalization, and on-demand shell degradation. Finally, current and potential applications of "cell-in-shell" systems for cell-based technologies with remaining challenges will be explored.

Fabrication and Characterization of Neurocompatible Ulvan-Based Layer-by-Layer Films

Construction of extracellular matrix-mimetic nanofilms has considerable potential in biomedical and nanomedicinal fields. In this work, we fabricated neurocompatible layer-by-layer (LbL) films based on ulvan (ULV), a highly sulfated polysaccharide having compositional similarity to glycosaminoglycans that play important functional roles in the brain. ULV was durably assembled as a film with chitosan, another marine-derived polysaccharide, and the film enabled the stable adhesion of primary hippocampal neurons with high viability, comparable to the conventional poly-d-lysine surface. Notably, the ULV-based LbL films accelerated neurite outgrowth and selectively suppressed the adhesion of astrocytes, highlighting its potential as an advanced platform for neural implants and devices.