Polydopamine nanocoated whole-cell asymmetric biocatalysts

Natural biomolecules for cell-interface engineering

Cell-interface engineering is a way to functionalize cells through direct or indirect self-assembly of functional materials around the cells, showing an enhancement to cell functions. Among the materials used in cell-interface engineering, natural biomolecules play pivotal roles in the study of biological interfaces, given that they have good advantages such as biocompatibility and rich functional groups. In this review, we summarize and overview the development of studies of natural biomolecules that have been used in cell-biointerface engineering and then review the five main types of biomolecules used in constructing biointerfaces, namely DNA polymers, amino acids, polyphenols, proteins and polysaccharides, to show their applications in green energy, biocatalysis, cell therapy and environmental protection and remediation. Lastly, the current prospects and challenges in this area are presented with potential solutions to solve these problems, which in turn benefits the design of next-generation cell engineering.

Immobilized Saccharomyces cerevisiae viable cells for electrochemical biosensing of Cu(II)

Electrodes functionalised with weak electroactive microorganisms offer a viable alternative to conventional chemical sensors for detecting priority pollutants in bioremediation processes. Biofilm-based biosensors have been proposed for this purpose. However, biofilm formation and maturation require 24-48 h, and the microstructure and coverage of the electrode surface cannot be controlled, leading to poorly reproducible signal and sensitivity. Alternatively, semiconductive biocompatible coatings can be used for viable cell immobilization, achieving reproducible coverage and resulting in a stable biosensor response. In this work, we use a polydopamine (PDA)-based coating to immobilize Saccharomyces cerevisiae yeast viable cells on carbon screen printed electrodes (SPE) for Cu(II) detection, with potassium ferricyanide (K3[Fe (CN)6]) as a redox mediator. Under these conditions, the current output correlates with Cu (II) concentration, reaching a limit of detection of 2.2 µM, as calculated from the chronoamperometric response. The bioelectrochemical results are supported by standard viability assays, microscopy, and electrochemical impedance spectroscopy. The PDA coatings can be functionalised with different mutant strains, thus expanding the toolbox for biosensor design in bioremediation.

Kill two birds with one stone: Biochar immobilised polydopamine coated compound bacterial agent for remediation of dibutyl phthalate contaminated soil

The severe contamination of the plasticiser dibutyl phthalate (DBP) in agriculture soils is often accompanied by a decrease in nutrient utilisation. Though the combined application of a variety of microorganisms can simultaneously address the problems of soil contamination and nutrient deprivation, the activity and function of microorganisms can be severely inhibited by DBP, and studies on their protection under DBP contamination are almost non-existent. In this study, a compound bacterial agent KPSB was prepared by optimising with Fe3O4-modified biochar loaded with DBP-degrading bacterium Enterobacterium sp. DNB-S2 and polydopamine (PDA)-coated potassium-solubilizing bacterium Paenibacillus sp. KT. The results showed that KPSB was able to simultaneously remove DBP and increase the soil available potassium (K) content. PDA has good biocompatibility and shielding effect, and the strain KT coated by it has more complete cell membrane and stronger ability to secrete low molecular weight organic acids to promote K solubilisation. The Fe3O4-modified biochar with suitable pore structure, large specific surface area and abundant functional groups could provide a good growth microenvironment for functional microorganisms and support the growth of strains while promoting the degradation of DBP. The expression of DBP-degradation-related genes was significantly increased in KPSB, which promoted the removal of DBP. In addition, KPSB has good acid and alkali resistance and a wide range of temperature adaptability, and is able to remove DBP and increase the available K content better under different environmental conditions. These results will provide new perspectives for the research of in situ soil remediation technology.

Engineering silica nanocoated whole-cell asymmetric biocatalyst for efficient preparation of a key chiral intermediate of (S)-Rivastigmine

In our previous study, the whole cells containing an aldo-keto reductase (yhdN) and glucose dehydrogenase (GDH) were constructed and applied in a stereoselective carbonyl reduction reaction to prepare (S)-NEMCA-HEPE, being a key chiral intermediate of (S)-Rivastigmine which is widely prescribed for the treatment of Alzheimer's disease. Although the conversion and enantiomeric excess (e.e.) could reach to 78.2 % and 99 %, respectively, ionic liquid as an additive was required to improve the permeability of cell membrane. To further simplify the reaction, the molecular docking and saturation mutagenesis technology were used here to obtain an activity-improved yhdN variant such as G19A. And then, both excellent conversion and e.e. of 99 % for (S)-NEMCA-HEPE could be achieved within 40 min by using only G19A-GDH whole cell as a catalyst without any additive. However, the use of the whole cells still faces the issues of poor operation stability and adverse application prospect. Subsequently, a hydrophobic "cell-in-shell" complex of G19A-GDH@O-Silica was constructed by using a silica nanocoated technology. The obtained G19A-GDH@O-Silica exhibited an excellent conversion towards the asymmetric carbonyl reduction, and a good tolerance in changing thermal, pH, and storage environmental. Giving 76.3 % of reaction conversion even after the 11th cycle of reuse, indicated that G19A-GDH@O-Silica also possessed ideal recyclability. The aim of this study is to provide a rapid, and cost-effective nanocoated whole-cell biocatalyst for efficient preparation of (S)-NEMCA-HEPE. The simplicity and robustness of the immobilization approach may become a powerful tool to utilize whole-cell catalysts towards organic catalysis.

Light Controlled Nanobiohybrids for Modulating Chiral Alcohol Synthesis

The modulation of whole-cell activity presents a considerable challenge in biocatalysis. Conventional approaches to whole-cell catalysis, while having their strengths, often rely on complex and deliberate enzyme designs, which could result in difficulties in activity modulation and prolonged response times. Additionally, the activity of intracellular enzymes in whole-cell catalysis is influenced by temperature. To address these limitations, we introduced a relationally designed nanobiohybrid system that utilized light to modulate whole-cell catalysis for chiral alcohol production. By incorporating platinum nanoparticles onto Rhodotorula sp. cell surfaces, the nanobiohybrid capitalized on the photothermal properties of the nanoparticles to regulate the overall cell activity. When exposed to light, the Pt nanoparticles generate heat through the photothermal effect, consequently leading to an increase in the catalytic activity of the whole cells. This innovative approach facilitates control over whole-cell production and provides an efficient method for regulating biocatalytic processes. The findings of this study demonstrate the significant potential of switchable control strategies in biomanufacturing across a wide range of industries.

External Electrons Directly Stimulate Escherichia coli for Enhancing Biological Hydrogen Production

External electric field has the potential to influence metabolic processes such as biological hydrogen production in microorganisms. Based on this concept, we designed and constructed an electroactive hybrid system for microbial biohydrogen production under an electric field comprised of polydopamine (PDA)-modified Escherichia coli (E. coli) and Ni foam (NF). In this system, electrons generated from NF directly migrate into E. coli cells to promote highly efficient biocatalytic hydrogen production. Compared to that generated in the absence of electric field stimulation, biohydrogen production by the PDA-modified E. coli-based system is significantly enhanced. This investigation has demonstrated the mechanism for electron transfer in a biohybrid system and gives insight into precise basis for the enhancement of hydrogen production by using the multifield coupling technology.

Dopamine Polymerization-Mediated Surface Functionalization toward Advanced Bacterial Therapeutics

Bacteria-based therapy has spotlighted an unprecedented potential in treating a range of diseases, given that bacteria can be used as both drug vehicles and therapeutic agents. However, the use of bacteria for disease treatment often suffers from unsatisfactory outcomes, due largely to their suboptimal bioavailability, dose-dependent toxicity, and low targeting colonization. In the past few years, substantial efforts have been devoted to tackling these difficulties, among which methods capable of integrating bacteria with multiple functions have been extensively pursued. Different from conventional genetic engineering and modern synthetic bioengineering, surface modification of bacteria has emerged as a simple yet flexible strategy to introduce different functional motifs. Polydopamine, which can be easily formed via in situ dopamine oxidation and self-polymerization, is an appealing biomimetic polymer that has been widely applied for interfacial modification and functionalization. By virtue of its catechol groups, polydopamine can be efficiently codeposited with a multitude of functional elements on diverse surfaces.In this Account, we summarize the recent advances from our group with a focus on the interfacial polymerization-mediated functionalization of bacteria for advanced microbial therapy. First, we present the optimized strategy for bacterial surface modification under cytocompatible conditions by in situ dopamine polymerization. Taking advantage of the hydrogen bonding, π-π stacking, Michael addition, and Schiff base reaction with polydopamine, diverse functional small molecules and macromolecules are facilely codeposited onto the bacterial surface. Namely, monomodal, dual-modal, and multimodal surface modification of bacteria can be achieved by dopamine self-deposition, codeposition with a unitary composition, and codeposition with a set of multiple components, respectively. Second, we outline the regulation of bacterial functions by surface modification. The formed polydopamine surface endows bacteria with the ability to resist in vivo insults, such as gastrointestinal tract stressors and immune clearance, resulting in greatly improved bioavailability. Integration with specific ligands or therapeutic components enables the modified bacteria to increase targeting accumulation and colonization at lesion sites or play synergistic effects in disease treatment. Bacteria codeposited with different bioactive moieties, such as protein antigens, antibodies, and immunoadjuvants, are even able to actively interact with the host, particularly to elicit immune responses by either suppressing immune overactivation to promote the reversion of pathological inflammations or provoking protective innate and/or adaptive immunity to inhibit pathogenic invaders. Third, we highlight the applications of surface-modified bacteria as multifunctional living therapeutics in disease treatment, especially alleviating inflammatory bowel diseases via oral delivery and intervening in different types of cancer through systemic or intratumoral injection. Finally, we discuss the challenges and prospects of dopamine polymerization-mediated multifunctionalization for preparing advanced bacterial therapeutics as well as their bench to bedside translation. We anticipate that this Account can provide an insightful overview of bacterial therapy and inspire innovative thinking and new efforts to develop next-generation living therapeutics for treating various diseases.

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.

A Semiconductor Biohybrid System for Photo-Synergetic Enhancement of Biological Hydrogen Production

CdS nanoparticles were introduced on E. coli cells to construct a hydrogen generating biohybrid system via the biointerface of tannic acid-Fe complex. This hybrid system promotes good biological activity in a high salinity environment. Under light illumination, the as-synthesized biohybrid system achieves a 32.44 % enhancement of hydrogen production in seawater through a synergistic effect.

Polydopamine at biological interfaces

In the last years coating of surfaces in the presence of dopamine or other catecholamines in oxidative conditions to yield "polydopamine" films has become a popular, easy and versatile coating methodology. Polydopamine(s) offer(s) also a rich chemistry allowing to post-functionalize the obtained coatings with metal nanoparticles with polymers and proteins. However, the interactions either of covalent or non-covalent nature between polydopamine and biomolecules has only been explored more recently. They allow polydopamine to become a material, in the form of nanoparticles, membranes and other assemblies, in its own right not just as a coating. It is the aim of this review to describe the most recent advances in the design of composites between polydopamine and related eumelanin like materials with biomolecules like proteins, nucleotides, oligosaccharides and lipid assemblies. Furthermore, the interactions between polydopamine and living cells will be also reported.

Artificially sporulated Escherichia coli cells as a robust cell factory for interfacial biocatalysis

The natural bacterial spores have inspired the development of artificial spores, through coating cells with protective materials, for durable whole-cell catalysis. Despite attractiveness, artificial spores developed to date are generally limited to a few microorganisms with their natural endogenous enzymes, and they have never been explored as a generic platform for widespread synthesis. Here, we report a general approach to designing artificial spores based on Escherichia coli cells with recombinant enzymes. The artificial spores are simply prepared by coating cells with polydopamine, which can withstand UV radiation, heating and organic solvents. Additionally, the protective coating enables living cells to stabilize aqueous-organic emulsions for efficient interfacial biocatalysis ranging from single reactions to multienzyme cascades. Furthermore, the interfacial system can be easily expanded to chemoenzymatic synthesis by combining artificial spores with metal catalysts. Therefore, this artificial-spore-based platform technology is envisioned to lay the foundation for next-generation cell factory engineering.

Alginate@polydopamine@SiO2 microcapsules with controlled porosity for whole-cell based enantioselective biosynthesis of (S)-1-phenylethanol

Whole-cell biocatalysis, owing to its high enantioselectivity, environment friendly and mild reaction condition, show a great prospect in chemical, pharmaceutical and fuel industry. However, several problems still limit its wide applications, mainly concerning the low productivity and poor stability. Although the biocatalyst encapsulated in the most-commonly-used alginate hydrogels demonstrate enhanced stability, it still suffers from low biocatalytic productivity, long-term reusability and poor mass diffusion control. In this work, hybrid alginate@polydopamine@SiO₂ microcapsules with controlled porosity are designed to encapsulate yeast cells for the asymmetric biosynthesis of (S)- 1-phenylethonal from acetophenone. The hybrid microcapsules are formed by the ionic cross-linking of alginate, the polymerization of dopamine monomers and the protamine-assisted colloidal packing of uniform-sized silica nanoparticles. Alginate provides the encapsulated cells with highly biocompatible environment. Polydopamine enables to stimulate the biocatalytic productivity of the encapsulated yeast cells. Silica shells can not only regulate the mass diffusion in biocatalysis but also enhance the long-term mechanical and chemical stability of the microcapsules. The morphology, structure, chemical composition, stability and molecular accessibility of the hybrid microcapsules are investigated in detail. The viability and asymmetric bioreduction performance of the cells encapsulated in microcapsules are evaluated. The 24 h product yield of the cells encapsulated in the hybrid microcapsules shows 1.75 times higher than that of the cells encapsulated in pure alginate microcapsules. After 6 batches, the 24 h product yield of the cells encapsulated in the hybrid microcapsules is well maintained and 2 times higher than that of the cells encapsulated in pure alginate microcapsules. Therefore, the hybrid microcapsules designed in this study enable to enhance the asymmetric biocatalytic activity, stability and reusability of the encapsulated cells, thus contributing to a significant progress in cell-encapsulating materials to be applied in biocatalytic asymmetric synthesis industry.

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.

Cell-based biocomposite engineering directed by polymers

Biological cells such as bacterial, fungal, and mammalian cells always exploit sophisticated chemistries and exquisite micro- and nano-structures to execute life activities, providing numerous templates for engineering bioactive and biomorphic materials, devices, and systems. To transform biological cells into functional biocomposites, polymer-directed cell surface engineering and intracellular functionalization have been developed over the past two decades. Polymeric materials can be easily adopted by various cells through polymer grafting or in situ hydrogelation and can successfully bridge cells with other functional materials as interfacial layers, thus achieving the manufacture of advanced biocomposites through bioaugmentation of living cells and transformation of cells into templated materials. This review article summarizes the recent progress in the design and construction of cell-based biocomposites by polymer-directed strategies. Furthermore, the applications of cell-based biocomposites in broad fields such as cell research, biomedicine, and bioenergy are discussed. Last, we provide personal perspectives on challenges and future trends in this interdisciplinary area.

Nanocell hybrids for green chemistry

Global concerns about reducing or minimizing the costs associated with toxic waste materials have driven the continuing development of green-cell-based biosynthesis methods. Inspired by the hybridization phenomenon of living organisms, recent interest has arisen in nanocell hybrids that possess multiple new functions. They have potential to propel biosynthesis into a new generation of green chemistry. This review article discusses the development of applications for nanocell hybrids in the areas of sustainable energy, clean environment, and green catalysis. Continuing advances in these hybrids will require combining knowledge from the fields of biology, physics, chemistry, material science, and engineering.

Nanomaterial Shape Influence on Cell Behavior

Nanomaterials are proven to affect the biological activity of mammalian and microbial cells profoundly. Despite this fact, only surface chemistry, charge, and area are often linked to these phenomena. Moreover, most attention in this field is directed exclusively at nanomaterial cytotoxicity. At the same time, there is a large body of studies showing the influence of nanomaterials on cellular metabolism, proliferation, differentiation, reprogramming, gene transfer, and many other processes. Furthermore, it has been revealed that in all these cases, the shape of the nanomaterial plays a crucial role. In this paper, the mechanisms of nanomaterials shape control, approaches toward its synthesis, and the influence of nanomaterial shape on various biological activities of mammalian and microbial cells, such as proliferation, differentiation, and metabolism, as well as the prospects of this emerging field, are reviewed.

Single-cell yolk-shell nanoencapsulation for long-term viability with size-dependent permeability and molecular recognition

Like nanomaterials, bacteria have been unknowingly used for centuries. They hold significant economic potential for fuel and medicinal compound production. Their full exploitation, however, is impeded by low biological activity and stability in industrial reactors. Though cellular encapsulation addresses these limitations, cell survival is usually compromised due to shell-to-cell contacts and low permeability. Here, we report ordered packing of silica nanocolloids with organized, uniform and tunable nanoporosities for single cyanobacterium nanoencapsulation using protamine as an electrostatic template. A space between the capsule shell and the cell is created by controlled internalization of protamine, resulting in a highly ordered porous shell-void-cell structure formation. These unique yolk-shell nanostructures provide long-term cell viability with superior photosynthetic activities and resistance in harsh environments. In addition, engineering the colloidal packing allows tunable shell-pore diameter for size-dependent permeability and introduction of new functionalities for specific molecular recognition. Our strategy could significantly enhance the activity and stability of cyanobacteria for various nanobiotechnological applications.

Synthesis of a Removable Cytoprotective Exoskeleton by Tea Polyphenol Complexes for Living Cell Encapsulation

Cell encapsulation is a chemical tool for endowing living cells with exogenous properties and enhancing their in vitro tolerance against lethal factors, which has shown promising prospects and potential applications in many fields such as cell transplantation, drug delivery, and tissue engineering. One-pot precipitation of a polyphenol-metal complex on cells protects cells from UV irradiation and lytic enzymes. However, the involvement of metal ions brings side effects on cell viability and growth. Moreover, an external removal agent is needed for cell division and growth. Herein, a polymer shell composed of hydrogen bonded constituents without affecting cell viability and growth by the precipitation of tea polyphenol and polyvinyl pyrrolidone is reported. The formation of the polymer shell was verified by the Au nanoparticle's laser scanning confocal reflectance and quartz crystal microbalance measurement. The thickness of the shell was managed by the concentration of the complex. When exposed to UV irradiation for 15 or 30 min, polymer-coating-protected Saccharomyces cerevisiae (yeast) had much higher cell viability than the native one. Exposed to a high temperature environment (60 °C), most of the coated yeasts survived in contrast to uncoated ones. For the cell division and growth curve, the polymer coating with various thicknesses had no difference to the native one, which indicated no suppression of cell growth and no external side effects involved. As applied to mammalian HeLa cells under UV irradiation for 15 min, the coated cells had an obvious higher cell viability than that of untreated ones. Therefore, the tea polyphenol-poly(vinylpyrrolidone) shell is a versatile tool for chemically controlling the external properties of cells without side effects on cell viability and growth.

Third Generation Whole-Cell Sensing Systems: Synthetic Biology Inside, Nanomaterial Outside

Whole-cell sensing systems (WCSSs) are highly anticipated in the field of on-site detection. However, due to their low specificity, poor stability, and potential environmental problems, their commercial application is unrealistic. Recently, synthetic biology and nanomaterials have provided potential solutions to these problems, propelling WCSSs into a new generation. Synthetic biology provides a complete solution for the intelligent design and assembly of elements, modules, and genetic circuits. Nanomaterials covering the exterior of the cells provide stable protection, remote control capability, and catalytic ability for the WCSSs, and they can limit the horizontal transfer of genetic elements. These advancements enable personalized customization, intelligent control, and self-destruction in the next generation of cell sensors, promoting their industrialization.

Immobilization of Cofactor Self-Sufficient Recombinant Escherichia coli for Enantioselective Biosynthesis of (R)-1-Phenyl-1,2-Ethanediol

(R)-1-phenyl-1,2-ethanediol is an important synthon for the preparation of β-adrenergic blocking agents. This study identified a (2R,3R)-butanediol dehydrogenase (KgBDH) from Kurthia gibsonii SC0312, which showed high enantioselectivity for production of (R)-1-phenyl-1,2-ethanediol by reduction of 2-hydroxyacetophenone. KgBDH was expressed in a recombinant engineered strain, purified, and characterized. It showed good catalytic activity at pH 6–8 and better stability in alkaline (pH 7.5–8) than an acidic environment (pH 6.0–7.0), providing approximately 73 and 88% of residual activity after 96 h at pH 7.5 and 8.0, respectively. The maximum catalytic activity was obtained at 45°C; nevertheless, poor thermal stability was observed at >30°C. Additionally, the examined metal ions did not activate the catalytic activity of KgBDH. A recombinant Escherichia coli strain coexpressing KgBDH and glucose dehydrogenase (GHD) was constructed and immobilized via entrapment with a mixture of activated carbon and calcium alginate via entrapment. The immobilized cells had 1.8-fold higher catalytic activity than that of cells immobilized by calcium alginate alone. The maximum catalytic activity of the immobilized cells was achieved at pH 7.5, and favorable pH stability was observed at pH 6.0–9.0. Moreover, the immobilized cells showed favorable thermal stability at 25–30°C and better operational stability than free cells, retaining approximately 55% of the initial catalytic activity after four cycles. Finally, 81% yields (195 mM product) and >99% enantiomeric excess (ee) of (R)-1-phenyl-1,2-ethanediol were produced within 12 h through a fed-batch strategy with the immobilized cells (25 mg/ml wet cells) at 35°C and 180 rpm, with a productivity of approximately 54 g/L per day.

Click Reaction for Reversible Encapsulation of Single Yeast Cells

Cell surface engineering is an emerging technology to encapsulate cells in order to enhance their functions. However, methods for reversible encapsulation of cells with abiotic functionalities are rare. Herein, we describe a phenylboronic acid based click reaction for encapsulation of single yeast cells using mesoporous silica nanoparticles (MSNs). This encapsulation does not impact natural growth of the cells and leads to a significant enhancement of cell survival in a variety of hostile environments. Owing to the glucose-responsiveness of the boronate ester bond between cell surface polysaccharides and B(OH)₂-grafted MSNs, encapsulation was reversible by addition or removal of glucose. This effort offers living cells effective protection under harsh conditions and enables reversible assembling-detaching of abiotic functions.

Flavin Conjugated Polydopamine Nanoparticles Displaying Light-Driven Monooxygenase Activity

A hybrid of flavin and polydopamine (PDA) has been explored as a photocatalyst, drawing inspiration from natural flavoenzymes. Light-driven monoxygenase activity has been demonstrated through the oxidation of indole under blue light irradiation in ambient conditions, to afford indigo and indirubin dyes. Compared to riboflavin, a flavin-polydopamine hybrid is shown to be more resistant to photobleaching and more selective toward dye production. In addition, it has been demonstrated that it can be recycled from the solution and used for up to four cycles without a marked loss of activity, which is a significant improvement compared to other heterogenous flavin catalysts. The mechanism of action has been explored, indicating that the PDA shell plays an important role in the stabilization of the intermediate flavin-peroxy species, an active component of the catalytic system rather than acting only as a passive nanocarrier of active centers.

Enhancement of biocatalyst activity and protection against stressors using a microbial exoskeleton

Whole cell biocatalysts can perform numerous industrially-relevant chemical reactions. While they are less expensive than purified enzymes, whole cells suffer from inherent reaction rate limitations due to transport resistance imposed by the cell membrane. Furthermore, it is desirable to immobilize the biocatalysts to enable ease of separation from the reaction mixture. In this study, we used a layer-by-layer (LbL) self-assembly process to create a microbial exoskeleton which, simultaneously immobilized, protected, and enhanced the reactivity of a whole cell biocatalyst. As a proof of concept, we used Escherichia coli expressing homoprotocatechuate 2,3-dioxygenase (HPCD) as a model biocatalyst and coated it with up to ten alternating layers of poly(diallyldimethylammonium chloride) (PDADMAC) and silica. The microbial exoskeleton also protected the biocatalyst against a variety of external stressors including: desiccation, freeze/thaw, exposure to high temperatures, osmotic shock, as well as against enzymatic attack by lysozyme, and predation by protozoa. While we observed increased permeability of the outer membrane after exoskeleton deposition, this had a moderate effect on the reaction rate (up to two-fold enhancement). When the exoskeleton construction was followed by detergent treatment to permeabilize the cytoplasmic membrane, up to 15-fold enhancement in the reaction rate was reached. With the exoskeleton, we increased in the reaction rate constants as much as 21-fold by running the biocatalyst at elevated temperatures ranging from 40 °C to 60 °C, a supraphysiologic temperature range not accessible by unprotected bacteria.

Polydopamine coating on individual cells for enhanced extracellular electron transfer

The double-mediator electron transport pathway was achieved by PDA coating on the surface of individual cells to facilitate EET.

Hybrid Alginate@TiO2 Porous Microcapsules as a Reservoir of Animal Cells for Cell Therapy

The number of patients suffering from diseases linked with hormone deficiency (e.g., type 1 diabetes mellitus) has significantly increased in recent years. As organ transplantation presents its limits, the design of novel robust devices for cell encapsulation is of great interest. The current study reports the design of a novel hybrid alginate microcapsule reinforced by titania via a biocompatible synthesis from an aqueous stable titania precursor (TiBALDH) and a cationic polyamine (PDDAC) under mild conditions. The biocompatibility of this one-pot synthesis was confirmed by evaluation of the cytotoxicity of the precursor, additive, product, and by-product. The morphology, structure, and properties of the obtained hybrid microcapsule were characterized in detail. The microcapsule displayed mesoporous, which was a key parameter to allow the diffusion of nutrients and metabolites and to avoid the entry of immune defenders. The hybrid microcapsule also showed enhanced mechanical stability compared to the pure alginate microcapsule, making it an ideal candidate as a cell reservoir. HepG2 model cells encapsulated in the hybrid microcapsules remained intact for 43 days as highlighted by fluorescent viability probes, their oxygen consumption, and their albumin secretion. The study provides a significant progress in the conception of the robust and biocompatible reservoirs of animal cells for cell therapy.

A bilayered nanoshell for durable protection of single yeast cells against multiple, simultaneous hostile stimuli

Single cell surface engineering provides the most efficient, non-genetic strategy to enhance cell stability. However, it remains a huge challenge to improve cell stability in complex artificial environments. Here, a soft biohybrid interfacial layer is fabricated on individual living-cell surfaces by their exposure to a suspension of gold nanoparticles and l-cysteine to form a protecting functional layer to which porous silica layers were bound yielding pores with a diameter of 3.9 nm. The living cells within the bilayered nanoshells maintained high viability (96 ± 2%) as demonstrated by agar plating, even after five cycles of simultaneous exposure to high temperature (40 °C), lyticase and UV light. Moreover, yeast cells encapsulated in bilayered nanoshells were more recyclable than native cells due to nutrient storage in the shell.

Strategic Advances in Formation of Cell-in-Shell Structures: From Syntheses to Applications

Single-cell nanoencapsulation, forming cell-in-shell structures, provides chemical tools for endowing living cells, in a programmed fashion, with exogenous properties that are neither innate nor naturally achievable, such as cascade organic-catalysis, UV filtration, immunogenic shielding, and enhanced tolerance in vitro against lethal factors in real-life settings. Recent advances in the field make it possible to further fine-tune the physicochemical properties of the artificial shells encasing individual living cells, including on-demand degradability and reconfigurability. Many different materials, other than polyelectrolytes, have been utilized as a cell-coating material with proper choice of synthetic strategies to broaden the potential applications of cell-in-shell structures to whole-cell catalysis and sensors, cell therapy, tissue engineering, probiotics packaging, and others. In addition to the conventional "one-time-only" chemical formation of cytoprotective, durable shells, an approach of autonomous, dynamic shellation has also recently been attempted to mimic the naturally occurring sporulation process and to make the artificial shell actively responsive and dynamic. Here, the recent development of synthetic strategies for formation of cell-in-shell structures along with the advanced shell properties acquired is reviewed. Demonstrated applications, such as whole-cell biocatalysis and cell therapy, are discussed, followed by perspectives on the field of single-cell nanoencapsulation.

Single cells in nanoshells for the functionalization of living cells

Inspired by the characteristics of cells in live organisms, new types of hybrids have been designed comprising live cells and abiotic materials having a variety of structures and functionalities. The major goal of these studies is to uncover hybridization approaches that promote cell stabilization and enable the introduction of new functions into living cells. Single-cells in nanoshells have great potential in a large number of applications including bioelectronics, cell protection, cell therapy, and biocatalysis. In this review, we discuss the results of investigations that have focused on the synthesis, structuration, functionalization, and applications of these single-cells in nanoshells. We describe synthesis methods to control the structural and functional features of single-cells in nanoshells, and further develop their applications in sustainable energy, environmental remediation, green biocatalysis, and smart cell therapy. Perceived limitations of single-cells in nanoshells have been also identified.