Encapsulation of bacterial spores in nanoorganized polyelectrolyte shells

Characterization of Polyallylamine/Polystyrene Sulfonate Polyelectrolyte Microcapsules Formed on Solid Cores: Morphology

Polyelectrolyte microcapsules (PMC) based on polyallylamine and polystyrene sulfonate are utilized in various fields of human activity, including medicine, textiles, and the food industry, among others. However, characteristics such as microcapsule size, shell thickness, and pore size are not sufficiently studied and systematized, even though they determine the possibility of using microcapsules in applied tasks. The aim of this review is to identify general patterns and gaps in the study of the morphology of polyelectrolyte microcapsules obtained by the alternate adsorption of polystyrene sulfonate and polyallylamine on different solid cores. First and foremost, it was found that the morphological change in polyelectrolyte microcapsules formed on different cores exhibits a significant difference in response to varying stimuli. Factors such as ionic strength, the acidity of the medium, and temperature have different effects on the size of the microcapsules, the thickness of their shells, and the number and size of their pores. At present, the morphology of the microcapsules formed on the melamine formaldehyde core has been most studied, while the morphology of microcapsules formed on other types of cores is scarcely studied. In addition, modern methods of nanoscale system analysis will allow for an objective assessment of PMC characteristics and provide a fresh perspective on the subject of research.

An Outer Membrane-Inspired Polymer Coating Protects and Endows Escherichia coli with Novel Functionalities

A bio-inspired membrane made of Pluronic L-121 is produced around Escherichia coli thanks to the simple co-extrusion of bacteria and polymer vesicles. The block copolymer-coated bacteria can withstand various harsh shocks, for example, temperature, pressure, osmolarity, and chemical agents. The polymer membrane also makes the bacteria resistant to enzymatic digestion and enables them to degrade toxic compounds, improving their performance as whole-cell biocatalysts. Moreover, the polymer membrane acts as an anchor layer for the surface modification of the bacteria. Being decorated with α-amylase or lysozyme, the cells are endowed with the ability to digest starch or self-predatory bacteria are created. Thus, without any genetic engineering, the phenotype of encapsulated bacteria is changed as they become sturdier and gain novel metabolic functionalities.

Anthrax revisited: how assessing the unpredictable can improve biosecurity

B. anthracis is one of the most often weaponized pathogens. States had it in their bioweapons programs and criminals and terrorists have used or attempted to use it. This study is motivated by the narrative that emerging and developing technologies today contribute to the amplification of danger through greater easiness, accessibility and affordability of steps in the making of an anthrax weapon. As states would have way better preconditions if they would decide for an offensive bioweapons program, we focus on bioterrorism. This paper analyzes and assesses the possible bioterrorism threat arising from advances in synthetic biology, genome editing, information availability, and other emerging, and converging sciences and enabling technologies. Methodologically we apply foresight methods to encourage the analysis of contemporary technological advances. We have developed a conceptual six-step foresight science framework approach. It represents a synthesis of various foresight methodologies including literature review, elements of horizon scanning, trend impact analysis, red team exercise, and free flow open-ended discussions. Our results show a significant shift in the threat landscape. Increasing affordability, widespread distribution, efficiency, as well as ease of use of DNA synthesis, and rapid advances in genome-editing and synthetic genomic technologies lead to an ever-growing number and types of actors who could potentially weaponize B. anthracis. Understanding the current and future capabilities of these technologies and their potential for misuse critically shapes the current and future threat landscape and underlines the necessary adaptation of biosecurity measures in the spheres of multi-level political decision making and in the science community.

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.

Polydopamine coating of living diatom microalgae

Many microorganisms produce specific structures, known as spores or cysts, to increase their resistance to adverse environmental conditions. Scientists have started to produce biomimetic materials inspired by these natural membranes, especially for industrial and biomedical applications. Here, we present biological data on the biocompatibility of a polydopamine-based artificial coating for diatom cells. In this work, living Thalassiosira weissflogii diatom cells are coated on their surface with a polydopamine layer mimicking mussel adhesive protein. Polydopamine does not affect diatoms growth kinetics, it enhances their resistance to degradation by treatment with detergents and acids, and it decreases the uptake of model staining emitters. These outcomes pave the way for the use of living diatom cells bearing polymer coatings for sensors based on living cells, resistant to artificial microenvironments, or acting as living devices for cells interface study.

Graphical abstract

Layer-by-Layer Cell Encapsulation for Drug Delivery: The History, Technique Basis, and Applications

The encapsulation of cells with various polyelectrolytes through layer-by-layer (LbL) has become a popular strategy in cellular function engineering. The technique sprang up in 1990s and obtained tremendous advances in multi-functionalized encapsulation of cells in recent years. This review comprehensively summarized the basis and applications in drug delivery by means of LbL cell encapsulation. To begin with, the concept and brief history of LbL and LbL cell encapsulation were introduced. Next, diverse types of materials, including naturally extracted and chemically synthesized, were exhibited, followed by a complicated basis of LbL assembly, such as interactions within multilayers, charge distribution, and films morphology. Furthermore, the review focused on the protective effects against adverse factors, and bioactive payloads incorporation could be realized via LbL cell encapsulation. Additionally, the payload delivery from cell encapsulation system could be adjusted by environment, redox, biological processes, and functional linkers to release payloads in controlled manners. In short, drug delivery via LbL cell encapsulation, which takes advantage of both cell grafts and drug activities, will be of great importance in basic research of cell science and biotherapy for various diseases.

There is still plenty of room for layer-by-layer assembly for constructing nanoarchitectonics-based materials and devices

Nanoarchitectonics approaches can produce functional materials from tiny units through combination of various processes including atom/molecular manipulation, chemical conversion, self-assembly/self-organization, microfabrication, and bio-inspired procedures. Existing fabrication approaches can be regarded as fitting into the same concept. In particular, the so-called layer-by-layer (LbL) assembly method has huge potential for preparing applicable materials with a great variety of assembling mechanisms. LbL assembly is a multistep process where different components can be organized in planned sequences while simple alignment options provide access to superstructures, for example helical structures, and anisotropies which are important aspects of nanoarchitectonics. In this article, newly-featured examples are extracted from the literature on LbL assembly discussing trends for composite functional materials according to (i) principles and techniques, (ii) composite materials, and (iii) applications. We present our opinion on the present trends, and the prospects of LbL assembly. While this method has already reached a certain maturity, there is still plenty of room for expanding its usefulness for the fabrication of nanoarchitectonics-based materials and devices.

Controlling the growth of Escherichia coli by layer-by-layer encapsulation

Escherichia coli is one of the most common commensal aerobic bacteria in the gut microbiota of humans (and other mammals). Nevertheless, if left free to proliferate, it can induce a large range of diseases from diarrhoea to extra-intestinal diseases. In recent years, this bacterium had become increasingly resistant to antibiotics. It is therefore essential to implement new approaches able to maintain both bacterial viability and to control their proliferation. In this context, we developed a process to encapsulate Escherichia coli in polymer shells. We took advantage of the fact that this bacterium has a negatively charged surface and modified it via a layer-by-layer process, i.e. with oppositely charged polyelectrolyte pairs (namely chitosan as the polycation and alginate or dextran sulfate as polyanion). We successfully demonstrate the controlled coating of the bacterial surface via zeta potential measurement, the viability of the encapsulated bacteria and a delay in growth due to the multilayer coating. This delay was dependent on the number of polyelectrolyte layers.

Research progress on enhancing the performance of autotrophic nitrogen removal systems using microbial immobilization technology

The autotrophic nitrogen removal process has great potential to be applied to the biological removal of nitrogen from wastewater, but its application is hindered by its unstable operation under adverse environmental conditions, such as those presented by low temperatures, high organic matter concentrations, or the presence of toxic substances. Granules and microbial entrapment technology can effectively retain and enrich microbial assemblages in reactors to improve operating efficiency and reactor stability. The carriers can also protect the reactor's internal microorganisms from interference from the external environment. This article critically reviews the existing literature on autotrophic nitrogen removal systems using immobilization technology. We focus our discussion on the natural aggregation process (granulation) and entrapment technology. The selection of carrier materials and entrapment methods are identified and described in detail and the mechanisms through which entrapment technology protects microorganisms are analyzed. This review will provide a better understanding of the mechanisms through which immobilization operates and the prospects for immobilization technology to be applied in autotrophic nitrogen removal systems.

High-Yield Production of Biohybrid Microalgae for On-Demand Cargo Delivery

Biohybrid microswimmers exploit the swimming and navigation of a motile microorganism to target and deliver cargo molecules in a wide range of biomedical applications. Medical biohybrid microswimmers suffer from low manufacturing yields, which would significantly limit their potential applications. In the present study, a biohybrid design strategy is reported, where a thin and soft uniform coating layer is noncovalently assembled around a motile microorganism. Chlamydomonas reinhardtii (a single-cell green alga) is used in the design as a biological model microorganism along with polymer-nanoparticle matrix as the synthetic component, reaching a manufacturing efficiency of ≈90%. Natural biopolymer chitosan is used as a binder to efficiently coat the cell wall of the microalgae with nanoparticles. The soft surface coating does not impair the viability and phototactic ability of the microalgae, and allows further engineering to accommodate biomedical cargo molecules. Furthermore, by conjugating the nanoparticles embedded in the thin coating with chemotherapeutic doxorubicin by a photocleavable linker, on-demand delivery of drugs to tumor cells is reported as a proof-of-concept biomedical demonstration. The high-throughput strategy can pave the way for the next-generation generation microrobotic swarms for future medical active cargo delivery tasks.

Inhibiting Cell Viability and Motility by Layer-by-Layer Assembly and Biomineralization

Herein, we proposed a drug-free strategy named cell surface shellization to inhibit the motility of SKOV-3 and HeLa cells. We alternately deposited two- or three-layer cationic polyelectrolyte (PE) and anionic PE films on the surface of SKOV-3 and HeLa cells. Then, a mineral shell (calcium carbonate, CaCO₃) was formed on the surface of polymer shells via electrostatic force and biomineralization. The CCK-8 assay results and live/dead staining showed that the surface shells strongly aggravated the cytotoxicity. The monolayer scratch wound migration assay results and immunofluorescence staining results showed that the shells, especially the mineral shells, could efficiently inhibit the migration of SKOV-3 and HeLa cells without any anticancer drugs. The immunofluorescence results of the three small G proteins of the cells showed that the immunofluorescence intensity in SKOV-3 did not change. Preliminary results from our laboratory showed an increase in MMP-9 secreted by cancer cells after coating with films or mineral shells. It suggests that mechanisms that inhibit cell migration are related to the MMP signaling pathway. All the results indicated that shellization (films or nanomineral shells) but not limited to calcification can be used as one of the tools to change the function of cells.

Biodegradable, lignin-based encapsulation enables delivery of Trichoderma reesei with programmed enzymatic release against grapevine trunk diseases

Antagonistic fungi such as Trichoderma reesei are promising alternatives to conventional fungicides in agriculture. This is especially true for worldwide occurring grapevine trunk diseases, causing losses of US$1.5 billion every year, at which conventional fungicides are mostly ineffective or prohibited by law. Yet, applications of Trichoderma against grapevine trunk diseases are limited to preventive measures, suffer from poor shelf life, or uncontrolled germination. Therefore, we developed a mild and spore-compatible layer-by-layer assembly to encapsulate spores of a new mycoparasitic strain of T. reesei IBWF 034-05 in a bio-based and biodegradable lignin shell. The encapsulation inhibits undesired premature germination and enables the application as an aqueous dispersion via trunk injection. First injected into a plant, the spores remain in a resting state. Second, when lignin-degrading fungi infect the plant, enzymatic degradation of the shell occurs and germination is selectively triggered by the pathogenic fungi itself, which was proven in vitro. Germinated Trichoderma antagonizes the fungal pathogens and finally supplants them from the plant. This concept enables Trichoderma spores for curative treatment of esca, one of the most infective grapevine trunk diseases worldwide.

Mechanistic Understanding of the Interactions of Cationic Conjugated Oligo- and Polyelectrolytes with Wild-type and Ampicillin-resistant Escherichia coli

An in-depth understanding of cell-drug binding modes and action mechanisms can potentially guide the future design of novel drugs and antimicrobial materials and help to combat antibiotic resistance. Light-harvesting π-conjugated molecules have been demonstrated for their antimicrobial effects, but their impact on bacterial outer cell envelope needs to be studied in detail. Here, we synthesized poly(phenylene) based model cationic conjugated oligo- (2QA-CCOE, 4QA-CCOE) and polyelectrolytes (CCPE), and systematically explored their interactions with the outer cell membrane of wild-type and ampicillin (amp)-resistant Gram-negative bacteria, Escherichia coli (E. coli). Incubation of the E. coli cells in CCOE/CCPE solution inhibited the subsequent bacterial growth in LB media. About 99% growth inhibition was achieved if amp-resistant E. coli was treated for ~3-5 min, 1 h and 6 h with 100 μM of CCPE, 4QA-CCOE, and 2QA-CCOE solutions, respectively. Interestingly, these CCPE and CCOEs inhibited the growth of both wild-type and amp-resistant E. coli to a similar extent. A large surface charge reversal of bacteria upon treatment with CCPE suggested the formation of a coating of CCPE on the outer surface of bacteria; while a low reversal of bacterial surface charge suggested intercalation of CCOEs within the lipid bilayer of bacteria.

Decapsulation of Dextran by Destruction of Polyelectrolyte Microcapsule Nanoscale Shell by Bacillus subtilis Bacteria

One of the prerequisites of successful address delivery is controlling the release of encapsulated drugs. The new method of bacterial spore encapsulation in polyelectrolyte microcapsules allows for degrading the nanoscale membrane shell of microcapsules. The possibility of encapsulating spore forms of Bacillus subtilis in polystyrenesulfonate sodium/ polyallylamine hydrochloride (PSS/PAH) polyelectrolyte microcapsules was demonstrated. The activation and growth on a nutrient medium of encapsulated bacterial spores led to 60% degradation of the microcapsules nanoscale membrane shell. As a result, 18.5% of Fluorescein isothiocyanatedextran was encapsulated into polyelectrolyte microcapsules, and 28.6% of the encapsulated concentration of FITC-dextran was released into the solution.

Bioelectrochemical Properties of Enzyme-Containing Multilayer Polyelectrolyte Microcapsules Modified with Multiwalled Carbon Nanotubes

This work investigated changes in the biochemical parameters of multilayer membrane structures, emerging at their modification with multiwalled carbon nanotubes (MWCNTs). The structures were represented by polyelectrolyte microcapsules (PMCs) containing glucose oxidase (GOx). PMCs were made using sodium polystyrene sulfonate (polyanion) and poly(allylamine hydrochloride) (polycation). Three compositions were considered: with MWCNTs incorporated between polyelectrolyte layers; with MWCNTs inserted into the hollow of the microcapsule; and with MWCNTs incorporated simultaneously into the hollow and between polyelectrolyte layers. The impedance spectra showed modifications using MWCNTs to cause a significant decrease in the PMC active resistance from 2560 to 25 kOhm. The cyclic current-voltage curves featured a current rise at modifications of multilayer MWCNT structures. A PMC-based composition was the basis of a receptor element of an amperometric biosensor. The sensitivity of glucose detection by the biosensor was 0.30 and 0.05 μA/mM for PMCs/MWCNTs/GOx and PMCs/GOx compositions, respectively. The biosensor was insensitive to the presence of ethanol or citric acid in the sample. Polyelectrolyte microcapsules based on a multilayer membrane incorporating the enzyme and MWCNTs can be efficient in developing biosensors and microbial fuel cells.

Biomedical Applications of Layer-by-Layer Self-Assembly for Cell Encapsulation: Current Status and Future Perspectives

Encapsulating living cells within multilayer functional shells is a crucial extension of cellular functions and a further development of cell surface engineering. In the last decade, cell encapsulation has been widely utilized in many cutting-edge biomedical fields. Compared with other techniques for cell encapsulation, layer-by-layer (LbL) self-assembly technology, due to the versatility and tunability to fabricate diverse multilayer shells with controllable compositions and structures, is considered as a promising approach for cell encapsulation. This review summarizes the state-of-the-art and potential future biomedical applications of LbL cell encapsulation. First of all, a brief introduction to the LbL self-assembly technique, including assembly mechanisms and technologies, is made. Next, different cell encapsulation strategies by LbL self-assembly techniques are explained. Then, the biomedical applications of LbL cell encapsulation in cell-based biosensors, cell transplantation, cell/molecule delivery, and tissue engineering, are highlighted. Finally, discussions on the current limitations and future perspectives of LbL cell encapsulation are also provided.

Controlling the Growth of Staphylococcus epidermidis by Layer-By-Layer Encapsulation

Commensal skin bacteria such as Staphylococcus epidermidis are currently being considered as possible components in skin-care and skin-health products. However, considering the potentially adverse effects of commensal skin bacteria if left free to proliferate, it is crucial to develop methodologies that are capable of maintaining bacteria viability while controlling their proliferation. Here, we encapsulate S. epidermidis in shells of increasing thickness using layer-by-layer assembly, with either a pair of synthetic polyelectrolytes or a pair of oppositely charged polysaccharides. We study the viability of the cells and their delay of growth depending on the composition of the shell, its thickness, the charge of the last deposited layer, and the degree of aggregation of the bacteria which is varied using different coating procedures-among which is a new scalable process that easily leads to large amounts of nonaggregated bacteria. We demonstrate that the growth of bacteria is not controlled by the mechanical properties of the shell but by the bacteriostatic effect of the polyelectrolyte complex, which depends on the shell thickness and charge of its outmost layer, and involves the diffusion of unpaired amine sites through the shell. The lag times of growth are sufficient to prevent proliferation for daily topical applications.

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.

Octahedron Iron Oxide Nanocrystals Prohibited Clostridium difficile Spore Germination and Attenuated Local and Systemic Inflammation

Clinical management of Clostridium difficile infection is still far from satisfactory as bacterial spores are resistant to many chemical agents and physical treatments. Certain types of nanoparticles have been demonstrated to exhibit anti-microbial efficacy even in multi-drug resistance bacteria. However, most of these studies failed to show biocompatibility to the mammalian host cells and no study has revealed in vivo efficacy in C. difficile infection animal models. The spores treated with 500 µg/mL Fe_3-δO₄ nanoparticles for 20 minutes, 64% of the spores were inhibited from transforming into vegetative cells, which was close to the results of the sodium hypochlorite-treated positive control. By cryo-electron micro-tomography, we demonstrated that Fe_3-δO₄ nanoparticles bind on spore surfaces and reduce the dipicolinic acid (DPA) released by the spores. In a C. difficile infection animal model, the inflammatory level triple decreased in mice with colonic C. difficile spores treated with Fe_3-δO₄ nanoparticles. Histopathological analysis showed a decreased intense neutrophil accumulation in the colon tissue of the Fe_3-δO₄ nanoparticle-treated mice. Fe_3-δO₄ nanoparticles, which had no influence on gut microbiota and apparent side effects in vivo, were efficacious inhibitors of C. difficile spore germination by attacking its surface and might become clinically feasible for prophylaxis and therapy.

Temporary Single-Cell Coating for Bioprocessing with a Cationic Polymer

Temporary single-cell coating is a useful tool for cell processing, allowing manipulation of cells to prevent cell attachment and agglomeration, before re-establishing normal cell function. In this work, a speckled coating method using a known polycation [poly(l-lysine), PLL] is described to induce cell surface electrostatic charges on three different cell types, namely, two bone cancer cell lines and fibroblasts. The morphology of the PLL speckled coating on the cell surface, internalization and metabolization of the polymer, and prevention of cellular aggregations are reported. Polymer concentration was found to be the key parameter controlling both capsule morphology and cell health. This approach allows a temporary cell coating over the course of 1-2 h, with cells exhibiting phenotypically normal behavior after ingesting and metabolizing the polymer. The process offers a fast and efficient alternative to aid single-cell manipulation for bioprocessing applications. Preliminary work on the application of PLL speckled cell coating in enabling reliable bioprinting is also presented.

Biomimetic Extracellular Environment Based on Natural Origin Polyelectrolyte Multilayers

Surface modification of biomaterials is a well-known approach to enable an adequate biointerface between the implant and the surrounding tissue, dictating the initial acceptance or rejection of the implantable device. Since its discovery in early 1990s layer-by-layer (LbL) approaches have become a popular and attractive technique to functionalize the biomaterials surface and also engineering various types of objects such as capsules, hollow tubes, and freestanding membranes in a controllable and versatile manner. Such versatility enables the incorporation of different nanostructured building blocks, including natural biopolymers, which appear as promising biomimetic multilayered systems due to their similarity to human tissues. In this review, the potential of natural origin polymer-based multilayers is highlighted in hopes of a better understanding of the mechanisms behind its use as building blocks of LbL assembly. A deep overview on the recent progresses achieved in the design, fabrication, and applications of natural origin multilayered films is provided. Such films may lead to novel biomimetic approaches for various biomedical applications, such as tissue engineering, regenerative medicine, implantable devices, cell-based biosensors, diagnostic systems, and basic cell biology.

Analysis of self-assembly of S-layer protein slp-B53 from Lysinibacillus sphaericus

The formation of stable and functional surface layers (S-layers) via self-assembly of surface-layer proteins on the cell surface is a dynamic and complex process. S-layers facilitate a number of important biological functions, e.g., providing protection and mediating selective exchange of molecules and thereby functioning as molecular sieves. Furthermore, S-layers selectively bind several metal ions including uranium, palladium, gold, and europium, some of them with high affinity. Most current research on surface layers focuses on investigating crystalline arrays of protein subunits in Archaea and bacteria. In this work, several complementary analytical techniques and methods have been applied to examine structure-function relationships and dynamics for assembly of S-layer protein slp-B53 from Lysinibacillus sphaericus: (1) The secondary structure of the S-layer protein was analyzed by circular dichroism spectroscopy; (2) Small-angle X-ray scattering was applied to gain insights into the three-dimensional structure in solution; (3) The interaction with bivalent cations was followed by differential scanning calorimetry; (4) The dynamics and time-dependent assembly of S-layers were followed by applying dynamic light scattering; (5) The two-dimensional structure of the paracrystalline S-layer lattice was examined by atomic force microscopy. The data obtained provide essential structural insights into the mechanism of S-layer self-assembly, particularly with respect to binding of bivalent cations, i.e., Mg²⁺ and Ca²⁺. Furthermore, the results obtained highlight potential applications of S-layers in the fields of micromaterials and nanobiotechnology by providing engineered or individual symmetric thin protein layers, e.g., for protective, antimicrobial, or otherwise functionalized surfaces.

Coating Strategies Using Layer-by-layer Deposition for Cell Encapsulation

The layer-by-layer (LbL) deposition technique is widely used to develop multilayered films based on the directed assembly of complementary materials. In the last decade, thin multilayers prepared by LbL deposition have been applied in biological fields, namely, for cellular encapsulation, due to their versatile processing and tunable properties. Their use was suggested as an alternative approach to overcome the drawbacks of bulk hydrogels, for endocrine cells transplantation or tissue engineering approaches, as effective cytoprotective agents, or as a way to control cell division. Nanostructured multilayered materials are currently used in the nanomodification of the surfaces of single cells and cell aggregates, and are also suitable as coatings for cell-laden hydrogels or other biomaterials, which may later be transformed to highly permeable hollow capsules. In this Focus Review, we discuss the applications of LbL cell encapsulation in distinct fields, including cell therapy, regenerative medicine, and biotechnological applications. Insights regarding practical aspects required to employ LbL for cell encapsulation are also provided.

Tuning cell surface charge in E. coli with conjugated oligoelectrolytes

Conjugated oligoelectrolytes intercalate into and associate with membranes, thereby changing the surface charge of microbes, as determined by zeta potential measurements.

Cationic conjugated oligoelectrolytes (COEs) varying in length and structural features are compared with respect to their association with E. coli and their effect on cell surface charge as determined by zeta potential measurements. Regardless of structural features, at high staining concentrations COEs with longer molecular dimensions associate less, but neutralize the negative surface charge of E. coli to a greater degree than shorter COEs.

Improving cell-based therapies by nanomodification

Cell-based therapies are emerging as a promising approach for various diseases. Their therapeutic efficacy depends on rational control and regulation of the functions and behaviors of cells during their treatments. Different from conventional regulatory strategy by chemical adjuvants or genetic engineering, which is restricted by limited synergistic regulatory efficiency or uncertain safety problems, a novel approach based on nanoscale artificial materials can be applied to modify living cells to endow them with novel functions and unique properties. Inspired by natural "nano shell" and "nano compass" structures, cell nanomodification can be developed through both external and internal pathways. In this review, some novel cell surface engineering and intracellular nanoconjugation strategies are summarized. Their potential applications are also discussed, including cell protection, cell labeling, targeted delivery and in situ regulation. It is believed that these novel cell-material complexes can have great potentials for biomedical applications.

Microencapsulation of Clostridium acetobutylicum ATCC 824 spores in gellan gum microspheres for the production of biobutanol

The purpose of the present study was to provide further insights on the applicability of microencapsulation using emulsification method, to immobilise Clostridium acetobutylicum ATCC 824 spores, for biobutanol production. The encapsulated spores were revived using heat shock treatment and the fermentation efficiency of the resultant encapsulated cells was compared with that of the free (non-encapsulated) cells. The microspheres were easily recovered from the fermentation medium by filtration and reused up to five cycles of fermentation. In contrast, the free (non-encapsulated) cells could be reused for two cycles only. The microspheres remained intact throughout repeated use. Although significant cell leakage was observed during the course of fermentation, the microspheres could be reused with relatively high butanol yield, demonstrating their role as microbial cell nurseries. Both encapsulated and liberated cells contributed to butanol production.

Silk macromolecules with amino acid-poly(ethylene glycol) grafts for controlling layer-by-layer encapsulation and aggregation of recombinant bacterial cells

This study introduces double-brush designs of functionalized silk polyelectrolytes based upon regenerated silk fibroin (SF), which is modified with poly-L-lysine (SF-PLL), poly-L-glutamic acid (SF-PGA), and poly(ethylene glycol) (PEG) side chains with different grafting architecture and variable amino acid-PEG graft composition for cell encapsulation. The molecular weight of poly amino acids (length of side chains), molecular weight and degree of PEG grafting (D) were varied in order to assess the formation of cytocompatible and robust layer-by-layer (LbL) shells on two types of bacterial cells (Gram-negative and Gram-positive bacteria). We observed that shells assembled with charged polycationic amino acids adversely effected the properties of microbial cells while promoting the formation of large cell aggregates. In contrast, hydrogen-bonded shells with high PEG grafting density were the most cytocompatible, while promoting formation of stable colloidal suspensions of individual cell encapsulates. The stability to degradation of silk shells (under standard cell incubation procedure) was related to the intrinsic properties of thermodynamic bonding forces, with shells based on electrostatic interactions having stronger resistance to deterioration compared to pure hydrogen-bonded silk shells. By optimizing the charge density of silk polyelectrolytes brushes, as well as the length and the degree of PEG side grafts, robust and cytocompatible cell coatings were engineered that can control aggregation of cells for biosensor devices and other potential biomedical applications.

"Self-repairing" nanoshell for cell protection

Self-repair is nature's way of protecting living organisms. However, most single cells are inherently less capable of self-repairing, which greatly limits their wide applications. Here, we present a self-assembly approach to create a nanoshell around the cell surface using nanoporous biohybrid aggregates. The biohybrid shells present self-repairing behaviour, resulting in high activity and extended viability of the encapsulated cells (eukaryotic and prokaryotic cells) in harsh micro-environments, such as under UV radiation, natural toxin invasion, high-light radiation and abrupt pH-value changes. Furthermore, an interaction mechanism is proposed and studied, which is successful to guide design and synthesis of self-repairing biohybrid shells using different bioactive molecules.

Colloidal micro- and nano-particles as templates for polyelectrolyte multilayer capsules

Colloidal particles play an important role in various areas of material and pharmaceutical sciences, biotechnology, and biomedicine. In this overview we describe micro- and nano-particles used for the preparation of polyelectrolyte multilayer capsules and as drug delivery vehicles. An essential feature of polyelectrolyte multilayer capsule preparations is the ability to adsorb polymeric layers onto colloidal particles or templates followed by dissolution of these templates. The choice of the template is determined by various physico-chemical conditions: solvent needed for dissolution, porosity, aggregation tendency, as well as release of materials from capsules. Historically, the first templates were based on melamine formaldehyde, later evolving towards more elaborate materials such as silica and calcium carbonate. Their advantages and disadvantages are discussed here in comparison to non-particulate templates such as red blood cells. Further steps in this area include development of anisotropic particles, which themselves can serve as delivery carriers. We provide insights into application of particles as drug delivery carriers in comparison to microcapsules templated on them.

Nanocoating of single cells: from maintenance of cell viability to manipulation of cellular activities

The chronological progresses in single-cell nanocoating are described. The historical developments in the field are divided into biotemplating, cytocompatible nanocoating, and cells in nano-nutshells, depending on the main research focuses. Each subfield is discussed in conjunction with the others, regarding how and why to manipulate living cells by nanocoating at the single-cell level.

25th anniversary article: Dynamic interfaces for responsive encapsulation systems

Encapsulation systems are urgently needed both as micrometer and sub-micrometer capsules for active chemicals' delivery, to encapsulate biological objects and capsules immobilized on surfaces for a wide variety of advanced applications. Methods for encapsulation, prolonged storage and controllable release are discussed in this review. Formation of stimuli responsive systems via layer-by-layer (LbL) assembly, as well as via mobile chemical bonding (hydrogen bonds, chemisorptions) and formation of special dynamic stoppers are presented. The most essential advances of the systems presented are multifunctionality and responsiveness to a multitude of stimuli - the possibility of formation of multi-modal systems. Specific examples of advanced applications - drug delivery, diagnostics, tissue engineering, lab-on-chip and organ-on-chip, bio-sensors, membranes, templates for synthesis, optical systems, and antifouling, self-healing materials and coatings - are provided. Finally, we try to outline emerging developments.

Bio-inspired encapsulation and functionalization of living cells with artificial shells

In nature, most single cells do not have structured shells to provide extensive protection apart from diatoms and radiolarians. Fabrication of biomimetic structures based on living cells encapsulated with artificial shells has a great impact on the area of cell-based sensors and devices as well as fundamental studies in cell biology. The past decade has witnessed a rapid increase of research concerning the new fabrication strategies, functionalization and applications of this kind of encapsulated cells. In this review, the latest fabrication strategies on how to encapsulate living cells with functional shells based on the diversity of artificial shells are discussed: hydrogel matrix shells, sol-gel shells, polymeric shells, and induced mineral shells. Classical different types of artificial shells are introduced and their advantages and disadvantages are compared and explained. The biomedical applications of encapsulated cells with particular emphasis on cell implant protection, cell separation, biosensors, cell therapy and tissue engineering are also described and a recap of this review and the future perspectives on these active areas is given finally.

Artificial spores: cytoprotective nanoencapsulation of living cells

In this Opinion we discuss the development of artificial spores and their maturation as an independent field of research. The robust cell-in-shell structures have displayed unprecedented characteristics, which include the retardation of cell division and extensive cytoprotective capabilities that encompass exposure to osmotic pressure, shear force, heat, UV radiation, and lytic enzymes. Additionally, the nanothin shells act as highly versatile scaffolds for chemical functionalization to equip cells for implementation in tissue engineering, biosensors, cell therapy, or other biotechnological applications. We also explore the future direction of this emerging field and dictate that the next phase of research should focus on attaining more intricate engineering to achieve stimulus-responsive shell-degradation, multilayer casings with orthogonal functions, and the encapsulation of multiple cells for multicellular artificial spores.

Nano-decoration of the Hemagglutinating Virus of Japan envelope (HVJ-E) using a layer-by-layer assembly technique

In this study, we created a nanoscale layer of hyaluronic acid (HA) on the inactivated Hemagglutinating Virus of Japan envelope (HVJ-E) via a layer-by-layer (LbL) assembly technique for CD-44 targeted delivery. HVJ-E was selected as the template virus because it has shown a tumor-suppressing ability by eliciting inflammatory cytokine production in dendritic cells. Although it has been required to increase the tumor-targeting ability and reduce nonspecific binding because HVJ-E fuses with virtually all cells and induces hemagglutination in the bloodstream, complete modifications of single-envelope-type viruses with HA have been difficult. Therefore, we studied the surface ζ potential of HVJ-E at different pH values and carefully examined the deposition conditions for the first layer using three cationic polymers: poly-L-lysine (PLL), chitosan (CH), and glycol chitosan (GC). GC-coated HVJ-E particles showed the highest disperse ability under physiological pH and salt conditions without aggregation. An HA layer was then prepared via alternating deposition of HA and GC. The successive decoration of multilayers on HVJ-E has been confirmed by dynamic light scattering (DLS), ζ potentials, and transmission electron microscopy (TEM). An enzymatic degradation assay revealed that only the outermost HA layer was selectively degraded by hyaluronidase. However, entire layers were destabilized at lower pH. Therefore, the HA/GC-coated HVJ-E describe here can be thought of as a potential bomb for cancer immunotherapy because of the ability of targeting CD44 as well as the explosion of nanodecorated HA/GC layers at endosomal pH while preventing nonspecific binding at physiological pH and salt conditions such as in the bloodstream or normal tissues.

Artificial spores: cytocompatible encapsulation of individual living cells within thin, tough artificial shells

Cells are encapsulated individually within thin and tough shells in a cytocompatible way, by mimicking the structure of bacterial endospores that survive under hostile conditions. The 3D 'cell-in-shell' structures-coined as 'artificial spores'-enable modulation and control over cellular metabolism, such as control of cell division, resistance to external stresses, and surface-functionalizability, providing a useful platform for applications, including cell-based sensors, cell therapy, regenerative medicine, as well as for fundamental studies on cellular metabolism at the single-cell level and cell-to-cell communications. This Concept focuses on chemical approaches to single-cell encapsulation with artificial shells for creating artificial spores, including cross-linked layer-by-layer assembly, bioinspired mineralization, and mussel-inspired polymerization. The current status and future prospects of this emerging field are also discussed.

Biomimetic cell-mediated three-dimensional assembly of halloysite nanotubes

Biomimetic architectural assembly of clay nanotube shells on yeast cells was demonstrated producing viable artificial hybrid inorganic-cellular structures (armoured cells). These modified cells were preserved for one generation resulting in the intact second generation of cells with delayed germination.

Development of functionalised polyelectrolyte capsules using filamentous Escherichia coli cells

Background

Escherichia coli is one of the best studied microorganisms and finds multiple applications especially as tool in the heterologous production of interesting proteins of other organisms. The heterologous expression of special surface (S-) layer proteins caused the formation of extremely long E. coli cells which leave transparent tubes when they divide into single E. coli cells. Such natural structures are of high value as bio-templates for the development of bio-inorganic composites for many applications. In this study we used genetically modified filamentous Escherichia coli cells as template for the design of polyelectrolyte tubes that can be used as carrier for functional molecules or particles. Diversity of structures of biogenic materials has the potential to be used to construct inorganic or polymeric superior hybrid materials that reflect the form of the bio-template. Such bio-inspired materials are of great interest in diverse scientific fields like Biology, Chemistry and Material Science and can find application for the construction of functional materials or the bio-inspired synthesis of inorganic nanoparticles.

Results

Genetically modified filamentous E. coli cells were fixed in 2% glutaraldehyde and coated with alternating six layers of the polyanion polyelectrolyte poly(sodium-4styrenesulfonate) (PSS) and polycation polyelectrolyte poly(allylamine-hydrochloride) (PAH). Afterwards we dissolved the E. coli cells with 1.2% sodium hypochlorite, thus obtaining hollow polyelectrolyte tubes of 0.7 μm in diameter and 5–50 μm in length. For functionalisation the polyelectrolyte tubes were coated with S-layer protein polymers followed by metallisation with Pd(0) particles. These assemblies were analysed with light microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy.

Conclusion

The thus constructed new material offers possibilities for diverse applications like novel catalysts or metal nanowires for electrical devices. The novelty of this work is the use of filamentous E. coli templates and the use of S-layer proteins in a new material construct.

Permeability and micromechanical properties of silk ionomer microcapsules

We studied the pH-responsive behavior of layer-by-layer (LbL) microcapsules fabricated from silk fibroin chemically modified with different poly amino acid side chains: cationic (silk-poly L-lysine, SF-PL) or anionic (silk-poly-L-glutamic acid, SF-PG). We observed that stable ultrathin shell microcapsules can be assembled with a dramatic increase in swelling, thickness, and microroughness at extremely acidic (pH < 2.5) and basic (pH > 11.0) conditions without noticeable disintegration. These changes are accompanied by dramatic changes in shell permeability with a 2 orders of magnitude increase in the diffusion coefficient. Moreover, the silk ionomer shells undergo remarkable softening with a drop in Young's modulus by more than 1 order of magnitude due to the swelling, stretching, and increase in material porosity. The ability to control permeability and mechanical properties over a wide range for the silk-based microcapsules, with distinguishing stability under harsh environmental conditions, provides an important system for controlled loading and release and applications in bioengineering.

UV-cross-linkable multilayer microcapsules made of weak polyelectrolytes

Microcapsules composed of weak polyelectrolytes modified with UV-responsive benzophenone (BP) groups were fabricated by the layer-by-layer (LbL) technique. Being exposed to UV lights, capsules shrunk in the time course of minutes at irradiation intensity of 5 mW/cm(2). The shrinkage adjusted the capsule permeability, providing a novel way to encapsulate fluorescence-labeled dextran molecules without heating. Cross-linking within the capsule shells based on hydrogen abstraction via excited benzophenone units by UV showed a reliable and swift approach to tighten and stabilize the capsule shell without losing the pH-responsive properties of the weak polyelectrolyte multilayers.

Bacterial sunscreen: layer-by-layer deposition of UV-absorbing polymers on whole-cell biosensors

UV-protective coatings on live bacterial cells were created from the assembly of cationic and UV-absorbing anionic polyelectrolytes using layer-by-layer (LbL) methodology. A cationic polymer (polyallylamine) and three different anionic polymers with varying absorbance in the UV range (poly(vinyl sulfate), poly(4-styrenesulfonic acid), and humic acid) were used to encapsulate Escherichia coli cells with two different green fluorescent protein (GFP) expression systems: constitutive expression of a UV-excitable GFP (GFPuv) and regulated expression of the intensely fluorescent GFP from amphioxus (GFPa1) through a theophylline-inducible riboswitch. Riboswitches activate protein expression after specific ligand-RNA binding events. Hence, they operate as a cellular biosensor that will activate reporter protein synthesis after exposure to a ligand target. E. coli cells coated with UV-absorbing polymers demonstrated enhanced protection of GFP stability, metabolic activity, and viability after prolonged exposure to radiation from a germicidal lamp. The results show the effectiveness of LbL coatings to provide UV protection to living cells for biotechnological applications.

"Face-lifting" and "make-up" for microorganisms: layer-by-layer polyelectrolyte nanocoating

Layer-by-layer encapsulation of living biological cells and other microorganisms via sequential adsorption of oppositely charged functional nanoscale components is a promising instrument for engineering cells with enhanced properties and artificial microorganisms. Such nanoarchitectural shells assembled in mild aqueous conditions provide cells with additional abilities, widening their functionality and applications in artificial spore formation, whole-cell biosensors, and fabrication of three-dimensional multicellular clusters.

pH-responsive layer-by-layer nanoshells for direct regulation of cell activity

Saccharomyces cerevisiae yeast cells encapsulated with pH-responsive synthetic nanoshells from lightly cross-linked polymethacrylic acid showed a high viability rate of around 90%, an indication of high biocompatibility of synthetic pH-responsive shells. We demonstrated that increasing pH above the isoelectric point of the polymer shell leads to a delay in growth rate; however, it does not affect the expression of enhanced green fluorescent protein. We suggest that progressive ionization and charge accumulation within the synthetic shells evoke a structural change in the outer shells which affect the membrane transport. This change facilitates the ability to manipulate growth kinetics and functionality of the cells with the surrounding environment. We observed that hollow layer-by layer nanoshells showed a remarkable degree of reversible swelling/deswelling over a narrow pH range (pH 5.0-6.0), but their assembly directly on the cell surface resulted in the suppression of large dimensional changes. We suggest that the variation in surface charges caused by deprotonation/protonation of carboxylic groups in the nanoshells controlled cell growth and cell function, which can be utilized for external chemical control of cell-based biosensors.