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

Development of Stimulus-Responsive Degradable Film via Codeposition of Dopamine and Cystamine

Herein, we report a degradable film that can be coated on various substrates by the codeposition of dopamine and cystamine. The thickness of the resulting film (pDC) varies depending on the initial ratio of dopamine/cystamine dissolved in a solution; the thickest film (ca. 60 nm) is obtained under optimized codeposition conditions. Selective degradation of pDC occurs in the presence of tris(2-carboxyethyl)phosphine (TCEP), the reaction kinetics of which are highly dependent on the TCEP concentration. For further application as a drug-delivery platform, doxorubicin can be loaded within the pDC film, which is released actively under film degradation in response to TCEP. We expect that the developed pDC film will be a useful tool for developing drug delivery cargo, antibacterial surface, and cell surface coating for various biomedical applications.

Single-Cell Nanoencapsulation: From Passive to Active Shells

Single-cell nanoencapsulation is an emerging field in cell-surface engineering, emphasizing the protection of living cells against external harmful stresses in vitro and in vivo. Inspired by the cryptobiotic state found in nature, cell-in-shell structures are formed, which are called artificial spores and which show suppression or retardation in cell growth and division and enhanced cell survival under harsh conditions. The property requirements of the shells suggested for realization of artificial spores, such as durability, permselectivity, degradability, and functionalizability, are demonstrated with various cytocompatible materials and processes. The first-generation shells in single-cell nanoencapsulation are passive in the operation mode, and do not biochemically regulate the cellular metabolism or activities. Recent advances indicate that the field has shifted further toward the formation of active shells. Such shells are intimately involved in the regulation and manipulation of biological processes. Not only endowing the cells with new properties that they do not possess in their native forms, active shells also regulate cellular metabolism and/or rewire biological pathways. Recent developments in shell formation for microbial and mammalian cells are discussed and an outlook on the field is given.

Single cell electron collectors for highly efficient wiring-up electronic abiotic/biotic interfaces

By electronically wiring-up living cells with abiotic conductive surfaces, bioelectrochemical systems (BES) harvest energy and synthesize electric-/solar-chemicals with unmatched thermodynamic efficiency. However, the establishment of an efficient electronic interface between living cells and abiotic surfaces is hindered due to the requirement of extremely close contact and high interfacial area, which is quite challenging for cell and material engineering. Herein, we propose a new concept of a single cell electron collector, which is in-situ built with an interconnected intact conductive layer on and cross the individual cell membrane. The single cell electron collector forms intimate contact with the cellular electron transfer machinery and maximizes the interfacial area, achieving record-high interfacial electron transfer efficiency and BES performance. Thus, this single cell electron collector provides a superior tool to wire living cells with abiotic surfaces at the single-cell level and adds new dimensions for abiotic/biotic interface engineering.

Synthesis and Characterization of Silk Ionomers for Layer-by-Layer Electrostatic Deposition on Individual Mammalian Cells

Nanocoating of individual mammalian cells with polymer layers has been of increasing interest in biotechnology and biomedical engineering applications. Electrostatic layer-by-layer (LbL) deposition of polyelectrolytes on negatively charged cell surfaces has been utilized for cell nanocoatings using synthetic or natural polymers with a net charge at physiological conditions. Here, our previous synthesis of silk-based ionomers through modification of silk fibroin (SF) with polyglutamate (PG) and polylysine (PL) was exploited for the nanocoating of mammalian cells. SF-PL constructs were cytotoxic to mammalian cells, thus an alternative approach for the synthesis of silk ionomers through carboxylation and amination of regenerated SF chains was utilized. Through the optimization of material properties and composition of incubation buffers, silk ionomers could be electrostatically assembled on the surface of murine fibroblasts and human mesenchymal stem cells (hMSCs) to form nanoscale multilayers without significantly impairing cell viability. The resulting silk-based protein nanoshells were transient and degraded over time, allowing for cell proliferation. The strategies presented here provide a basis for the cytocompatible nanoencapsulation of mammalian cells within silk-based artificial cell walls, with potential benefits for future studies on surface engineering of mammalian cells, as well as for utility in cell therapies, 3D printing, and preservation.

Enzymatically degradable, starch-based layer-by-layer films: application to cytocompatible single-cell nanoencapsulation

The build-up and degradation of cytocompatible nanofilms in a controlled fashion have great potential in biomedical and nanomedicinal fields, including single-cell nanoencapsulation (SCNE). Herein, we report the fabrication of biodegradable films of cationic starch (c-ST) and anionic alginate (ALG) by electrostatically driven layer-by-layer (LbL) assembly technology and its application to the SCNE. The [c-ST/ALG] multilayer nanofilms, assembled either on individual Saccharomyces cerevisiae or on the 2D flat gold surface, degrade on demand, in a cytocompatible fashion, via treatment with α-amylase. Their degradation profiles are investigated, while systematically changing the α-amylase concentration, by several surface characterization techniques, including quartz crystal microbalance with dissipation monitoring (QCM-D) and ellipsometry. DNA incorporation in the LbL nanofilms and its controlled release, upon exposure of the nanofilms to an aqueous α-amylase solution, are demonstrated. The highly cytocompatible nature of the film-forming and -degrading conditions is assessed in the c-ST/ALG-shell formation and degradation of S. cerevisiae. We envisage that the cytocompatible, enzymatic degradation of c-ST-based nanofilms paves the way for developing advanced biomedical devices with programmed dissolution in vivo.

Biodegradable nanofibrous temperature-responsive gelling microspheres for heart regeneration

Myocardial infarction (heart attack) is the number one killer of heart patients. Existing treatments for heart attack do not address the underlying problem of cardiomyocyte (CM) loss and cannot regenerate the myocardium. Introducing exogenous cardiac cells is required for heart regeneration due to the lack of resident progenitor cells and very limited proliferative potential of adult CMs. Poor retention of transplanted cells is the critical bottleneck of heart regeneration. Here, we report the invention of a poly(l-lactic acid)-b-poly(ethylene glycol)-b-poly(N-Isopropylacrylamide) copolymer and its self-assembly into nanofibrous gelling microspheres (NF-GMS). The NF-GMS undergo thermally responsive transition to form not only a 3D hydrogel after injection in vivo, but also exhibit architectural and structural characteristics mimicking the native extracellular matrix (ECM) of nanofibrous proteins and gelling proteoglycans or polysaccharides. By integrating the ECM-mimicking features, injectable form, and the capability of maintaining 3D geometry after injection, the transplantation of hESC-derived CMs carried by NF-GMS led to a striking 10-fold graft size increase over direct CM injection in an infarcted rat model, which is the highest reported engraftment to date. Furthermore, NF-GMS carried CM transplantation dramatically reduced infarct size, enhanced integration of transplanted CMs, stimulated vascularization in the infarct zone, and led to a substantial recovery of cardiac function. The NF-GMS may also serve as advanced injectable and integrative biomaterials for cell/biomolecule delivery in a variety of biomedical applications.

Nanobiohybrids: Materials approaches for bioaugmentation

Nanobiohybrids, synthesized by integrating functional nanomaterials with living systems, have emerged as an exciting branch of research at the interface of materials engineering and biological science. Nanobiohybrids use synthetic nanomaterials to impart organisms with emergent properties outside their scope of evolution. Consequently, they endow new or augmented properties that are either innate or exogenous, such as enhanced tolerance against stress, programmed metabolism and proliferation, artificial photosynthesis, or conductivity. Advances in new materials design and processing technologies made it possible to tailor the physicochemical properties of the nanomaterials coupled with the biological systems. To date, many different types of nanomaterials have been integrated with various biological systems from simple biomolecules to complex multicellular organisms. Here, we provide a critical overview of recent developments of nanobiohybrids that enable new or augmented biological functions that show promise in high-tech applications across many disciplines, including energy harvesting, biocatalysis, biosensing, medicine, and robotics.

Astrocyte-Encapsulated Hydrogel Microfibers Enhance Neuronal Circuit Generation

Astrocytes, the most representative glial cells in the brain, play a multitude of crucial functions for proper neuronal development and synaptic-network formation, including neuroprotection as well as physical and chemical support. However, little attention has been paid, in the neuroregenerative medicine and related fields, to the cytoprotective incorporation of astrocytes into neuron-culture scaffolds and full-fledged functional utilization of encapsulated astrocytes for controlled neuronal development. In this article, a 3D neurosupportive culture system for enhanced induction of neuronal circuit generation is reported, where astrocytes are confined in hydrogel microfibers and protected from the outside. The astrocyte-encapsulated microfibers significantly accelerate the neurite outgrowth and guide its directionality, and enhance the synaptic formation, without any physical contact with the neurons. This astrocyte-laden system provides a pivotal culture scaffold for advanced development of cell-based therapeutics for neural injuries, such as spinal cord injury.

Enzyme-Instructed Self-Assembly for Cancer Therapy and Imaging

Enzymatic reactions and self-assembly are two fundamental attributes of cells. It is not surprising that one can use enzyme-instructed self-assembly (EISA)-the integration of enzymatic transformation and molecular self-assembly-to modulate the emergent properties of supramolecular assemblies for controlling cell behaviors. The exploration of EISA for developing cancer therapy and imaging has made considerable progress over the last five years. In this Topical Review, we discuss these exciting results and the future promise of EISA. After describing several key studies to illustrate the progress of EISA in developing cancer therapy, we discuss the use of EISA for molecular imaging. Then, we give the outlook of EISA for developing supramolecular anticancer medicine that inhibits multiple hallmark capabilities of cancer.

Advanced Bottom-Up Engineering of Living Architectures

Bottom-up tissue engineering is a promising approach for designing modular biomimetic structures that aim to recapitulate the intricate hierarchy and biofunctionality of native human tissues. In recent years, this field has seen exciting progress driven by an increasing knowledge of biological systems and their rational deconstruction into key core components. Relevant advances in the bottom-up assembly of unitary living blocks toward the creation of higher order bioarchitectures based on multicellular-rich structures or multicomponent cell-biomaterial synergies are described. An up-to-date critical overview of long-term existing and rapidly emerging technologies for integrative bottom-up tissue engineering is provided, including discussion of their practical challenges and required advances. It is envisioned that a combination of cell-biomaterial constructs with bioadaptable features and biospecific 3D designs will contribute to the development of more robust and functional humanized tissues for therapies and disease models, as well as tools for fundamental biological studies.

Hollow Alginate-Poly-L-Lysine-Alginate Microspheres Promoted an Epithelial-Mesenchymal Transition in Human Colon Adenocarcinoma Cells

Purpose: Today, there is an urgent need to develop a three-dimentional culture systems mimicking native in vivo condition in order to screen potency of drugs and possibly any genetic alterations in tumor cells. Due to the existence of limitations in animal models, the development of three dimensional systems is highly recommended. To this end, we encapsulated human colon adenocarcinoma cell line HT29 with alginate-poly-L-lysine (Alg-PLL) microspheres and the rate of epithelial-mesenchymal transition was monitored. Methods: Cells were randomly divided into three groups; control, alginate and Alg-PLL. To encapsulate cells, we mixed HT-29 cells (1 × 10⁶ ) with 1 mL of 0.05% PLL and 1% Alg mixture and electrosprayed into CaCl2 solution by using a high-voltage power. Cells from all groups were maintained at 37˚C in a humidified atmosphere containing 5% CO₂ for 7 days. Cell viability was assessed by MTT assay. To monitor the stemness feature, we measured the transcription of genes such as Snail, Zeb, and Vimentin by using real-time PCR analysis. Results: Addition of PLL to Alg in a hallowed state increased the cell survival rate compared to the control and Alg groups (P<0.05). Cells inside Alg-PLL tended to form microcellular aggregates while in Alg microspheres an even distribution of HT-29 cells was found. Real-time PCR analysis showed the up-regulation of Snail, Zeb, and Vimentin in Alg-PLL microspheres compared to the other groups, showing the acquisition of stemness feature (P<0.05). Conclusion: This study showed that hallow Alg-PLL microspheres increased the epithelialmesenchymal transition rate after 7 days in in vitro condition. Such approaches could be touted as appropriate in vitro models for drug screening.

Comparison of different zinc precursors for the construction of zeolitic imidazolate framework-8 artificial shells on living cells

The robust cell-in-shell structure is highly desirable for endowing living cells with an artificial exoskeleton to defend them from many environmental factors such as osmotic pressure, shear force, heat, UV radiation, and enzymes. Cell encapsulation has shown potential applications in many fields and attracted increasing interest. However, the influences of the precursors on the cell viability during the shell formation process are not clear and seldom investigated. Here, zinc nitrite, zinc acetate and zinc sulfate were applied individually to synthesize zeolitic imidazolate framework-8 (ZIF-8) shells on living cells. All the zinc salt precursors could convert to a ZIF-8 layer on the living cell surface. The zinc salts and organic ligand did not exhibit obvious toxicity to yeast cells when applied individually. However, dead cells were observed during the living cell encapsulation process using different zinc precursors. Compared with zinc nitrate and zinc acetate, ZIF-8 formed by zinc sulfate led to a higher percentage of cell death, especially under high concentrations of zinc sulfate. Cell division was suppressed by the ZIF-8 shell but restored fully upon shell removal by EDTA solution or pH 4.0 buffer. Escherichia coli (E. coli) cells showed a lower percentage of cell death, indicating excellent tolerance to the ZIF-8 encapsulation process. This work illustrates the cell toxicity during the formation of ZIF-8 cell shells by different zinc salts and engineering of the cell growth by MOF coating, which could provide a foundation for further quantitative analysis and potential applications in biomedicine and bioengineering.

Ascorbic acid-mediated reductive disassembly of Fe3+-tannic acid shells in degradable single-cell nanoencapsulation

The simple use of vitamin C leads to the reductive disassembly of the Fe³⁺-TA complex and in situ artificial shell degradation in single-cell nanoencapsulation.

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.

Interfacing the Cell with "Biomimetic Membrane Proteins"

Integral membrane proteins mediate a myriad of cellular processes and are the target of many therapeutic drugs. Enhancement and extension of the functional scope of membrane proteins can be realized by membrane incorporation of engineered nanoparticles designed for specific diagnostic and therapeutic applications. In contrast to hydrophobic insertion of small amphiphilic molecules, delivery and membrane incorporation of particles on the nanometric scale poses a crucial barrier for technological development. In this perspective, the transformative potential of biomimetic membrane proteins (BMPs), current state of the art, and the barriers that need to be overcome in order to advance the field are discussed.

Transmission and regulation of biochemical stimulus via a nanoshell directly adsorbed on the cell membrane to enhance chondrogenic differentiation of mesenchymal stem cell

A nanoscale artificial extracellular matrix (nanoshell) formed by layer-by-layer adsorption can enhance and modulate the function of stem cells by transferring biochemical stimulus to the cell directly. Here, the nanoshell composed of fibronectin (FN) and chondroitin sulfate (CS) is demonstrated to promote chondrogenic differentiation of mesenchymal stem cells (MSCs). The multilayer structure of nanoshell is formed by repeating self-assembly of FN and CS, and its thickness can be controlled through the number of layers. The expression of chondrogenic markers in MSCs coated with the FN/CS nanoshell was increased as the number of bilayers in the nanoshell increased until four, but when it exceeds five bilayers, the effect began to decrease. Finally, the MSCs coated with optimized four bilayers of FN/CS nanoshell have high chondrogenic differentiation efficiency and showed the potential to increase formation of cartilage tissue when it is transplanted into mouse kidney. So, the precise regulation of stem cell fate at single cell level can be possible through the cellular surface modification by self-assembled polymeric film.

An overview on enrichment methods for cell surface proteome profiling

Cell surface proteins are essential for many important biological processes, including cell-cell interactions, signal transduction, and molecular transportation. With the characteristics of low abundance, high hydrophobicity, and high heterogeneity, it is difficult to get a comprehensive view of cell surface proteome by direct analysis. Thus, it is important to selectively enrich the cell surface proteins before liquid chromatography with mass spectrometry analysis. In recent years, a variety of enrichment methods have been developed. Based on the separation mechanism, these methods could be mainly classified into three types. The first type is based on their difference in the physicochemical property, such as size, density, charge, and hydrophobicity. The second one is based on the bimolecular affinity interaction with lectin or antibody. And the third type is based on the chemical covalent coupling to free side groups of surface-exposed proteins or carbohydrate chains, such as primary amines, carboxyl groups, glycan side chains. In addition, metabolic labeling and enzymatic reaction-based methods have also been employed to selectively isolate cell surface proteins. In this review, we will provide a comprehensive overview of the enrichment methods for cell surface proteome profiling.

Cell armor for protection against environmental stress: Advances, challenges and applications in micro- and nanoencapsulation of mammalian cells

Unlike unicellular organisms and plant cells surrounded with a cell wall, naked plasma membranes of mammalian cells make them more susceptible to environmental stresses encountered during in vitro biofabrication and in vivo cell therapy applications. Recent advances in micro- and nanoencapsulation of single mammalian cells provide an effective strategy to isolate cells from their surroundings and protect them against harsh environmental conditions. Microemulsification and droplet-based microfluidics have enabled researchers to encapsulate single cells within a variety of microscale hydrogel materials with a range of biochemical and mechanical properties and functionalities including enhanced cell-matrix interactions or on-demand degradation. In addition to microcapsules, nanocoatings of various organic and inorganic substances on mammalian cells have allowed for the formation of protective shells. A wide range of synthetic and natural polymers, minerals and supramolecular metal-organic complexes have been deposited as nanolayers on the cells via electrostatic interactions, receptor-ligand binding, non-specific interactions, and in situ polymerization/crosslinking. Here, current strategies in encapsulation of single mammalian cells along with challenges and advances are reviewed. Protection of encapsulated stem cells, fibroblasts, red and white blood cells and cancer cells against harsh in vitro and in vivo conditions including anoikis, UV radiation, physical forces, proteolytic enzymes and immune clearance are discussed. STATEMENT OF SIGNIFICANCE: The mechanical fragility of the plasma membrane and susceptibility to extracellular biochemical factors due to the lack of a physical barrier like a tough cell wall or exoskeleton make mammalian cells extra sensitive to harsh environmental conditions. This sensitively, in turn, limits the ex vivo storage, handling and manipulation of mammalian cells, as well as their in vivo applications. Environmental stresses such as exposure to UV, reactive chemicals and mechanical stress during biofabrication processes like 3D bioprinting can often compromise cell viability and function. Micro- and nanoencapsulation of single mammalian cells in protective shells have emerged as promising approaches to isolate cells from their surroundings and enhance resistance against perturbations in conditions during regenerative medicine and tissue engineering applications. In this review, the current state of art of single cell encapsulation strategies and the challenges associated with these technologies are discussed in detail. This is followed by the review of the protection provided by cell armor against a range of harsh in vitro and in vivo conditions.

Antifouling Surface Coating Using Droplet-Based SI-ARGET ATRP of Carboxybetaine under Open-Air Conditions

The formation of a dense zwitterionic brush through surface-initiated atom transfer radical polymerization (SI-ATRP) is a typical graft-from approach used to achieve antifouling surfaces with high fidelity; however, their air-tightness may cause inconvenience to users. In this context, activator regenerated by electron transfer (ARGET) ATRP is emerging as an alternative surface-coating tool because limited amount of air is allowed to form a dense polymer brush. However, the degree of air tolerance that can ensure a thick polymer brush has not been clearly defined, limiting its practical usage under ambient-air conditions. In this study, we investigated the SI-ARGET ATRP of carboxybetaine (CB) by changing the air conditions, along with the air-related parameters, such as the concentration of the reducing agent, the volume of the polymerization solution (PS), or the solvent composition, and correlated their effects with the poly(CB) thickness. Based on the optimized reaction conditions, a poly(CB) brush with reliable thickness was feasibly formed even under open-air conditions without a degassing step. In addition, a microliter droplet (∼100 μL) of PS was sufficient to proceed with the SI-ARGET ATRP for the covering of a poly(CB) brush on the surface area of interest. By applying an optimized SI-ARGET ATRP of CB, antifouling was feasibly achieved in the surface region of interest using an array to form a large surface area under fully exposed air conditions. In other words, optimized SI-ARGET ATRP enabled the formation of a thick poly(CB) brush on the surfaces of various dimensions under open-air conditions.

A Chain-Elongated Oligophenylenevinylene Electrolyte Increases Microbial Membrane Stability

A novel conjugated oligoelectrolyte (COE) material, named S6, is designed to have a lipid-bilayer stabilizing topology afforded by an extended oligophenylenevinylene backbone. S6 intercalates biological membranes acting as a hydrophobic support for glycerophospholipid acyl chains. Indeed, Escherichia coli treated with S6 exhibits a twofold improvement in butanol tolerance, a relevant feature to achieve within the general context of modifying microorganisms used in biofuel production. Filamentous growth, a morphological stress response to butanol toxicity in E. coli, is observed in untreated cells after incubation with 0.9% butanol (v/v), but is mitigated by S6 treatment. Real-time fluorescence imaging using giant unilamellar vesicles reveals the extent to which S6 counters membrane instability. Moreover, S6 also reduces butanol-induced lipopolysaccharide release from the outer membrane to further maintain cell integrity. These findings highlight a deliberate effort in the molecular design of a chain-elongated COE to stabilize microbial membranes against environmental challenges.

Enzyme-Modulated Anaerobic Encapsulation of Chlorella Cells Allows Switching from O2 to H2 Production

Single-cell encapsulation has become an effective strategy in cell surface engineering; however, the construction of cell wall-like layers that allow the switching of the inherent functionality of the engineered cell is still rare. In this study, we show a universal way to create an enzyme-modulated oxygen-consuming sandwich-like layer by using polydopamine, laccase, and tannic acid as building blocks, which then could generate an anaerobic microenvironment around the cell. This layer protected the encapsulated C. pyrenoidosa cell against external stresses and enabled it to switch from normal photosynthetic O₂ production to photobiological H₂ production. The layer showed an smaller effect on the PSII activity, which contributed a significant enhancement on the rate (0.32 μmol H₂  h^-1  (mg chlorophyll)^-1 ) and the duration (7 d) of H₂ production. This strategy is expected to provide a pathway for modulating the functionality of cells and for breakthroughs in the development of green energy alternatives.

Encapsulation of individual living cells with enzyme responsive polymer nanoshell

Cell delivery in cell therapy is typically challenged by the low cell survival rate and immunological rejection during cells injection and circulation. Encapsulation of cells with semipermeable hydrogels or membranes can improve cell viability by resisting high shear force and inhibit immune response with the physical isolation effect. Herein, the individual HeLa cells and human mesenchymal stem cells (hMSCs) were encapsulated with enzyme responsive polymer nanoshell. The encapsulation shell was prepared via the Layer-by-Layer (LbL) assembly of functionalized gelatin and click chemistry of peptide linker and gelatin. The encapsulated cells showed high cell viability and could resist the physical stress. Moreover, the encapsulation shell had a prolonged encapsulation sustaining period and could effectively prevent the invasion of external entities. In addition, on-site cell release was realized via enzymolysis of the encapsulation shell by human matrix metalloproteinase-7 (MMP-7), an overexpressed enzyme on tumor area. The finding of this study proved a potential approach in cell therapy, especially for cell-based cancer therapy.

Iron gall ink revisited: hierarchical formation of Fe(iii)–tannic acid coacervate particles in microdroplets for protein condensation

We report a hierarchical self-assembly approach to form Fe(iii)–tannic acid particles in microdroplets and its application to protein condensation.

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.

Nanoarchitectonics meets cell surface engineering: shape recognition of human cells by halloysite-doped silica cell imprints

Cell surface engineering, as a practical manifestation of nanoarchitectonics, is a powerful tool to modify and enhance properties of live cells. In turn, cells may serve as sacrificial templates to fabricate cell-mimicking materials. Herein we report a facile method to produce cell-recognising silica imprints capable of the selective detection of human cells. We used HeLa cells to template silica inorganic shells doped with halloysite clay nanotubes. The shells were destroyed by sonication resulting in the formation of polydisperse hybrid imprints that were used to recognise HeLa cells in liquid media supplemented with yeast. We believe that methodology reported here will find applications in biomedical and clinical research.

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

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

Salt-Induced, Continuous Deposition of Supramolecular Iron(III)-Tannic Acid Complex

One-step assembly of iron(III)-tannic acid (Fe³⁺-TA) complex forms nanothin (∼10 nm) films on various substrates within minutes. In this deposition scheme, however, the film does not grow continuously over time even though Fe³⁺-TA complex is still abundant in the coating solution. In this paper, we report that the salt addition dramatically changes the one-off coating characteristic to continuous one, and each salt has its optimum concentration ( C_MFT) that produces maximum film thickness. For detailed investigation of the salt effects, we employed various salts, including LiCl, NaCl, KCl, CaCl₂, SrCl₂, BaCl₂, NaBr, and NaNO₃, and found that only cations played an important role in the continuous deposition of the Fe³⁺-TA complex, with smaller C_MFT values for the cations of higher valency and larger size. On the basis of the results, we suggested that the positively charged cations screened the negative surface charges of Fe³⁺-TA complex particles, leading to coagulation and continuous deposition, further supported by the ζ-potential measurement and time-resolved dynamic light-scattering analysis.

Cell-Surface Engineering for Advanced Cell Therapy

Stem cells opened great opportunity to overcome diseases that conventional therapy had only limited success. Use of scaffolds made from biomaterials not only helps handling of stem cells for delivery or transplantation but also supports enhanced cell survival. Likewise, cell encapsulation can provide stability for living animal cells even in a state of separateness. Although various chemical reactions were tried to encapsulate stolid microbial cells such as yeasts, a culture environment for the growth of animal cells allows only highly biocompatible reactions. Therefore, the animal cells were mostly encapsulated in hydrogels, which resulted in enhanced cell survival. Interestingly, major findings of chemistry on biological interfaces demonstrate that cell encapsulation in hydrogels have a further a competence for modulating cell characteristics that can go beyond just enhancing the cell survival. In this review, we present a comprehensive overview on the chemical reactions applied to hydrogel-based cell encapsulation and their effects on the characteristics and behavior of living animal cells.

Enzymatic film formation of nature-derived phenolic amines

An enzyme-instructed method is developed for material-independent, cytocompatible coating of phenolic amines, inspired by melanogenesis found in nature. Tyrosinase-based film formation proceeds smoothly in an aqueous solution at neutral pH, and can use various phenolic amines including catecholamines, such as tyrosine, tyramine, dopamine, norepinephrine, and DOPA, as a coating precursor. Compared with polydopamine coating, the method is fast and efficient, and forms uniform films. Its high cytocompatibility is advantageously applied to cell-surface engineering, where chemically labile Jurkat cells are coated individually without any noticeable decrease in viability. Considering the huge potential of polyphenolic-based coatings, the strategy developed herein will provide an advanced tool for manipulating biological entities, including living cells, in biomedical and medicinal applications.