Protection of mammalian cell used in biosensors by coating with a polyelectrolyte shell

Conformal encapsulation of mammalian stem cells using modified hyaluronic acid

Micro- and nanoencapsulation of cells has been studied as a strategy to protect cells from environmental stress and promote survival during delivery. Hydrogels used in encapsulation can be modified to influence cell behaviors and direct assembly in their surroundings. Here, we report a system that conformally encapsulated stem cells using hyaluronic acid (HA). We successfully modified HA with lipid, thiol, and maleimide pendant groups to facilitate a hydrogel system in which HA was deposited onto cell plasma membranes and subsequently crosslinked through thiol-maleimide click chemistry. We demonstrated conformal encapsulation of both neural stem cells (NSCs) and mesenchymal stromal cells (MSCs), with viability of both cell types greater than 90% after encapsulation. Additional material could be added to the conformal hydrogel through alternating addition of thiol-modified and maleimide-modified HA in a layering process. After encapsulation, we tracked egress and viability of the cells over days and observed differential responses of cell types to conformal hydrogels both according to cell type and the amount of material deposited on the cell surfaces. Through the design of the conformal hydrogels, we showed that multicellular assembly could be created in suspension and that encapsulated cells could be immobilized on surfaces. In conjunction with photolithography, conformal hydrogels enabled rapid assembly of encapsulated cells on hydrogel substrates with resolution at the scale of 100 μm.

Cell-drug conjugates

By combining living cells with therapeutics, cell-drug conjugates can potentiate the functions of both components, particularly for applications in drug delivery and therapy. The conjugates can be designed to persist in the bloodstream, undergo chemotaxis, evade surveillance by the immune system, proliferate, or maintain or transform their cellular phenotypes. In this Review, we discuss strategies for the design of cell-drug conjugates with specific functions, the techniques for their preparation, and their applications in the treatment of cancers, autoimmune diseases and other pathologies. We also discuss the translational challenges and opportunities of this class of drug-delivery systems and therapeutics.

Investigation on Adaptability and Applicability of Polymer-Mediated Cell Surface Engineering by Ligation with Transglutaminase

Polymer-mediated cell surface engineering can be a powerful tool to modify the cell's biological behavior, but a simple ligation strategy must be identified. This manuscript assessed the use of transglutamination as a versatile and adaptable approach for cell surface engineering in various cellular models relevant to biomedical applications. This enzymatic approach was evaluated for its feasibility and potential for conjugating polymers to diverse cell surfaces and its biological effects. Transglutaminase-mediated ligation was successfully performed at temperatures ranging from 4 to 37 °C in as quickly as 30 min, while maintaining biocompatibility and preserving cell viability. This approach was successfully applied to nine different cell surfaces (including adherent cells and suspension cells) by optimizing the enzyme source (guinea pig liver vs microbial), buffer compositions, and incubation conditions. Finally, polymer-mediated cell surface engineering using transglutaminase exhibited immunocamouflage abilities for endothelial cells, T cells, and red blood cells by preventing the recognition of cell surface proteins by antibodies. Employing transglutaminase in polymer-mediated cell surface engineering is a promising approach to maximize its application in cell therapy and other biomedical applications.

Yolk-Shell Encapsulation of Cells by Biomimetic Mineralization and Visible Light-Induced Surface Graft Polymerization

The pursuit of low-cytotoxicity modification strategies represents a prominent avenue in cell coating research, holding immense significance for the advancement of practical living cell-related technologies. Here, we presented a novel method to fabricate encapsulated yeast cells with a yolk-shell structure by biomimetic mineralization and visible-light-induced surface graft polymerization. In this approach, an amorphous calcium carbonate (ACC) shell was first deposited on the surface of a yeast cell (cell@ACC) modified with 4 layers of self-assembled poly(diallyl dimethylammonium chloride) (PDADMAC)/poly(acrylic acid) (PAA) film using a biomimetic mineralization technique. Subsequently, polyethylenimine (PEI) was absorbed on the surface of cell@ACC by electrostatic interaction. Then, a cross-linked shell was introduced by surface-initiated graft polymerization of poly(ethylene glycol) diacrylate (PEGDA) on cell@ACC under irradiation of visible light using thioxanthone catechol-O,O'-diacetic acid as the photosensitizer. After the removal of the inner ACC shell, the yolk-shell-structured yeast cells (cell@PHS) were obtained. Due to the mild conditions of the strategy, the cell@PHS could retain 98.81% of its original viability. The introduction of the shell layer significantly prolonged the lag phase of yeast cells, which could be tuned between 5 and 25 h by regulating the thickness of the shell. Moreover, the cell@PHS showed improved resistance against lyticase due to the presence of a protective shell. After 30 days of storage, the viability of cell@PHS was 81.09%, which is significantly higher than the 19.89% viability of native yeast cells.

Mechanobiology of Ferroptotic Cancer Cells as a Novel "Eat-Me" Signal: Regulating Efferocytosis through Layer-by-Layer Coating

The importance of the clearance of dead cells is shown to have a regulatory role for normal tissue homeostasis and for the modulation of immune responses. However, how mechanobiological properties of dead cells affect efferocytosis remains largely unknown. Here, it is reported that the Young's modulus of cancer cells undergoing ferroptosis is reduced. To modulate their Young's modulus a layer-by-layer (LbL) nanocoating is developed. Scanning electron and fluorescence microscopy confirm coating efficiency of ferroptotic cells while atomic force microscopy reveals encapsulation of the dead cells increases their Young's modulus dependent on the number of applied LbL layers which increases their efferocytosis by primary macrophages. This work demonstrates the crucial role of mechanobiology of dead cells in regulating their efferocytosis by macrophages which can be exploited for the development of novel therapeutic strategies for diseases where modulation of efferocytosis can be potentially beneficial and for the design of drug delivery systems for cancer therapy.

Recent Advances in the Nanoshells Approach for Encapsulation of Single Probiotics

The intestine, often referred to as the "second brain" of the human body, houses a vast microbial community that plays a crucial role in maintaining the host's balance and directly impacting overall health. Probiotics, a type of beneficial microorganism, offer various health benefits when consumed. However, probiotics face challenges such as acidic conditions in the stomach, bile acids, enzymes, and other adverse factors before they can colonize the intestinal tissues. At present, pills, dry powder, encapsulation, chemically modified bacteria, and genetically engineered bacteria have emerged as the preferred method for the stable and targeted delivery of probiotics. In particular, the use of nanoshells on the surface of single probiotics has shown promise in regulating their growth and differentiation. These nanoshells can detach from the probiotics' surface upon reaching the intestine, facilitating direct contact between the probiotics and intestinal mucosa. In this perspective, we provide an overview of the current developments in the formation of nanoshells mediated by single probiotics. We also discuss the advantages and disadvantages of different nanocoating strategies and explore future trends in probiotic protection.

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

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

Biomineralization: An Opportunity and Challenge of Nanoparticle Drug Delivery Systems for Cancer Therapy

Biomineralization is a common process in organisms to produce hard biomaterials by combining inorganic ions with biomacromolecules. Multifunctional nanoplatforms are developed based on the mechanism of biomineralization in many biomedical applications. In the past few years, biomineralization-based nanoparticle drug delivery systems for the cancer treatment have gained a lot of research attention due to the advantages including simple preparation, good biocompatibility, degradability, easy modification, versatility, and targeting. In this review, the research trends of biomineralization-based nanoparticle drug delivery systems and their applications in cancer therapy are summarized. This work aims to promote future researches on cancer therapy based on biomineralization. Rational design of nanoparticle drug delivery systems can overcome the bottleneck in the clinical transformation of nanomaterials. At the same time, biomineralization has also provided new research ideas for cancer treatment, i.e., targeted therapy, which has significantly better performance.

Potential of Cell Surface Engineering with Biocompatible Polymers for Biomedical Applications

The regulation of the cellular surface with biomaterials can contribute to the progress of biomedical applications. In particular, the cell surface is exposed to immunological surveillance and reactions in transplantation therapy, and modulation of cell surface properties might improve transplantation outcomes. The transplantation of therapeutic cells, tissue, and organs is an effective and fundamental treatment and has contributed to saving lives and improving quality of life. Because of shortages, donor cells, tissues, and organs are carefully transplanted with the goal of retaining activity and viability. However, some issues remain to be resolved in terms of reducing side effects, improving graft survival, managing innate and adaptive immune responses, and improving transplant storage and procedures. Given that the transplantation process involves multiple steps and is technically complicated, an engineering approach together with medical approaches to resolving these issues could enhance success. In particular, cell surface engineering with biocompatible polymers looks promising for improving transplantation therapy and has potential for other biomedical applications. Here we review the significance of polymer-based surface modification of cells and organs for biomedical applications, focusing on the following three topics: Cell protection: cellular protection through local immune regulation using cell surface modification with biocompatible polymers. This protection could extend to preventing attack by the host immune system, freeing recipients from taking immunosuppressive drugs, and avoiding a second transplantation. Cell attachment: cell manipulation, which is an important technique for delivery of therapeutic cells and their alignment for recellularization of decellularized tissues and organs in regenerative therapy. Cell fusion: fusion of different cells, which can lead to the formation of new functional cells that could be useful for generating, e.g., immunologically competent or metabolically active cells.

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

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

100th Anniversary of Macromolecular Science Viewpoint: Re-Engineering Cellular Interfaces with Synthetic Macromolecules Using Metabolic Glycan Labeling

Cell-surface functionality is largely programmed by genetically encoded information through modulation of protein expression levels, including glycosylation enzymes. Genetic tools enable control over protein-based functionality, but are not easily adapted to recruit non-native functionality such as synthetic polymers and nanomaterials to tune biological responses and attach therapeutic or imaging payloads. Similar to how polymer-protein conjugation evolved from nonspecific PEGylation to site-selective bioconjugates, the same evolution is now occurring for polymer-cell conjugation. This Viewpoint discusses the potential of using metabolic glycan labeling to install bio-orthogonal reactive cell-surface anchors for the recruitment of synthetic polymers and nanomaterials to cell surfaces, exploring the expanding therapeutic and diagnostic potential. Comparisons to conventional approaches that target endogenous membrane components, such as hydrophobic, protein coupling and electrostatic conjugation, as well as enzymatic and genetic tools, have been made to highlight the huge potential of this approach in the emerging cellular engineering field.

Silk Fibroin: An Emerging Biocompatible Material for Application of Enzymes and Whole Cells in Bioelectronics and Bioanalytical Sciences

Enzymes and whole cells serve as the active biological entities in a myriad of applications including bioprocesses, bioanalytics, and bioelectronics. Conserving the natural activity of these functional biological entities during their prolonged use is one of the major goals for validating their practical applications. Silk fibroin (SF) has emerged as a biocompatible material to interface with enzymes as well as whole cells. These biomaterials can be tailored both physically and chemically to create excellent scaffolds of different forms such as fibers, films, and powder for immobilization and stabilization of enzymes. The secondary structures of the SF-protein can be attuned to generate hydrophobic/hydrophilic pockets suitable to create the biocompatible microenvironments. The fibrous nature of the SF protein with a dominant hydrophobic property may also serve as an excellent support for promoting cellular adhesion and growth. This review compiles and discusses the recent literature on the application of SF as a biocompatible material at the interface of enzymes and cells in various fields, including the emerging area of bioelectronics and bioanalytical sciences.

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.

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.

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.

Cell surface engineering and application in cell delivery to heart diseases

Cell-based therapy has expanded its influence in cancer immunotherapy, regenerative medicine, and tissue engineering. Due to their secretory functions, differentiation capabilities, specific homing effects through chemotaxis, distinctive therapeutic potentials, and ex vivo expandability, cells have become an attractive reagent for advanced therapeutic strategies. Therefore, the ability to modify cells and manipulate their functions according to intended therapeutic designs has been the central scientific interest in the field of biomedical research. Many innovative methods have been developed with genetic modification of cells being the most advanced cell surface engineering technique. Although genetic modification is a powerful tool, it has a limited applicability due to the permanent modifications made on cells. Alternatively, many endeavors have been made to develop surface engineering techniques that can circumvent the limitations of genetic modification. In this review, current methods of non-genetic cell surface modification, including chemical conjugations, polymeric encapsulation, hydrophobic insertion, enzymatic and metabolic addition, will be introduced. Moreover, cell surface engineering plausible for cardiac remodeling and the future prospective will be discussed at the end.

Subcellular Fate of a Fluorescent Cholesterol-Poly(ethylene glycol) Conjugate: An Excellent Plasma Membrane Imaging Reagent

Cholesterol-containing molecules or nanoparticles play a significant role in achieving favorable plasma membrane imaging and efficient cellular uptake of drugs by the excellent membrane anchoring capability of the cholesterol moiety. By linking cholesterol to a water-soluble component (such as poly(ethylene glycol), PEG), the resulting cholesterol-PEG conjugate can form micelles in aqueous solution through self-assembly, and such a micellar structure represents an important drug delivery vehicle in which hydrophobic drugs can be encapsulated. However, the understanding of the subcellular fate and cytotoxicity of cholesterol-PEG conjugates themselves remains elusive. Herein, by using cholesterol-PEG2000-fluorescein isothiocyanate (Chol-PEG-FITC) as a model system, we found that the Chol-PEG-FITC molecules could attach to the plasma membranes of mammalian cells within 10 min and such a firm membrane attachment could last at least 1 h, displaying excellent plasma membrane staining performance that surpassed that of commonly used commercial membrane dyes such as DiD and CellMask. Besides, we systematically studied the endocytosis pathway and intracellular distribution of Chol-PEG-FITC and found that the cell surface adsorption and endocytosis processes of Chol-PEG-FITC molecules were lipid-raft-dependent. After internalization, the Chol-PEG-FITC molecules gradually reached many organelles with membrane structures. At 5 h, they were mainly distributed in lysosomes and the Golgi apparatus, with some in the endoplasmic reticulum (ER) and very few in the mitochondrion. At 12 h, the Chol-PEG-FITC molecules mostly aggregated in the Golgi apparatus and ER close to the nucleus. Finally, we demonstrated that Chol-PEG-FITC was toxic to mammalian cells only at concentrations above 50 μM. In summary, Chol-PEG-FITC can be a promising plasma membrane imaging reagent to avoid the fast cellular internalization and quick membrane detachment problems faced by commercial membrane dyes. We believe that the investigation of the dynamic subcellular fate of Chol-PEG-FITC can provide important knowledge to facilitate the use of cholesterol-PEG conjugates in fields such as cell surface engineering and drug delivery.

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.

Cell surface engineering to control cellular interactions

Cell surface composition determines all interactions of the cell with is environment, thus cell functions such as adhesion, migration and cell-cell interactions are likely to be controlled by engineering and manipulating cell membrane. Cell membranes present a rich repertoire of molecules, therefore a versatile ground for modification. However the complex and dynamic nature of the cell surface is also a major challenge for cell surface engineering that should also involve strategies compatible with cell viability. Cell surface engineering by selective chemical reactions or by the introduction of exogenous targeting ligands can be powerful tools for engineering novel interactions and control cell function. In addition to chemical conjugation and modification of functional groups, ligands of interest to modify the surface of cells include recombinant proteins, liposomes or nanoparticles. Here, we review recent efforts to perform changes to cell surface composition. We focus on the engineering of the cell surface with biological, chemical or physical methods to modulate cell functions and control cell-cell and cell-microenvironment interactions. Potential applications of cell surface engineering are also stated.

Interaction of poly(ethylene glycol)-conjugated phospholipids with supported lipid membranes and their influence on protein adsorption

We studied real-time interaction between poly(ethylene glycol)-conjugated phospholipids (PEG-lipids) and a supported lipid membrane by surface plasmon resonance (SPR) spectroscopy to understand dynamic behaviors of PEG-lipids on living cell membranes. Supported lipid membranes formed on a hydrophobic surface were employed as a model of living cell membrane. We prepared three kinds of PEG-lipids that carried alkyl chains of different lengths for SPR measurements and also performed fluorescence recovery after photobleaching (FRAP) to study the influence of acyl chain length on dynamics on the supported membrane. PEG-lipids were uniformly anchored to lipid membranes with high fluidity without clustering. Incorporation and dissociation rates of PEG-lipids into supported membranes strongly depended on the length of acyl chains; longer acyl chains reduced the incorporation rate and the dissociation rate of PEG-lipid. Furthermore, protein adsorption experiment with bovine serum albumin indicated that PEG modification prevented the adsorption of bovine serum albumin on such supported membrane.

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.

Mapping single macromolecule chains using the colloid deposition method: PDADMAC on mica

Monolayers of the cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC) on mica were thoroughly characterized using the streaming potential and the colloid deposition methods. Initially, the stability of the monolayers was determined by performing desorption experiments carried out under diffusion-controlled regime. It was shown that the desorption of the polyelectrolyte at the ionic strength range 0.01-0.15 M is negligible over the time of 20 h. The structure of PDADMAC monolayers and orientation of molecules were evaluated using the colloid deposition measurements involving negatively charged polystyrene latex microspheres, 820 nm in diameter. The functional relationships between the polyelectrolyte coverage and latex coverage deposited within 20 h were acquired by direct optical microscope. In this way the influence of ionic strength varied in the range 0.15-0.01 M on the molecule orientation in monolayers was determined. It was shown that for ionic strength of 0.15 M nearly one to one mapping of polyelectrolyte chains by colloid particles can be achieved for PDADMAC coverage below 0.1%. In this way, because of a considerable surface area ratio between the macromolecule and the colloid particle, an enhancement factor of 10(3) can be attained. This behavior was quantitatively interpreted in terms of the random site adsorption model whereas the classical mean-field theory proved inadequate. On the other hand, for lower ionic strength, it was confirmed that an irreversible immobilization of latex particles can only occur at a few closely spaced PDADMAC chains. It was shown that these experimental results were consistent with the side-on adsorption mechanisms of PDADMAC at mica for the above ionic strength.

Imaging plasma membranes without cellular internalization: multisite membrane anchoring reagents based on glycol chitosan derivatives

Using a multisite membrane anchoring strategy, a new plasma membrane imaging reagent without cellular internalization was designed.

Cell Surface Engineering for Regulation of Immune Reactions in Cell Therapy

Transplantation of the pancreatic islets of Langerhans (islets) is a promising cell therapy for treating insulin-dependent type 1 diabetes mellitus. Islet transplantation is a minimally-invasive technique involving relatively simple surgery. However, after intraportal transplantation, the transplanted islets are attacked by the recipient's immune system, because they activate a number of systems, including coagulation, complement response, inflammation, immune rejection, and recurrence of autoimmune disease. We have developed a surface modification and microencapsulation technique that protects cells and islets with biomaterials and bioactive substances, which may be useful in clinical settings. This approach employs amphiphilic polymers, which can interact with lipid bilayer membranes, without increasing cell volume. Molecules attached to these polymers can protect transplanted cells and islets from attack by the host immune system. We expect that this surface modification technique will improve graft survival in clinical islet transplantation.

Nano-labelled cells-a functional tool in biomedical applications

Nanotechnology offers an unprecedented number of opportunities for biomedical research, utilizing the unusual functionalities of nanosized materials. Here we describe the recent advances in fabrication and utilization of nanoparticle-labelled cells. We present a brief overview of the most promising techniques, namely layer-by-layer polyelectrolyte assembly on cells and intracellular and extracellular labelling with magnetic nanoparticles. Several important practical application of nanofucntionalized cells, including tissue engineering and tumour therapy, are reviewed.

Amphiphilic macromolecules on cell membranes: from protective layers to controlled permeabilization

Antimicrobial and cell-penetrating peptides have inspired developments of abiotic membrane-active polymers that can coat, penetrate, or break lipid bilayers in model systems. Application to cell cultures is more recent, but remarkable bioactivities are already reported. Synthetic polymer chains were tailored to achieve (i) high biocide efficiencies, and selectivity for bacteria (Gram-positive/Gram-negative or bacterial/mammalian membranes), (ii) stable and mild encapsulation of viable isolated cells to escape immune systems, (iii) pH-, temperature-, or light-triggered interaction with cells. This review illustrates these recent achievements highlighting the use of abiotic polymers, and compares the major structural determinants that control efficiency of polymers and peptides. Charge density, sp. of cationic and guanidinium side groups, and hydrophobicity (including polarity of stimuli-responsive moieties) guide the design of new copolymers for the handling of cell membranes. While polycationic chains are generally used as biocidal or hemolytic agents, anionic amphiphilic polymers, including Amphipols, are particularly prone to mild permeabilization and/or intracell delivery.

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.

pH-responsive hydrogel cubes for release of doxorubicin in cancer cells

Doxorubicin (DOX)-loaded poly(methacrylic acid) hydrogel cubes release the drug at pH <5. These hydrogels are developed for shape-directed cellular uptake for drug delivery.

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.

An automated process for layer-by-layer assembly of polyelectrolyte multilayer thin films on viable cell aggregates

An automated process for modifying the surface of pancreatic islets grows uniform polyelectrolyte multilayer thin films, eliminating user variability associated with previous manual methods. Machine vision feedback allows for tight control of small fluid volumes, maintaining an islet microenvironment. This process is adaptable to other fragile micrometer-scale particle systems.

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.

"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.

Multicore-shell PNIPAm-co-PEGMa microcapsules for cell encapsulation

The overall goal of this study was to fabricate multifunctional core-shell microcapsules with biological cells encapsulated within the polymer shell. Biocompatible temperature responsive microcapsules comprised of silicone oil droplets (multicores) and yeast cells embedded in a polymer matrix (shell) were prepared using a novel microarray approach. The cross-linked polymer shell and silicone multicores were formed in situ via photopolymerization of either poly(N-isopropylacryamide)(PNIPAm) or PNIPAm, copolymerized with poly(ethylene glycol monomethyl ether monomethacrylate) (PEGMa) within the droplets of an oil-in-water-in-oil double emulsion. An optimized recipe yielded a multicore-shell morphology, which was characterized by optical and laser scanning confocal microscopy (LSCM) and theoretically confirmed by spreading coefficient calculations. Spreading coefficients were calculated from interfacial tension and contact angle measurements as well as from the determination of the Hamaker constants and the pair potential energies. The effects of the presence of PEGMa, its molecular weight (M(n) 300 and 1100 g/mol), and concentration (10, 20, and 30 wt %) were also investigated, and they were found not to significantly alter the morphology of the microcapsules. They were found, however, to significantly improve the viability of the yeast cells, which were encapsulated within PNIPAm-based microcapsules by direct incorporation into the monomer solutions, prior to polymerization. Under LSCM, the fluorescence staining for live and dead cells showed a 30% viability of yeast cells entrapped within the PNIPAm matrix after 45 min of photopolymerization, but an improvement to 60% viability in the presence of PEGMa. The thermoresponsive behavior of the microcapsules allows the silicone oil cores to be irreversibly ejected, and so the role of the silicone oil is 2-fold. It facilitates multifunctionality in the microcapsule by first being used as a template to obtain the desired core-shell morphology, and second it can act as an encapsulant for oil-soluble drugs. It was shown that the encapsulated oil droplets were expelled above the volume phase transition temperature of the polymer, while the collapsed microcapsule remained intact. When these microcapsules were reswollen with an aqueous solution, it was observed that the hollow compartments refilled. In principle, these hollow-core microcapsules could then be filled with water-soluble drugs that could be delivered in vivo in response to temperature.

Polyelectrolyte multilayers in tissue engineering

The layer-by-layer assembly of sequentially adsorbed, alternating polyelectrolytes has become increasingly important over the past two decades. The ease and versatility in assembling polyelectrolyte multilayers (PEMs) has resulted in numerous wide ranging applications of these materials. More recently, PEMs are being used in biological applications ranging from biomaterials, tissue engineering, regenerative medicine, and drug delivery. The ability to manipulate the chemical, physical, surface, and topographical properties of these multilayer architectures by simply changing the pH, ionic strength, thickness, and postassembly modifications render them highly suitable to probe the effects of external stimuli on cellular responsiveness. In the field of regenerative medicine, the ability to sequester growth factors and to tether peptides to PEMs has been exploited to direct the lineage of progenitor cells and to subsequently maintain a desired phenotype. Additional novel applications include the use of PEMs in the assembly of three-dimensional layered architectures and as coatings for individual cells to deliver tunable payloads of drugs or bioactive molecules. This review focuses on literature related to the modulation of chemical and physical properties of PEMs for tissue engineering applications and recent research efforts in maintaining and directing cellular phenotype in stem cell differentiation.

POLYELECTROLYTE MULTILAYER STAMPING IN AQUEOUS PHASE AND NON-CONTACT MODE

Polyelectrolyte multilayer (PEM) transfer printing has been previously achieved by stamping under dry conditions. Here, we show for the first time, that PEM can be transferred from a stamp to the base substrate under aqueous conditions whereby the two surfaces are in a non-contact mode. Degradable multilayers of (PAA/PEG)(10.5) followed by non-degradable multilayers of (PDAC/SPS)(80.5) were fabricated under acidic pH conditions on either PDMS or glass (stamp), and subsequently transferred over top of another multilayer prepared on a different substrate (base substrate), with a spacing of ~ 200 μm between the stamping surface and the base substrate. This multilayer transfer was performed under physiological pH conditions. This process is referred to herein as non-contact, aqueous-phase multilayer (NAM) transfer. NAM transfer can be useful for applications such as fabricating three-dimensional (3-D) cellular scaffolds. We attempted to create a 3-D cellular scaffold using NAM transfer, and characterized the scaffolds with conventional and fluorescence microscopy.

Live celloidosome structures based on the assembly of individual cells by colloid interactions

A new class of colloid structures, celloidosomes, has been developed which represent hollow microcapsules whose membranes consist of a single monolayer of living cells. Two routes for producing these structures were designed based on templating of: (i) air bubbles and (ii) anisotropic microcrystals of calcium carbonate with living cells, which allowed us to fabricate celloidosomes of spherical, rhombohedral and needle-like morphologies. Air microbubbles were templated by yeast cells coated with poly(allylamine hydrochloride) (PAH), then coated with carboxymethylcellulose and rehydrated resulting in the formation of spherical multicellular structures. Similarly, calcium carbonate microcrystals of anisotropic shapes were coated with several consecutive layers of oppositely charged polyelectrolytes to obtain a positive surface charge which was used to immobilise yeast cells coated with anionic polyelectrolyte of their surfaces. After dissolving of sacrificial cores, hollow multicellular structures were obtained. The viability of the cells in the produced structures was confirmed by using fluorescein diacetate. In order to optimize the separation of celloidosomes from free cells magnetic nanoparticles were immobilised onto the surface of templates prior to the cells deposition, which greatly facilitated the separation using a permanent magnet. Two alternative approaches were developed to form celloidosome structures using magnetically functionalised core-shell microparticles which resulted in the formation of celloidosomes with needle-like and cubic-like geometries which follows the original morphology of the calcium carbonate microcrystals. Our methods for fabrication of celloidosomes may found applications in the development of novel symbiotic bio-structures, artificial multicellular organisms and in tissue engineering. The unusual structure of celloidosomes resembles the primitive forms of multicellular species, like Volvox, and other algae and could be regarded as one possible mechanism of the evolutionary development of multicellularity.