Cell-selective encapsulation in hydrogel sheaths via biospecific identification and biochemical cross-linking

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

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

Nematode surface functionalization with hydrogel sheaths tailored in situ

Engineering the surfaces of biological organisms allows the introduction of novel functions and enhances their native functions. However, studies on surface engineering remained limited to unicellular organisms. Herein, nematode surfaces are engineered through in situ hydrogelation mediated by horseradish peroxidase (HRP) anchored to nematode cuticles. With this method, hydrogel sheaths of approximately 10-μm thickness are fabricated from a variety of polysaccharides, proteins, and synthetic polymers. Caenorhabditis elegans and Anisakis simplex coated with a hydrogel sheath showed a negligible decrease in viability, chemotaxis and locomotion. Hydrogel sheaths containing UV-absorbable groups and catalase functioned as shields to protect nematodes from UV and hydrogen peroxide, respectively. The results also showed that hydrogel sheaths containing glucose oxidase have the potential to be used as living drug delivery systems for cancer therapy. The nematode functionalization method developed in this study has the potential to impact a wide range of fields from agriculture to medicine.

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Technique to modify the surface of nematode with hydrogel is presented.

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Hydrogel is fabricated in situ using enzymatic cross-linking reaction.

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The technique is compatible with different materials and different species of nematodes.

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Hydrogel sheath protects the nematode from environmental stress.

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Nematode coated with drug-loaded hydrogel has a potential as living drug delivery system.

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.

Static and dynamic culture of human endothelial cells encapsulated inside alginate-gelatin microspheres

This study aimed to explore the angiogenesis potential of human endothelial cells encapsulated inside alginate-gelatin microspheres under static and dynamic culture systems after 7 days. Human umbilical vein endothelial cells were encapsulated inside alginate (1%) and gelatin (1.2%) using an electrostatic encapsulation method. Cells were incubated for 7 days in vitro. The cell survival rate was measured using the MTT assay. The expression of VEGFR-2 and von Willebrand factor genes was studied by real-time PCR assay. Using western blot analysis, we monitored the protein contents of VEGFR-2, vWF, and Caspase 3. The levels of SOD and GPx enzymes were calculated using biochemical kits. Angiogenesis potential was assessed using in vitro Matrigel assay. Data showed an increased survival rate in encapsulated cells cultured under the static condition compared to the conventional 2D condition (p < 0.05). The culture of encapsulated cells under a dynamic bioreactor system did not alter cell viability. Compared to the dynamic culture system, the incubation of encapsulated cells in the static culture system swelled the microspheres (p < 0.05). Both dynamic and static culture models increased the expression of VEGFR-2 and von Willebrand factor in encapsulated cells compared to 2D culture (p < 0.05), showing enhanced functional maturation. Data showed a significant increase of vWF and reduction of apoptosis marker Caspase in the dynamic culture system (p < 0.05). The levels of SOD and GPx were significantly increased in dynamic and static culture models as compared to the control 2D group (p < 0.05). In vitro tubulogenesis assay showed significant induction of angiogenesis in dynamic encapsulated HUVECs indicated with a large number of vascular tubes and arborized ECs compared to the control and static encapsulated HUVECs (p < 0.05). The current study suggests a bioreactor dynamic system is a reliable approach, similar to a static condition, for the expansion of encapsulated human ECs in a 3D milieu.

Increased yield of gelatin coated therapeutic cells through cholesterol insertion

Gelatin coatings are effective in increasing the retention of MSCs injected into the heart and minimizing the damage from acute myocardial infarction (AMI), but early studies suffered from low fractions of the MSCs coated with gelatin. Biotinylation of the MSC surface is a critical first step in the gelatin coating process, and in this study, we evaluated the use of biotinylated cholesterol "lipid insertion" anchors as a substitute for the covalent NHS-biotin anchors to the cell surface. Streptavidin-eosin molecules, where eosin is our photoinitiator, can then be bound to the cell surface through biotin-streptavidin affinity. The use of cholesterol anchors increased streptavidin density on the surface of MSCs further driving polymerization and allowing for an increased fraction of MSCs coated with gelatin (83%) when compared to NHS-biotin (52%). Additionally, the cholesterol anchors increased the uniformity of the coating on the MSC surface and supported greater numbers of coated MSCs even when the streptavidin density was slightly lower than that of an NHS-biotin anchoring strategy. Critically, this improvement in gelatin coating efficiency did not impact cytokine secretion and other critical MSC functions. Proper selection of the cholesterol anchor and the biotinylation conditions supports cellular function and densities of streptavidin on the MSC surface of up to ~105 streptavidin molecules/μm2 . In all, these cholesterol anchors offer an effective path towards the formation of conformal coatings on the majority of MSCs to improve the retention of MSCs in the heart following AMI.

Surface-Anchored Nanogel Coating Endows Stem Cells with Stress Resistance and Reparative Potency via Turning Down the Cytokine-Receptor Binding Pathways

Stem cell-based therapy has great potential in regenerative medicine. However, the survival and engraftment rates of transplanted stem cells in disease regions are poor and limit the effectiveness of cell therapy due to the fragility of stem cells. Here, an approach involving a single-cell coating of surface-anchored nanogel to regulate stem cell fate with anti-apoptosis capacity in the hypoxic and ischemic environment of infarcted hearts is developed for the first time. A polysialic acid-based system is used to anchor microbial transglutaminase to the external surface of the cell membrane, where it catalyzes the crosslinking of gelatin. The single-cell coating with surface-anchored nanogel endows mesenchymal stem cells (MSCs) with stress resistance by blocking the activity of apoptotic cytokines including the binding of tumor necrosis factor α (TNFα) to tumor necrosis factor receptor, which in turn maintains mitochondrial integrity, function and protects MSCs from TNFα-induces apoptosis. The administration of surface engineered MSCs to hearts results in significant improvements in engraftment, cardiac function, infarct size, and vascularity compared with using uncoated MSCs in treating myocardial infarction. The surface-anchored, biocompatible cell surface engineering with nanogel armor provides a new way to produce robust therapeutic stem cells and may explore immense potentials in cell-based therapy.

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.

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.

Coatings on mammalian cells: interfacing cells with their environment

The research community is intent on harnessing increasingly complex biological building blocks. At present, cells represent a highly functional component for integration into higher order systems. In this review, we discuss the current application space for cellular coating technologies and emphasize the relationship between the target application and coating design. We also discuss how the cell and the coating interact in common analytical techniques, and where caution must be exercised in the interpretation of results. Finally, we look ahead at emerging application areas that are ideal for innovation in cellular coatings. In all, cellular coatings leverage the machinery unique to specific cell types, and the opportunities derived from these hybrid assemblies have yet to be fully realized.

Horseradish peroxidase-catalyzed hydrogelation for biomedical applications

Hydrogels catalyzed by horseradish peroxidase (HRP) serve as an efficient and effective platform for biomedical applications due to their mild reaction conditions for cells, fast and adjustable gelation rate in physiological conditions, and an abundance of substrates as water-soluble biocompatible polymers.

Use of Tethered Hydrogel Microcoatings for Mesenchymal Stem Cell Equilibrium, Differentiation, and Self-Organization into Microtissues

Therapeutic adult mesenchymal stem cells (MSCs) lose multipotency and multilineage specialization in culture and after transplantation due to the absence of complex biological architecture. Here, it is shown that a transient ultrathin covering of permeable biomaterial can be differentially formulated to either preserve multipotency or induce multidifferentiation. Accordingly, populations of single, spherical MSCs in suspended media with high selectivity and specificity can be coated. Assembly of single, double, and triple hydrogel layers at MSC membranes is initiated by first attaching MSC-specific immunoglobulins onto CD90 or Stro-1 receptors and UEA-1 and soybean lectins. A secondary biotinylated immunoglobulin is targeted for avidin binding, which becomes an attractor for biotinylated alginate or hyaluronate, which are subsequently stiffened and gelled, in situ around the entire cell surface. Alginate microcoatings permeated with mobile BMP-2-induced osteospecialized tissue, vascular endothelial growth factor (VEGF) induced microcapillary formation, while microcoatings, with selected basement membrane proteins, preserve the multipotent phenotype of MSCs, for continuing rounds of culture and directed specialization. Furthermore, forced packing of microcoated MSC populations creates prototypical tissue compartments: the coating partially simulating the extracellular matrix structures. Remarkably, microcoated MSC clusters show a tremendous simulation of a common embryological tissue transformation into the epithelium. Thus, confinement of free morphology exerts another control on tissue specialization and formation.

High performances of dual network PVA hydrogel modified by PVP using borax as the structure-forming accelerator

A dual network hydrogel made up of polyvinylalcohol (PVA) crosslinked by borax and polyvinylpyrrolidone (PVP) was prepared by means of freezing-thawing circles. Here PVP was incorporated by linking with PVA to form a network structure, while the introduction of borax played the role of crosslinking PVA chains to accelerate the formation of a dual network structure in PVA/PVP composite hydrogel, thus endowing the hydrogel with high mechanical properties. The effects of both PVP and borax on the hydrogels were evaluated by comparing the two systems of PVA/PVP/borax and PVA/borax hydrogels. In the former system, adding 4.0% PVP not only increased the water content and the storage modulus but also enhanced the mechanical strength of the final hydrogel. But an overdose of PVP just as more than 4.0% tended to undermine the structure of hydrogels, and thus deteriorated hydrogels’ properties because of the weakened secondary interaction between PVP and PVA. Likewise, increasing borax could promote the gel crosslinking degree, thus making gels show a decrease in water content and swelling ratio, meanwhile shrinking the pores inside the hydrogels and finally enhancing the mechanical strength of hydrogels prominently. The developed hydrogel with high performances holds great potential for applications in biomedical and industrial fields.

Cancer-associated fibroblasts as target and tool in cancer therapeutics and diagnostics

Cancer-associated fibroblasts (CAFs) are drivers of tumour progression and are considered as a target and a tool in cancer diagnostic and therapeutic applications. An increased abundance of CAFs or CAF signatures are recognized as a bad prognostic marker in several cancer types. Tumour-environment biomimetics strongly improve our understanding of the communication between CAFs, cancer cells and other host cells. Several experimental drugs targeting CAFs are in clinical trials for multiple tumour entities; alternatively, CAFs can be exploited as a tool to characterize the functionality of circulating tumour cells or to capture them as a tool to prevent metastasis. The continuous interaction between tissue engineers, biomaterial experts and cancer researchers creates the possibility to biomimic the tumour-environment and provides new opportunities in cancer diagnostics and management.