Cytoprotective Silica Coating of Individual Mammalian Cells through Bioinspired Silicification

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.

Ultrathin silica-tiling on living cells for chemobiotic catalysis

Harnessing the power of cell biocatalysis for sustainable chemical synthesis requires rational integration of living cells with the modern synthetic catalysts. Here, we develop silica-tiling strategy that constructs a hierarchical, inorganic, protocellular confined nanospace around the individual living cell to accommodate molecularly accessible abiotic catalytic sites. This empowers the living microorganisms for new-to-nature chemical synthesis without compromising the cellular regenerative process. Yeast cell, a widely used biocatalyst, is upgraded via highly controlled self-assembly of 2D-bilayer silica-based catalytic modules on cell surfaces, opening the avenues for diverse chemobiotic reactions. For example, combining [AuPt]-catalyzed NADH regeneration, light-induced [Pd]-catalyzed C-C cross-coupling or lipase-catalyzed esterification reactions-with the natural ketoreductase activity inside yeast cell. The conformal silica bilayer provides protection while allowing proximity to catalytic sites and preserving natural cell viability and proliferation. These living nanobiohybrids offer to bridge cell's natural biocatalytic capabilities with customizable heterogeneous metal catalysis, enabling programmable reaction sequences for sustainable chemical synthesis.

Impact of Silk-Ionomer Encapsulation on Immune Cell Mechanical Properties and Viability

Encapsulation of single cells is a powerful technique used in various fields, such as regenerative medicine, drug delivery, tissue regeneration, cell-based therapies, and biotechnology. It offers a method to protect cells by providing cytocompatible coatings to strengthen cells against mechanical and environmental perturbations. Silk fibroin, derived from the silkworm Bombyx mori, is a promising protein biomaterial for cell encapsulation due to the cytocompatibility and capacity to maintain cell functionality. Here, THP-1 cells, a human leukemia monocytic cell line, were encapsulated with chemically modified silk polyelectrolytes through electrostatic layer-by-layer deposition. The effectiveness of the silk nanocoating was assessed using scanning electron microscopy (SEM) and confocal microscopy and on cell viability and proliferation by Alamar Blue assay and live/dead staining. An analysis of the mechanical properties of the encapsulated cells was conducted using atomic force microscopy nanoindentation to measure elasticity maps and cellular stiffness. After the cells were encapsulated in silk, an increase in their stiffness was observed. Based on this observation, we developed a mechanical predictive model to estimate the variations in stiffness in relation to the thickness of the coating. By tuning the cellular assembly and biomechanics, these encapsulations promote systems that protect cells during biomaterial deposition or processing in general.

Cell Membrane as A Promising Therapeutic Target: From Materials Design to Biomedical Applications

The cell membrane is a crucial component of cells, protecting their integrity and stability while facilitating signal transduction and information exchange. Therefore, disrupting its structure or impairing its functions can potentially cause irreversible cell damage. Presently, the tumor cell membrane is recognized as a promising therapeutic target for various treatment methods. Given the extensive research focused on cell membranes, it is both necessary and timely to discuss these developments, from materials design to specific biomedical applications. This review covers treatments based on functional materials targeting the cell membrane, ranging from well-known membrane-anchoring photodynamic therapy to recent lysosome-targeting chimaeras for protein degradation. The diverse therapeutic mechanisms are introduced in the following sections: membrane-anchoring phototherapy, self-assembly on the membrane, in situ biosynthesis on the membrane, and degradation of cell membrane proteins by chimeras. In each section, we outline the conceptual design or general structure derived from numerous studies, emphasizing representative examples to understand advancements and draw inspiration. Finally, we discuss some challenges and future directions in membrane-targeted therapy from our perspective. This review aims to engage multidisciplinary readers and encourage researchers in related fields to advance the fundamental theories and practical applications of membrane-targeting therapeutic agents.

Organismal Function Enhancement through Biomaterial Intervention

Living organisms in nature, such as magnetotactic bacteria and eggs, generate various organic-inorganic hybrid materials, providing unique functionalities. Inspired by such natural hybrid materials, researchers can reasonably integrate biomaterials with living organisms either internally or externally to enhance their inherent capabilities and generate new functionalities. Currently, the approaches to enhancing organismal function through biomaterial intervention have undergone rapid development, progressing from the cellular level to the subcellular or multicellular level. In this review, we will concentrate on three key strategies related to biomaterial-guided bioenhancement, including biointerface engineering, artificial organelles, and 3D multicellular immune niches. For biointerface engineering, excess of amino acid residues on the surfaces of cells or viruses enables the assembly of materials to form versatile artificial shells, facilitating vaccine engineering and biological camouflage. Artificial organelles refer to artificial subcellular reactors made of biomaterials that persist in the cytoplasm, which imparts cells with on-demand regulatory ability. Moreover, macroscale biomaterials with spatiotemporal regulation characters enable the local recruitment and aggregation of cells, denoting multicellular niche to enhance crosstalk between cells and antigens. Collectively, harnessing the programmable chemical and biological attributes of biomaterials for organismal function enhancement shows significant potential in forthcoming biomedical applications.

Cytoprotective Metal-Phenolic Network Sporulation to Modulate Microalgal Mobility and Division

Synthetic cell exoskeletons created from abiotic materials have attracted interest in materials science and biotechnology, as they can regulate cell behavior and create new functionalities. Here, a facile strategy is reported to mimic microalgal sporulation with on-demand germination and locomotion via responsive metal-phenolic networks (MPNs). Specifically, MPNs with tunable thickness and composition are deposited on the surface of microalgae cells via one-step coordination, without any loss of cell viability or intrinsic cell photosynthetic properties. The MPN coating keeps the cells in a dormant state, but can be disassembled on-demand in response to environmental pH or chemical stimulus, thereby reviving the microalgae within 1 min. Moreover, the artificial sporulation of microalgae resulted in resistance to environmental stresses (e.g., metal ions and antibiotics) akin to the function of natural sporulation. This strategy can regulate the life cycle of complex cells, providing a synthetic strategy for designing hybrid microorganisms.

Cell Surface Engineering Tools for Programming Living Assemblies

Breakthroughs in precision cell surface engineering tools are supporting the rapid development of programmable living assemblies with valuable features for tackling complex biological problems. Herein, the authors overview the most recent technological advances in chemically- and biologically-driven toolboxes for engineering mammalian cell surfaces and triggering their assembly into living architectures. A particular focus is given to surface engineering technologies for enabling biomimetic cell-cell social interactions and multicellular cell-sorting events. Further advancements in cell surface modification technologies may expand the currently available bioengineering toolset and unlock a new generation of personalized cell therapeutics with clinically relevant biofunctionalities. The combination of state-of-the-art cell surface modifications with advanced biofabrication technologies is envisioned to contribute toward generating living materials with increasing tissue/organ-mimetic bioactivities and therapeutic potential.

Advancing cell surface modification in mammalian cells with synthetic molecules

Biological cells, being the fundamental entities of life, are widely acknowledged as intricate living machines. The manipulation of cell surfaces has emerged as a progressively significant domain of investigation and advancement in recent times. Particularly, the alteration of cell surfaces using meticulously crafted and thoroughly characterized synthesized molecules has proven to be an efficacious means of introducing innovative functionalities or manipulating cells. Within this realm, a diverse array of elegant and robust strategies have been recently devised, including the bioorthogonal strategy, which enables selective modification. This review offers a comprehensive survey of recent advancements in the modification of mammalian cell surfaces through the use of synthetic molecules. It explores a range of strategies, encompassing chemical covalent modifications, physical alterations, and bioorthogonal approaches. The review concludes by addressing the present challenges and potential future opportunities in this rapidly expanding field.

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.

Biomimetic Mineralization: From Microscopic to Macroscopic Materials and Their Biomedical Applications

Biomineralization is an attractive pathway to produce mineral-based biomaterials with high performance and hierarchical structures. To date, the biomineralization process and mechanism have been extensively studied, especially for the formation of bone, teeth, and nacre. Inspired by those, abundant biomimetic mineralized materials have been fabricated for biomedical applications. Those bioinspired materials generally exhibit great mechanical properties and biological functions. Nevertheless, substantial gaps remain between biomimetic materials and natural materials, particularly with respect to mechanical properties and mutiscale structures. This Review summarizes the recent progress of micro- and macroscopic biomimetic mineralization from the perspective of materials synthesis and biomedical applications. To begin with, we discuss the progress of biomimetic mineralization at the microscopic level. The mechanical strength, stability, and functionality of the nano- and micromaterials are significantly improved by introducing biominerals, such as DNA nanostructures, nanovaccines, and living cells. Next, numerous biomimetic strategies based on biomineralization at the macroscopic scale are highlighted, including in situ mineralization and bottom-up assembly of mineralized building blocks. Finally, challenges and future perspectives regarding the development of biomimetic mineralization are also presented with the aim of offering insights for the rational design and fabrication of next-generation biomimetic mineralized materials.

Applications and Future Prospects of Micro/Nanorobots Utilizing Diverse Biological Carriers

Targeted drug delivery using micro-nano robots (MNRs) is a rapidly advancing and promising field in biomedical research. MNRs enable precise delivery of drugs, addressing a wide range of healthcare needs. However, the application of MNRs in vivo is limited by power issues and specificity in different scenarios. Additionally, the controllability and biological safety of MNRs must be considered. To overcome these challenges, researchers have developed bio-hybrid micro-nano motors that offer improved accuracy, effectiveness, and safety for targeted therapies. These bio-hybrid micro-nano motors/robots (BMNRs) use a variety of biological carriers, blending the benefits of artificial materials with the unique features of different biological carriers to create tailored functions for specific needs. This review aims to give an overview of the current progress and application of MNRs with various biocarriers, while exploring the characteristics, advantages, and potential hurdles for future development of these bio-carrier MNRs.

Biohybrid materials: Structure design and biomedical applications

Biohybrid materials are proceeded by integrating living cells and non-living materials to endow materials with biomimetic properties and functionalities by supporting cell proliferation and even enhancing cell functions. Due to the outstanding biocompatibility and programmability, biohybrid materials provide some promising strategies to overcome current problems in the biomedical field. Here, we review the concept and unique features of biohybrid materials by comparing them with conventional materials. We emphasize the structure design of biohybrid materials and discuss the structure-function relationships. We also enumerate the application aspects of biohybrid materials in biomedical frontiers. We believe this review will bring various opportunities to promote the communication between cell biology, material sciences, and medical engineering.

Cell-in-Catalytic-Shell Nanoarchitectonics: Catalytic Empowerment of Individual Living Cells by Single-Cell Nanoencapsulation

Cell-in-shell biohybrid structures, synthesized by encapsulating individual living cells with exogenous materials, have emerged as exciting functional entities for engineered living materials, with emergent properties outside the scope of biochemical modifications. Artificial exoskeletons have, to date, provided physicochemical shelters to the cells inside in the first stage of technological development, and further advances in the field demand catalytically empowered, cellular hybrid systems that augment the biological functions of cells and even introduce completely new functions to the cells. This work describes a facile and generalizable strategy for empowering living cells with extrinsic catalytic capability through nanoencapsulation of living cells with a supramolecular metal-organic complex of Fe³⁺ and benzene-1,3,5-tricarboxylic acid (BTC). A series of enzymes are embedded in situ, without loss of catalytic activity, in the Fe³⁺ -BTC shells, not to mention the superior characteristics of cytocompatible and rapid shell-forming processes. The nanoshell enhances the catalytic efficiency of multienzymatic cascade reactions by confining reaction intermediates to its internal voids and the nanoencapsulated cells acquire exogenous biochemical functions, including enzymatic cleavage of lethal octyl-β-d-glucopyranoside into d-glucose, with autonomous cytoprotection. The system will provide a versatile, nanoarchitectonic tool for interfacing biological cells with functional materials, especially for catalytic bioempowerment of living cells.

Cell-based biocomposite engineering directed by polymers

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

Robust and Long-Term Cellular Protein and Enzymatic Activity Preservation in Biomineralized Mammalian Cells

Preservation of evolved biological structure and function in robust engineering materials is of interest for storage of biological samples before diagnosis and development of vaccines, sensors, and enzymatic reactors and has the potential to avoid cryopreservation and its associated cold-chain issues. Here, we demonstrate that "freezing cells in amorphous silica" is a powerful technique for long-term preservation of whole mammalian cell proteomic structure and function at room temperature. Biomimetic silicification employs the crowded protein microenvironment of mammalian cells as a catalytic framework to proximally transform monomeric silicic acid into silicates forming a nanoscopic silica shell over all biomolecular interfaces. Silicification followed by dehydration preserves and passivates proteomic information within a nanoscale thin silica coating that exhibits size selective permeability (<3.6 nm), preventing protein leaching and protease degradation of cellular contents, while providing access of small molecular constituents for cellular enzymatic reaction. Exposure of dehydrated silicified cells to mild etchant or prolonged hydrolysis removes the silica, completely rerevealing biomolecular components and restoring their accessibility and functionality.

Multifunctional Metal-Organic Framework Exoskeletons Protect Biohybrid Sperm Microrobots for Active Drug Delivery from the Surrounding Threats

Utilizing spermatozoa as the engine unit of robotic systems at a microscale has brought revolutionized inspirations and strategies to the biomedical community. However, the motility of sperms is impaired by the surrounding threats. For example, the antisperm antibody (AsA) can specifically bind with surface antigens on the sperm membrane and adversely affect their propulsion, hindering the operation of sperm-based microrobots in practical environments. In the present work, we report a biohybrid sperm microrobot by encapsulating sperm cells within metal-organic frameworks (MOFs) and zeolitic imidazolate framework-8 (ZIF-8) nanoparticles (NPs) (ZIFSpermbot), capable of active drug delivery and cytoprotection from the biological threats of AsA. ZIF-8 NPs can be facilely coated on the sperm membrane through complexation with tannic acid. Such cell surface engineering has a negligible impact on sperm motility under optimized conditions. The selective permeability of the resulting porous ZIF-8 wrappings protects ZIFSpermbots from the specific binding of AsA, enabling the preservation of intrinsic propulsion of the sperm engine. Besides, ZIF-8 wrappings sustainably release zinc ions and attenuate the oxidative damage generated in sperm cells, allowing the maintenance of sperm movement. Combining the effective protection of sperm propulsion with the drug-loading capacity of ZIF-8 NPs provides new applicability to ZIFSpermbots in risky surroundings with AsA, exhibiting rapid migration in a microfluidic device for active drug delivery with enhanced therapeutic efficacy due to their retained effective propulsion. Imparting bioengine-based microrobots with multifunctional wrappings holds great promise for designing adaptive cell robots that endure harsh environments toward locally extended and diverse operations, facilitating their use in practical and clinical applications.

Diatom microalgae as smart nanocontainers for biosensing wastewater pollutants: recent trends and innovations

Microalgae have been recognized as one of the most efficient microorganisms to remediate industrial effluents. Among microalgae diatoms are silica shelled unicellular eukaryotes, found in all types of water bodies and flourish very well even in wastewater. They have their silica cell wall made up of nano arrayed pores arranged in a uniform fashion. Therefore, they act as smart nanocontainers to adsorb various trace metals, dyes, polymers, and drugs which are hazardous to human as well to aquatic life. The beautiful nanoarchitecture in diatoms allows them to easily bind to ligands of choice to form a nanocomposite structure with the pollutants which can be a chemical or biological component. Such naturally available diatom nanomaterials are economical and highly sensitive compared to manmade artificial silica nanomaterials to help in facile removal of the toxic pollutants from wastewater. This review is thus focused on employing diatoms to remediate various pollutants such as heavy metals, dyes, hydrocarbons detected in the wastewater. It also includes different microalgae as biosensors for determination of pollutants in effluents and the perspectives for nanotechnological applications in the field of remediating pollutants through microalgae. The review also discusses in length the hurdles and perspectives of employing microalgae in wastewater remediation.

A Versatile Strategy to Coat Individual Cell with Fully/Partially Covered Shell for Preparation of Self-Propelling Living Cells

Coating living cells with a functional shell has been regarded as an effective way to protect them against environmental stress, regulate their biological behaviors, or extend their functionalities. Here, we reported a facile method to prepare fully or partially coated shells on an individual yeast cell surface by visible light-induced graft polymerization. In this strategy, yeast cells that were surface-absorbed with polyethylenimine (PEI) were deposited on the negatively charged glass slide to form a single layer by electrostatic interaction. Then, surface-initiated graft polymerization of poly(ethylene glycol) diacrylate (PEGDA) on yeast cells under visible light irradiation was carried out to generate cross-linked shells on the cells. The process of surface modification had negligible influence on the viability of yeast cells due to the mild reaction condition. Additionally, compared to the native yeast cells, a 17.5 h of delay in division was observed when the graft polymerization was performed under 15 mW/cm² irradiation for 30 min. Introducing artificial shell endowed yeast cells with significant resistance against lyticase, and the protection can be enhanced by increasing the thickness of shell. Moreover, the partially coated yeast cells would be prepared by simply adjusting the reaction condition such as irradiation density and time. By immobilizing urease on the functional patch, the asymmetrically modified yeast cells exhibited self-propelling capability, and the speed of directional movement reached 4 μm/s in the presence of 200 mM urea. This tunable coating individual cell strategy with varying functionality has great potential applications in fields of cell-based drug delivery, cell therapy, biocatalysis, and tissue engineering.

Polymer-Assisted Metallization of Mammalian Cells

Developing biotemplating techniques to translate microorganisms and cultured mammalian cells into metallic biocomposites is of great interest for biosensors, electronics, and energy. The metallization of viruses and microbial cells is successfully demonstrated via a genetic engineering strategy or electroless deposition. However, it is difficult to transform mammalian cells into metallic biocomposites because of the complicated genes and the delicate morphological features. Herein, "polymer-assisted cell metallization" (PACM) is reported as a general method for the transformation of mammalian cells into metallic biocomposites. PACM includes a first step of in situ polymerization of functional polymer on the surface and in the interior of the mammalian cells, and a subsequent electroless deposition of metal to convert the polymer-functionalized cells into metallic biocomposites, which retain the micro- and nanostructures of the mammalian cells. This new biotemplating method is compatible with different cell types and metals to yield a wide variety of metallic biocomposites with controlled structures and properties.

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.

Coating with flexible DNA network enhanced T-cell activation and tumor killing for adoptive cell therapy

Adoptive cell therapy (ACT) is an emerging powerful cancer immunotherapy, which includes a complex process of genetic modification, stimulation and expansion. During these in vitro or ex vivo manipulation, sensitive cells are inescapability subjected to harmful external stimuli. Although a variety of cytoprotection strategies have been developed, their application on ACT remains challenging. Herein, a DNA network is constructed on cell surface by rolling circle amplification (RCA), and T cell-targeted trivalent tetrahedral DNA nanostructure is used as a rigid scaffold to achieve high-efficient and selective coating for T cells. The cytoprotective DNA network on T-cell surface makes them aggregate over time to form cell clusters, which exhibit more resistance to external stimuli and enhanced activities in human peripheral blood mononuclear cells and liver cancer organoid killing model. Overall, this work provides a novel strategy for in vitro T cell-selective protection, which has a great potential for application in ACT.

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

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

Bioinspired Cell Silicification: From Extracellular to Intracellular

In nature, biosilicification directs the formation of elaborate amorphous silica exoskeletons that provide diatoms mechanically strong, chemically inert, non-decomposable silica armor conferring chemical and thermal stability as well as resistance to microbial attack, without changing the optical transparency or adversely effecting nutrient and waste exchange required for growth. These extraordinary silica/cell biocomposites have inspired decades of biomimetic research aimed at replication of diatoms' hierarchically organized exoskeletons, immobilization of cells or living organisms within silica matrices and coatings to protect them against harmful external stresses, genetic re-programming of cellular functions by virtue of physico-chemical confinement within silica, cellular integration into devices, and endowment of cells with non-native, abiotic properties through facile silica functionalization. In this Perspective, we focus our discussions on the development and concomitant challenges of bioinspired cell silicification ranging from "cells encapsulated within 3D silica matrices" and "cells encapsulated within 2D silica shells" to extra- and intracellular silica replication, wherein all biomolecular interfaces are encased within nanoscopic layers of amorphous silica. We highlight notable examples of advances in the science and technology of biosilicification and consider challenges to advancing the field, where we propose cellular "mineralization" with arbitrary nanoparticle exoskeletons as a generalizable means to impart limitless abiotic properties and functions to cells, and, based on the interchangeability of water and silicic acid and analogies between amorphous ice and amorphous silica, we consider "freezing" cells within amorphous silica as an alternative to cryo-preservation.

Polymerization-Mediated Multifunctionalization of Living Cells for Enhanced Cell-Based Therapy

Surface decoration of living cells by exogenous substances offers a unique tool for understanding and tuning cell behaviors, which plays a critical role in cell-based therapy. Here, a facile yet versatile approach for decorating individual living cells with multimodal coatings is reported. By simply co-depositing with dopamine under a cytocompatible condition, various functional small molecules and polymers can be encoded to form a multifunctional coating on a cell's surface. The accessibility and versatility of this method to decorate diverse cells, including bacteria, fungi, and mammalian cells is demonstrated. With the ability to tune surface functions, ligand co-deposited gut microbiota is prepared as oral therapeutics for targeted treatment of colitis. Given the dual cytoprotective and targeting effects of the coating, decorated cells show more than 30-times higher bioavailability in the gut and fourfold higher accumulation in the inflamed tissue in comparison with those of uncoated bacteria. Multimodal therapeutic cells further validate strikingly increased treatment efficacy over clinical aminosalicylic acid in colitis mice. Decorating with multifunctional coatings proposes a robust platform for developing multimodal cells for enhanced cell-based therapy.

Artificial Bioaugmentation of Biomacromolecules and Living Organisms for Biomedical Applications

The synergistic union of nanomaterials with biomaterials has revolutionized synthetic chemistry, enabling the creation of nanomaterial-based biohybrids with distinct properties for biomedical applications. This class of materials has drawn significant scientific interest from the perspective of functional extension via controllable coupling of synthetic and biomaterial components, resulting in enhancement of the chemical, physical, and biological properties of the obtained biohybrids. In this review, we highlight the forefront materials for the combination with biomacromolecules and living organisms and their advantageous properties as well as recent advances in the rational design and synthesis of artificial biohybrids. We further illustrate the incredible diversity of biomedical applications stemming from artificially bioaugmented characteristics of the nanomaterial-based biohybrids. Eventually, we aim to inspire scientists with the application horizons of the exciting field of synthetic augmented biohybrids.

Recent Progress in Magnetically Actuated Microrobots for Targeted Delivery of Therapeutic Agents

Therapeutic agents, such as drugs and cells, play an essential role in virtually every treatment of injury, illness, or disease. However, the conventional practices of drug delivery often result in undesirable side effects caused by drug overdose and off-target delivery. In the case of cell delivery, the survival rate of the transplanted cells is extremely low and difficulties with the administration route of cells remain a problem. Recently, magnetically actuated microrobots have started offering unique opportunities in targeted therapeutic delivery due to their tiny size and ability to access hard-to-reach lesions in a minimally invasive manner; considerable advances in this regard have been made over the past decade. Here, recent progress in magnetically actuated microrobots, developed for targeted drug/cell delivery, is presented, with a focus on their design features and mechanisms for controlled therapeutic release. Additionally, the practical challenges faced by the microrobots, and future research directions toward the swift bench-to-bedside translation of the microrobots are addressed.

Resilient three-dimensional ordered architectures assembled from nanoparticles by DNA

Rapid developments of DNA-based assembly methods provide versatile capabilities in organizing nanoparticles (NPs) in three-dimensional (3D) organized nanomaterials, which is important for optics, catalysis, mechanics, and beyond. However, the use of these nanomaterials is often limited by the narrow range of conditions in which DNA lattices are stable. We demonstrate here an approach to creating an inorganic, silica-based replica of 3D periodic DNA-NP structures with different lattice symmetries. The created ordered nanomaterials, through the precise 3D mineralization, maintain the spatial topology of connections between NPs by DNA struts and exhibit a controllable degree of the porosity. The formed silicated DNA-NP lattices exhibit excellent resiliency. They are stable when exposed to extreme temperatures (>1000°C), pressures (8 GPa), and harsh radiation conditions and can be processed by the conventional nanolithography methods. The presented approach allows the use of a DNA assembly strategy to create organized nanomaterials for a broad range of operational conditions.

Encapsulation of bacterial cells in cytoprotective ZIF-90 crystals as living composites

Exploiting metal-organic frameworks (MOFs) as selectively permeable shelters for encapsulating engineered cells to form hybrid living materials has attracted increasing attention in recent years. Optimizing the synthesis process to improve encapsulation efficiency (EE) is critical for further technological development and applications. Here, using ZIF-90 and genetically engineered Escherichia coli (E. coli) as a demo, we fabricated E. coli@ZIF-90 living composites in which E. coli cells were encapsulated in ZIF-90 crystals. We illustrated that ZIF-90 could serve as a protective porous cage for cells to shield against toxic bactericides including benzaldehyde, cinnamaldehyde, and kanamycin. Notably, the E. coli cells remained alive and could self-reproduce after removing the ZIF-90 crystal cages in ethylenediaminetetraacetic acid, suggesting a feasible route for protecting and prolonging the lifespan of bacterial cells. Moreover, an aqueous multiple-step deposition approach was developed to improve EE of the E. coli@ZIF-90 composites: the EE increased to 61.9 ± 5.2%, in contrast with the efficiency of the traditional method (21.3 ± 4.4%) prepared with PBS buffer. In short, we develop a simple yet viable strategy to manufacture MOF-based living hybrid materials that promise new applications across diverse fields.

Novel nanomaterial-organism hybrids with biomedical potential

Instinctive hierarchically biomineralized structures of various organisms, such as eggs, algae, and magnetotactic bacteria, afford extra protection and distinct performance, which endow fragile organisms with a tenacious ability to adapt and survive. However, spontaneous formation of hybrid materials is difficult for most organisms in nature. Rapid development of chemistry and materials science successfully obtained the combinations of organisms with nanomaterials by biomimetic mineralization thus demonstrating the reproduction of the structures and functions and generation of novel functions that organisms do not possess. The rational design of biomaterial-organism hybridization can control biological recognition, interactions, and metabolism of the organisms. Thus, nanomaterial-organism hybrids represent a next generation of organism engineering with great potential biomedical applications. This review summarizes recent advances in material-directed organism engineering and is mainly focused on biomimetic mineralization technologies and their outstanding biomedical applications. Three representative types of biomimetic mineralization are systematically introduced, including external mineralization, internal mineralization, and genetic engineering mineralization. The methods involving hybridization of nanomaterials and organisms based on biomimetic mineralization strategies are described. These strategies resulted in applications of various nanomaterial-organism hybrids with multiplex functions in cell engineering, cancer treatment, and vaccine improvement. Unlike classical biological approaches, this material-based bioregulation is universal, effective, and inexpensive. In particular, instead of traditional medical solutions, the integration of nanomaterials and organisms may exploit novel strategies to solve current biomedical problems. This article is categorized under: Implantable Materials and Surgical Technologies > Nanomaterials and Implants Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

Construction of bifunctional living red blood cells for combined photothermal-chemotherapy

Modifying living cells using in-situ synthesized nanomaterials to endow them with new functions is highly desirable. Herein we report intra- and extra-cellular dual-modified red blood cells (RBCs) with intracellular CaCO₃ nanoparticles (NPs) and extracellular polypyrrole-folic acid (PPy-FA) coating, which are exploited as a bifunctional drug carrier. The functionalized living cells (CaCO₃@RBC@PPy-FA) are fabricated through first the intracellular in situ reaction of exogenous Ca²⁺ and CO₃^2- ions to generate CaCO₃ NPs, then polymerization of pyrrole and finally modification of folic acid (FA) on the membrane of individual cells, forming a CaCO₃@RBC@PPy-FA structure. As a result, such dual-modified RBCs not only preserve the original performances of the cells but also possess the desirable properties as a drug carrier, such as high loading capacity due to the action of CaCO₃ NPs, targeting and light-controlled drug release due to the action of PPy-FA. Under NIR laser stimulation, these bifunctional RBCs (DOX-CaCO₃@RBC@PPy-FA) present an instant release profile of doxorubicin (DOX) and have high targeting-ability toward cancer cells, achieving a marked synergistic combined photothermal-chemotherapy effect.

Cryptobiosis-inspired assembly of "AND" logic gate platform for potential tumor-specific drug delivery

Developing tumor-specific drug delivery systems with minimized off-target cargo leakage remains an enduring challenge. In this study, inspired from the natural cryptobiosis explored by certain organisms and stimuli-responsive polyphenol‒metal coordination chemistry, doxorubicin (DOX)-conjugated gelatin nanoparticles with protective shells formed by complex of tannic acid and Fe^III (DG@TA-Fe^III NPs) were successfully developed as an “AND” logic gate platform for tumor-targeted DOX delivery. Moreover, benefiting from the well-reported photothermal conversion ability of TA-Fe^III complex, a synergistic tumor inhibition effect was confirmed by treating 4T1 tumor-bearing mice with DG@TA-Fe^III NPs and localized near-infrared (NIR) laser irradiation. As a proof of concept study, this work present a simple strategy for developing “AND” logic gate platforms by coating enzyme-degradable drug conjugates with detachable polyphenol‒metal shells.

Biomimetic and bioinspired silicifications: Recent advances for biomaterial design and applications

The rational design and controllable synthesis of functional silica-based materials have gained increased interest in a variety of biomedical and biotechnological applications due to their unique properties. The current review shows that marine organisms, such as siliceous sponges and diatoms, could be the inspiration for the fabrication of advanced biohybrid materials. Several biomolecules were involved in the molecular mechanism of biosilicification in vivo. Mimicking their behavior, functional silica-based biomaterials have been generated via biomimetic and bioinspired silicification in vitro. Additionally, several advanced technologies were developed for in vitro and in vivo immobilization of biomolecules with potential applications in biocatalysis, biosensors, bioimaging, and immunoassays. A thin silica layer could coat a single living cell or virus as a protective shell offering new opportunities in biotechnology and nanomedicine fields. Promising nanotechnologies have been developed for drug encapsulation and delivery in a targeted and controlled manner, in particular for poorly soluble hydrophobic drugs. Moreover, biomimetic silica, as a morphogenetically active biocompatible material, has been utilized in the field of bone regeneration and in the development of biomedical implantable devices. STATEMENT OF SIGNIFICANCE: In nature, silica-based biomaterials, such as diatom frustules and sponge spicules, with high mechanical and physical properties were created under biocompatible conditions. The fundamental knowledge underlying the molecular mechanisms of biosilica formation could inspire engineers and chemists to design novel hybrid biomaterials using molecular biomimetic strategies. The production of such biohybrid materials brings the biosilicification field closer to practical applications. This review starts with the biosilicification process of sponges and diatoms with recently updated researches. Then, this article covers recent advances in the design of silica-based biomaterials and their potential applications in the fields of biotechnology and nanomedicine, highlighting several promising technologies for encapsulation of functional proteins and living cells, drug delivery and the preparation of scaffolds for bone regeneration.

Improvement of organisms by biomimetic mineralization: A material incorporation strategy for biological modification

Biomineralization, a bio-organism controlled mineral formation process, plays an important role in linking biological organisms and mineral materials in nature. Inspired by biomineralization, biomimetic mineralization is used as a bridge tool to integrate biological organisms and functional materials together, which can be beneficial for the development of diversified functional organism-material hybrids. In this review, recent progresses on the techniques of biomimetic mineralization for organism-material combinations are summarized and discussed. Based upon these techniques, the preparations and applications of virus-, prokaryotes-, and eukaryotes-material hybrids have been presented and they demonstrate the great potentials in the fields of vaccine improvement, cell protection, energy production, environmental and biomedical treatments, etc. We suggest that more researches about functional organism and material combination with more biocompatible techniques should be developed to improve the design and applications of specific organism-material hybrids. These rationally designed organism-material hybrids will shed light on the production of "live materials" with more advanced functions in future. STATEMENT OF SIGNIFICANCE: This review summaries the recent attempts on improving biological organisms by their integrations with functional materials, which can be achieved by biomimetic mineralization as the combination tool. The integrated materials, as the artificial shells or organelles, confer diversified functions on the enclosed organisms. The successful constructions of various virus-, prokaryotes-, and eukaryotes-material hybrids have demonstrated the great potentials of the material incorporation strategy in vaccine development, cancer treatment, biological photosynthesis and environment protection etc. The suggested challenges and perspectives indicate more inspirations for the future development of organism-material 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.

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.

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.

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

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

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.

Remodeling of Cellular Surfaces via Fast Disulfide-Thiol Exchange To Regulate Cell Behaviors

Remodeling of cellular surfaces is shown highly effective in the manipulation and control of cell behaviors via nonbiological means. By 5-thio-2-nitrobenzoate-mediated, fast, and reversible disulfide-thiol exchange, a sequential layer by layer assembly process was developed to grow albumin protein shells on cellular surfaces fixed by a disulfide-linked network, in a cytocompatible manner. The artificial shells, accomplished by a double-assembly process, were sustainable up to >1 day, and thereafter gradually bioabsorbed with unaffected cell viability. The surface engineering process enabled dynamic remodeling of cellular surfaces that effectively controlled cell behaviors including regulated cell proliferation, enhanced uptake efficiency of dextran-fluorescein isothiocyanate that is known for cell-impermeability, and targeted imaging. This unique approach was well-validated on tumor cells (B16), immune cells (DC2.4), and neutrophils, showing its potential universality for most of the cells that are rich in thiols. The new strategy will show promise in cell manipulation and targeted imaging.

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.