Single-Cell Nanoencapsulation: Chemical Synthesis of Artificial Cell-in-Shell Spores

Nature has evolved adaptive strategies to protect living cells and enhance their resilience against hostile environments, exemplified by bacterial and fungal spores. Inspired by cryptobiosis in nature, chemists have designed and synthesized artificial "cell-in-shell" structures, endowed with the protective and functional capabilities of nanoshells. The cell-in-shells hold the potential to overcome the inherent limitations of biologically naı̈ve cells, enabling the acquisition of exogenous phenotypic traits through the chemical process known as single-cell nanoencapsulation (SCNE). This review highlights recent advancements in the development of artificial spores, with sections organized based on the categorization of material types utilized in SCNE, specifically organic, hybrid, and inorganic types. Particular emphasis is placed on the cytoprotective and multifunctional roles of nanoshells, demonstrating potential applications of SCNEd cells across diverse fields, including synthetic biology, biochemistry, materials science, and biomedical engineering. Furthermore, the perspectives outlined in this review propose future research directions in SCNE, with the goal of achieving fine-tuned precision in chemical modulation at both intracellular and pericellular levels, paving the way for the design and construction of customized artificial spores tailored to meet specific functional needs.

Artificial Polymerizations in Living Organisms for Biomedical Applications

Within living organisms, numerous nanomachines are constantly involved in complex polymerization processes, generating a diverse array of biomacromolecules for maintaining biological activities. Transporting artificial polymerizations from lab settings into biological contexts has expanded opportunities for understanding and managing biological events, creating novel cellular compartments, and introducing new functionalities. This review summarizes the recent advancements in artificial polymerizations, including those responding to external stimuli, internal environmental factors, and those that polymerize spontaneously. More importantly, the cutting-edge biomedical application scenarios of artificial polymerization, notably in safeguarding cells, modulating biological events, improving diagnostic performance, and facilitating therapeutic efficacy are highlighted. Finally, this review outlines the key challenges and technological obstacles that remain for polymerizations in biological organisms, as well as offers insights into potential directions for advancing their practical applications and clinical trials.

Materials for Cell Surface Engineering

Cell therapies are emerging as a promising new therapeutic modality in medicine, generating effective treatments for previously incurable diseases. Clinical success of cell therapies has energized the field of cellular engineering, spurring further exploration of novel approaches to improve their therapeutic performance. Engineering of cell surfaces using natural and synthetic materials has emerged as a valuable tool in this endeavor. This review summarizes recent advances in the development of technologies for decorating cell surfaces with various materials including nanoparticles, microparticles, and polymeric coatings, focusing on the ways in which surface decorations enhance carrier cells and therapeutic effects. Key benefits of surface-modified cells include protecting the carrier cell, reducing particle clearance, enhancing cell trafficking, masking cell-surface antigens, modulating inflammatory phenotype of carrier cells, and delivering therapeutic agents to target tissues. While most of these technologies are still in the proof-of-concept stage, the promising therapeutic efficacy of these constructs from in vitro and in vivo preclinical studies has laid a strong foundation for eventual clinical translation. Cell surface engineering with materials can imbue a diverse range of advantages for cell therapy, creating opportunities for innovative functionalities, for improved therapeutic efficacy, and transforming the fundamental and translational landscape of cell therapies.

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.

Polymerization in living organisms

Vital biomacromolecules, such as RNA, DNA, polysaccharides and proteins, are synthesized inside cells via the polymerization of small biomolecules to support and multiply life. The study of polymerization reactions in living organisms is an emerging field in which the high diversity and efficiency of chemistry as well as the flexibility and ingeniousness of physiological environment are incisively and vividly embodied. Efforts have been made to design and develop in situ intra/extracellular polymerization reactions. Many important research areas, including cell surface engineering, biocompatible polymerization, cell behavior regulation, living cell imaging, targeted bacteriostasis and precise tumor therapy, have witnessed the elegant demeanour of polymerization reactions in living organisms. In this review, recent advances in polymerization in living organisms are summarized and presented according to different polymerization methods. The inspiration from biomacromolecule synthesis in nature highlights the feasibility and uniqueness of triggering living polymerization for cell-based biological applications. A series of examples of polymerization reactions in living organisms are discussed, along with their designs, mechanisms of action, and corresponding applications. The current challenges and prospects in this lifeful field are also proposed.

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.

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.

Effect of cell culture media on photopolymerizations

Radical polymerization is one of the most widely used methods for the synthesis of polymeric materials for biomedical applications, such as drug delivery, 3D cell culture, and regenerative medicine. Among radical polymerization reactions, thiol-ene click chemistry has shown excellent orthogonality in diverse reaction conditions. However, our preliminary investigations revealed that it fails in cell culture environment. Herein, we investigate the mechanisms by which cell culture media interfere with radical photoreactions. Three different models including free radical linear photopolymerization (N,N-dimethylacrylamide photopolymerization), free radical photohydrogelation (poly(ethylene glycol) diacrylate photohydrogelation), and thiol-ene photohydrogelation (4-arm poly(ethylene glycol)-norbornene thiol-ene photohydrogelation) were investigated. We showed that common cell culture media ingredients can interfere with radical polymerization by two different pathways; namely, radical chain transfer and radical scavenging effects. Thiol-ene photoclick hydrogelation was seriously affected by cell culture media especially under the alkaline conditions of many of them, due to the impact of deprotonation of the thiol reactant. We intend these findings to serve as a reference guide to researchers employing free radical-based molecular synthesis in cell culture settings. The nonbenign impact of media components, pH, and concentration should provide a cue for future studies that aim to prepare well-defined polymeric materials in the presence of cell culture media.

A Removable Artificial Cell Wall for Withstanding Ciprofloxacin

The pollution of antibiotics in aquaculture environment is increasingly serious, and excessive antibiotics will kill the probiotics in aquaculture feed. How to improve the viability of probiotics in the antibiotics-contaminated environment is of significance. In this study, a new strategy for protecting Saccharomyces cerevisiae cells in situ against antibiotics is constructed based on cell surface engineering technology by putting on wearable protective layers for cells. The protective layer is constructed around cellular surface via the self-assembly of coacervate microdroplets that consist of carboxymethyl chitosan and carboxyl dextran. Without affecting the cell viability, the protective layer can grasp ciprofloxacin and decrease the contact of ciprofloxacin to cells and consequently improve the survival rate of cells when exposing to ciprofloxacin. This work highlights a facile strategy to establish removable artificial cell wall by biodegradable polysaccharides for improving the productivity of probiotics in antibiotic environments.

An overview on enrichment methods for cell surface proteome profiling

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