Cytocompatible Polymer Grafting from Individual Living Cells by Atom-Transfer Radical Polymerization

Protein-Polymer Conjugates as Biocompatible and Recyclable ATRP Catalysts

Atom transfer radical polymerization (ATRP) is a leading method for creating polymers with precise control over molecular weight, yet its reliance on metal catalysts limits its application in metal-sensitive and environmental contexts. Addressing these limitations, we have developed a recyclable, biocompatible, robust, and tunable ATRP catalyst composed of a protein-polymer-copper conjugate, synthesized by polymerizing an L-proline-based monomer onto bovine serum albumin and complexing with Cu(II). The use of this conjugate catalyst maintains ATRP's precision while ensuring biocompatibility with bothEscherichia coli and HEK 293 cells, and its high molecular weight allows for easy recycling through dialysis. Therefore, our efforts extend ATRP's applicability across diverse fields, including biotechnology and green chemistry, marking a significant advance toward environmentally friendly and safe polymerization technologies.

Tumor Receptor-Mediated Morphological Transformation and In Situ Polymerization of Diacetylene-Containing Lipidated Peptide Amphiphile on Cell Membranes for Tumor Suppression

In situ polymerization on cell membranes can decrease cell mobility, which may inhibit tumor growth and invasion. However, the initiation of radical polymerization traditionally requires exogenous catalysts or free radical initiators, which might cause side effects in normal tissues. Herein, we synthesized a Y-type diacetylene-containing lipidated peptide amphiphile (TCDA-KFFFFK(GRGDS)-YIGSR, Y-DLPA) targeting integrins and laminin receptors on murine mammary carcinoma 4T1 cells, which underwent nanoparticle-to-nanofiber morphological transformation and in situ polymerization on cell membranes. Specifically, the polymerized Y-DLPA induced 4T1 cell apoptosis and disturbed the substance exchange and metabolism. In vitro assays demonstrated that the polymerized Y-DLPA nanofibers decreased the migration capacity of 4T1 cells, potentially suppressing tumor invasion and metastasis. When administered locally to 4T1 tumor-bearing mice, the Y-DLPA nanoparticles formed a biomimetic extracellular matrix that effectively suppressed tumor growth. This study provides an in situ polymerization strategy that can serve as an effective drug-free biomaterial with low side effects for antitumor therapy.

Nanoencapsulation of Living Microbial Cells in Porous Covalent Organic Framework Shells

Encapsulating living cells within nanoshells offers an important approach to enhance their stability against environmental stressors and broaden their application scope. However, this often leads to impaired mass transfer at the cell biointerface. Strengthening the protective shell with well-defined, ordered transport channels is crucial to regulating molecular transport and maintaining cell viability and biofunctionality. Herein, we report the construction of covalent organic framework (COF) mesoporous shells for single-cell nanoencapsulation, providing selective permeability and comprehensive protection for living microbial cells. The COF shells ensure nutrient uptake while blocking large harmful molecules and UV-C radiation, thereby preserving cell viability and metabolic activity. Integration of such crystalline porous shells with genetically modified cell factories for metabolic production is further investigated, revealing no adverse effects, as demonstrated by riboflavin production. Moreover, the COF shell effectively shields cells, ensuring efficient bioproduction even after being treated under harsh conditions. This versatile encapsulation approach is applicable for different cell types, providing a robust platform for cell surface engineering.

Biocompatible hydrogel coating on single living cells through visible light-induced polymerization

Visible light-mediated photocatalysis leads to the efficient hydrogel coating of individual mammalian cells, functionalized with biocompatible anchor molecules tagged with fluorescein serving as a trifecta: photocatalyst, initiator, and fluorophore. NIH3T3 fibroblast cells are encapsulated within hydrogel shells of poly(ethylene glycol) diacrylate (PEGDA) and N-vinylpyrrolidone without any noticeable decrease in cell viability.

Individual cell modification with cell surface specific atom transfer radical polymerization for enhanced Cr(VI) removal

Modifying cells with polymers on the surface can enable them to gain or enhance function with various applications, wherein the atom transfer radical polymerization (ATRP) has garnered significant potential due to its biocompatibility. However, specifically initiating ATRP from the cell surface for in-situ modification remains challenging. This study established a bacterial surface-initiated ATRP method and further applied it for enhanced Cr(VI) removal. The cell surface specificity was facilely achieved by cell surface labelling with azide substrates, following alkynyl ATRP initiator specifically anchoring with azide-alkyne click chemistry. Then, the ATRP polymerization was initiated from the cell surface, and different polymers were successfully applied to in-situ modification. Further analysis revealed that the modification of Shewanella oneidensis with poly (4-vinyl pyridine) and sodium polymethacrylate improved the heavy metal tolerance and enhanced the Cr(VI) removal rate of 2.6 times from 0.088 h-1 to 0.314 h-1. This work provided a novel idea for bacterial surface modification and would extend the application of ATRP in bioremediation.

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.

Engineering Shewanella oneidensis-Carbon Felt Biohybrid Electrode Decorated with Bacterial Cellulose Aerogel-Electropolymerized Anthraquinone to Boost Energy and Chemicals Production

Interfacial electron transfer between electroactive microorganisms (EAMs) and electrodes underlies a wide range of bio-electrochemical systems with diverse applications. However, the electron transfer rate at the biotic-electrode interface remains low due to high transmembrane and cell-electrode interfacial electron transfer resistance. Herein, a modular engineering strategy is adopted to construct a Shewanella oneidensis-carbon felt biohybrid electrode decorated with bacterial cellulose aerogel-electropolymerized anthraquinone to boost cell-electrode interfacial electron transfer. First, a heterologous riboflavin synthesis and secretion pathway is constructed to increase flavin-mediated transmembrane electron transfer. Second, outer membrane c-Cyts OmcF is screened and optimized via protein engineering strategy to accelerate contacted-based transmembrane electron transfer. Third, a S. oneidensis-carbon felt biohybrid electrode decorated with bacterial cellulose aerogel and electropolymerized anthraquinone is constructed to boost the interfacial electron transfer. As a result, the internal resistance decreased to 42 Ω, 480.8-fold lower than that of the wild-type (WT) S. oneidensis MR-1. The maximum power density reached 4286.6 ± 202.1 mW m-2, 72.8-fold higher than that of WT. Lastly, the engineered biohybrid electrode exhibited superior abilities for bioelectricity harvest, Cr6+ reduction, and CO2 reduction. This study showed that enhancing transmembrane and cell-electrode interfacial electron transfer is a promising way to increase the extracellular electron transfer of EAMs.

Stimuli-Responsive Phosphate Hydrogel: A Study on Swelling Behavior, Mechanical Properties, and Application in Expansion Microscopy

Phosphorus-based stimuli-responsive hydrogels have potential in a wide range of applications due to their ionizable phosphorus groups, biocompatibility, and tunable swelling capacity utilizing hydrogel design parameters and external stimuli. In this study, poly(2-methacryloyloxyethyl phosphate) (PMOEP) hydrogels were synthesized via aqueous activators regenerated by electron transfer atomic transfer radical polymerization using ascorbic acid as the reducing agent. Swelling and deswelling behaviors of PMOEP hydrogels were examined in different salt solutions, pH conditions, and temperatures. The degree of swelling in salt solutions followed CaCl2 < MgCl2 < KCl < NaCl with a decrease in swelling rate at higher concentrations until reaching a saturation point. In water, the degree of swelling increased significantly around neutral pH and remained constant at basic pH values. The effects of polymerization conditions, including pH, temperature (30, 40, 50 °C), and MOEP concentration (40, 50, 60% v/v MOEP/H2O), on the hydrogel swelling behavior in various salt solutions were also investigated. PMOEP hydrogels showed a decrease in the degree of swelling as the pH was increased above the native pH of the monomer solution. Scanning electron microscopy and energy-dispersive spectroscopy were utilized to examine the microstructure and chemical composition of the dried hydrogel after salt solution swelling. Cytotoxicity testing using rat bone marrow stem cells confirmed the biocompatibility of the PMOEP hydrogels. A unique feature of this effort was evaluation of these phosphate hydrogels for use in expansion microscopy where a significant twofold enhancement in cellular expansion capacity was showcased utilizing 4T1 mouse breast cancer cells. This comprehensive study provides valuable insights into the stimuli-responsive behavior and expansion characteristics of phosphate hydrogels, highlighting their potential in diverse biomedical applications.

In Situ Synthesis and Assembly of Functional Materials and Devices in Living Systems

Integrating functional materials and devices with living systems enables novel methods for recording, manipulating, or augmenting organisms not accessible by traditional chemical, optical, or genetic approaches. (The term "device" refers to the fundamental components of complex electronic systems, such as transistors, capacitors, conductors, and electrodes.) Typically, these advanced materials and devices are synthesized, either through chemical or physical reactions, outside the biological systems (ex situ) before they are integrated. This is due in part to the more limited repertoire of biocompatible chemical transformations available for assembling functional materials in vivo. Given that most of the assembled bulk materials are impermeable to cell membranes and cannot go through the blood-brain barrier (BBB), the external synthesis poses challenges when trying to interface these materials and devices with cells precisely and in a timely manner and at the micro- and nanoscale─a crucial requirement for modulating cellular functions. In contrast to presynthesis in a separate location, in situ assembly, wherein small molecules or building blocks are directly assembled into functional materials within a biological system at the desired site of action, has offered a potential solution for spatiotemporal and genetic control of material synthesis and assembly. In this Account, we highlight recent advances in spatially and temporally targeted functional material synthesis and assembly in living cells, tissues and animals and provide perspective on how they may enable novel probing, modulation, or augmentation of fundamental biology. We discuss several strategies, starting from the traditional nontargeted methods to targeted assembly of functional materials and devices based on the endogenous markers of the biological system. We then focus on genetically targeted assembly of functional materials, which employs enzymatic catalysis centers expressed in living systems to assemble functional materials in specific molecular-defined cell types. We introduce the recent efforts of our group to modulate membrane capacitance and neuron excitability using in situ synthesized electrically functional polymers in a genetically targetable manner. These advances demonstrate the promise of in situ synthesis and assembly of functional materials and devices, including the optogenetic polymerization developed by our lab, to interface with cells in a cellular- or subcellular-specific manner by incorporating genetic and/or optical control over material assembly. Finally, we discuss remaining challenges, areas for improvement, potential applications to other biological systems, and novel methods for the in situ synthesis of functional materials that could be elevated by incorporating genetic or material design strategies. As researchers expand the toolkit of biocompatible in situ functional material synthetic techniques, we anticipate that these advancements could potentially offer valuable tools for exploring biological systems and developing therapeutic solutions.

Sensing, Imaging, and Therapeutic Strategies Endowing by Conjugate Polymers for Precision Medicine

Conjugated polymers (CPs) have promising applications in biomedical fields, such as disease monitoring, real-time imaging diagnosis, and disease treatment. As a promising luminescent material with tunable emission, high brightness and excellent stability, CPs are widely used as fluorescent probes in biological detection and imaging. Rational molecular design and structural optimization have broadened absorption/emission range of CPs, which are more conductive for disease diagnosis and precision therapy. This review provides a comprehensive overview of recent advances in the application of CPs, aiming to elucidate their structural and functional relationships. The fluorescence properties of CPs and the mechanism of detection signal amplification are first discussed, followed by an elucidation of their emerging applications in biological detection. Subsequently, CPs-based imaging systems and therapeutic strategies are illustrated systematically. Finally, recent advancements in utilizing CPs as electroactive materials for bioelectronic devices are also investigated. Moreover, the challenges and outlooks of CPs for precision medicine are discussed. Through this systematic review, it is hoped to highlight the frontier progress of CPs and promote new breakthroughs in fundamental research and clinical transformation.

Dopamine Polymerization-Mediated Surface Functionalization toward Advanced Bacterial Therapeutics

Bacteria-based therapy has spotlighted an unprecedented potential in treating a range of diseases, given that bacteria can be used as both drug vehicles and therapeutic agents. However, the use of bacteria for disease treatment often suffers from unsatisfactory outcomes, due largely to their suboptimal bioavailability, dose-dependent toxicity, and low targeting colonization. In the past few years, substantial efforts have been devoted to tackling these difficulties, among which methods capable of integrating bacteria with multiple functions have been extensively pursued. Different from conventional genetic engineering and modern synthetic bioengineering, surface modification of bacteria has emerged as a simple yet flexible strategy to introduce different functional motifs. Polydopamine, which can be easily formed via in situ dopamine oxidation and self-polymerization, is an appealing biomimetic polymer that has been widely applied for interfacial modification and functionalization. By virtue of its catechol groups, polydopamine can be efficiently codeposited with a multitude of functional elements on diverse surfaces.In this Account, we summarize the recent advances from our group with a focus on the interfacial polymerization-mediated functionalization of bacteria for advanced microbial therapy. First, we present the optimized strategy for bacterial surface modification under cytocompatible conditions by in situ dopamine polymerization. Taking advantage of the hydrogen bonding, π-π stacking, Michael addition, and Schiff base reaction with polydopamine, diverse functional small molecules and macromolecules are facilely codeposited onto the bacterial surface. Namely, monomodal, dual-modal, and multimodal surface modification of bacteria can be achieved by dopamine self-deposition, codeposition with a unitary composition, and codeposition with a set of multiple components, respectively. Second, we outline the regulation of bacterial functions by surface modification. The formed polydopamine surface endows bacteria with the ability to resist in vivo insults, such as gastrointestinal tract stressors and immune clearance, resulting in greatly improved bioavailability. Integration with specific ligands or therapeutic components enables the modified bacteria to increase targeting accumulation and colonization at lesion sites or play synergistic effects in disease treatment. Bacteria codeposited with different bioactive moieties, such as protein antigens, antibodies, and immunoadjuvants, are even able to actively interact with the host, particularly to elicit immune responses by either suppressing immune overactivation to promote the reversion of pathological inflammations or provoking protective innate and/or adaptive immunity to inhibit pathogenic invaders. Third, we highlight the applications of surface-modified bacteria as multifunctional living therapeutics in disease treatment, especially alleviating inflammatory bowel diseases via oral delivery and intervening in different types of cancer through systemic or intratumoral injection. Finally, we discuss the challenges and prospects of dopamine polymerization-mediated multifunctionalization for preparing advanced bacterial therapeutics as well as their bench to bedside translation. We anticipate that this Account can provide an insightful overview of bacterial therapy and inspire innovative thinking and new efforts to develop next-generation living therapeutics for treating various diseases.

Surface Functionalization with Polymer Brushes via Surface-Initiated Atom Transfer Radical Polymerization: Synthesis, Applications, and Current Challenges

Polymer brushes have received great attention in recent years due to their distinctive properties and wide range of applications. The synthesis of polymer brushes typically employs surface-initiated atom transfer radical polymerization (SI-ATRP) techniques. To realize the control of the polymerization process in different environments, various SI-ATRP techniques triggered by different stimuli have been developed. This review focuses on the latest developments in different stimuli-triggered SI-ATRP methods, such as electrochemically mediated, photoinduced, enzyme-assisted, mechanically controlled, and organocatalyzed ATRP. Additionally, SI-ATRP technology triggered by a combination of multiple stimuli sources is also discussed. Furthermore, the applications of polymer brushes in lubrication, biological applications, antifouling, and catalysis are also systematically summarized and discussed. Despite the advancements in the synthesis of various types of 1D, 2D, and 3D polymer brushes via controlled radical polymerization, contemporary challenges remain in the quest for more efficient and straightforward synthetic protocols that allow for precise control over the composition, structure, and functionality of polymer brushes. We anticipate the readers could promote the understanding of surface functionalization based on ATRP-mediated polymer brushes and envision future directions for their application in surface coating technologies.

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.

Site-selected in situ polymerization for living cell surface engineering

The construction of polymer-based mimicry on cell surface to manipulate cell behaviors and functions offers promising prospects in the field of biotechnology and cell therapy. However, precise control of polymer grafting sites is essential to successful implementation of biomimicry and functional modulation, which has been overlooked by most current research. Herein, we report a biological site-selected, in situ controlled radical polymerization platform for living cell surface engineering. The method utilizes metabolic labeling techniques to confine the growth sites of polymers and designs a Fenton-RAFT polymerization technique with cytocompatibility. Polymers grown at different sites (glycans, proteins, lipids) have different membrane retention time and exhibit differential effects on the recognition behaviors of cellular glycans. Of particular importance is the achievement of in situ copolymerization of glycomonomers on the outermost natural glycan sites of cell membrane, building a biomimetic glycocalyx with distinct recognition properties.

Red-Light-Driven Atom Transfer Radical Polymerization for High-Throughput Polymer Synthesis in Open Air

Photoinduced reversible-deactivation radical polymerization (photo-RDRP) techniques offer exceptional control over polymerization, providing access to well-defined polymers and hybrid materials with complex architectures. However, most photo-RDRP methods rely on UV/visible light or photoredox catalysts (PCs), which require complex multistep synthesis. Herein, we present the first example of fully oxygen-tolerant red/NIR-light-mediated photoinduced atom transfer radical polymerization (photo-ATRP) in a high-throughput manner under biologically relevant conditions. The method uses commercially available methylene blue (MB+) as the PC and [X-CuII/TPMA]+ (TPMA = tris(2-pyridylmethyl)amine) complex as the deactivator. The mechanistic study revealed that MB+ undergoes a reductive quenching cycle in the presence of the TPMA ligand used in excess. The formed semireduced MB (MB•) sustains polymerization by regenerating the [CuI/TPMA]+ activator and together with [X-CuII/TPMA]+ provides control over the polymerization. This dual catalytic system exhibited excellent oxygen tolerance, enabling polymerizations with high monomer conversions (>90%) in less than 60 min at low volumes (50-250 μL) and high-throughput synthesis of a library of well-defined polymers and DNA-polymer bioconjugates with narrow molecular weight distributions (Đ < 1.30) in an open-air 96-well plate. In addition, the broad absorption spectrum of MB+ allowed ATRP to be triggered under UV to NIR irradiation (395-730 nm). This opens avenues for the integration of orthogonal photoinduced reactions. Finally, the MB+/Cu catalysis showed good biocompatibility during polymerization in the presence of cells, which expands the potential applications of this method.

Graphene-encapsulated yeast cells in harsh conditions

Yeast, as a versatile microorganism, holds significant importance in various industries and research fields due to its remarkable characteristics. In the pursuit of biotechnological applications, cell-surface engineering including encapsulation has been proposed as a new strategy to interface with individual living yeast cells. While previous researches of yeast encapsulation with materials have shown promise, it often involves complex processes and lacks confirmation of condition-dependent yeast viability under harsh conditions. To address these issues, we present a rational and facile design for graphene-encapsulated yeast cells. Through a straightforward blending technique, yeast cells are encapsulated with graphene layers, demonstrating the unique properties of yeast cells in structural and functional aspects with graphene. We show graphene layer-dependent functions of yeast cells under various conditions, including pH and temperature-dependent conditions. The layer of graphene can induce the delayed lag time without the transfer of graphene-layered membrane. Our findings highlight the high potential of graphene-encapsulated yeast cells for various industrial applications, offering new avenues for exploration in biotechnology.

Catalytic metal-nucleotide coordinative cytoskeleton on algae cell towards photosynthetic hydrogen production under air

A metal-nucleotide coordinative cytoskeleton with ascorbate oxidase-like catalytic behavior was constructed on an individual algae cell wall, which endows the engineered cells with the capability of self-generating a localized hypoxic microenvironment around the cell surface, and thus allows the functionality switching from photosynthetic oxygen production to efficient hydrogen evolution for over one month.

"Dramatic Growth" of Microbial Aerosols for Visualization and Accurate Counting of Bioaerosols

While the global COVID-19 pandemic has subsided, microbial aerosol detection has become of high concern. Timely, accurate, and highly sensitive monitoring of microbial aerosols in indoor air is the basis for effective prevention and control of infectious diseases. At present, no commercial equipment or reliable technology can simultaneously control the detection time and limit at 6 h and 102 CFU/mL, respectively. Based on the "safety size range" of particulate matter in the air, we propose a new method of microbial dilation detection, which enables the pathogen to grow rapidly and dramatically into a polymeric microsphere, larger in size than the coexisting aerosol particles. "Like a crane standing among chickens", the microorganism can be easily visualized and counted. Different from routine chemical and biological sensing technologies, this method can achieve absolute counting of microbial particles, and the simple principles can be developed into devices for different life scenarios.

Surface-Initiated Zerovalent Metal-Mediated Controlled Radical Polymerization (SI-Mt0CRP) for Brush Engineering

ConspectusThe surface-tethered polymer brush has become a powerful approach to tailoring the chemical and physical properties of surfaces and interfaces and revealed broad application prospects in widespread fields such as self-cleaning, surface lubrication, and antibiofouling. Access to these diverse functional polymer brushes is highly dependent on versatile and powerful surface-initiated controlled radical polymerization (SI-CRP) strategies. However, conventional SI-CRP typically requires oxygen exclusion, large amounts of catalysts and monomer solution, and a long reaction time, making it time-consuming and sophisticated. When using a two-plate system consisting of an initiator-bearing substrate and a metal plate, we and our collaborators introduced surface-initiated zerovalent metal-mediated controlled radical polymerization (SI-Mt0CRP). In the SI-Mt0CRP setup, a metal(0) plate (Cu, Fe, Zn, or Sn) is placed proximately to an initiator-functionalized substrate and forms a confined polymerization system which considerably simplifies the synthesis of a wide range of polymer brushes with high grafting densities over large areas (up to the meter scale).In comparison to classical SI-ATRP (catalyzed by metal salts), SI-Mt0CRP demonstrates oxygen tolerance, high controllability, good retention of chain-end functionality, and facile recyclability of the metal catalysts (i.e., metal foil/plate). Taking advantage of the confined geometry of the SI-Mt0CRP setup, polymer brushes with various conformations and architectures are easily accessible while consuming only microliter volumes of monomer solution and without complicated operations under ambient conditions. Owing to these attractive characteristics, SI-Mt0CRP has become a versatile technique for functionalizing materials for targeted applications, ranging from the areas of surface science to materials science and nanotechnology.In this Account, we summarize the recent advances of SI-Mt0CRP catalyzed by zerovalent metals (e.g., Cu, Fe, Zn, and Sn) and highlight the intrinsic advantages of the featured experimental setup, compared with the "classical" SI-CRP in which metal salt, powder, or wire is applied. We further discuss the synthetic features and proposed mechanism of SI-Mt0CRP while emphasizing the various external technologies' (including "on water" reaction, galvanic replacement, lithography, and capillary microfluidic) integrated polymerization systems. We also describe structural polymer brushes, including block copolymers, patterned and gradient structures, and arrayed and binary polymer brushes. Finally, we introduce the diverse polymer brushes that have been prepared using these techniques, with a focus on targeted and emerging applications. We anticipate that the discussion presented in this Account will promote a better understanding of the SI-Mt0CRP technique and advance the future development of practical surface brushing.

Tyrosine residues initiated photopolymerization in living organisms

Towards intracellular engineering of living organisms, the development of new biocompatible polymerization system applicable for an intrinsically non-natural macromolecules synthesis for modulating living organism function/behavior is a key step. Herein, we find that the tyrosine residues in the cofactor-free proteins can be employed to mediate controlled radical polymerization under 405 nm light. A proton-coupled electron transfer (PCET) mechanism between the excited-state TyrOH* residue in proteins and the monomer or the chain transfer agent is confirmed. By using Tyr-containing proteins, a wide range of well-defined polymers are successfully generated. Especially, the developed photopolymerization system shows good biocompatibility, which can achieve in-situ extracellular polymerization from the surface of yeast cells for agglutination/anti-agglutination functional manipulation or intracellular polymerization inside yeast cells, respectively. Besides providing a universal aqueous photopolymerization system, this study should contribute a new way to generate various non-natural polymers in vitro or in vivo to engineer living organism functions and behaviours.

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.

Surface-Initiated Synthesis of Cell-Specific Glycopolymers Using Live Mammalian Cells as Templates

Molecular recognition is an important process in life activities where specificity is the key. However, the method to gain specificity are often complex and time-consuming. Herein, a novel, versatile, and effective way is developed to obtain cell-specific glycosurfaces by surface-initiated Cu-mediated reversible deactivation radical polymerization (Cu-RDRP) in an open to air fashion. Mammalian cells are used for the first time as live templates to realize cell-sugar monomer-aptation-polymerization which can produce cell-specific glycosurfaces. Both epithelial cell adhesion molecule (EpCAM) positive cells L929 and EpCAM negative cells Hela as models are used to acquire two cell-specific glycosurfaces, which can distinguish template-cells from others. The strategy is effective and convenient without the need of fixative pretreatment of cells. It is found that the specific capture does not rely on EpCAM antibodies, and the specificity is related to the composition and chain sequence of the glycopolymer brushes rather than surface morphology. In addition, these glycosurfaces keep the ability to identify the target cells after ten regenerative treatments, which provides another advantage for practical applications.

Tinware-Inspired Aerobic Surface-Initiated Controlled Radical Polymerization (SI-Sn0CRP) for Biocompatible Surface Engineering

Surface anchored polymer brushes prepared by surface-initiated controlled radical polymerization (SI-CRP) have raised considerable interest in biomaterials and bioengineering. However, undesired residues of noxious transition metal catalysts critically restrain their widespread biomedical applications. Herein, we present a robust and biocompatible surface-initiated controlled radical polymerization catalyzed by a Sn(0) sheet (SI-Sn⁰CRP) under ambient conditions. Through this approach, microliter volumes of vinyl monomers with diverse functions (heterocyclic, ionic, hydrophilic, and hydrophobic) could be efficiently converted to homogeneous polymer brushes. The excellent controllability of SI-Sn⁰CRP strategy is further demonstrated by the exquisite fabrication of predetermined block and patterned polymer brushes through chain extension and photolithography, respectively. Additionally, in virtue of intrinsic biocompatibility of Sn, the resultant polymer brushes present transcendent affinity toward blood and cell, in marked contrast to those of copper-based approaches. This strategy could provide an avenue for the controllable fabrication of biocompatible polymer brushes toward biological applications.

Polymer Chemistry in Living Cells

The polymerization of biomolecules is a central operation in biology that connects molecular signals with proliferative and information-rich events in cells. As molecules arrange precisely across 3-D space, they create new functional capabilities such as catalysis and transport highways and exhibit new phase separation phenomena that fuel nonequilibrium dynamics in cells. Hence, the observed polymer chemistry manifests itself as a molecular basis leading to cellular phenotypes, expressed as a multitude of hierarchical structures found in cell biology. Although many milestone discoveries had accompanied the rise of the synthetic polymer era, fundamental studies were realized within a closed, pristine environment and that their behavior in a complex multicomponent system remains challenging and thus unexplored. From this perspective, there is a rich trove of undiscovered knowledge that awaits the polymer science community that can revolutionize understanding in the interactive nanoscale world of the living cell.In this Account, we discuss the strategies that have enabled synthetic polymer chemistry to be conducted within the cells (membrane inclusive) and to establish monomer design principles that offer spatiotemporal control of the polymerization. As reaction considerations such as monomer concentration, polymer growth dynamics, and reactivities are intertwined with the subcellular environment and transport processes, we first provide a chemical narrative of each major cellular compartment. The conditions within each compartment will therefore set the boundaries on the type of polymer chemistry that can be conducted. Both covalent and supramolecular polymerization concepts are explored separately in the context of scaffold design, polymerization mechanism, and activation. To facilitate transport into a localized subcellular space, we show that monomers can be reversibly modified by targeting groups or stimulus-responsive motifs that react within the specific compartment. Upon polymerization, we discuss the characterization of the resultant polymeric structures and how these phase-separated structures would impact biological processes such as cell cycle, metabolism, and apoptosis. As we begin to integrate cellular biochemistry with in situ polymer science, we identify landmark challenges and technological hurdles that, when overcome, would lead to invaluable discoveries in macromolecular therapeutics and biology.

Open-air green-light-driven ATRP enabled by dual photoredox/copper catalysis

Photoinduced atom transfer radical polymerization (photo-ATRP) has risen to the forefront of modern polymer chemistry as a powerful tool giving access to well-defined materials with complex architecture. However, most photo-ATRP systems can only generate radicals under biocidal UV light and are oxygen-sensitive, hindering their practical use in the synthesis of polymer biohybrids. Herein, inspired by the photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization, we demonstrate a dual photoredox/copper catalysis that allows open-air ATRP under green light irradiation. Eosin Y was used as an organic photoredox catalyst (PC) in combination with a copper complex (X-CuII/L). The role of PC was to trigger and drive the polymerization, while X-CuII/L acted as a deactivator, providing a well-controlled polymerization. The excited PC was oxidatively quenched by X-CuII/L, generating CuI/L activator and PC˙+. The ATRP ligand (L) used in excess then reduced the PC˙+, closing the photocatalytic cycle. The continuous reduction of X-CuII/L back to CuI/L by excited PC provided high oxygen tolerance. As a result, a well-controlled and rapid ATRP could proceed even in an open vessel despite continuous oxygen diffusion. This method allowed the synthesis of polymers with narrow molecular weight distributions and controlled molecular weights using Cu catalyst and PC at ppm levels in both aqueous and organic media. A detailed comparison of photo-ATRP with PET-RAFT polymerization revealed the superiority of dual photoredox/copper catalysis under biologically relevant conditions. The kinetic studies and fluorescence measurements indicated that in the absence of the X-CuII/L complex, green light irradiation caused faster photobleaching of eosin Y, leading to inhibition of PET-RAFT polymerization. Importantly, PET-RAFT polymerizations showed significantly higher dispersity values (1.14 ≤ Đ ≤ 4.01) in contrast to photo-ATRP (1.15 ≤ Đ ≤ 1.22) under identical conditions.

Biomimetic materials based on zwitterionic polymers toward human-friendly medical devices

This review summarizes recent research on the design of polymer material systems based on biomimetic concepts and reports on the medical devices that implement these systems. Biomolecules such as proteins, nucleic acids, and phospholipids, present in living organisms, play important roles in biological activities. These molecules are characterized by heterogenic nature with hydrophilicity and hydrophobicity, and a balance of positive and negative charges, which provide unique reaction fields, interfaces, and functionality. Incorporating these molecules into artificial systems is expected to advance material science considerably. This approach to material design is exceptionally practical for medical devices that are in contact with living organisms. Here, it is focused on zwitterionic polymers with intramolecularly balanced charges and introduce examples of their applications in medical devices. Their unique properties make these polymers potential surface modification materials to enhance the performance and safety of conventional medical devices. This review discusses these devices; moreover, new surface technologies have been summarized for developing human-friendly medical devices using zwitterionic polymers in the cardiovascular, cerebrovascular, orthopedic, and ophthalmology fields.

Bacteria-mediated in situ polymerization of peptide-modified acrylamide for enhancing antimicrobial activity

Bacteria-mediated reactions can utilize the natural activities of bacteria to produce bioactive products. Here, bacteria-mediated polymerization of the acrylamide-functionalized peptide Trp-Arg-Lys (Am-WRK) afforded an antibacterial polymer, PAm-WRK, which simulates the cationic and hydrophobic structures of antimicrobial peptides. Facultative anaerobes with strong reductive abilities exhibited better reactivity and achieved selective antibacterial effects through non-covalent interactions with bacterial membranes. This bacteria-mediated synthesis of AMP-mimic polymers provides a new strategy for overcoming bacterial resistance and for the in situ generation of bioactive functional materials.

Artificially sporulated Escherichia coli cells as a robust cell factory for interfacial biocatalysis

The natural bacterial spores have inspired the development of artificial spores, through coating cells with protective materials, for durable whole-cell catalysis. Despite attractiveness, artificial spores developed to date are generally limited to a few microorganisms with their natural endogenous enzymes, and they have never been explored as a generic platform for widespread synthesis. Here, we report a general approach to designing artificial spores based on Escherichia coli cells with recombinant enzymes. The artificial spores are simply prepared by coating cells with polydopamine, which can withstand UV radiation, heating and organic solvents. Additionally, the protective coating enables living cells to stabilize aqueous-organic emulsions for efficient interfacial biocatalysis ranging from single reactions to multienzyme cascades. Furthermore, the interfacial system can be easily expanded to chemoenzymatic synthesis by combining artificial spores with metal catalysts. Therefore, this artificial-spore-based platform technology is envisioned to lay the foundation for next-generation cell factory engineering.

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.

In situ silver nanoparticle coating of virions for quantification at single virus level

In situ labelling and encapsulation of biological entities, such as of single viruses, may provide a versatile approach to modulate their functionality and facilitate their detection at single particle level. Here, we introduce a novel virus metallization approach based on in situ coating of viruses in solution with silver nanoparticles (AgNP) in a two-step synthetic process, i.e. surface activation with a tannic acid - Sn(II) coordination complex, which subsequently induces silver ion (I) reduction. The metalic coating on the virus surface opens the opportunity for electrochemical quantification of the AgNP-tagged viruses by nano-impact electrochemistry on a microelectrode with single particle sensitivity, i.e. enable the detection of particles oherwise undetectable. We show that the silver coating of the virus particles impacting the electrode can be oxidized to produce distinct current peaks the frequency of which show a linear correlation with the virus count. The proof of the concept was done with inactivated Influenza A (H3N2) viruses resulting in their quantitation down to the femtomolar concentrations (ca. 5 × 10⁷ particles per mL) using 50 s counting sequences.

A comparison of RAFT and ATRP methods for controlled radical polymerization

Reversible addition-fragmentation chain-transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP) are the two most common controlled radical polymerization methods. Both methods afford functional polymers with a predefined length, composition, dispersity and end group. Further, RAFT and ATRP tame radicals by reversibly converting active polymeric radicals into dormant chains. However, the mechanisms by which the ATRP and RAFT methods control chain growth are distinct, so each method presents unique opportunities and challenges, depending on the desired application. This Perspective compares RAFT and ATRP by identifying their mechanistic strengths and weaknesses, and their latest synthetic applications.

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.

Site-Selective and Biocompatible Growth of Polymers from Glycan Moieties of Glycoproteins and Living Cells

Formation of protein-polymer conjugates (PPCs) is critical for many studies in chemical biology, biomedicine, and enzymatic catalysis. Polymers with coordinated physicochemical properties confer synergistic functions to PPCs that overcome the inherent limitation of proteins. However, application of PPCs has been synthetically restricted by the limited modification sites and polymer grafting method. Here, we present a versatile strategy for site-selective PPC synthesis. The initiator was specifically tethered to the preoxidized glycan moieties through oxime chemistry. Polymer brushes were grown in situ from the glycan by atom-transfer radical polymerization to generate well-controlled PPCs. Notably, the modification is site-specific, multivalent, and alterable depending on protein glycosylation. Additionally, we demonstrated that the cytocompatible method enabled the growth of polymer chains from the surface of living yeast cells. These results verified a facile technology for surface modification of biomacromolecules by desired polymers for various biomedical applications.

Oxidative Polymerization in Living Cells

Intracellular polymerization is an emerging technique that can potentially modulate cell behavior, but remains challenging because of the complexity of the cellular environment. Herein, taking advantage of the chemical properties of organotellurides and the intracellular redox environment, we develop a novel oxidative polymerization reaction that can be conducted in cells without external stimuli. We demonstrate that this polymerization reaction is triggered by the intracellular reactive oxygen species (ROS), thus selectively proceeding in cancer cells and inducing apoptosis via a unique self-amplification mechanism. The polymerization products are shown to disrupt intracellular antioxidant systems through interacting with selenoproteins, leading to greater oxidative stress that would further the oxidative polymerization and eventually activate ROS-related apoptosis pathways. The selective anticancer efficacy and biosafety of our strategy are proven both in vitro and in vivo. Ultimately, this study enables a new possibility for chemists to manipulate cellular proliferation and apoptosis through artificial chemical reactions.

Reverse Actuation of Polyelectrolyte Effect for In Vivo Antifouling

Zwitterionic polymers have extraordinary properties, that is, significant hydration and the so-called antipolyelectrolyte effect, which make them suitable for biomedical applications. The hydration induces an antifouling effect, and this has been investigated significantly. The antipolyelectrolyte effect refers to the extraordinary ion-responsive behavior of particular polymers that swell and hydrate considerably in physiological solutions. This actuation begins to attract attention to achieve in vivo antifouling that is challenging for general polyelectrolytes. In this study, we established the sophisticated cornerstone of the antipolyelectrolyte effect in detail, including (i) the essential parameters, (ii) experimental verifications, and (iii) effect of improving antifouling performance. First, we find that both osmotic force and charge screening are essential factors. Second, we identify the antipolyelectrolyte effect by visualizing the swelling and hydration dynamics. Finally, we verify that the antifouling performance can be enhanced by exploiting the antipolyelectrolyte effect and report reduction of 85% and 80% in ex and in vivo biofilm formation, respectively.

Making ATRP More Practical: Oxygen Tolerance

Atom-transfer radical polymerization (ATRP) is a well-known technique for the controlled polymerization of vinyl monomers under mild conditions. However, as with any other radical polymerization, ATRP typically requires rigorous oxygen exclusion, making it time-consuming and challenging to use by nonexperts. In this Account, we discuss various approaches to achieving oxygen tolerance in ATRP, presenting the overall progress in the field.Copper-mediated ATRP, which we first discovered in the late 1990s, uses a Cu^I/L activator that reversibly reacts with the dormant C(sp³)-X polymer chain end, forming a X-Cu^II/L deactivator and a propagating radical. Oxygen interferes with activation and chain propagation by quenching the radicals and oxidizing the activator. At ATRP equilibrium, the activator is present at a much higher concentration than the propagating radicals. Thus, oxidation of the activator is the dominant inhibition pathway. In conventional ATRP, this reaction is irreversible, so oxygen must be strictly excluded to achieve good results.Over the last two decades, our group has developed several ATRP techniques based on the concept of regenerating the activator. When the oxidized activator is continuously converted back to its active reduced form, then the catalytic system itself can act as an oxygen scavenger. Regeneration can be accomplished by reducing agents and photo-, electro-, and mechanochemical stimuli. This family of methods offers a degree of oxygen tolerance, but most of them can tolerate only a limited amount of oxygen and do not allow polymerization in an open vessel.More recently, we discovered that enzymes can be used in auxiliary catalytic systems that directly deoxygenate the reaction medium and protect the polymerization process. We developed a method that uses glucose oxidase (GOx), glucose, and sodium pyruvate to very effectively scavenge oxygen and enable open-vessel ATRP. By adding a second enzyme, horseradish peroxidase (HPR), we managed to extend the role of the auxiliary enzymatic system to generating carbon-based radicals and changed ATRP from an oxygen-sensitive to an oxygen-fueled reaction.While performing control experiments for the enzymatic methods, we noticed that using sodium pyruvate under UV irradiation triggers polymerization without the presence of GOx. This serendipitous discovery allowed us to develop the first oxygen-proof, small-molecule-based, photoinduced ATRP system. It has oxygen tolerance similar to that of the enzymatic methods, exhibits superior compatibility with both aqueous media and organic solvents, and avoids problems associated with purifying polymers from enzymes. The system was able to rapidly polymerize N-isopropylacrylamide, a challenging monomer, with a high degree of control.These contributions have substantially simplified the use of ATRP, making it more practical and accessible to everyone.

Engineering exosome polymer hybrids by atom transfer radical polymerization

Exosomes are emerging as ideal drug delivery vehicles due to their biological origin and ability to transfer cargo between cells. However, rapid clearance of exogenous exosomes from the circulation as well as aggregation of exosomes and shedding of surface proteins during storage limit their clinical translation. Here, we demonstrate highly controlled and reversible functionalization of exosome surfaces with well-defined polymers that modulate the exosome's physiochemical and pharmacokinetic properties. Using cholesterol-modified DNA tethers and complementary DNA block copolymers, exosome surfaces were engineered with different biocompatible polymers. Additionally, polymers were directly grafted from the exosome surface using biocompatible photo-mediated atom transfer radical polymerization (ATRP). These exosome polymer hybrids (EPHs) exhibited enhanced stability under various storage conditions and in the presence of proteolytic enzymes. Tuning of the polymer length and surface loading allowed precise control over exosome surface interactions, cellular uptake, and preserved bioactivity. EPHs show fourfold higher blood circulation time without altering tissue distribution profiles. Our results highlight the potential of precise nanoengineering of exosomes toward developing advanced drug and therapeutic delivery systems using modern ATRP methods.

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.

DNA-Polymer Nanostructures by RAFT Polymerization and Polymerization-Induced Self-Assembly

Nanostructures derived from amphiphilic DNA-polymer conjugates have emerged prominently due to their rich self-assembly behavior; however, their synthesis is traditionally challenging. Here, we report a novel platform technology towards DNA-polymer nanostructures of various shapes by leveraging polymerization-induced self-assembly (PISA) for polymerization from single-stranded DNA (ssDNA). A "grafting from" protocol for thermal RAFT polymerization from ssDNA under ambient conditions was developed and utilized for the synthesis of functional DNA-polymer conjugates and DNA-diblock conjugates derived from acrylates and acrylamides. Using this method, PISA was applied to manufacture isotropic and anisotropic DNA-polymer nanostructures by varying the chain length of the polymer block. The resulting nanostructures were further functionalized by hybridization with a dye-labelled complementary ssDNA, thus establishing PISA as a powerful route towards intrinsically functional DNA-polymer nanostructures.

Single-Cell Nanoencapsulation: From Passive to Active Shells

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

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

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