Engineering Cyborg Bacteria Through Intracellular Hydrogelation

Fabrication of cyborg bacterial cells as living cell-material hybrids using intracellular hydrogelation

The production of living therapeutics, cell-based delivery of drugs and gene-editing tools and the manufacturing of bio-commodities all share a common concept: they use either a synthetic or a living cell chassis to achieve their primary engineering or therapeutic goal. Live-cell chassis face limitations inherent to their auto-replicative nature and the complexity of the cellular context. This limitation highlights the need for a new chassis combining the engineering simplicity of synthetic materials and the functionalities of natural cells. Here, we describe a protocol to assemble a synthetic polymeric network inside bacterial cells, rendering them incapable of cell division and allowing them to resist environmental stressors such as high pH, hydrogen peroxide and cell-wall-targeting antibiotics that would otherwise kill unmodified bacteria. This cellular bioengineering protocol details how bacteria can be transformed into single-lifespan devices that are resistant to environmental stressors and possess programable functionality. We designate the modified bacteria as cyborg bacterial cells. This protocol expands the synthetic biology toolset, conferring precise control over living cells and creating a versatile cell chassis for biotechnology, biomedical engineering and living therapeutics. The protocol, including the preparation of gelation reagents and chassis strain, can be completed in 4 d. The implementation of the protocol requires expertise in microbiology techniques, hydrogel chemistry, fluorescence microscopy and flow cytometry. Further functionalization of the cyborg bacterial cells and adaptation of the protocol requires skills ranging from synthetic genetic circuit engineering to hydrogel polymerization chemistries.

Engineering Cyborg Pathogens through Intracellular Hydrogelation

Synthetic biology primarily focuses on two kinds of cell chassis: living cells and nonliving systems. Living cells are autoreplicating systems that have active metabolism. Nonliving systems, including artificial cells and nanoparticles, are nonreplicating systems typically lacking active metabolism. In recent work, Cyborg bacteria that are nonreplicating-but-metabolically active have been engineered through intracellular hydrogelation. Intracellular hydrogelation is conducted by infusing gel monomers and photoactivators into cells, followed by the activation of polymerization of the gel monomers inside the cells. However, the previous work investigated only Escherichia coli cells. Extending the Cyborg-Cell method to pathogenic bacteria could enable the exploitation of their pathogenic properties in biomedical applications. Here, we focus on different strains of Pseudomonas aeruginosa, Staphylococcus aureus, and Klebsiella pneumoniae. To synthesize the Cyborg pathogens, we first reveal the impact of different hydrogel concentrations on the metabolism, replication, and intracellular gelation of Cyborg pathogens. Next, we demonstrate that the Cyborg pathogens are taken up by macrophages in a similar magnitude as wild-type pathogens through confocal microscopy and real-time PCR. Finally, we show that the macrophage that takes up the Cyborg pathogen exhibits a similar phenotypic response to the wild-type pathogen. Our work generalizes the intracellular hydrogelation approach from lab strains of E. coli to bacterial pathogens. The new Cyborg pathogens could be applied in biomedical applications ranging from drug delivery to immunotherapy.

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.

A promising strategy to improve the stability and immunogenicity of killed but metabolically active vaccines: low-temperature preparation and coating of nanoparticles

Bacteria are becoming an increasingly serious threat to human health. The emergence of super bacteria makes clinical treatment more difficult. Vaccines are one of the most effective means of preventing and treating bacterial infections. As a new class of vaccines, killed but metabolically active (KBMA) vaccines provide the immunogenicity of live vaccines and the safety of inactivated vaccines. Herein, a promising strategy is proposed to improve the stability and immunogenicity of KBMA vaccines. KBMA vaccines were produced at low temperature (4 °C), and the bacterial surface was engineered using mesoporous silica nanoparticle (MSN) coating. Compared to vaccines prepared at room temperature, the metabolic activity of KBMA vaccines prepared at 4 °C remarkably improved. Benefiting from the induction of MSNs, the stability of KBMA vaccines was increased and the preservation time was prolonged at 4 °C. Meanwhile, metabolomics analysis showed that the metabolite spectrum of live bacteria changed after photochemical treatment and MSN coating, which interfered with organic acid metabolism pathways, lipid metabolism and biosynthesis of secondary metabolites. Furthermore, the immune response in the mice treated with KBMA/MSN vaccines was similar to that in those treated with live vaccines and stronger than that in those treated with inactivated vaccines. In comparison with the control group, bacteria tissue burdens of KBMA/MSN group were significantly reduced. CD4+ T cells dominated immune responses for the protection of mice. Thus, the current work promotes the application of KBMA vaccines, providing an alternative choice for treating bacterial infections.

Intracellular Gelation-Mediated Living Bacteria for Advanced Biotherapeutics in Mouse Models

Despite its significant potential in various disease treatments and diagnostics, microbiotherapy is consistently plagued by multiple limitations ranging from manufacturing challenges to in vivo functionality. Inspired by the strategy involving nonproliferating yet metabolically active microorganisms, we report an intracellular gelation approach that can generate a synthetic polymer network within bacterial cells to solve these challenges. Specifically, poly(ethylene glycol dimethacrylate) (PEGDA, 700 Da) monomers are introduced into the bacterial cytosol through a single cycle of freeze-thawing followed by the initiation of intracellular free radical polymerization by UV light to create a macromolecular PEGDA gel within the bacterial cytosol. The molecular crowding resulting from intracytoplasmic gelation prohibits bacterial division and confers robust resistance to simulated gastrointestinal fluids and bile acids while retaining the ability to secrete functional proteins. Biocompatibility assessments demonstrate that the nondividing gelatinized bacteria are effective in alleviating systemic inflammation triggered by intravenous Escherichia coli injection. Furthermore, the therapeutic efficacy of gelatinized Lactobacillus rhamnosus in colitis mice provides additional support for this approach. Collectively, intracellular gelation indicates a universal strategy to manufacture next-generation live biotherapeutics for advanced microbiotherapy.

Bio-Hybrid Magnetic Robots: From Bioengineering to Targeted Therapy

Magnetic robots possess an innate ability to navigate through hard-to-reach cavities in the human body, making them promising tools for diagnosing and treating diseases minimally invasively. Despite significant advances, the development of robots with desirable locomotion and full biocompatibility under harsh physiological conditions remains challenging, which put forward new requirements for magnetic robots' design and material synthesis. Compared to robots that are synthesized with inorganic materials, natural organisms like cells, bacteria or other microalgae exhibit ideal properties for in vivo applications, such as biocompatibility, deformability, auto-fluorescence, and self-propulsion, as well as easy for functional therapeutics engineering. In the process, these organisms can provide autonomous propulsion in biological fluids or external magnetic fields, while retaining their functionalities with integrating artificial robots, thus aiding targeted therapeutic delivery. This kind of robotics is named bio-hybrid magnetic robotics, and in this mini-review, recent progress including their design, engineering and potential for therapeutics delivery will be discussed. Additionally, the historical context and prominent examples will be introduced, and the complexities, potential pitfalls, and opportunities associated with bio-hybrid magnetic robotics will be discussed.

Reversible Intracellular Gelation of MCF10A Cells Enables Programmable Control Over 3D Spheroid Growth

In nature, some organisms survive extreme environments by inducing a biostatic state wherein cellular contents are effectively vitrified. Recently, a synthetic biostatic state in mammalian cells is achieved via intracellular network formation using bio-orthogonal strain-promoted azide-alkyne cycloaddition (SPAAC) reactions between functionalized poly(ethylene glycol) (PEG) macromers. In this work, the effects of intracellular network formation on a 3D epithelial MCF10A spheroid model are explored. Macromer-transfected cells are encapsulated in Matrigel, and spheroid area is reduced by ≈50% compared to controls. The intracellular hydrogel network increases the quiescent cell population, as indicated by increased p21 expression. Additionally, bioenergetics (ATP/ADP ratio) and functional metabolic rates are reduced. To enable reversibility of the biostasis effect, a photosensitive nitrobenzyl-containing macromer is incorporated into the PEG network, allowing for light-induced degradation. Following light exposure, cell state, and proliferation return to control levels, while SPAAC-treated spheroids without light exposure (i.e., containing intact intracellular networks) remain smaller and less proliferative through this same period. These results demonstrate that photodegradable intracellular hydrogels can induce a reversible slow-growing state in 3D spheroid culture.

Macrophage-Based Microrobots for Anticancer Therapy: Recent Progress and Future Perspectives

Macrophages, which are part of the mononuclear phagocytic system, possess sensory receptors that enable them to target cancer cells. In addition, they are able to engulf large amounts of particles through phagocytosis, suggesting a potential "Trojan horse" drug delivery approach to tumors by facilitating the engulfment of drug-hidden particles by macrophages. Recent research has focused on the development of macrophage-based microrobots for anticancer therapy, showing promising results and potential for clinical applications. In this review, we summarize the recent development of macrophage-based microrobot research for anticancer therapy. First, we discuss the types of macrophage cells used in the development of these microrobots, the common payloads they carry, and various targeting strategies utilized to guide the microrobots to cancer sites, such as biological, chemical, acoustic, and magnetic actuations. Subsequently, we analyze the applications of these microrobots in different cancer treatment modalities, including photothermal therapy, chemotherapy, immunotherapy, and various synergistic combination therapies. Finally, we present future outlooks for the development of macrophage-based microrobots.

Special Issue "Synthetic Biology for Biosensing in Health and Environmental Applications"

Biosensors are analytical devices that utilize biological sensing elements, such as enzymes, antibodies, nucleic acids, or cells, to detect a given analyte [...].

Engineering Cyborg Bacteria Through Intracellular Hydrogelation

Natural and artificial cells are two common chassis in synthetic biology. Natural cells can perform complex tasks through synthetic genetic constructs, but their autonomous replication often causes safety concerns for biomedical applications. In contrast, artificial cells based on nonreplicating materials, albeit possessing reduced biochemical complexity, provide more defined and controllable functions. Here, for the first time, the authors create hybrid material-cell entities termed Cyborg Cells. To create Cyborg Cells, a synthetic polymer network is assembled inside each bacterium, rendering them incapable of dividing. Cyborg Cells preserve essential functions, including cellular metabolism, motility, protein synthesis, and compatibility with genetic circuits. Cyborg Cells also acquire new abilities to resist stressors that otherwise kill natural cells. Finally, the authors demonstrate the therapeutic potential by showing invasion into cancer cells. This work establishes a new paradigm in cellular bioengineering by exploiting a combination of intracellular man-made polymers and their interaction with the protein networks of living cells.