Mastering Complexity: Towards Bottom-up Construction of Multifunctional Eukaryotic Synthetic Cells

12-Hydroxyoctadecanoic acid forms two kinds of supramolecular gels in nanostructured protic ionic liquids

HYPOTHESIS

We postulate that the amphiphilic nanostructure of ionic liquids, consisting of interpenetrating networks of polar and apolar domains, may enable them to support distinct self-assembled organogel-like and hydrogel-like structures.

EXPERIMENTS

The structures of gels formed by the low molecular weight gelator 12-hydroxystearic acid (12HSA) and its ammonium salts have been investigated from the molecular to the microscale by a combination of powder X-ray diffraction, SAXS/WAXS, FTIR, CD, and optical microscopy, together with rheological characterisation of the gels formed.

FINDINGS

12HSA is shown to form long-lived ionogels in ethylammonium and propylammonium nitrate ionic liquids at low concentrations via two distinct mechanisms; supramolecular, hydrogen-bond driven aggregation of the acid and amphiphilic assembly of the conjugate base. 12HSA gel structures were shown to consist of high aspect-ratio twisted crystalline fibrils assembled from H-bonded dimers, similar to organogels, while 12HS salts form an elongated rectangular ribbon of solvophobically-associated lamellar stacks with an opposite twist to the acid form. Partial neutralisation of 12HSA gels with base can generate coexisting mixtures of both types of gel in these ILs.

Nuclear Assembly in Giant Unilamellar Vesicles Encapsulating Xenopus Egg Extract

The reconstitution of a cell nucleus in a lipid bilayer-enclosed synthetic cell makes great strides in bottom-up synthetic biology. In this study, a method for assembling a nucleus in giant unilamellar vesicles (GUVs) is proposed. To induce reconstitution of the nucleus, the interphase egg extract of African clawed frogs Xenopus laevis is utilized, known as a biochemically controllable cell-free system capable of transforming an added sperm chromatin into a nucleus in vitro. The GUV formation efficiency is enhanced by the inverted emulsion method through incorporating prolonged waiting time and adding chloroform into lipid-dispersed oil, facilitating subsequent nuclear assembly reactions in the GUVs. Characterization of nucleus-like structures formed in the GUVs revealed the presence of dense DNA and accumulated GFP-NLS in the structure, indicative of functional nuclear import. Immunostaining further validated the presence of nuclear pore complexes on the surfaces of these nucleus-like structures. The approach offers a versatile platform for constructing artificial cellular systems that closely mimic eukaryotic cells.

Genetic encoding and expression of RNA origami cytoskeletons in synthetic cells

Bottom-up synthetic biology seeks to engineer a cell from molecular building blocks. Using DNA nanotechnology, building blocks, such as cytoskeletons, have been reverse-engineered. However, DNA nanostructures rely on chemical synthesis and thermal annealing, and therefore synthetic cells cannot produce them from their constituents such as nucleotides. Here we introduce RNA origami cytoskeleton mimics as alternative nucleic acid-based molecular hardware for synthetic cells, which we express directly inside giant unilamellar lipid vesicles (GUVs) containing a DNA template and a polymerase, chemically fuelled by feeding nucleotides from the outside. We designed RNA origami tiles that fold upon transcription and self-assemble into micrometre-long, three-dimensional RNA origami nanotubes under isothermal conditions. We observe that sequence mutations on the DNA template lead to RNA origami nanotubes and closed-ring phenotypes. Molecular dynamics simulations show that these phenotypic transitions are governed by alterations in the stability of RNA secondary structures. In addition, we achieve cortex formation with aptamer-functionalized RNA nanotubes and show that nanotube polymerization leads to membrane deformation. Altogether, our data suggest that the expression of RNA origami-based hardware will help to explore active, evolvable and RNA-based synthetic cells.

Alternating Binary Droplets-Based Protocell Networks Driven by Heterogeneous Liquid-Liquid Phase Separation

As the emergence of prototissues promotes the evolutionary transformations of protolife, tissue-like networks derived from cytomimetic systems have been studied by using artificial cells as building blocks to mimic prototissues at a higher organizational level. However, liquid-like networks originating from liquid-liquid phase separation (LLPS), especially heterogeneous LLPS, are less reported. Herein, we report a binary liquid droplet-based protocell network composed of coacervates and aqueous two-phase systems (ATPS) droplets arranged in an alternating sequence, integrating both associative and segregative LLPS. This network with worm-like chains can be specifically achieved only when the attached droplets are partially engulfed, mediated by the interfacial tension between coacervate and ATPS droplets. Notably, the interconnected droplets within the network are capable of spatially self-sorting of biomacromolecules into separate domains, thereby facilitating biomacromolecular extraction and biological reactions within designated droplets. Upon changes in the external environment, the network can be reconfigured to enable morphological regulation of trienzymatic cascade reactions. Overall, this work highlights that an all-aqueous network, coupling both associative and segregative LLPS, can be engineered as a possible route toward a hybrid prototissue-like system, offering new insights into the design of higher-ordered biomimetic systems utilizing liquid soft matter.

STAT Signature Dish: Serving Immunity with a Side of Dietary Control

Immunity is a fundamental aspect of animal biology, defined as the host's ability to detect and defend against harmful pathogens and toxic substances to preserve homeostasis. However, immune defenses are metabolically demanding, requiring the efficient allocation of limited resources to balance immune function with other physiological and developmental needs. To achieve this balance, organisms have evolved sophisticated signaling networks that enable precise, context-specific responses to internal and external cues. These networks are essential for survival and adaptation in multicellular systems. Central to this regulatory architecture is the STAT (signal transducer and activator of Transcription) family, a group of versatile signaling molecules that govern a wide array of biological processes across eukaryotes. STAT signaling demonstrates remarkable plasticity, from orchestrating host defense mechanisms to regulating dietary metabolism. Despite its critical role, the cell-specific and context-dependent nuances of STAT signaling remain incompletely understood, highlighting a significant gap in our understanding. This review delves into emerging perspectives on immunity, presenting dynamic frameworks to explore the complexity and adaptability of STAT signaling and the underlying logic driving cellular decision-making. It emphasizes how STAT pathways integrate diverse physiological processes, from immune responses to dietary regulation, ultimately supporting organismal balance and homeostasis.

Public attitudes to potential synthetic cells applications: Pragmatic support and ethical acceptance

Synthetic cells constructed bottom-up represent a novel direction in Synthetic Biology. It has the potential to deepen the scientific understanding of life and, in the longer run, to open up new pathways for medical and environmental applications. Mapping preliminary public attitudes towards emerging technologies is an important step to further societal discussion and stakeholder participation. We conducted a vignette survey with nationally representative samples from 13 European countries (Czech Republic, France, Germany, Greece, Hungary, Italy, the Netherlands, Poland, Romania, Spain, Sweden, Turkey, and UK; N =  8,382) to explore public attitudes towards prospective synthetic cell technologies, such as anticancer therapy, CO2 emissions conversion to biofuel, and industrial waste recycling. Using data-driven techniques, we built a decision tree model of the factors affecting participants' attitudes and summarized the prevalent themes behind one's motivation. Our findings suggest substantial public support for prospective synthetic cell applications in the societally beneficial fields, most notably in healthcare.

Spontaneous Emergence of Lipid Vesicles in a Coacervate-Based Compartmentalized System

The spontaneous emergence of lipid vesicles in the absence of evolved biological machinery represents a major challenge for bottom-up synthetic biology. We show that coacervate microdroplets could create a compartmentalized environment that enriches lipid molecules and facilitates their spontaneous assembly into lipid vesicles. These vesicles can escape from the coacervate microdroplets in a continuous process under non-equilibrium conditions, resembling a constant production process akin to a "primitive enzyme" factory assembly line. These findings significantly extend our understanding of the intricate interaction between lipid molecules and coacervate microdroplets, shedding light on the emergence of cellular systems and offering a new perspective on the conditions necessary for the development of life on Earth.

SNARE-Mediated Membrane Fusion Probed Using a Synthetic Organelle in the Living Bacterium

Studies on the mechanisms and regulation of functional assemblies of SNARE proteins mediating membrane fusion essentially make use of recombinant proteins and artificial phospholipid bilayers. We have developed an easy-to-use in vivo system reconstituting membrane fusion in living bacteria. It relies on the formation of caveolin-dependent intracytoplasmic cisternae followed by the controlled synthesis of members of the synaptic SNARE machinery. Only when a SNARE complex is formed with its intact components does the docking and subsequent fusion occur between the cisternae and the plasma membrane that is accompanied by the disappearance of the former. The phenotypic response of the bacterial cell to fusion events is a remarkable increase in cell body length due to an expansion of the plasma membrane. Therefore, such an easy-to-observe phenotype makes this system amenable to structure-function studies of SNAREs. We describe here the specific ways to produce caveolin and the SNARE proteins from compatible plasmids upon bacterial transformation and to obtain the elongated cell phenotype. We also provide protocols to carry out the preparation of cell culture samples suitable for biochemical and light microscopy analysis.

Tyrosinase Oxidative Cross-Linking in the Cell-Like Crowded Microenvironment for Visible Inhibitor Screening

Owing to many diseases and disorders being caused by dysfunctional or over/underexpressed enzymes, screening for inhibitors of pharmacologically relevant enzymes has emerged as a promising tool for drug discovery, clinical diagnostics, enzyme engineering, and other medical fields. However, despite the recent advances, most inhibitor screenings are still usually conducted in dilute media, at concentrations far from the media in which the enzymes are actually found, which may cause drugs to fail when translated to in vivo. Herein, we build a gel-like intracellular biological environment in vitro using a tyrosinase oxidative cross-linking hydrogel system that is closer to the real catalytic environment of enzymes. We report a straightforward and effective inhibitor evaluation strategy that can quickly compare the inhibitory strengths of inhibitors based on the principle that adding inhibitors causes color changes and mechanical changes in the system. Enabled by molecular docking, we further demonstrate the different performances of the inhibitors at different concentrations. By construction of the cell-like crowded environment in vitro, this system shows an appealing application prospect for new drug development.

Biomimetic Materials to Fabricate Artificial Cells

As the foundation of life, a cell is generally considered an advanced microreactor with a complicated structure and function. Undeniably, this fascinating complexity motivates scientists to try to extricate themselves from natural living matter and work toward rebuilding artificial cells in vitro. Driven by synthetic biology and bionic technology, the research of artificial cells has gradually become a subclass. It is not only held import in many disciplines but also of great interest in its synthesis. Therefore, in this review, we have reviewed the development of cell and bionic strategies and focused on the efforts of bottom-up strategies in artificial cell construction. Different from starting with existing living organisms, we have also discussed the construction of artificial cells based on biomimetic materials, from simple cell scaffolds to multiple compartment systems, from the construction of functional modules to the simulation of crucial metabolism behaviors, or even to the biomimetic of communication networks. All of them could represent an exciting advance in the field. In addition, we will make a rough analysis of the bottlenecks in this field. Meanwhile, the future development of this field has been prospecting. This review may bridge the gap between materials engineering and life sciences, forming a theoretical basis for developing various life-inspired assembly materials.

Bottom-up synthetic immunology

Infectious diseases and cancer evade immune surveillance using similar mechanisms. Targeting immune mechanisms using common strategies thus represents a promising avenue to improve prevention and treatment. Synthetic immunology can provide such strategies by applying engineering principles from synthetic biology to immunology. Synthetic biologists engineer cells by top-down genetic manipulation or bottom-up assembly from nanoscale building blocks. Recent successes in treating advanced tumours and diseases using genetically engineered immune cells highlight the power of the top-down synthetic immunology approach. However, genetic immune engineering is mostly limited to ex vivo applications and is subject to complex counter-regulation inherent to immune functions. Bottom-up synthetic biology can harness the rich nanotechnology toolbox to engineer molecular and cellular systems from scratch and equip them with desired functions. These are beginning to be tailored to perform targeted immune functions and should hence allow intervention strategies by rational design. In this Perspective we conceptualize bottom-up synthetic immunology as a new frontier field that uses nanotechnology for crucial innovations in therapy and the prevention of infectious diseases and cancer.

Synthetic biology in plants

Synthetic biology, an interdisciplinary field at the intersection of engineering and biology, has garnered considerable attention for its potential applications in plant science. By exploiting engineering principles, synthetic biology enables the redesign and construction of biological systems to manipulate plant traits, metabolic pathways, and responses to environmental stressors. This review explores the evolution and current state of synthetic biology in plants, highlighting key achievements and emerging trends. Synthetic biology offers innovative solutions to longstanding challenges in agriculture and biotechnology for improvement of nutrition and photosynthetic efficiency, useful secondary metabolite production, engineering biosensors, and conferring stress tolerance. Recent advances, such as genome editing technologies, have facilitated precise manipulation of plant genomes, creating new possibilities for crop improvement and sustainable agriculture. Despite its transformative potential, ethical and biosafety considerations underscore the need for responsible deployment of synthetic biology tools in plant research and development. This review provides insights into the burgeoning field of plant synthetic biology, offering a glimpse into its future implications for food security, environmental sustainability, and human health.

Compound giant unilamellar vesicles as a bio-mimetic model for electrohydrodynamics of a nucleate cell

The understanding obtained by studies on the electrohydrodynamics (EHD) of single giant unilamellar vesicles (sGUVs) has contributed significantly towards a better comprehension of the response of biological cells to electric fields. This has subsequently helped in developing technologies such as cell dielectrophoresis and cell electroporation. For nucleate eukaryotic cells though, a vesicle-in-vesicle compound giant unilamellar vesicle (cGUV) is a more appropriate bio-mimic than a sGUV. In this work, we present an improvised method for the formation of cGUVs, wherein the electrical conductivities of the inner, annular and outer regions of the cGUVs can be modified. A comprehensive experimental study is presented on the EHD of these cGUVs under weak AC fields over a wide range of frequencies, and an encouraging agreement is observed between the experiments and earlier published theoretical studies on concentric cGUVs. The spherical, prolate or oblate spheroidal deformations of a cGUV under AC electric fields depend upon the membrane electromechanical properties as well as the magnitude and direction of the electric traction at the membrane produced by the Maxwell stress that varies with the relative timescales associated with the frequency of the applied AC electric field and that of the membrane charging time and the Maxwell-Wagner relaxation time. This work establishes cGUVs as appropriate bio-mimics for conducting EHD studies relevant to eukaryotic cells.

Functional Integration of Synthetic Cells into 3D Microfluidic Devices for Artificial Organ-On-Chip Technologies

Microfluidics plays a pivotal role in organ-on-chip technologies and in the study of synthetic cells, especially in the development and analysis of artificial cell models. However, approaches that use synthetic cells as integral functional components for microfluidic systems to shape the microenvironment of natural living cells cultured on-chip are not explored. Here, colloidosome-based synthetic cells are integrated into 3D microfluidic devices, pioneering the concept of synthetic cell-based microenvironments for organs-on-chip. Methods are devised to create dense and stable networks of silica colloidosomes, enveloped by supported lipid bilayers, within microfluidic channels. These networks promote receptor-ligand interactions with on-chip cultured cells. Furthermore, a technique is introduced for the controlled release of growth factors from the synthetic cells into the channels, using a calcium alginate-based hydrogel formation within the colloidosomes. To demonstrate the potential of the technology, a modular plug-and-play lymph-node-on-a-chip prototype that guides the expansion of primary human T cells by stimulating receptor ligands on the T cells and modulating their cytokine environment is presented. This integration of synthetic cells into microfluidic systems offers a new direction for organ-on-chip technologies and suggests further avenues for exploration in potential therapeutic applications.

Bioprinting of Synthetic Cell-like Lipid Vesicles to Augment the Functionality of Tissues after Manufacturing

Bioprinting is an automated bioassembly method that enables the formation of human tissue-like constructs to restore or replace damaged tissues. Regardless of the employed bioprinting method, cells undergo mechanical stress that can impact their survival and function postprinting. In this study, we investigate the use of a synthetic cell-like unit, giant unilamellar vesicles (GUVs), as adjuvants of the cellular function of human cells postprinting, or in future as the complete replacement of human cells. We analyzed the impact of two nozzle-based bioprinting methods (drop-on-demand and extrusion bioprinting) on the structure, stability, and function of GUVs. We showed that over 65% of the GUVs remain intact when printing at 0.5 bar, demonstrating the potential of using GUVs as a synthetic cell source. We further increased the stability of GUVs in a cell culture medium by introducing polyethylene glycol (PEG) into the GUV lipid membrane. The presence of PEG, however, diminished the structural properties of GUVs postprinting, and reduced the interaction of GUVs with human cells. Although the design of PEG-GUVs can still be modified in future studies for better cell-GUV interactions, we demonstrated that GUVs are functional postprinting. Chlorin e6-PEG-GUVs loaded with a fluorescent dye were bioprinted, and they released the dye postprinting only upon illumination. This is a new strategy to deliver carriers, such as growth factors, drugs, nutrients, or gases, inside large bioprinted specimens on a millimeter to centimeter scale. Overall, we showed that printed GUVs can augment the functionality of manufactured human tissues.

Living cells and biological mechanisms as prototypes for developing chemical artificial intelligence

Artificial Intelligence (AI) is having a revolutionary impact on our societies. It is helping humans in facing the global challenges of this century. Traditionally, AI is developed in software or through neuromorphic engineering in hardware. More recently, a brand-new strategy has been proposed. It is the so-called Chemical AI (CAI), which exploits molecular, supramolecular, and systems chemistry in wetware to mimic human intelligence. In this work, two promising approaches for boosting CAI are described. One regards designing and implementing neural surrogates that can communicate through optical or chemical signals and give rise to networks for computational purposes and to develop micro/nanorobotics. The other approach concerns "bottom-up synthetic cells" that can be exploited for applications in various scenarios, including future nano-medicine. Both topics are presented at a basic level, mainly to inform the broader audience of non-specialists, and so favour the rise of interest in these frontier subjects.

Synthetic Cells from Droplet-Based Microfluidics for Biosensing and Biomedical Applications

Synthetic cells function as biological mimics of natural cells by mimicking salient features of cells such as metabolism, response to stimuli, gene expression, direct metabolism, and high stability. Droplet-based microfluidic technology presents the opportunity for encapsulating biological functional components in uni-lamellar liposome or polymer droplets. Verified by its success in the fabrication of synthetic cells, microfluidic technology is widely replacing conventional labor-intensive, expensive, and sophisticated techniques justified by its ability to miniaturize and perform batch production operations. In this review, an overview of recent research on the preparation of synthetic cells through droplet-based microfluidics is provided. Different synthetic cells including lipid vesicles (liposome), polymer vesicles (polymersome), coacervate microdroplets, and colloidosomes, are systematically discussed. Efforts are then made to discuss the design of a variety of microfluidic chips for synthetic cell preparation since the combination of microfluidics with bottom-up synthetic biology allows for reproductive and tunable construction of batches of synthetic cell models from simple structures to higher hierarchical structures. The recent advances aimed at exploiting them in biosensors and other biomedical applications are then discussed. Finally, some perspectives on the challenges and future developments of synthetic cell research with microfluidics for biomimetic science and biomedical applications are provided.

Designer peptide-DNA cytoskeletons regulate the function of synthetic cells

The bottom-up engineering of artificial cells requires a reconfigurable cytoskeleton that can organize at distinct locations and dynamically modulate its structural and mechanical properties. Here, inspired by the vast array of actin-binding proteins and their ability to reversibly crosslink or bundle filaments, we have designed a library of peptide-DNA crosslinkers varying in length, valency and geometry. Peptide filaments conjoint through DNA hybridization give rise to tactoid-shaped bundles with tunable aspect ratios and mechanics. When confined in cell-sized water-in-oil droplets, the DNA crosslinker design guides the localization of cytoskeletal structures at the cortex or within the lumen of the synthetic cells. The tunable spatial arrangement regulates the passive diffusion of payloads within the droplets and complementary DNA handles allow for the reversible recruitment and release of payloads on and off the cytoskeleton. Heat-induced reconfiguration of peptide-DNA architectures triggers shape deformations of droplets, regulated by DNA melting temperatures. Altogether, the modular design of peptide-DNA architectures is a powerful strategy towards the bottom-up assembly of synthetic cells.

DNA-empowered synthetic cells as minimalistic life forms

Cells, the fundamental units of life, orchestrate intricate functions - motility, adaptation, replication, communication, and self-organization within tissues. Originating from spatiotemporally organized structures and machinery, coupled with information processing in signalling networks, cells embody the 'sensor-processor-actuator' paradigm. Can we glean insights from these processes to construct primitive artificial systems with life-like properties? Using de novo design approaches, what can we uncover about the evolutionary path of life? This Review discusses the strides made in crafting synthetic cells, utilizing the powerful toolbox of structural and dynamic DNA nanoscience. We describe how DNA can serve as a versatile tool for engineering entire synthetic cells or subcellular entities, and how DNA enables complex behaviour, including motility and information processing for adaptive and interactive processes. We chart future directions for DNA-empowered synthetic cells, envisioning interactive systems wherein synthetic cells communicate within communities and with living cells.

Biomimetic Vesicles with Designer Phospholipids Can Sense Environmental Redox Cues

Cell-like materials that sense environmental cues can serve as next-generation biosensors and help advance the understanding of intercellular communication. Currently, bottom-up engineering of protocell models from molecular building blocks remains a grand challenge chemists face. Herein, we describe giant unilamellar vesicles (GUVs) with biomimetic lipid membranes capable of sensing environmental redox cues. The GUVs employ activity-based sensing through designer phospholipids that are fluorescently activated in response to specific reductive (hydrogen sulfide) or oxidative (hydrogen peroxide) conditions. These synthetic phospholipids are derived from 1,2-dipalmitoyl-rac-glycero-3-phosphocholine and they possess a headgroup with heterocyclic aromatic motifs. Despite their structural deviation from the phosphocholine headgroup, the designer phospholipids (0.5-1.0 mol %) mixed with natural lipids can vesiculate, and the resulting GUVs (7-20 μm in diameter) remain intact over the course of redox sensing. All-atom molecular dynamics simulations gave insight into how these lipids are positioned within the hydrophobic core of the membrane bilayer and at the membrane-water interface. This work provides a purely chemical method to investigate potential redox signaling and opens up new design opportunities for soft materials that mimic protocells.

Synthetic Vesicles for Sustainable Energy Recycling and Delivery of Building Blocks for Lipid Biosynthesis†

ATP is a universal energy currency that is essential for life. l-Arginine degradation via deamination is an elegant way to generate ATP in synthetic cells, which is currently limited by a slow l-arginine/l-ornithine exchange. We are now implementing a new antiporter with better kinetics to obtain faster ATP recycling. We use l-arginine-dependent ATP formation for the continuous synthesis and export of glycerol 3-phosphate by including glycerol kinase and the glycerol 3-phosphate/Pi antiporter. Exported glycerol 3-phosphate serves as a precursor for the biosynthesis of phospholipids in a second set of vesicles, which forms the basis for the expansion of the cell membrane. We have therefore developed an out-of-equilibrium metabolic network for ATP recycling, which has been coupled to lipid synthesis. This feeder-utilizer system serves as a proof-of-principle for the systematic buildup of synthetic cells, but the vesicles can also be used to study the individual reaction networks in confinement.

An Efficient Method for the Production of High-Purity Bioinspired Large Unilamellar Vesicles

In order to recapitulate complex eukaryotic compartmentalization, synthetic biology aims to recreate cellular membrane-lined compartments from the bottom-up. Many important cellular organelles and cell-produced extracellular vesicles are in the size range of several hundreds of nanometers. Although attaining a fundamental characterization and mimicry of their cellular functions is a compelling goal, the lack of methods for controlled vesicle formation in this size range has hindered full understanding. Here, we show the optimization of a simple and efficient protocol for the production of large unilamellar vesicles (LUVs) with a median diameter in the range of 450-550 nm with high purity. Importantly, we rely on commercial reagents and common laboratory equipment. We thoroughly characterize the influence of different experimental parameters on the concentration and size of the resulting vesicles and assess changes in their lipid composition and surface charge. We provide guidance for researchers to optimize LUV production further to suit specific applications.

Artificial Methylotrophic Cells via Bottom-Up Integration of a Methanol-Utilizing Pathway

Methanol has gained substantial attention as a substrate for biomanufacturing due to plentiful stocks and nonreliance on agriculture, and it can be sourced renewably. However, due to inevitable complexities in cell metabolism, microbial methanol conversion requires further improvement before industrial applicability. Here, we present a novel, parallel strategy using artificial cells to provide a simplified and well-defined environment for methanol utilization as artificial methylotrophic cells. We compartmentalized a methanol-utilizing enzyme cascade, including NAD-dependent methanol dehydrogenase (Mdh) and pyruvate-dependent aldolase (KHB aldolase), in cell-sized lipid vesicles using the inverted emulsion method. The reduction of cofactor NAD+ to NADH was used to quantify the conversion of methanol within individual artificial methylotrophic cells via flow cytometry. Compartmentalization of the reaction cascade in liposomes led to a 4-fold higher NADH production compared with bulk enzyme experiments, and the incorporation of KHB aldolase facilitated another 2-fold increase above the Mdh-only reaction. This methanol-utilizing platform can serve as an alternative route to speed up methanol biological conversion, eventually shifting sugar-based bioproduction toward a sustainable methanol bioeconomy.

Synthetic Cells Revisited: Artificial Cells Construction Using Polymeric Building Blocks

The exponential growth of research on artificial cells and organelles underscores their potential as tools to advance the understanding of fundamental biological processes. The bottom-up construction from a variety of building blocks at the micro- and nanoscale, in combination with biomolecules is key to developing artificial cells. In this review, artificial cells are focused upon based on compartments where polymers are the main constituent of the assembly. Polymers are of particular interest due to their incredible chemical variety and the advantage of tuning the properties and functionality of their assemblies. First, the architectures of micro- and nanoscale polymer assemblies are introduced and then their usage as building blocks is elaborated upon. Different membrane-bound and membrane-less compartments and supramolecular structures and how they combine into advanced synthetic cells are presented. Then, the functional aspects are explored, addressing how artificial organelles in giant compartments mimic cellular processes. Finally, how artificial cells communicate with their surrounding and each other such as to adapt to an ever-changing environment and achieve collective behavior as a steppingstone toward artificial tissues, is taken a look at. Engineering artificial cells with highly controllable and programmable features open new avenues for the development of sophisticated multifunctional systems.

Top-down and bottom-up microbiome engineering approaches to enable biomanufacturing from waste biomass

Growing environmental concerns and the need to adopt a circular economy have highlighted the importance of waste valorization for resource recovery. Microbial consortia-enabled biotechnologies have made significant developments in the biomanufacturing of valuable resources from waste biomass that serve as suitable alternatives to petrochemical-derived products. These microbial consortia-based processes are designed following a top-down or bottom-up engineering approach. The top-down approach is a classical method that uses environmental variables to selectively steer an existing microbial consortium to achieve a target function. While high-throughput sequencing has enabled microbial community characterization, the major challenge is to disentangle complex microbial interactions and manipulate the structure and function accordingly. The bottom-up approach uses prior knowledge of the metabolic pathway and possible interactions among consortium partners to design and engineer synthetic microbial consortia. This strategy offers some control over the composition and function of the consortium for targeted bioprocesses, but challenges remain in optimal assembly methods and long-term stability. In this review, we present the recent advancements, challenges, and opportunities for further improvement using top-down and bottom-up approaches for microbiome engineering. As the bottom-up approach is relatively a new concept for waste valorization, this review explores the assembly and design of synthetic microbial consortia, ecological engineering principles to optimize microbial consortia, and metabolic engineering approaches for efficient conversion. Integration of top-down and bottom-up approaches along with developments in metabolic modeling to predict and optimize consortia function are also highlighted.

ONE-SENTENCE SUMMARY

This review highlights the microbial consortia-driven waste valorization for biomanufacturing through top-down and bottom-up design approaches and describes strategies, tools, and unexplored opportunities to optimize the design and stability of such consortia.

Developing a Graduate Class on Synthetic Cells at a Minority Serving Institution: Lessons from the University of New Mexico

This article describes the development, methodology, enrollment, and outcomes of a graduate technical elective course on synthetic cells and organelles offered at the University of New Mexico, a minority-majority institution, in Fall 2022. The course had a significant ethics component and took advantage of readily available, low cost, and no-cost teaching materials that are available online. The course was effective in attracting a diverse enrollment of graduate students and senior undergraduates, some of whom participated in a survey of their backgrounds and motivations after the course was over. The article also provides results from this survey. Courses such as the one described have the potential to increase access and participation in emerging fields of research and technology such as synthetic cells.

Preparation and biomedical applications of artificial cells

Artificial cells have received much attention in recent years as cell mimics with typical biological functions that can be adapted for therapeutic and diagnostic applications, as well as having an unlimited supply. Although remarkable progress has been made to construct complex multifunctional artificial cells, there are still significant differences between artificial cells and natural cells. It is therefore important to understand the techniques and challenges for the fabrication of artificial cells and their applications for further technological advancement. The key concepts of top-down and bottom-up methods for preparing artificial cells are summarized, and the advantages and disadvantages of the bottom-up methods are compared and critically discussed in this review. Potential applications of artificial cells as drug carriers (microcapsules), as signaling regulators for coordinating cellular communication and as bioreactors for biomolecule fabrication, are further discussed. The challenges and future trends for the development of artificial cells simulating the real activities of natural cells are finally described.

Interfacing Coacervates with Membranes: From Artificial Organelles and Hybrid Protocells to Intracellular Delivery

Compartmentalization is crucial for the functioning of cells. Membranes enclose and protect the cell, regulate the transport of molecules entering and exiting the cell, and organize cellular machinery in subcompartments. In addition, membraneless condensates, or coacervates, offer dynamic compartments that act as biomolecular storage centers, organizational hubs, or reaction crucibles. Emerging evidence shows that phase-separated membraneless bodies in the cell are involved in a wide range of functional interactions with cellular membranes, leading to transmembrane signaling, membrane remodeling, intracellular transport, and vesicle formation. Such functional and dynamic interplay between phase-separated droplets and membranes also offers many potential benefits to artificial cells, as shown by recent studies involving coacervates and liposomes. Depending on the relative sizes and interaction strength between coacervates and membranes, coacervates can serve as artificial membraneless organelles inside liposomes, as templates for membrane assembly and hybrid artificial cell formation, as membrane remodelers for tubulation and possibly division, and finally, as cargo containers for transport and delivery of biomolecules across membranes by endocytosis or direct membrane crossing. Here, recent experimental examples of each of these functions are reviewed and the underlying physicochemical principles and possible future applications are discussed.

Synthetic Membraneless Droplets for Synaptic-Like Clustering of Lipid Vesicles

In eukaryotic cells, the membraneless organelles (MLOs) formed via liquid-liquid phase separation (LLPS) are found to interact intimately with membranous organelles (MOs). One major mode is the clustering of MOs by MLOs, such as the formation of clusters of synaptic vesicles at nerve terminals mediated by the synapsin-rich MLOs. Aqueous droplets, including complex coacervates and aqueous two-phase systems, have been plausible MLO-mimics to emulate or elucidate biological processes. However, neither of them can cluster lipid vesicles (LVs) like MLOs. In this work, we develop a synthetic droplet assembled from a combination of two different interactions underlying the formation of these two droplets, namely, associative and segregative interactions, which we call segregative-associative (SA) droplets. The SA droplets cluster and disperse LVs recapitulating the key functional features of synapsin condensates, which can be attributed to the weak electrostatic interaction environment provided by SA droplets. This work suggests LLPS with combined segregative and associative interactions as a possible route for synaptic clustering of lipid vesicles and highlights SA droplets as plausible MLO-mimics and models for studying and mimicking related cellular dynamics.

Sponge-phase Lipid Droplets as Synthetic Organelles: An Ultrafast Study of Hydrogen Bonding and Interfacial Environments

Bottom-up design of biomimetic organelles has gained recent attention as a route towards understanding the transition between non-living matter and life. Despite various artificial lipid membranes being developed, the specific relations between lipid structure, composition, interfacial properties, and morphology are not currently understood. Sponge-phase droplets contain dense, nonlamellar lipid bilayer networks that capture the complexities of the endoplasmic reticulum (ER), making them ideal artificial models of such organelles. Here, we combine ultrafast two-dimensional infrared (2D IR) spectroscopy and molecular dynamics simulations to investigate the interfacial H-bond networks in sponge-phase droplets composed of glycolipid and nonionic detergents. In the sponge phase, the interfacial environments are more hydrated and water molecules confined to the nanometer-scale aqueous channels in the sponge phase exhibit dynamics that are significantly slower compared to bulk water. Surfactant configurations and microscopic phase separation play a dominant role in determining membrane curvature and slow dynamics observed in the sponge phase. The studies suggest that H-bond networks within the nanometer-scale channels are disrupted not only by confinement but also by the interactions of surfactants, which extend 1-2 nm from the bilayer surface. The results provide a molecular-level description for controlling phase and morphology in the design of synthetic lipid organelles.

Engineering DNA-based cytoskeletons for synthetic cells

The development and bottom-up assembly of synthetic cells with a functional cytoskeleton sets a major milestone to understand cell mechanics and to develop man-made machines on the nano- and microscale. However, natural cytoskeletal components can be difficult to purify, deliberately engineer and reconstitute within synthetic cells which therefore limits the realization of multifaceted functions of modern cytoskeletons in synthetic cells. Here, we review recent progress in the development of synthetic cytoskeletons made from deoxyribonucleic acid (DNA) as a complementary strategy. In particular, we explore the capabilities and limitations of DNA cytoskeletons to mimic functions of natural cystoskeletons like reversible assembly, cargo transport, force generation, mechanical support and guided polymerization. With recent examples, we showcase the power of rationally designed DNA cytoskeletons for bottom-up assembled synthetic cells as fully engineerable entities. Nevertheless, the realization of dynamic instability, self-replication and genetic encoding as well as contractile force generating motors remains a fruitful challenge for the complete integration of multifunctional DNA-based cytoskeletons into synthetic cells.

Reaction-driven assembly: controlling changes in membrane topology by reaction cycles

Chemical reaction cycles are prototypical examples how to drive systems out of equilibrium and introduce novel, life-like properties into soft-matter systems. We report simulations of amphiphilic molecules in aqueous solution. The molecule's head group is permanently hydrophilic, whereas the reaction cycle switches the molecule's tail from hydrophilic (precursor) to hydrophobic (amphiphile) and vice versa. The reaction cycle leads to an arrest in coalescence and results in uniform vesicle sizes that can be controlled by the reaction rate. Using a continuum description and particle-based simulation, we study the scaling of the vesicle size with the reaction rate. The chemically active vesicles are inflated by precursor, imparting tension onto the membrane and, for specific parameters, stabilize pores.

Exploring the Synergies of Single-Molecule Fluorescence and 2D Materials Coupled by DNA

The world of 2D materials is steadily growing, with numerous researchers attempting to discover, elucidate, and exploit their properties. Approaches relying on the detection of single fluorescent molecules offer a set of advantages, for instance, high sensitivity and specificity, that allow the drawing of conclusions with unprecedented precision. Herein, it is argued how the study of 2D materials benefits from fluorescence-based single-molecule modalities, and vice versa. A special focus is placed on DNA, serving as a versatile adaptor when anchoring single dye molecules to 2D materials. The existing literature on the fruitful combination of the two fields is reviewed, and an outlook on the additional synergies that can be created between them provided.

Phase Separation of DNA-Encoded Artificial Cells Boosts Signal Amplification for Biosensing

Life-like hierarchical architecture shows great potential for advancing intelligent biosensing, but modular expansion of its sensitivity and functionality remains a challenge. Drawing inspiration from intracellular liquid-liquid phase separation, we discovered that a DNA-encoded artificial cell with a liquid core (LAC) can enhance peroxidase-like activity of Hemin and its DNA G-quadruplex aptamer complex (DGAH) without substrate-selectivity, unlike its gelled core (GAC) counterpart. The LAC is easily engineered as an ultrasensitive biosensing system, benefiting from DNA's high programmability and unique signal amplification capability mediated by liquid-liquid phase separation. As proof of concept, its versatility was successfully demonstrated by coupling with two molecular recognition elements to monitor tumor-related microRNA and profile cancer cell phenotypes. This scalable design philosophy offers new insights into the design of next generation of artificial cells-based biosensors.

Nanotechnology-Boosted Biomaterials for Osteoarthritis Treatment: Current Status and Future Perspectives

Osteoarthritis (OA) is a prevalent global health concern, posing a significant and increasing public health challenge worldwide. Recently, nanotechnology-boosted biomaterials have emerged as a highly promising strategy for OA therapy due to their exceptional physicochemical properties and capacity to regulate pathological processes. However, there is an urgent need for a deeper understanding of the potential therapeutic applications of these biomaterials in the clinical management of diseases, particularly in the treatment of OA. In this comprehensive review, we present an extensive discussion of the current status and future prospects concerning nanotechnology-boosted biomaterials for OA therapy. Initially, we discuss the pathophysiology of OA and the constraints associated with existing treatment modalities. Subsequently, various types of nanomaterials utilized for OA therapy, including nanoparticles, nanofibers, and nanocomposites, are thoroughly discussed and summarized, elucidating their respective advantages and challenges. Furthermore, we analyze recent preclinical and clinical studies that highlight the potential of nanotechnology-boosted biomaterials in OA therapy. Additionally, future research directions in this evolving field are highlighted. By establishing a link between the structural properties of nanotechnology-boosted biomaterials and their therapeutic functions in OA treatment, we aim to foster advances in designing sophisticated nanomaterials for OA, ultimately resulting in improved therapeutic efficacy of OA therapy through translation into clinical setting in the near future.

Functionalization and higher-order organization of liposomes with DNA nanostructures

Small unilamellar vesicles (SUVs) are indispensable model membranes, organelle mimics, and drug and vaccine carriers. However, the lack of robust techniques to functionalize or organize preformed SUVs limits their applications. Here we use DNA nanostructures to coat, cluster, and pattern sub-100-nm liposomes, generating distance-controlled vesicle networks, strings and dimers, among other configurations. The DNA coating also enables attachment of proteins to liposomes, and temporal control of membrane fusion driven by SNARE protein complexes. Such a convenient and versatile method of engineering premade vesicles both structurally and functionally is highly relevant to bottom-up biology and targeted delivery.

Mechanoresponsive Drug Delivery Systems for Vascular Diseases

Mechanoresponsive drug delivery systems (DDS) have emerged as promising candidates to improve the current effectiveness and lower the side effects typically associated with direct drug administration in the context of vascular diseases. Despite tremendous research efforts to date, designing drug delivery systems able to respond to mechanical stimuli to potentially treat these diseases is still in its infancy. By understanding relevant biological forces emerging in healthy and pathological vascular endothelium, it is believed that better-informed design strategies can be deduced for the fabrication of simple-to-complex macromolecular assemblies capable of sensing mechanical forces. These responsive systems are discussed through insights into essential parameter design (composition, size, shape, and aggregation state) , as well as their functionalization with (macro)molecules that are intrinsically mechanoresponsive (e.g., mechanosensitive ion channels and mechanophores). Mechanical forces, including the pathological shear stress and exogenous stimuli (e.g., ultrasound, magnetic fields), used for the activation of mechanoresponsive DDS are also introduced, followed by in vitro and in vivo experimental models used to investigate and validate such novel therapies. Overall, this review aims to propose a fresh perspective through identified challenges and proposed solutions that could be of benefit for the further development of this exciting field.

Charge controlled interactions between DNA-modified silica nanoparticles and fluorosurfactants in microfluidic water-in-oil droplets

Microfluidic droplets are an important tool for studying and mimicking biological systems, e.g., to examine with high throughput the interaction of biomolecular components and the functionality of natural cells, or to develop basic principles for the engineering of artificial cells. Of particular importance is the approach to generate a biomimetic membrane by supramolecular self-assembly of nanoparticle components dissolved in the aqueous phase of the droplets at the inner water/oil interface, which can serve both to mechanically reinforce the droplets and as an interaction surface for cells and other components. While this interfacial assembly driven by electrostatic interaction of surfactants is quite well developed for water/mineral oil (W/MO) systems, no approaches have yet been described to exploit this principle for water/fluorocarbon oil (W/FO) emulsion droplets. Since W/FO systems exhibit not only better compartmentalization but also gas solubility properties, which is particularly crucial for live cell encapsulation and cultivation, we report here the investigation of charged fluorosurfactants for the self-assembly of DNA-modified silica nanoparticles (SiNP-DNA) at the interface of microfluidic W/FO emulsions. To this end, an efficient multicomponent Ugi reaction was used to synthesize the novel fluorosurfactant M4SURF to study the segregation and accumulation of negatively charged SiNP-DNA at the inner interface of microfluidic droplets. Comparative measurements were performed with the negatively charged fluorosurfactant KRYTOX, which can also induce SiNP-DNA segregation in the presence of cations. The segregation dynamics is characterized and preliminary results of cell encapsulation in the SiNP-DNA functionalized droplets are shown.

Self-Regulated and Bidirectional Communication in Synthetic Cell Communities

Cell-to-cell communication is not limited to a sender releasing a signaling molecule and a receiver perceiving it but is often self-regulated and bidirectional. Yet, in communities of synthetic cells, such features that render communication efficient and adaptive are missing. Here, we report the design and implementation of adaptive two-way signaling with lipid-vesicle-based synthetic cells. The first layer of self-regulation derives from coupling the temporal dynamics of the signal, H2O2, production in the sender to adhesions between sender and receiver cells. This way the receiver stays within the signaling range for the duration sender produces the signal and detaches once the signal fades. Specifically, H2O2 acts as both a forward signal and a regulator of the adhesions by activating photoswitchable proteins at the surface for the duration of the chemiluminescence. The second layer of self-regulation arises when the adhesions render the receiver permeable and trigger the release of a backward signal, resulting in bidirectional exchange. These design rules provide a concept for engineering multicellular systems with adaptive communication.

Engineering membrane architecture for biotechnological applications

Cellular membranes, predominantly described as a dynamic bilayer, are composed of different lipids, transmembrane proteins, and carbohydrates. Most research on biological membranes focuses on the identification, characterization, and mechanistic aspects of their different components. These studies provide a fundamental understanding of membrane structure, function, and dynamics, establishing a basis for the development of membrane engineering strategies. To date, approaches in this field concentrate on membrane adaptation to harsh conditions during industrial fermentation, which can be caused by temperature, osmotic, or organic solvent stress. With advances in the field of metabolic engineering and synthetic biology, recent breakthroughs include proof of concept microbial production of essential medicines, such as cannabinoids and vinblastine. However, long pathways, low yields, and host adaptation continue to pose challenges to the efficient scale up production of many important compounds. The lipid bilayer is profoundly linked to the activity of heterologous membrane-bound enzymes and transport of metabolites. Therefore, strategies for improving enzyme performance, facilitating pathway reconstruction, and enabling storage of products to increase the yields directly involve cellular membranes. At the forefront of membrane engineering research are re-emerging approaches in lipid research and synthetic biology that manipulate membrane size and composition and target lipid profiles across species. This review summarizes engineering strategies applied to cellular membranes and discusses the challenges and future perspectives, particularly with regards to their applications in host engineering and bioproduction.

Digital nanoreactors to control absolute stoichiometry and spatiotemporal behavior of DNA receptors within lipid bilayers

Interactions between membrane proteins are essential for cell survival but are often poorly understood. Even the biologically functional ratio of components within a multi-subunit membrane complex-the native stoichiometry-is difficult to establish. Here we demonstrate digital nanoreactors that can control interactions between lipid-bound molecular receptors along three key dimensions: stoichiometric, spatial, and temporal. Each nanoreactor is based on a DNA origami ring, which both templates the synthesis of a liposome and provides tethering sites for DNA-based receptors (modelling membrane proteins). Receptors are released into the liposomal membrane using strand displacement and a DNA logic gate measures receptor heterodimer formation. High-efficiency tethering of receptors enables the kinetics of receptors in 1:1 and 2:2 absolute stoichiometries to be observed by bulk fluorescence, which in principle is generalizable to any ratio. Similar single-molecule-in-bulk experiments using DNA-linked membrane proteins could determine native stoichiometry and the kinetics of membrane protein interactions for applications ranging from signalling research to drug discovery.

Creating complex protocells and prototissues using simple DNA building blocks

Building synthetic protocells and prototissues hinges on the formation of biomimetic skeletal frameworks. Recreating the complexity of cytoskeletal and exoskeletal fibers, with their widely varying dimensions, cellular locations and functions, represents a major material hurdle and intellectual challenge which is compounded by the additional demand of using simple building blocks to ease fabrication and control. Here we harness simplicity to create complexity by assembling structural frameworks from subunits that can support membrane-based protocells and prototissues. We show that five oligonucleotides can anneal into nanotubes or fibers whose tunable thicknesses and lengths spans four orders of magnitude. We demonstrate that the assemblies' location inside protocells is controllable to enhance their mechanical, functional and osmolar stability. Furthermore, the macrostructures can coat the outside of protocells to mimic exoskeletons and support the formation of millimeter-scale prototissues. Our strategy could be exploited in the bottom-up design of synthetic cells and tissues, to the generation of smart material devices in medicine.

Confining the Sol-Gel Reaction at the Water/Oil Interface: Creating Compartmentalized Enzymatic Nano-Organelles for Artificial Cells

Living organisms compartmentalize their catalytic reactions in membranes for increased efficiency and selectivity. To mimic the organelles of eukaryotic cells, we develop a mild approach for in situ encapsulating enzymes in aqueous-core silica nanocapsules. In order to confine the sol-gel reaction at the water/oil interface of miniemulsion, we introduce an aminosilane to the silica precursors, which serves as both catalyst and an amphiphilic anchor that electrostatically assembles with negatively charged hydrolyzed alkoxysilanes at the interface. The semi-permeable shell protects enzymes from proteolytic attack, and allows the transport of reactants and products. The enzyme-carrying nanocapsules, as synthetic nano-organelles, are able to perform cascade reactions when enveloped in a polymer vesicle, mimicking the hierarchically compartmentalized reactions in eukaryotic cells. This in situ encapsulation approach provides a versatile platform for the delivery of biomacromolecules.

Genotype-phenotype mapping with polyominos made from DNA origami tiles

The correlation between genetic information and characteristics of a living cell-its genotype and its phenotype-constitutes the basis of genetics. Here, we experimentally realize a primitive form of genotype-phenotype mapping with DNA origami. The DNA origami can polymerize into two-dimensional lattices (phenotype) via blunt-end stacking facilitated by edge staples at the seam of the planar DNA origami. There are 80 binding positions for edge staples, which allow us to translate an 80-bit long binary code (genotype) onto the DNA origami. The presence of an edge staple thus corresponds to a "1" and its absence to a "0." The interactions of our DNA-based system can be reproduced by a polyomino model. Polyomino growth simulations qualitatively reproduce our experimental results. We show that not only the absolute number of base stacks but also their sequence position determine the cluster size and correlation length of the orientation of single DNA origami within the cluster. Importantly, the mutation of a few bits can result in major morphology changes of the DNA origami cluster, while more often, major sequence changes have no impact. Our experimental realization of a correlation between binary information ("genotype") and cluster morphology ("phenotype") thus reproduces key properties of genotype-phenotype maps known from living systems.

Stepwise remodeling and subcompartment formation in individual vesicles by three ESCRT-III proteins

The endosomal sorting complex required for transport (ESCRT) is a multi-protein machinery involved in several membrane remodeling processes. Different approaches have been used to resolve how ESCRT proteins scission membranes. However, the underlying mechanisms generating membrane deformations are still a matter of debate. Here, giant unilamellar vesicles, microfluidic technology, and micropipette aspiration are combined to continuously follow the ESCRT-III-mediated membrane remodeling on the single-vesicle level for the first time. With this approach, we identify different mechanisms by which a minimal set of three ESCRT-III proteins from Entamoeba histolytica reshape the membrane. These proteins modulate the membrane stiffness and spontaneous curvature to regulate bud size and generate intraluminal vesicles even in the absence of ATP. We demonstrate that the bud stability depends on the protein concentration and membrane tension. The approaches introduced here should open the road to diverse applications in synthetic biology for establishing artificial cells with several membrane compartments.

DNA-Based Optical Quantification of Ion Transport across Giant Vesicles

Accurate measurements of ion permeability through cellular membranes remains challenging due to the lack of suitable ion-selective probes. Here we use giant unilamellar vesicles (GUVs) as membrane models for the direct visualization of mass translocation at the single-vesicle level. Ion transport is indicated with a fluorescently adjustable DNA-based sensor that accurately detects sub-millimolar variations in K⁺ concentration. In combination with microfluidics, we employed our DNA-based K⁺ sensor for extraction of the permeation coefficient of potassium ions. We measured K⁺ permeability coefficients at least 1 order of magnitude larger than previously reported values from bulk experiments and show that permeation rates across the lipid bilayer increase in the presence of octanol. In addition, an analysis of the K⁺ flux in different concentration gradients allows us to estimate the complementary H⁺ flux that dissipates the charge imbalance across the GUV membrane. Subsequently, we show that our sensor can quantify the K⁺ transport across prototypical cation-selective ion channels, gramicidin A and OmpF, revealing their relative H⁺/K⁺ selectivity. Our results show that gramicidin A is much more selective to protons than OmpF with a H⁺/K⁺ permeability ratio of ∼10⁴.

Stimuli-responsive vesicles as distributed artificial organelles for bacterial activation

Intercellular communication is a hallmark of living systems. As such, engineering artificial cells that possess this behavior has been at the heart of activities in bottom-up synthetic biology. Communication between artificial and living cells has potential to confer novel capabilities to living organisms that could be exploited in biomedicine and biotechnology. However, most current approaches rely on the exchange of chemical signals that cannot be externally controlled. Here, we report two types of remote-controlled vesicle-based artificial organelles that translate physical inputs into chemical messages that lead to bacterial activation. Upon light or temperature stimulation, artificial cell membranes are activated, releasing signaling molecules that induce protein expression in Escherichia coli. This distributed approach differs from established methods for engineering stimuli-responsive bacteria. Here, artificial cells (as opposed to bacterial cells themselves) are the design unit. Having stimuli-responsive elements compartmentalized in artificial cells has potential applications in therapeutics, tissue engineering, and bioremediation. It will underpin the design of hybrid living/nonliving systems where temporal control over population interactions can be exerted.

Synthetic Biology: Bottom-Up Assembly of Molecular Systems

The bottom-up assembly of biological and chemical components opens exciting opportunities to engineer artificial vesicular systems for applications with previously unmet requirements. The modular combination of scaffolds and functional building blocks enables the engineering of complex systems with biomimetic or new-to-nature functionalities. Inspired by the compartmentalized organization of cells and organelles, lipid or polymer vesicles are widely used as model membrane systems to investigate the translocation of solutes and the transduction of signals by membrane proteins. The bottom-up assembly and functionalization of such artificial compartments enables full control over their composition and can thus provide specifically optimized environments for synthetic biological processes. This review aims to inspire future endeavors by providing a diverse toolbox of molecular modules, engineering methodologies, and different approaches to assemble artificial vesicular systems. Important technical and practical aspects are addressed and selected applications are presented, highlighting particular achievements and limitations of the bottom-up approach. Complementing the cutting-edge technological achievements, fundamental aspects are also discussed to cater to the inherently diverse background of the target audience, which results from the interdisciplinary nature of synthetic biology. The engineering of proteins as functional modules and the use of lipids and block copolymers as scaffold modules for the assembly of functionalized vesicular systems are explored in detail. Particular emphasis is placed on ensuring the controlled assembly of these components into increasingly complex vesicular systems. Finally, all descriptions are presented in the greater context of engineering valuable synthetic biological systems for applications in biocatalysis, biosensing, bioremediation, or targeted drug delivery.

Implanted synthetic cells trigger tissue angiogenesis through de novo production of recombinant growth factors

Progress in bottom-up synthetic biology has stimulated the development of synthetic cells (SCs), autonomous protein-manufacturing particles, as dynamic biomimetics for replacing diseased natural cells and addressing medical needs. Here, we report that SCs genetically encoded to produce proangiogenic factors triggered the physiological process of neovascularization in mice. The SCs were constructed of giant lipid vesicles and were optimized to facilitate enhanced protein production. When introduced with the appropriate genetic code, the SCs synthesized a recombinant human basic fibroblast growth factor (bFGF), reaching expression levels of up to 9⋅106 protein copies per SC. In culture, the SCs induced endothelial cell proliferation, migration, tube formation, and angiogenesis-related intracellular signaling, confirming their proangiogenic activity. Integrating the SCs with bioengineered constructs bearing endothelial cells promoted the remodeling of mature vascular networks, supported by a collagen-IV basement membrane-like matrix. In vivo, prolonged local administration of the SCs in mice triggered the infiltration of blood vessels into implanted Matrigel plugs without recorded systemic immunogenicity. These findings emphasize the potential of SCs as therapeutic platforms for activating physiological processes by autonomously producing biological drugs inside the body.