Enteropathogenic Escherichia coli (EPEC) and Citrobacter rodentium (CR) are extracellular enteric attaching and effacing (A/E) pathogens of humans and mice, respectively. Their virulence relies on intimate bacterial attachment and a network of type III secretion system effectors. Here, through systematic reduction and redesign of the effector network in CR, we develop an attenuated strain, CRV (CR Vaccine), encoding a subset of ten effectors. CRV colonises C57BL/6 mice ~100-fold lower than wild type CR (CRWT) without causing overt pathogenesis. Moreover, C3H/HeN mice, which succumb to CRWT infection, survive CRV challenge. Vaccination with CRV confers protection against subsequent CRWT infection in both mouse strains. Serological analysis reveals a repertoire of dominant CR antigens, including the O-antigen, the virulence factors intimin, EspA and Tir and the outer membrane proteins Lpp, OmpA, MetQ and CARC (an AIDA-like autotransporter). We show that CRWT and CRV immunisation elicits comparable B cell and antibody responses, which is contingent on intimate bacterial attachment. A corresponding EPEC strain (E. coli Vaccine, ECV) effectively colonises epithelial cells in a gut-on-chip model. These findings establish effector network minimisation as a generalisable strategy for rational bacterial attenuation and live-attenuated vaccine design.

Artificial cells assembled from materials such as hydrogels have emerged as platforms to replicate and understand biological functionalities, processes, and behaviors. However, hydrogels lack a lipid membrane, a vital property of cellular systems. Here we develop a process for the assembly of a fluid and stable lipid membrane which coats the hydrogel mesh network within the particle, through electostatically-mediated fusion of nanoscale lipid vesicles. This confers cell-mimetic and biotechnologically relevant properties upon microscale, cell sized, hydrogel artificial cells generated through microfluidics. We exploit the properties of the created membrane to augment existing hydrogel properties through permeability alteration and protection of the hydrogel from small molecule degraders. Furthermore, we show that the lipid membrane is compatible with organelle substructures within the hydrogels, which enables the exploitation of an enhanced material design space to build hydrogel artificial cells that increasingly mimic the organization of cells. This platform paves the way for producing next generation artificial cells and functional microdevices from interfaced hydrogel-lipid materials. Our technologies may underpin new opportunities for integrating membranes into hydrogel-based systems, inlcuding for drug delivery and tissue engineering.

Lipid nanocarriers utilise the self-assembly of amphiphilic molecules to generate particle formulations capable of drug encapsulation and dynamic interactions with user-defined cell types, enabling applications within targeted therapeutic delivery. This offers increased bioavailability, stability, and reduced off-target effects, with the promise of application to numerous cell types and consequently, diseases. Here, we have developed a highly accessible, cleanroom-free method for the fabrication of poly(methyl methacrylate) millifluidic vertical flow focusing (VFF) devices via laser cutting, multilayered solvent and heat-assisted bonding. We demonstrate that these can be used for one-step production of targeted lipid nanocarriers via the production of cardiomyocyte-targeting vesicle nanoparticles loaded with the hydrophobic drug menadione. We characterise vesicle size using dynamic light scattering (DLS) and cryogenic transmission electron microscopy (cryo-TEM), whilst also probing the membrane viscosity of vesicles produced via flow-focusing for the first time using molecular rotors. Finally, we apply cardiomyocyte-targeting, menadione-loaded vesicles to H9C2 tissue culture demonstrating significant inhibition of cell viability via targeted delivery, showcasing the potential of our device to produce formulations for therapeutic delivery. As a flow-based method, VFF can facilitate rapid formulation investigation and produce large sample volumes for cell-based validation studies, whilst avoiding inter-batch sample variation. Furthermore, the accessible nature of this VFF approach will help to democratise millifluidics, facilitating the wider adoption of flow-based production methods to develop nanomedical formulations.

Stimuli-responsive polymeric vesicles offer a versatile platform for mimicking dynamic cell-like behaviors for synthetic cell applications. In this study, thermally responsive polymeric droplets derived from poly(ethylene oxide)-poly(butylene oxide) (PEO-PBO) polymersomes, aiming to create synthetic cell models that mimic key biological functions are developed. Upon heating, the nanoscale vesicles undergo fusion, transforming into sponge-like microscale droplets enriched with membrane features. By modulating the temperature, these droplets display dynamic properties such as contractility, temperature-induced fusion, and cargo trapping, including small molecules and bacteria, thereby demonstrating their ability to dynamically interface with biological entities. The findings demonstrate the potential of our sponge-like droplets in synthetic cell applications, contributing to the understanding of PEO-PBO polymersomes' unique characteristics, expanding the capabilities of synthetic cell structures, and representing an exciting possibility for advancing soft matter engineering to cell-like behaviors.

Artificial cells serve as promising micro-robotic platforms that replicate cellular features. One ubiquitous characteristic of living cells is compartmentalization of content in distinct and well-defined locations. Herein, a microfluidic strategy to mimic compartmentalization is developed through the production of micron-scale two and three compartment biomimetic microgels, where hydrogel compartment number, composition, size, and shape can be controlled. Our lab-on-chip system enables the incorporation of various synthetic organelles into spatially separated compartments within the microgels. This design concept allows for the introduction of a variety of individually triggered bioinspired behaviors, including protein capture, enzyme-mediated content release, and stimuli-triggered motility, each isolated in a distinct compartment enabling the use of the microgels as compartmentalized artificial cells. With this approach, the division of content and function seen in biological cells can be mirrored, which will underpin the generation of increasingly sophisticated and functional soft matter microdevices using bottom-up synthetic biology principles.

High pressure is both an environmental challenge to which deep sea biology has to adapt, and a highly sensitive thermodynamic tool that can be used to trigger structural changes in biological molecules and assemblies. Lipid membranes are amongst the most pressure sensitive biological assemblies and pressure can have a large influence on their structure and properties. In this chapter, we will explore the use of high pressure small angle X-ray diffraction and high pressure microscopy to measure and quantify changes in the lateral structure of lipid membranes under both equilibrium high pressure conditions and in response to pressure jumps.

Synthetic cells have emerged as a promising tool for understanding cellular processes and developing novel biotechnological applications. In this study, we engineer dynamic and biomimetic behaviours in polymersomes, aiming to create synthetic cells that mimic key biological functions. These vesicles exhibit a temperature-driven fusogenic property, enabling the transformation of nanoscale vesicles into microsized sponge-like polymeric droplets. These droplets, rich in membrane content, can act as synthetic cells analogues with the capability for controlled cargo release. Moreover, the thermoresponsive nature of our polymersomes makes them versatile components for the construction of lipid-based synthetic cells, allowing for controllable cargo release and dynamic organelle-like functionalities. We also demonstrate that the microscale polymer droplets possess biomimetic properties including contractility, a behaviour typically observed in biological systems. By modulating the temperature, it is possible to induce these contractile behaviours as well as other functions, including controlled fusion and efficient bacteria capture.

Synthetic cells can be constructed from diverse molecular components, without the design constraints associated with modifying 'living' biological systems. This can be exploited to generate cells with abiotic components, creating functionalities absent in biology. One example is magnetic responsiveness, the activation and modulation of encapsulated biochemical processes using a magnetic field, which is absent from existing synthetic cell designs. This is a critical oversight, as magnetic fields are uniquely bio-orthogonal, noninvasive, and highly penetrative. Here, we address this by producing artificial magneto-responsive organelles by coupling thermoresponsive membranes with hyperthermic Fe3O4 nanoparticles and embedding them in synthetic cells. Combining these systems enables synthetic cell microreactors to be built using a nested vesicle architecture, which can respond to alternating magnetic fields through in situ enzymatic catalysis. We also demonstrate the modulation of biochemical reactions by using different magnetic field strengths and the potential to tune the system using different lipid compositions. This platform could unlock a wide range of applications for synthetic cells as programmable micromachines in biomedicine and biotechnology.

Artificial lipids have become increasingly important in generating novel nanoenzymes and nanoparticles. Imidazole has been well established as a versatile catalyst in synthetic chemistry and through its related amino acid histidine in enzymes. By exploiting the transphosphatidylation reaction of phospholipase D, the choline headgroup of phosphatidyl choline was exchanged for the imidazole moiety containing histidinol. Here, we introduce a novel phosphatidylhistidinol (PtdHisOH) lipid and characterise it with respect to its catalytic abilities and its ability to modulate vesicle size. Our data reveal a zinc-dependent esterase activity that was strongest in vesicles and micelles, with slower catalytic rates being observed in flat lipid presentation systems and two-phase systems, indicating the importance of surface presentation and curvature effects on the catalytic activity of PtdHisOH. Such lipids offer the opportunity to impart de novo catalytic functionality to self-assembled lipid systems such as synthetic cells, leading to the development of new technologies for biocatalysis applications.

Encapsulating biological and non-biological materials in lipid vesicles presents significant potential in both industrial and academic settings. When smaller than 100 nm, lipid vesicles and lipid nanoparticles are ideal vehicles for drug delivery, facilitating the delivery of payloads, improving pharmacokinetics, and reducing the off-target effects of therapeutics. When larger than 1 μm, vesicles are useful as model membranes for biophysical studies, as synthetic cell chassis, as bio-inspired supramolecular devices, and as the basis of protocells to explore the origin of life. As applications of lipid vesicles gain prominence in the fields of nanomedicine, biotechnology, and synthetic biology, there is a demand for advanced technologies for their controlled construction, with microfluidic methods at the forefront of these developments. Compared to conventional bulk methods, emerging microfluidic methods offer advantages such as precise size control, increased production throughput, high encapsulation efficiency, user-defined membrane properties (i.e., lipid composition, vesicular architecture, compartmentalisation, membrane asymmetry, etc.), and potential integration with lab-on-chip manipulation and analysis modules. We provide a review of microfluidic lipid vesicle generation technologies, focusing on recent advances and state-of-the-art techniques. Principal technologies are described, and key research milestones are highlighted. The advantages and limitations of each approach are evaluated, and challenges and opportunities for microfluidic engineering of lipid vesicles to underpin a new generation of therapeutics, vaccines, sensors, and bio-inspired technologies are presented.

Artificial cells are biomimetic structures formed from molecular building blocks that replicate biological processes, behaviors, and architectures. Of these building blocks, hydrogels have emerged as ideal, yet underutilized candidates to provide a gel -like chassis in which to incorporate both biological and nonbiological componentry which enables the replication of cellular functionality. Here, we demonstrate a microfluidic strategy to assemble biocompatible cell -sized hydrogel- based artificial cells with a variety of different embedded functional subcompartments, which act as engineered synthetic organelles. The organelles enable the recreation of increasingly biomimetic behaviors, including stimulus-induced motility, content release through activation of membrane-associated proteins, and enzymatic communication with surrounding bioinspired compartments. In this way, we showcase a foundational strategy for the bottom-up construction of hydrogel- based artificial cell microsystems which replicate fundamental cellular behaviors, paving the way for the construction of next-generation biotechnological devices.

One of the main drivers within the field of bottom-up synthetic biology is to develop artificial chemical machines, perhaps even living systems, that have programmable functionality. Numerous toolkits exist to generate giant unilamellar vesicle-based artificial cells. However, methods able to quantitatively measure their molecular constituents upon formation is an underdeveloped area. We report an artificial cell quality control (AC/QC) protocol using a microfluidic-based single-molecule approach, enabling the absolute quantification of encapsulated biomolecules. While the measured average encapsulation efficiency was 11.4 ± 6.8%, the AC/QC method allowed us to determine encapsulation efficiencies per vesicle, which varied significantly from 2.4 to 41%. We show that it is possible to achieve a desired concentration of biomolecule within each vesicle by commensurate compensation of its concentration in the seed emulsion. However, the variability in encapsulation efficiency suggests caution is necessary when using such vesicles as simplified biological models or standards.

Recent years have seen substantial efforts aimed at constructing artificial cells from various molecular components with the aim of mimicking the processes, behaviours and architectures found in biological systems. Artificial cell development ultimately aims to produce model constructs that progress our understanding of biology, as well as forming the basis for functional bio-inspired devices that can be used in fields such as therapeutic delivery, biosensing, cell therapy and bioremediation. Typically, artificial cells rely on a bilayer membrane chassis and have fluid aqueous interiors to mimic biological cells. However, a desire to more accurately replicate the gel-like properties of intracellular and extracellular biological environments has driven increasing efforts to build cell mimics based on hydrogels. This has enabled researchers to exploit some of the unique functional properties of hydrogels that have seen them deployed in fields such as tissue engineering, biomaterials and drug delivery. In this Review, we explore how hydrogels can be leveraged in the context of artificial cell development. We also discuss how hydrogels can potentially be incorporated within the next generation of artificial cells to engineer improved biological mimics and functional microsystems.

Simple diffusion of molecular entities through a phospholipid bilayer, is a phenomenon of great importance to the pharmaceutical and agricultural industries. Current model lipid systems to probe this typically only employ fluorescence as a readout, thus limiting the range of assessable chemical matter that can be studied. We report a new technology platform, the UV-DIB, which facilitates label free measurement of small molecule translocation rates. This is based upon the coupling of droplet interface bilayer technology with implemented fiber optics to facilitate analysis via ultraviolet spectroscopy, in custom designed PMMA wells. To improve on current DIB technology, the platform was designed to be reusable, with a high sampling rate and a limit of UV detection in the low μM regime. We demonstrate the use of our system to quantify passive diffusion in a reproducible and rapid manner where the system was validated by investigating multiple permeants of varying physicochemical properties across a range of lipid interfaces, each demonstrating differing kinetics. Our system permits the interrogation of structural dependence on the permeation rate of a given compound. We present this ability from two structural perspectives, that of the membrane, and the permeant. We observed a reduction in permeability between pure DOPC and DPhPC interfaces, concurring with literature and demonstrating our ability to study the effects of lipid composition on permeability. In relation to the effects of permeant structure, our device facilitated the rank ordering of various compounds from the xanthine class of compounds, where the structure of each permeant differed by a single group alteration. We found that DIBs were stable up to 5% DMSO, a molecule often used to aid solubilisation of pharmaceutical and agrochemical compounds. The ability of our device to rank-order compounds with such minor structural differences provides a level of precision that is rarely seen in current, industrially applied technologies.

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.

Lipid membranes are vital in a wide range of biological and biotechnical systems; underpinning functions from modulation of protein activity to drug uptake and delivery. Rapid in situ determination of phase behaviour is a key experimental objective.

Artificial cells are minimal structures constructed from biomolecular building blocks designed to mimic cellular processes, behaviors, and architectures. One near-ubiquitous feature of cellular life is the spatial organization of internal content. We know from biology that organization of content (including in membrane-bound organelles) is linked to cellular functions and that this feature is dynamic: the presence, location, and degree of compartmentalization changes over time. Vesicle-based artificial cells, however, are not currently able to mimic this fundamental cellular property. Here, we describe an artificial cell design strategy that addresses this technological bottleneck. We create a series of artificial cell architectures which possess multicompartment assemblies localized either on the inner or on the outer surface of the artificial cell membrane. Exploiting liquid-liquid phase separation, we can also engineer spatially segregated regions of condensed subcompartments attached to the cell surface, aligning with coexisting membrane domains. These structures can sense changes in environmental conditions and respond by reversibly transitioning from condensed multicompartment layers on the membrane surface to a dispersed state in the cell lumen, mimicking the dynamic compartmentalization found in biological cells. Likewise, we engineer exosome-like subcompartments that can be released to the environment. We can achieve this by using two types of triggers: chemical (addition of salts) and mechanical (by pulling membrane tethers using optical traps). These approaches allow us to control the compartmentalization state of artificial cells on population and single-cell levels.

The interactions between small molecules and keratins are poorly understood. In this paper, a nuclear magnetic resonance method is presented to measure changes in the 1H T1 relaxation times of small molecules in human hair keratin to quantify their interaction with the fibre. Two populations of small-molecule compounds were identified with distinct relaxation times, demonstrating the partitioning of the compounds into different keratin environments. The changes in relaxation time for solvent in hair compared with bulk solvent were shown to be related to the molecular weight (MW) and the partition coefficient, LogP, of the solvent investigated. Compounds with low MWs and high hydrophilicities had greater reductions in their T1 relaxation times and therefore experienced increased interactions with the hair fibre. The relative population sizes were also calculated. This is a significant step towards modelling the behaviour of small molecules in keratinous materials and other large insoluble fibrous proteins.

Cellular life relies on membranes, which provide a resilient and adaptive cell boundary. Many essential processes depend upon the ease with which the membrane is able to deform and bend, features that can be characterized by the bending rigidity. Quantitative investigations of such mechanical properties of biological membranes have primarily been undertaken in solely lipid bilayers and frequently in the absence of buffers. In contrast, much less is known about the influence of integral membrane proteins on bending rigidity under physiological conditions. We focus on an exemplar member of the ubiquitous major facilitator superfamily of transporters and assess the influence of lactose permease on the bending rigidity of lipid bilayers. Fluctuation analysis of giant unilamellar vesicles (GUVs) is a useful means to measure bending rigidity. We find that using a hydrogel substrate produces GUVs that are well suited to fluctuation analysis. Moreover, the hydrogel method is amenable to both physiological salt concentrations and anionic lipids, which are important to mimic key aspects of the native lactose permease membrane. Varying the fraction of the anionic lipid in the lipid mixture DOPC/DOPE/DOPG allows us to assess the dependence of membrane bending rigidity on the topology and concentration of an integral membrane protein in the lipid bilayer of GUVs. The bending rigidity gradually increases with the incorporation of lactose permease, but there is no further increase with greater amounts of the protein in the membrane.

Droplet microcompartments linked by lipid bilayers show great promise in the construction of synthetic minimal tissues. Central to controlling the flow of information in these systems are membrane proteins, which can gate in response to specific stimuli in order to control the molecular flux between membrane separated compartments. This has been demonstrated with droplet interface bilayers (DIBs) using several different membrane proteins combined with electrical, mechanical, and/or chemical activators. Here we report the activation of the bacterial mechanosensitive channel of large conductance (MscL) in a dioleoylphosphatidylcholine:dioleoylphosphatidylglycerol DIB by controlling membrane asymmetry. We show using electrical measurements that the incorporation of lysophosphatidylcholine (LPC) into one of the bilayer leaflets triggers MscL gating in a concentration-dependent manner, with partial and full activation observed at 10 and 15 mol% LPC respectively. Our findings could inspire the design of new minimal tissues where flux pathways are dynamically defined by lipid composition.