Response‐Retaliation Behavior in Synthetic Protocell Communities

Models of Chemical Communication for Micro/Nanoparticles

Engineering chemical communication between micro/nanosystems (via the exchange of chemical messengers) is receiving increasing attention from the scientific community. Although a number of micro- and nanodevices (e.g., drug carriers, sensors, and artificial cells) have been developed in the last decades, engineering communication at the micro/nanoscale is a recent emergent topic. In fact, most of the studies in this research area have been published within the last 10 years. Inspired by nature─where information is exchanged by means of molecules─the development of chemical communication strategies holds wide implications as it may provide breakthroughs in many areas including nanotechnology, artificial cell research, biomedicine, biotechnology, and ICT. Published examples rely on nanotechnology and synthetic biology for the creation of micro- and nanodevices that can communicate. Communication enables the construction of new complex systems capable of performing advanced coordinated tasks that go beyond those carried out by individual entities. In addition, the possibility to communicate between synthetic and living systems can further advance our understanding of biochemical processes and provide completely new tailored therapeutic and diagnostic strategies, ways to tune cellular behavior, and new biotechnological tools. In this Account, we summarize advances by our laboratories (and others) in the engineering of chemical communication of micro- and nanoparticles. This Account is structured to provide researchers from different fields with general strategies and common ground for the rational design of future communication networks at the micro/nanoscale. First, we cover the basis of and describe enabling technologies to engineer particles with communication capabilities. Next, we rationalize general models of chemical communication. These models vary from simple linear communication (transmission of information between two points) to more complex pathways such as interactive communication and multicomponent communication (involving several entities). Using illustrative experimental designs, we demonstrate the realization of these models which involve communication not only between engineered micro/nanoparticles but also between particles and living systems. Finally, we discuss the current state of the topic and the future challenges to be addressed.

Superstructural ordering in self-sorting coacervate-based protocell networks

Bottom-up assembly of higher-order cytomimetic systems capable of coordinated physical behaviours, collective chemical signalling and spatially integrated processing is a key challenge in the study of artificial multicellularity. Here we develop an interactive binary population of coacervate microdroplets that spontaneously self-sort into chain-like protocell networks with an alternating sequence of structurally and compositionally dissimilar microdomains with hemispherical contact points. The protocell superstructures exhibit macromolecular self-sorting, spatially localized enzyme/ribozyme biocatalysis and interdroplet molecular translocation. They are capable of topographical reconfiguration using chemical or light-mediated stimuli and can be used as a micro-extraction system for macroscale biomolecular sorting. Our methodology opens a pathway towards the self-assembly of multicomponent protocell networks based on selective processes of coacervate droplet-droplet adhesion and fusion, and provides a step towards the spontaneous orchestration of protocell models into artificial tissues and colonies with ordered architectures and collective functions.

Autonomic Integration in Nested Protocell Communities

The self-driven organization of model protocells into higher-order nested cytomimetic systems with coordinated structural and functional relationships offers a step toward the autonomic implementation of artificial multicellularity. Here, we describe an endosymbiotic-like pathway in which proteinosomes are captured within membranized alginate/silk fibroin coacervate vesicles by guest-mediated reconfiguration of the host protocells. We demonstrate that interchange of coacervate vesicle and droplet morphologies through proteinosome-mediated urease/glucose oxidase activity produces discrete nested communities capable of integrated catalytic activity and selective disintegration. The self-driving capacity is modulated by an internalized fuel-driven process using starch hydrolases sequestered within the host coacervate phase, and structural stabilization of the integrated protocell populations can be achieved by on-site enzyme-mediated matrix reinforcement involving dipeptide supramolecular assembly or tyramine-alginate covalent cross-linking. Our work highlights a semi-autonomous mechanism for constructing symbiotic cell-like nested communities and provides opportunities for the development of reconfigurable cytomimetic materials with structural, functional, and organizational complexity.

An Overview of Coacervates: The Special Disperse State of Amphiphilic and Polymeric Materials in Solution

Individual amphiphiles, polymers, and colloidal dispersions influenced by temperature, pH, and environmental conditions or interactions between their oppositely charged pairs in solvent medium often produce solvent-rich and solvent-poor phases in the system. The solvent-poor denser phase found either on the top or the bottom of the system is called coacervate. Coacervates have immense applications in various technological fields. This review comprises a concise introduction, focusing on the types of coacervates, and the influence of different factors in their formation, structures, and stability. In addition, their physicochemical properties, thermodynamics of formation, and uses and multifarious applications are also concisely presented and discussed.

Fatty Acid-Based Coacervates as a Membrane-free Protocell Model

Membrane-less scenarios that involve liquid-liquid phase separation (coacervation) provide clues for how protocells might emerge. Here, we report a versatile approach to construct coacervates by mixing fatty acid with biomolecule dopamine as the protocell model. The coacervate droplets are easily formed over a wide range of concentrations. The solutes with different interaction characteristics, including cationic, anionic, and hydrophobic dyes, can be well concentrated within the coacervates. In addition, reversible self-assemblies of the coacervates can be controlled by concentration, pH, temperature, salinity, and bioreaction realizing cycles between compartmentalization and noncompartmentalization. Through in situ dopamine polymerization, the stability of coacervate droplets is significantly improved, leading to higher resistance toward external factors. Therefore, the coacervates based on fatty acid and dopamine could serve as a bottom-up membrane-less protocell model that provides the links between the simple (small molecule) and complex (macromolecule) systems in the process of cell evolution.

Construction of protocell-based artificial signal transduction pathways

The maintenance of an orderly and controllable multicellular society depends on the communication and signal regulation between various types of biological cells. How to replicate complicated signal transduction pathways in synthetic protocellular communities remains a key challenge in bottom-up synthetic biology. Herein, we review recent advances in the design and construction of interactive protocell communities, or protocell communities and biological communities, and explore the ways of designing and constructing artificial paracrine-like signaling pathways and juxtacrine-like signaling pathways. Key molecules involved in the signaling pathways that can be used to connect two or more spatially separated communities, and diverse signal outputs generated by the communication are summarized. We also propose the limitations, challenges and opportunities in this field.

Therapeutic nanoreactors for detoxification of xenobiotics: Concepts, challenges and biotechnological trends with special emphasis to organophosphate bioscavenging

The introduction of enzyme nanoreactors in medicine is relatively new. However, this technology has already been experimentally successful in cancer treatments, struggle against toxicity of reactive oxygen species in inflammatory processes, detoxification of drugs and xenobiotics, and correction of metabolic and genetic defects by using encapsulated enzymes, acting in single or cascade reactions. Biomolecules, e.g. enzymes, antibodies, reactive proteins capable of inactivating toxicants in the body are called bioscavengers. In this review, we focus on enzyme-containing nanoreactors for in vivo detoxification of organophosphorous compounds (OP) to be used for prophylaxis and post-exposure treatment of OP poisoning. A particular attention is devoted to bioscavenger-containing injectable nanoreactors operating in the bloodstream. The nanoreactor concept implements single or multiple enzymes and cofactors co-encapsulated in polymeric semi-permeable nanocontainers. Thus, the detoxification processes take place in a confined space containing highly concentrated bioscavengers. The article deals with historical and theoretical backgrounds about enzymatic detoxification of OPs in nanoreactors, nanoreactor polymeric enveloppes, realizations and advantages over other approaches using bioscavengers.

Interfacing Living and Synthetic Cells as an Emerging Frontier in Synthetic Biology

The construction of artificial cells from inanimate molecular building blocks is one of the grand challenges of our time. In addition to being used as simplified cell models to decipher the rules of life, artificial cells have the potential to be designed as micromachines deployed in a host of clinical and industrial applications. The attractions of engineering artificial cells from scratch, as opposed to re-engineering living biological cells, are varied. However, it is clear that artificial cells cannot currently match the power and behavioural sophistication of their biological counterparts. Given this, many in the synthetic biology community have started to ask: is it possible to interface biological and artificial cells together to create hybrid living/synthetic systems that leverage the advantages of both? This article will discuss the motivation behind this cellular bionics approach, in which the boundaries between living and non-living matter are blurred by bridging top-down and bottom-up synthetic biology. It details the state of play of this nascent field and introduces three generalised hybridisation modes that have emerged.

Interfacing Living and Synthetic Cells as an Emerging Frontier in Synthetic Biology

The construction of artificial cells from inanimate molecular building blocks is one of the grand challenges of our time. In addition to being used as simplified cell models to decipher the rules of life, artificial cells have the potential to be designed as micromachines deployed in a host of clinical and industrial applications. The attractions of engineering artificial cells from scratch, as opposed to re-engineering living biological cells, are varied. However, it is clear that artificial cells cannot currently match the power and behavioural sophistication of their biological counterparts. Given this, many in the synthetic biology community have started to ask: is it possible to interface biological and artificial cells together to create hybrid living/synthetic systems that leverage the advantages of both? This article will discuss the motivation behind this cellular bionics approach, in which the boundaries between living and non-living matter are blurred by bridging top-down and bottom-up synthetic biology. It details the state of play of this nascent field and introduces three generalised hybridisation modes that have emerged.