Subcompartmentalized Nanoreactors as Artificial Organelle with Intracellular Activity

Organismal Function Enhancement through Biomaterial Intervention

Living organisms in nature, such as magnetotactic bacteria and eggs, generate various organic-inorganic hybrid materials, providing unique functionalities. Inspired by such natural hybrid materials, researchers can reasonably integrate biomaterials with living organisms either internally or externally to enhance their inherent capabilities and generate new functionalities. Currently, the approaches to enhancing organismal function through biomaterial intervention have undergone rapid development, progressing from the cellular level to the subcellular or multicellular level. In this review, we will concentrate on three key strategies related to biomaterial-guided bioenhancement, including biointerface engineering, artificial organelles, and 3D multicellular immune niches. For biointerface engineering, excess of amino acid residues on the surfaces of cells or viruses enables the assembly of materials to form versatile artificial shells, facilitating vaccine engineering and biological camouflage. Artificial organelles refer to artificial subcellular reactors made of biomaterials that persist in the cytoplasm, which imparts cells with on-demand regulatory ability. Moreover, macroscale biomaterials with spatiotemporal regulation characters enable the local recruitment and aggregation of cells, denoting multicellular niche to enhance crosstalk between cells and antigens. Collectively, harnessing the programmable chemical and biological attributes of biomaterials for organismal function enhancement shows significant potential in forthcoming biomedical applications.

Enzyme-active liquid coacervate microdroplets as artificial membraneless organelles for intracellular ROS scavenging

Artificial organelles are microcompartments capable of performing catalytic reactions in living cells to replace absent or lost cellular functions. Coacervate microdroplets, formed via liquid-liquid phase separation, have been developed as...

Chemical communication at the synthetic cell/living cell interface

Although the complexity of synthetic cells has continued to increase in recent years, chemical communication between protocell models and living organisms remains a key challenge in bottom-up synthetic biology and bioengineering. In this Review, we discuss how communication channels and modes of signal processing can be established between living cells and cytomimetic agents such as giant unilamellar lipid vesicles, proteinosomes, polysaccharidosomes, polymer-based giant vesicles and membrane-less coacervate micro-droplets. We describe three potential modes of chemical communication in consortia of synthetic and living cells based on mechanisms of distributed communication and signal processing, physical embodiment and nested communication, and network-based contact-dependent communication. We survey the potential for applying synthetic cell/living cell communication systems in biomedicine, including the in situ production of therapeutics and development of new bioreactors. Finally, we present a short summary of our findings.

Validating an artificial organelle: Studies of lipid droplet-specific proteins on adiposome platform

New strategies are urgently needed to characterize the functions of the lipid droplet (LD). Here, adiposome, an artificial LD mimetic platform, was validated by comparative in vitro bioassays. Scatchard analysis found that the binding of perilipin 2 (PLIN2) to the adiposome surface was saturable. Phosphatidylinositol (PtdIns) was found to inhibit PLIN2 binding while it did not impede perilipin 3 (PLIN3). Structural analysis combined with mutagenesis revealed that the 73rd glutamic acid of PLIN2 is significant for the effect of PtdIns on the PLIN2 binding. Furthermore, adiposome was also found to be an ideal platform for in situ enzymatic activity measurement of adipose triglyceride lipase (ATGL). The significant serine mutants of ATGL were found to cause the loss of lipase activity. Our study demonstrates the adiposome as a powerful, manipulatable model system that mimics the function of LD for binding and enzymatic activity studies of LD proteins in vitro.

Artificial Organelles: Towards Adding or Restoring Intracellular Activity

Compartmentalization is one of the main characteristics that define living systems. Creating a physically separated microenvironment allows nature a better control over biological processes, as is clearly specified by the role of organelles in living cells. Inspired by this phenomenon, researchers have developed a range of different approaches to create artificial organelles: compartments with catalytic activity that add new function to living cells. In this review we will discuss three complementary lines of investigation. First, orthogonal chemistry approaches are discussed, which are based on the incorporation of catalytically active transition metal-containing nanoparticles in living cells. The second approach involves the use of premade hybrid nanoreactors, which show transient function when taken up by living cells. The third approach utilizes mostly genetic engineering methods to create bio-based structures that can be ultimately integrated with the cell's genome to make them constitutively active. The current state of the art and the scope and limitations of the field will be highlighted with selected examples from the three approaches.

Enzyme-Loaded Nanoreactors Enable the Continuous Regeneration of Nicotinamide Adenine Dinucleotide in Artificial Metabolisms

Nicotinamide adenine dinucleotide (NAD) is an essential coenzyme for numerous biocatalytic pathways. While in nature, NAD+ is continuously regenerated from NADH by enzymes, all synthetic NAD+ regeneration strategies require a continuous supply of expensive reagents and generate byproducts, making these strategies unattractive. In contrast, we present an artificial enzyme combination that produces NAD+ from oxygen and water continuously; no additional organic substrates are required once a minimal amount pyruvate is supplied. Three enzymes, i.e., LDH, LOX, and CAT, are covalently encapsulated into a substrate-permeable silica nanoreactor by a mild fluoride-catalyzed sol-gel process. The enzymes retain their activity inside of the nanoreactors and are protected against proteolysis and heat. We successfully used NAD+ from the nanoreactors for the continuous production of NAD+ i) to sense glucose in artificial glucose metabolism, and ii) to reduce the non-oxygen binding methemoglobin to oxygen-binding hemoglobin. This latter conversion might be used for the treatment of Methemoglobinemia. We believe that this versatile tool will allow the design of artificial NAD+ -dependent metabolisms or NAD+ -mediated redox-reactions.

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.

Self-sustaining enzyme nanocapsules perform on-site chemical reactions

Nanoreactors offer a great platform for the onsite generation of functional products. However, the production of the desired compound is often limited by either the availability of the reagents or their diffusion across the nanoreactor shell. To overcome this issue, we synthesized self-sustaining nanoreactors carrying the required reagents with them. They are composed of active enzymes crosslinked as nanocapsules and the inner core serves as a reservoir for reagents. Upon trigger, the enzymatic shell catalyzes the conversion of the encapsulated payload. This concept was demonstrated by the preparation of nanoreactors loaded with sensing molecules for the detection of glucose in biological media. More importantly, the system introduced here serves as an adaptable platform for biomedical applications, since the nanoreactors display good cellular uptake and high activity within cells. Consequently, they could act as nanofactories for the in situ generation of functional molecules.

Polymer-Lipid Hybrid Vesicles and Their Interaction with HepG2 Cells

Polymer-lipid hybrid vesicles are an emerging type of nano-assemblies that show potential as artificial organelles among others. Phospholipids and poly(cholesteryl methacrylate)-block-poly(methionine methacryloyloxyethyl ester (METMA)-random-2-carboxyethyl acrylate (CEA)) labeled with a Förster resonance energy transfer (FRET) reporter pair are used for the assembly of small and giant hybrid vesicles with homogenous distribution of both building blocks in the membrane as confirmed by the FRET effect. These hybrid vesicles have no inherent cytotoxicity when incubated with HepG2 cells up to 1.1 × 10¹¹ hybrid vesicles per mL, and they are internalized by the cells. In contrast to the fluorescent signal originating from the block copolymer, the fluorescent signal coming from the lipids is barely detectable in cells incubated with hybrid vesicles for 6 h followed by 24 h in cell media, suggesting that the two building blocks have a different intracellular fate. These findings provide important insight into the design criteria of artificial organelles with potential structural integrity.

Biomolecule–polymer hybrid compartments: combining the best of both worlds

Recent advances in bio/polymer hybrid compartments in the quest to obtain artificial cells, biosensors and catalytic compartments.

A dual-component carrier with both non-enzymatic and enzymatic antioxidant activity towards ROS depletion

While ROS display crucial functions in many physiological processes, elevated ROS levels are also related to the initiation and progression of many severe diseases such as cancer, cardiovascular conditions or neurologic disorders. Research approaches to diminish ROS levels during disease progression are currently being focused on the therapeutic administration of antioxidant enzymes. However, enzyme administration suffers from several limitations including their fast elimination from blood upon administration, thus making crucial the development of enzyme encapsulating platforms. We have recently reported a multicompartment architecture constituted by two inherently different types of materials, i.e., polymeric microgels and liposomes. Poly(N-isopropylacrylamide-co-acrylic acid) microgels decorated with liposomes and subsequently coated by a protective poly(dopamine) shell (PDA) combine the benefits of both systems while minimizing some of their drawbacks. Herein, we exploit this dual-component platform as a microreactor for ROS depletion. We combine the intrinsic PDA's antioxidant properties with the encapsulation of the catalase enzyme within the liposomal compartments. The surface of the carrier is further functionalised with a poly(ethylene glycol) layer and the low fouling properties are demonstrated in terms of reduction of protein adsorption and cellular uptake. The potential of the carrier as an antioxidant microreactor is shown by its ability to deplete superoxide radicals and hydrogen peroxide, which can also take place in the presence of the two relevant cell lines.

Mimicking Cellular Compartmentalization in a Hierarchical Protocell through Spontaneous Spatial Organization

A systemic feature of eukaryotic cells is the spatial organization of functional components through compartmentalization. Developing protocells with compartmentalized synthetic organelles is, therefore, a critical milestone toward emulating one of the core characteristics of cellular life. Here we demonstrate the bottom-up, multistep, noncovalent, assembly of rudimentary subcompartmentalized protocells through the spontaneous encapsulation of semipermeable, polymersome proto-organelles inside cell-sized coacervates. The coacervate microdroplets are membranized using tailor-made terpolymers, to complete the hierarchical self-assembly of protocells, a system that mimics both the condensed cytosol and the structure of a cell membrane. In this way, the spatial organization of enzymes can be finely tuned, leading to an enhancement of functionality. Moreover, incompatible components can be sequestered in the same microenvironments without detrimental effect. The robust stability of the subcompartmentalized coacervate protocells in biocompatible milieu, such as in PBS or cell culture media, makes it a versatile platform to be extended toward studies in vitro, and perhaps, in vivo.

Hybrid vesicles as intracellular reactive oxygen species and nitric oxide generators

Artificial organelles are envisioned as nanosized assemblies with intracellular biocatalytic activity to provide the host cells with non-native or missing/lost function. Hybrid vesicles loaded with glucose oxidase (NRGOx) or β-galactosidase (NRβ-Gal) and equipped with lysosomal escape ability are assembled using phospholipids and the block copolymer poly(cholesteryl methacrylate)-block-poly(2-(dimethylamino)ethyl methacrylate). The co-localization of the building blocks and the catalytic activity of NRGOx and NRβ-Gal are illustrated. The intracellular activity of the nanoreactors in RAW 264.7 macrophages is confirmed by an enhanced reduction in viability for cells pre-incubated with NRGOx in the presence of glucose due to the generation of cytotoxic hydrogen peroxide compared to the controls. In addition, RAW 264.7 macrophages and primary human macrophages equipped with NRβ-Gal are able to intracellularly convert β-Gal-NONOate into nitric oxide. The successful use of these hybrid vesicles to equip host macrophages with additional catalytic activity diversifies the available toolbox of nanocarriers with envisioned application in cell mimicry.

Tyrosinase-Loaded Multicompartment Microreactor toward Melanoma Depletion

Melanoma is malignant skin cancer occurring with increasing prevalence with no effective treatment. A unique feature of melanoma cells is that they require higher concentrations of ltyrosine (l-tyr) for expansion than normal cells. As such, it has been demonstrated that dietary l-tyr restriction lowers systemic l-tyr and suppresses melanoma advancement in mice. Unfortunately, this diet is not well tolerated by humans. An alternative approach to impede melanoma progression will be to administer the enzyme tyrosinase (TYR), which converts l-tyr into melanin. Herein, a multicompartment carrier consisting of a polymer shell entrapping thousands of liposomes is employed to act as a microreactor depleting l-tyr in the presence of melanoma cells. It is shown that the TYR enzyme can be incorporated within the liposomal subunits with preserved catalytic activity. Aiming to mimic the dynamic environment at the tumor site, l-tyr conversion is conducted by co-culturing melanoma cells and microreactors in a microfluidic setup with applied intratumor shear stress. It is demonstrated that the microreactors are concurrently depleting l-tyr, which translates into inhibited melanoma cell growth. Thus, the first microreactor where the depletion of a substrate translates into antitumor properties in vitro is reported.

Intrinsically permeable polymer vesicles based on carbohydrate-conjugated poly(2-oxazoline)s synthesized using a carbohydrate-based initiator system

A thermo-responsive poly(n-propyl oxazoline) block was employed as the hydrophobic segment in an amphiphilic glyco polymer. This approach affords intrinsically permeable polymer vesicles for water-soluble compounds.

Biotransporting Biocatalytic Reactors toward Therapeutic Nanofactories

Drug-delivery systems (DDSs), in which drug encapsulation in nanoparticles enables targeted delivery of therapeutic agents and their release at specific disease sites, are important because they improve drug efficacy and help to decrease side effects. Although significant progress has been made in the development of DDSs for the treatment of a wide range of diseases, new approaches that increase the scope and effectiveness of such systems are still needed. Concepts such as nanoreactors and nanofactories are therefore attracting much attention. Nanoreactors, which basically consist of vesicle-encapsulated enzymes, provide prodrug conversion to therapeutic agents rather than simple drug delivery. Nanofactories are an extension of this concept and combine the features of nanoreactors and delivery carriers. Here, the required features of nanofactories are discussed and an overview of current strategies for the design and fabrication of different types of nanoreactors, i.e., systems based on lipid or polymer vesicles, capsules, mesoporous silica, viral capsids, and hydrogels, and their respective advantages and shortcomings, is provided. In vivo applications of biocatalytic reactors in the treatment of cancer, glaucoma, neuropathic pain, and alcohol intoxication are also discussed. Finally, the prospects for further progress in this important and promising field are outlined.

Biomimetic Cascade Network between Interactive Multicompartments Organized by Enzyme-Loaded Silica Nanoreactors

Physical separation of reactions by interactive multicompartments in biological cells is an attractive motif to design efficient microreactors that create biomimetic cascade reactions. We present an aqueous compartment with three different subcompartments that comprise of silica nanoreactors with encapsulated enzymes, namely, β-glucosidase, glucose oxidase, and peroxidase, providing a model cascade reaction in confinement. The encapsulated enzymes retain their activity as the substrate can reach the active site and the silica shell further protects the enzymes from external stresses, such as heat and proteolytic degradation. We demonstrate the biomimetic cascade reaction in between the compartments ("organelles") inside of an additional microconfinement (water-in-oil emulsion). This strategy will allow us to design efficient multicompartmentalized reactors for further biological and organic reactions.

Biomimetic artificial organelles with in vitro and in vivo activity triggered by reduction in microenvironment

Despite tremendous efforts to develop stimuli-responsive enzyme delivery systems, their efficacy has been mostly limited to in vitro applications. Here we introduce, by using an approach of combining biomolecules with artificial compartments, a biomimetic strategy to create artificial organelles (AOs) as cellular implants, with endogenous stimuli-triggered enzymatic activity. AOs are produced by inserting protein gates in the membrane of polymersomes containing horseradish peroxidase enzymes selected as a model for natures own enzymes involved in the redox homoeostasis. The inserted protein gates are engineered by attaching molecular caps to genetically modified channel porins in order to induce redox-responsive control of the molecular flow through the membrane. AOs preserve their structure and are activated by intracellular glutathione levels in vitro. Importantly, our biomimetic AOs are functional in vivo in zebrafish embryos, which demonstrates the feasibility of using AOs as cellular implants in living organisms. This opens new perspectives for patient-oriented protein therapy.

The efficacy of stimuli-responsive enzyme delivery systems is usually limited to in vitro applications. Here the authors form artificial organelles by inserting stimuli-responsive protein gates in membranes of polymersomes loaded with enzymes and obtain a triggered functionality both in vitro and in vivo.

Recent Progress in Micro/Nanoreactors toward the Creation of Artificial Organelles

Artificial organelles created from a bottom up approach are a new type of engineered materials, which are not designed to be living but, instead, to mimic some specific functions inside cells. By doing so, artificial organelles are expected to become a powerful tool in biomedicine. They can act as nanoreactors to convert a prodrug into a drug inside the cells or as carriers encapsulating therapeutic enzymes to replace malfunctioning organelles in pathological conditions. For the design of artificial organelles, several requirements need to be fulfilled: a compartmentalized structure that can encapsulate the synthetic machinery to perform an enzymatic function, as well as a means to allow for communication between the interior of the artificial organelle and the external environment, so that substrates and products can diffuse in and out the carrier allowing for continuous enzymatic reactions. The most recent and exciting advances in architectures that fulfill the aforementioned requirements are featured in this review. Artificial organelles are classified depending on their constituting materials, being lipid and polymer-based systems the most prominent ones. Finally, special emphasis will be put on the intracellular response of these newly emerging systems.

Interaction of cells with patterned reactors

The patterning of subcompartmentalized enzyme-loaded reactors is illustrated and the effect of triggered encapsulated catalysis on adhering cells is reported.

Morphology Under Control: Engineering Biodegradable Stomatocytes

Biodegradable nanoarchitectures, with well-defined morphological features, are of great importance for nanomedical research; however, understanding (and thereby engineering) their formation is a substantial challenge. Herein, we uncover the supramolecular potential of PEG-PDLLA copolymers by exploring the physicochemical determinants that result in the transformation of spherical polymersomes into stomatocytes. To this end, we have engineered blended polymersomes (comprising copolymers with varying lengths of PEG), which undergo solvent-dependent reorganization inducing negative spontaneous membrane curvature. Under conditions of anisotropic solvent composition across the PDLLA membrane, facilitated by the dialysis methodology, we demonstrate osmotically induced stomatocyte formation as a consequence of changes in PEG solvation, inducing negative spontaneous membrane curvature. Controlled formation of unprecedented, biodegradable stomatocytes represents the unification of supramolecular engineering with the theoretical understanding of shape transformation phenomena.

Planar and Cell Aggregate-Like Assemblies Consisting of Microreactors and HepG2 Cells

The assembly of microreactors has made considerable progress toward the fabrication of artificial cells. However, their characterization remains largely limited to buffer solution-based assays in the absence of their natural role model-the biological cells. Herein, the combination of microreactors with HepG2 cells either in planar cell cultures or in the form of cell aggregates is reported. Alginate (Alg)-based microreactors loaded with catalase are assembled by droplet microfluidics, and their activity is confirmed. The acceptance of polymer-coated ∼40 μm Alg particles by proliferating HepG2 cells is depending on the terminating polymer layer. When these functional microreactors are cocultured with HepG2 cells, they can be employed for detoxification, that is, hydrogen peroxide removal, and by doing so, they assist the cells to survive. This report is among the first successful combination of microreactors with biological cells, that is, HepG2 cells, contributing to the fundamental understanding of integrating synthetic and biological partners toward the maturation of this semisynthetic concept for biomedical applications.

Biomimetic Strategy To Reversibly Trigger Functionality of Catalytic Nanocompartments by the Insertion of pH-Responsive Biovalves

We describe an innovative strategy to generate catalytic compartments with triggered functionality at the nanoscale level by combining pH-reversible biovalves and enzyme-loaded synthetic compartments. The biovalve has been engineered by the attachment of stimuli-responsive peptides to a genetically modified channel porin, enabling a reversible change of the molecular flow through the pores of the porin in response to a pH change in the local environment. The biovalve functionality triggers the reaction inside the cavity of the enzyme-loaded compartments by switching the in situ activity of the enzymes on/off based on a reversible change of the permeability of the membrane, which blocks or allows the passage of substrates and products. The complex functionality of our catalytic compartments is based on the preservation of the integrity of the compartments to protect encapsulated enzymes. An increase of the in situ activity compared to that of the free enzyme and a reversible on/off switch of the activity upon the presence of a specific stimulus is achieved. This strategy provides straightforward solutions for the development of catalytic nanocompartments efficiently producing desired molecules in a controlled, stimuli-responsive manner with high potential in areas, such as medicine, analytical chemistry, and catalysis.

Enzymes as key features in therapeutic cell mimicry

Cell mimicry is a nature inspired concept that aims to substitute for missing or lost (sub)cellular function. This review focuses on the latest advancements in the use of enzymes in cell mimicry for encapsulated catalysis and artificial motility in synthetic bottom-up assemblies with emphasis on the biological response in cell culture or more rarely in animal models. Entities across the length scale from nano-sized enzyme mimics, sub-micron sized artificial organelles and self-propelled particles (swimmers) to micron-sized artificial cells are discussed. Although the field remains in its infancy, the primary aim of this review is to illustrate the advent of nature-mimicking artificial molecules and assemblies on their way to become a complementary alternative to their role models for diverse biomedical purposes.

Microinjection for the ex Vivo Modification of Cells with Artificial Organelles

Microinjection is extensively used across fields to deliver material intracellularly. Here we address the fundamental aspects of introducing exogenous organelles into cells to endow them with artificial functions. Nanocarriers encapsulating biologically active cargo or extreme intraluminal pH were injected directly into the cytosol of cells, where they bypassed subcellular processing pathways and remained intact for several days. Nanocarriers' size was found to dictate their intracellular distribution pattern upon injection, with larger vesicles adopting polarized agglomerated distributions and smaller colloids spreading evenly in the cytosol. This in turn determined the symmetry or asymmetry of their dilution following cell division, ultimately affecting the intracellular dose at a cell population level. As an example of microinjection's applicability, a cell type relevant for cell-based therapies (dendritic cells) was injected with vesicles, and its migratory properties were studied in a co-culture system mimicking lymphatic capillaries.

Small Subcompartmentalized Microreactors as Support for Hepatocytes

Mimicking specific structural or functional aspects of cells is considered a promising approach to substitute for missing or lost cellular functions. However, the interaction of such artificial assemblies with their biological counterparts including the exploitation of the activity of the synthetic partner remains thus-far a rather unexplored avenue. Herein, the assembly of active microreactors with similar size to hepatocytes is reported. These microreactors are successfully cocultured with hepatocytes into bionic tissue for up to 10 d. Further, microreactors loaded with the liver enzyme catalase are effective in alleviating external pressure, induced by the addition of hydrogen peroxide, from such bionic tissue in an attempt to mimic the detoxification ability of hepatocytes. Taken together, the findings open up a different route in combining synthetic and biological entities for tissue engineering by using the former partner not only as structural support, but also to induce beneficial activity.

Multicompartment Artificial Organelles Conducting Enzymatic Cascade Reactions inside Cells

Cell organelles are subcellular structures entrapping a set of enzymes to achieve a specific functionality. The incorporation of artificial organelles into cells is a novel medical paradigm which might contribute to the treatment of various cell disorders by replacing malfunctioning organelles. In particular, artificial organelles are expected to be a powerful solution in the context of enzyme replacement therapy since enzymatic malfunction is the primary cause of organelle dysfunction. Although several attempts have been made to encapsulate enzymes within a carrier vehicle, only few intracellularly active artificial organelles have been reported to date and they all consist of single-compartment carriers. However, it is noted that biological organelles consist of multicompartment architectures where enzymatic reactions are executed within distinct subcompartments. Compartmentalization allows for multiple processes to take place in close vicinity and in a parallel manner without the risk of interference or degradation. Here, we report on a subcompartmentalized and intracellularly active carrier, a crucial step for advancing artificial organelles. In particular, we develop and characterize a novel capsosome system, which consists of multiple liposomes and fluorescent gold nanoclusters embedded within a polymer carrier capsule. We subsequently demonstrate that encapsulated enzymes preserve their activity intracellularly, allowing for controlled enzymatic cascade reaction within a host cell.

Biomimetic Engineering Using Cancer Cell Membranes for Designing Compartmentalized Nanoreactors with Organelle-Like Functions

A new biomimetic nanoreactor design is presented based on cancer cell membrane material in combination with porous silicon nanoparticles. This cellular nanoreactor features a biocompartment enclosed by a cell membrane and readily integrated with cells and supplementing the cellular functions under oxidative stress. The study demonstrates the impact of the nanoreactors on improving cellular functions with a potential to serve as artificial organelles.

Intracellular Microreactors as Artificial Organelles to Conduct Multiple Enzymatic Reactions Simultaneously

The creation of artificial organelles is a new paradigm in medical therapy that aims to substitute for missing cellular function by replenishing a specific cellular task. Artificial organelles tackle the challenge of mimicking metabolism, which is the set of chemical reactions that occur within a cell, mainly catalyzed by enzymes. So far, the few reported carriers able to conduct enzymatic reactions intracellularly are based on single-compartment carriers. However, cell organelles outperform by conducting multiple reactions simultaneously within confined sub-compartments. Here, the field of artificial organelles is advanced by reporting the assembly of a microreactor consisting of polymer capsules entrapping gold nanoclusters (AuNCs) and liposomes as sub-compartments. The fluorescence properties of AuNCs are employed to monitor the microreactors uptake by macrophages. Encapsulation is demonstrated and functionality of microreactors with trypsin (TRP) and horseradish peroxidase (HRP)-loaded liposomes is preserved. Multiple enzymatic reactions taking place simultaneously is demonstrated by exposing macrophages with the internalized microreactors to bis-(benzyloxycarbonyl-Ile-Pro-Arg)-Rho-110 and Amplex Red substrates, which are specific for TRP and HRP, respectively. Conversion of the substrates into the respective fluorescent products is observed. This report on the first microreactor conducting multiple enzymatic reactions simultaneously inside a cell is a considerable step in the field of artificial organelles.

Bio-inspired engineering proteinosomes with a cell-wall-like protective shell by self-assembly of a metal-chelated complex

A cell-wall-like shell is constructed around proteinosomes by coordination complexes of tannic acid and Fe³⁺, which endows the engineered proteinosomes with an enhanced Young's modulus of the membrane, protease resistant ability, EDTA-mediated release of loaded DNA, and electrostatic gated encapsulated enzyme activity, as well as antioxidant capacity.