Can polymeric vesicles that confine enzymatic reactions act as simplified organelles?

Enhanced precision and efficiency in metabolic regulation: Compartmentalized metabolic engineering

Metabolic engineering has witnessed remarkable advancements, enabling successful large-scale, cost-effective and efficient production of numerous compounds. However, the predominant expression of heterologous genes in the cytoplasm poses limitations, such as low substrate concentration, metabolic competition and product toxicity. To overcome these challenges, compartmentalized metabolic engineering allows the spatial separation of metabolic pathways for the efficient and precise production of target compounds. Compartmentalized metabolic engineering and its common strategies are comprehensively described in this study, where various membranous compartments and membraneless compartments have been used for compartmentalization and constructive progress has been made. Additionally, the challenges and future directions are discussed in depth. This review is dedicated to providing compartmentalized, precise and efficient methods for metabolic production, and provides valuable guidance for further development in the field of metabolic engineering.

Photocatalytic Removal of the Greenhouse Gas Nitrous Oxide by Liposomal Microreactors

Nitrous oxide (N₂ O) is a potent greenhouse and ozone-reactive gas for which emissions are growing rapidly due to increasingly intensive agriculture. Synthetic catalysts for N₂ O decomposition typically contain precious metals and/or operate at elevated temperatures driving a desire for more sustainable alternatives. Here we demonstrate self-assembly of liposomal microreactors enabling catalytic reduction of N₂ O to the climate neutral product N₂ . Photoexcitation of graphitic N-doped carbon dots delivers electrons to encapsulated N₂ O Reductase enzymes via a lipid-soluble biomolecular wire provided by the MtrCAB protein complex. Within the microreactor, electron transfer from MtrCAB to N₂ O Reductase is facilitated by the general redox mediator methyl viologen. The liposomal microreactors use only earth-abundant elements to catalyze N₂ O removal in ambient, aqueous conditions.

Photocatalytic Removal of the Greenhouse Gas Nitrous Oxide by Liposomal Microreactors

Nitrous oxide (N2O) is a potent greenhouse and ozone-reactive gas for which emissions are growing rapidly due to increasingly intensive agriculture. Synthetic catalysts for N2O decomposition typically contain precious metals and/or operate at elevated temperatures driving a desire for more sustainable alternatives. Here we demonstrate self-assembly of liposomal microreactors enabling catalytic reduction of N2O to the climate neutral product N2. Photoexcitation of graphitic N-doped carbon dots delivers electrons to encapsulated N2O Reductase enzymes via a lipid-soluble biomolecular wire provided by the MtrCAB protein complex. Within the microreactor, electron transfer from MtrCAB to N2O Reductase is facilitated by the general redox mediator methyl viologen. The liposomal microreactors use only earth-abundant elements to catalyze N2O removal in ambient, aqueous conditions.

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.

Nanozyme-Based Artificial Organelles: An Emerging Direction for Artificial Organelles

Artificial organelles are compartmentalized nanoreactors, in which enzymes or enzyme-mimic catalysts exhibit cascade catalytic activities to mimic the functions of natural organelles. Importantly, research on artificial organelles paves the way for the bottom-up design of synthetic cells. Due to the separation effect of microcompartments, the catalytic reactions of enzymes are performed without the influence of the surrounding medium. The current techniques for synthesizing artificial organelles rely on the strategies of encapsulating enzymes into vesicle-structured materials or reconstituting enzymes onto the microcompartment materials. However, there are still some problems including limited functions, unregulated activities, and difficulty in targeting delivery that hamper the applications of artificial organelles. The emergence of nanozymes (nanomaterials with enzyme-like activities) provides novel ideas for the fabrication of artificial organelles. Compared with natural enzymes, nanozymes are featured with multiple enzymatic activities, higher stability, easier to synthesize, lower cost, and excellent recyclability. Herein, the most recent advances in nanozyme-based artificial organelles are summarized. Moreover, the benefits of compartmental structures for the applications of nanozymes, as well as the functional requirements of microcompartment materials are also introduced. Finally, the potential applications of nanozyme-based artificial organelles in biomedicine and the related challenges are discussed.

Polymersomes: Soft Nanoparticles from Miktoarm Stars for Applications in Drug Delivery

Self-assembly of amphiphilic macromolecules has provided an advantageous platform to address significant issues in a variety of areas, including biology. Such soft nanoparticles with a hydrophobic core and hydrophilic corona, referred to as micelles, have been extensively investigated for delivering lipophilic therapeutics by physical encapsulation. Polymeric vesicles or polymersomes with similarities in morphology to liposomes continue to play an essential role in understanding the behavior of cell membranes and, in addition, have offered opportunities in designing smart nanoformulations. With the evolution in synthetic methodologies to macromolecular precursors, the construction of such assemblies can now be modulated to tailor their properties to match desired needs. This review brings into focus the current state-of-the-art in the design of polymersomes using amphiphilic miktoarm star polymers through a detailed analysis of the synthesis of miktoarm star polymers with tuned lengths of varied polymeric arms, their self-assembly, and applications in drug delivery.

Biocatalytic self-assembled synthetic vesicles and coacervates: From single compartment to artificial cells

Compartmentalization is an intrinsic feature of living cells that allows spatiotemporal control over the biochemical pathways expressed in them. Over the years, a library of compartmentalized systems has been generated, which includes nano to micrometer sized biomimetic vesicles derived from lipids, amphiphilic block copolymers, peptides, and nanoparticles. Biocatalytic vesicles have been developed using a simple bag containing enzyme design of liposomes to multienzymes immobilized multi-vesicular compartments for artificial cell generation. Additionally, enzymes were also entrapped in membrane-less coacervate droplets to mimic the cytoplasmic macromolecular crowding mechanisms. Here, we have discussed different types of single and multicompartment systems, emphasizing their recent developments as biocatalytic self-assembled structures using recent examples. Importantly, we have summarized the strategies in the development of the self-assembled structure to improvise their adaptivity and flexibility for enzyme immobilization. Finally, we have presented the use of biocatalytic assemblies in mimicking different aspects of living cells, which further carves the path for the engineering of a minimal cell.

Shape-transformation of polymersomes from glassy and crosslinkable ABA triblock copolymers

Recent developments in the field of polymer vesicles, i.e. polymersomes, have demonstrated that disrupting the equilibrium conditions of the milieu could lead to shape transformation into stable non-spherical morphologies, bringing on-demand shape control to reality and bearing great promise for cell mimicry and a variety of biomedical applications. Here, we studied the self-assembly behavior of glassy amphiphilic triblock copolymers, poly(ethylene glycol)-block-polystyrene-stat-poly(coumarin methacrylate)-block-poly(ethylene glycol) (PEG-b-P(S-stat-CMA)-b-PEG), and their response to various stimuli. By changing the respective molecular weights of both the hydrophobic P(S-stat-CMA) and the hydrophilic PEG blocks, we varied the hydrophobic volume fraction thereby accessing a range of morphologies from spherical and worm-like micelles, as well as polymersomes. For the latter, we observed that slow osmotic pressure changes induced by dialysis led to a decrease in size while rapid osmotic pressure changes by addition of a PEG fusogen led to morphological transformations into rod-like and tubular polymersomes. We also found out that chemically crosslinking the vesicles before inducing osmotic pressure changes led to the vesicles exhibiting hypotonic shock, atypical for glassy polymersomes. We believe that this approach combining the robustness of triblock copolymers and light-based transformations will help expand the toolbox to design ever more complex biomimetic constructs.

Artificial Organelles Based on Cross-Linked Zwitterionic Vesicles

Artificial organelles (AOs) are typical microcompartments with intracellular biocatalytic activity aimed to replace missing or lost cellular functions. Currently, liposomes or polymersomes are popular microcompartments to build AOs by embedding channel proteins in their hydrophobic domain and entrapping natural enzymes in their cavity. Herein, a new microcompartment is established by using monolayer cross-linked zwitterionic vesicles (cZVs) with a carboxylic acid saturated cavity. The monolayer structure endows the cZVs with intrinsic permeability; the cavity supplies the cZVs ability of in situ synthesis of artificial enzymes, and the pH-dependent charge-change property makes it possible to overcome the biological barriers. Typically, nanozymes of CeO₂ and Pt NPs were synthesized in the cZVs to mimic peroxisome. In vitro experiments confirmed that the resulting artificial peroxisome (AP) could resist protein adsorption, endocytose efficiently, and escape from the lysosome. In vivo experiments demonstrated that the APs held a good therapeutic effect in ROS-induced ear-inflammation.

Antimicrobial Honey-Inspired Glucose-Responsive Nanoreactors by Polymerization-Induced Self-Assembly

The rise of antimicrobial resistance is at the forefront of global healthcare challenges, with antimicrobial infections on track to overtake cancer as a leading cause of death by 2050. The high effectiveness of antimicrobial enzymes used in combination with the protective, inert nature of polymer materials represents a highly novel approach toward tackling microbial infections. Herein, we have developed biohybrid glucose oxidase-loaded semipermeable polymersome nanoreactors, formed using polymerization-induced self-assembly, and demonstrate for the first time their ability to "switch on" their antimicrobial activity in response to glucose, a ubiquitous environmental stimulus. Using colony-counting assays, it was demonstrated that the nanoreactors facilitate up to a seven-log reduction in bacterial growth at high glucose concentrations against a range of Gram-negative and Gram-positive bacterial pathogens, including a methicillin-resistant Staphylococcus aureus clinical isolate. After demonstrating the antimicrobial properties of these materials, their toxicity against human fibroblasts was assessed and the dosage of the nanoreactors further optimized for use as nontoxic agents against Gram-positive bacteria under physiological blood glucose concentrations. It is envisaged that such biohybrid nanomaterials will become an important new class of antimicrobial biomaterials for the treatment of bacterial infections.

Emerging Biomimetic Applications of DNA Nanotechnology

Re-engineering cellular components and biological processes has received great interest and promised compelling advantages in applications ranging from basic cell biology to biomedicine. With the advent of DNA nanotechnology, the programmable self-assembly ability makes DNA an appealing candidate for rational design of artificial components with different structures and functions. This Forum Article summarizes recent developments of DNA nanotechnology in mimicking the structures and functions of existing cellular components. We highlight key successes in the achievements of DNA-based biomimetic membrane proteins and discuss the assembly behavior of these artificial proteins. Then, we focus on the construction of higher-order structures by DNA nanotechnology to recreate cell-like structures. Finally, we explore the current challenges and speculate on future directions of DNA nanotechnology in biomimetics.

Towards feedback-controlled nanomedicines for smart, adaptive delivery

IMPACT STATEMENT

The timing and rate of release of pharmaceuticals from advanced drug delivery systems is an important property that has received considerable attention in the scientific literature. Broadly, these mostly fall into two classes: controlled release with a prolonged release rate or triggered release where the drug is rapidly released in response to an environmental stimulus. This review aims to highlight the potential for developing adaptive release systems that more subtlety modulate the drug release profile through continuous communication with its environment facilitated through feedback control. By reviewing the key elements of this approach in one place (fundamental principles of nanomedicine, enzymatic nanoreactors for medical therapies and feedback-controlled chemical systems) and providing additional motivating case studies in the context of chronobiology, we hope to inspire innovative development of novel "chrononanomedicines."

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.

The hallmarks of living systems: towards creating artificial cells

Despite the astonishing diversity and complexity of living systems, they all share five common hallmarks: compartmentalization, growth and division, information processing, energy transduction and adaptability. In this review, we give not only examples of how cells satisfy these requirements for life and the ways in which it is possible to emulate these characteristics in engineered platforms, but also the gaps that remain to be bridged. The bottom-up synthesis of life-like systems continues to be driven forward by the advent of new technologies, by the discovery of biological phenomena through their transplantation to experimentally simpler constructs and by providing insights into one of the oldest questions posed by mankind, the origin of life on Earth.

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.

Encapsulation of catalyst in block copolymer micelles for the polymerization of ethylene in aqueous medium

The catalytic emulsion polymerization of ethylene has been a long-lasting technical challenge as current techniques still suffer some limitations. Here we report an alternative strategy for the production of semi-crystalline polyethylene latex. Our methodology consists of encapsulating a catalyst precursor within micelles composed of an amphiphilic block copolymer. These micelles act as nanoreactors for the polymerization of ethylene in water. Phosphinosulfonate palladium complexes were used to demonstrate the success of our approach as they were found to be active for hours when encapsulated in micelles. Despite this long stability, the activity of the catalysts in micelles remains significantly lower than in organic solvent, suggesting some catalyst inhibition. The inhibition strength of the different chemicals present in the micelle were determined and compared. The combination of the small volume of the micelles, and the coordination of PEG appear to be the culprits for the low activity observed in micelles.

Cell Membrane-Based Nanoreactor To Mimic the Bio-Compartmentalization Strategy of a Cell

Organelles of eukaryotic cells are structures made up of membranes, which carry out a majority of functions necessary for the surviving of the cell itself. Organelles also differentiate the prokaryotic and eukaryotic cells, and are arranged to form different compartments guaranteeing the activities for which eukaryotic cells are programmed. Cell membranes, containing organelles, are isolated from cancer cells and erythrocytes and used to form biocompatible and long-circulating ghost nanoparticles delivering payloads or catalyzing enzymatic reactions as nanoreactors. In this attempt, red blood cell membranes were isolated from erythrocytes, and engineered to form nanoerythrosomes (NERs) of 150 nm. The horseradish peroxidase, used as an enzyme model, was loaded inside the aqueous compartment of NERs, and its catalytic reaction with Resorufin was monitored. The resulting nanoreactor protected the enzyme from proteolytic degradation, and potentiated the enzymatic reaction in situ as demonstrated by maximal velocity (V_max) and Michaelis constant (K_m), thus suggesting the high catalytic activity of nanoreactors compared to the pure enzymes.

High efficiency and long-term intracellular activity of an enzymatic nanofactory based on metal-organic frameworks

Enhancing or restoring enzymatic function in cells is highly desirable in applications ranging from ex vivo cellular manipulations to enzyme replacement therapies in humans. However, because enzymes degrade in biological milieus, achieving long-term enzymatic activities can be challenging. Herein we report on the in cellulo properties of nanofactories that consist of antioxidative enzymes encapsulated in metal-organic frameworks (MOFs). We demonstrate that, while free enzymes display weak activities for only a short duration, these efficient nanofactories protect human cells from toxic reactive oxygen species for up to a week. Remarkably, these results are obtained in spite of the nanofactories being localized in lysosomes, acidic organelles that contain a variety of proteases. The long-term persistence of the nanofactories is attributed to the chemical stability of MOF in low pH environment and to the protease resistance provided by the protective cage formed by the MOF around the encapsulated enzymes.

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.

Stability of polymersomes with focus on their use as nanoreactors

The increased membrane stability of polymersomes compared to their liposomal counterparts is one of their most important advantages. Due to this benefit, polymer vesicles are intended to be used not only as carrier systems for drug delivery purposes but also as nanoreactors for biotechnological applications. Within this work, the stability of polymersomes made of the triblock copolymer poly(2-methyloxazoline)₁₅-poly(dimethylsiloxane)₆₈-poly(2-methyloxazoline)₁₅ (PMOXA₁₅-PDMS₆₈-PMOXA₁₅) toward mechanical stress, typically prevailing in stirred-tank reactors being the most often used reactor type in the biotechnological industry, was characterized. Dynamic light scattering and turbidity measurements showed that stirrer rotation causing a maximum local energy dissipation of up to 1.23 W/kg^-1 did not result in any loss of vesicle quality or quantity. Nevertheless, most probably due to local membrane defects, 6.6% release of the previously encapsulated model dye calcein was recognized at 25°C within 48 h. Moreover, increased temperature, leading to decreased membrane viscosity and increased membrane fluidity, respectively, led to a higher molecule leakage. Besides, the stability of polymersomes in two-phase systems was investigated. Although alkanes and ionic liquids were shown not to lead to complete vesicle damage, no efficient calcein retention was achieved in either case.

Liposomes in Polymersomes: Multicompartment System with Temperature-Triggered Release

Multicompartmentalization is a key feature of eukaryotic cells, allowing separation and protection of species within the membrane walls. During the last years, several methods have been reported to afford synthetic multicompartment lipidic or polymeric vesicles that mimic biological cells and that allow cascade chemical or enzymatic reactions within their lumen. We hereby report on the preparation and study of liposomes in polymersomes (LiPs) systems. We discuss on the loading and coloading of lipidic nanovesicles made of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dipentadecanoyl-sn-glycero-3-phosphocholine (diC15-PC), or 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) inside the lumen of giant poly(butadiene)-b-poly(ethylene oxide) (PBut-b-PEO) polymersomes. These LiPs systems were characterized by confocal microscopy and UV-visible spectroscopy. We further demonstrate that we can achieve controlled sequential release of dyes from diC15-PC and DPPC liposomes at defined temperatures inside the giant PBut-b-PEO polymersomes. This controlled release could be used as a means to initiate cascade reactions on demand in confined microreactors.

Determination of Permeability Coefficients of Polymersomal Membranes for Hydrophilic Molecules

Polymer vesicles, so-called polymersomes, can be applied as carrier-systems and universal reaction compartments, due to the possibility to encapsulate guest molecules. Compared to common lipid vesicles, polymersomes show an increased stability and decreased membrane permeability. Control of the mass transport across the membrane is necessary for any application, requiring the precise knowledge of the permeability. So far, data on permeability coefficients of polymersomal membranes are scarce because commonly applied release assays are confronted with the challenge of high detection limits and alternative methods developed so far are either restricted to the use of a certain permeating molecule or rely on the use of nuclear magnetic resonance measurements. In contrast, an influx assay that is broadly applicable to hydrophilic molecules and does not involve specialized equipment was developed in this work, which is based on the passive diffusion of compounds into initially empty vesicles. The method is valid for hydrophilic molecules that show no membrane retention and, thus, do not accumulate within the membrane. Using this method, the permeability of polymersomes made of poly(2-methyloxazoline)₁₅-poly(dimethylsiloxane)₆₈-poly(2-methyloxazoline)₁₅ for seven model compounds was investigated under varying conditions. Permeability coefficients as low as 1.9 × 10^-14 cm s^-1 could be measured.

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.

Co-assembly behaviour of Janus nanoparticles and amphiphilic block copolymers in dilute solution

This work not only provides insights into assembly behaviors of Janus nanoparticle solutions, but also offers strategies for permeable membranes.

Polymersomes for biotechnological applications: Large-scale production of nano-scale vesicles

Polymersomes have some fundamental advantages compared to their liposomal counterparts. Due to the increased stability of the polymeric membrane, polymersomes are intended to be reasonably applicable as carrier-systems and universal reaction compartments for diverse medical and biotechnological applications. Regardless of the application area, suitable methods to produce large vesicle quantities in a controlled and cost-effective manner have to be developed to put polymersome technology into action at the industrial scale. In this work, the amphiphilic triblock copolymer poly(2-methyloxazoline)₁₅-poly(dimethylsiloxane)₆₈-poly(2-methyloxazoline)₁₅ was formed into uniform polymersomes. A recently established production process, based on the use of miniaturized stirred-tank reactors at the milliliter-scale (12 mL), was successfully scaled-up to the liter-scale (1.5 L) based on solid process engineering parameters. Dynamic light scattering measurements show that using standard propeller stirrers with a dimensionless diameter d D - 1 ≥0.65 in an unbaffled stirred-tank reactor led to a narrow particle size distribution when providing a Froude number of F r = 6.52 at the same time. Polymersomes with a mean diameter of 180 nm and a low polydispersity index (PDI<0.2) were generated within about 1 h in one single production step. Thus, this work provides the fundamental basis for further scale-up purposes, regarding polymersome production in stirred-tank reactors at the industrial scale.

Bioinspired polymer vesicles and membranes for biological and medical applications

Biological membranes play an essential role in living organisms by providing stable and functional compartments, supporting signalling and selective transport. Combining synthetic polymer membranes with biological molecules promises to be an effective strategy to mimic the functions of cell membranes and apply them in artificial systems.

Co-Delivery of angiostatin and curcumin by a biodegradable polymersome for antiangiogenic therapy

Illustration of the AS–Cur-loaded polymersomes formed by block polymers for antiangiogenic therapy.

Intracellular implantation of enzymes in hollow silica nanospheres for protein therapy: cascade system of superoxide dismutase and catalase

An approach for enzyme therapeutics is elaborated with cell-implanted nanoreactors that are based on multiple enzymes encapsulated in hollow silica nanospheres (HSNs). The synthesis of HSNs is carried out by silica sol-gel templating of water-in-oil microemulsions so that polyethyleneimine (PEI) modified enzymes in aqueous phase are encapsulated inside the HSNs. PEI-grafted superoxide dismutase (PEI-SOD) and catalase (PEI-CAT) encapsulated in HSNs are prepared with quantitative control of the enzyme loadings. Excellent activities of superoxide dismutation by PEI-SOD@HSN are found and transformation of H2 O2 to water by PEI-CAT@HSN. When PEI-SOD and PEI-CAT are co-encapsulated, cascade transformation of superoxide through hydrogen peroxide to water was facile. Substantial fractions of HSNs exhibit endosome escape to cytosol after their delivery to cells. The production of downstream reactive oxygen species (ROS) and COX-2/p-p38 expression show that co-encapsulated SOD/CAT inside the HSNs renders the highest cell protection against the toxicant N,N'-dimethyl-4,4'-bipyridinium dichloride (paraquat). The rapid cell uptake and strong detoxification effect on superoxide radicals by the SOD/CAT-encapsulated hollow mesoporous silica nanoparticles demonstrate the general concept of implanting catalytic nanoreactors in biological cells with designed functions.

Cross-linked polymersomes as nanoreactors for controlled and stabilized single and cascade enzymatic reactions

Polymeric vesicles or polymersomes are one of the supramolecular entities at the leading edge of synthetic biology. These small compartments have shown to be feasible candidates as nanoreactors, especially for enzymatic reactions. Once cross-linked and equipped with a pH sensitive material, the reaction can be switched off (pH 8) and on (pH 6) in accordance with the increased permeability of the polymersome membranes under acidic conditions. Thus cross-linked and pH sensitive polymersomes provide a basis for pH controlled enzymatic reactions where no integrated transmembrane protein is needed for regulating the uptake and release of educts and products in the polymersome lumen. This pH-tunable working tool was further used to investigate their use in sequential enzymatic reactions (glucose oxidase and myoglobin) where enzymes are loaded in one common polymersome or in two different polymersomes. Crossing membranes and overcoming the space distance between polymersomes were shown successfully, meaning that educts and products can be exchanged between enzyme compartments for successful enzymatic cascade reactions. Moreover the stabilizing effect of polymersomes is also observable by single enzymatic reactions as well as a sequence. This study is directed to establish robust and controllable polymersome nanoreactors for enzymatic reactions, describing a switch between an off (pH 8) and on (pH 6) state of polymersome membrane permeability with no transmembrane protein needed for transmembrane exchange.

Enzyme encapsulated hollow silica nanospheres for intracellular biocatalysis

Hollow silica nanospheres (HSN) with low densities, large interior spaces and permeable silica shells are suitable for loading enzymes in the cavity to carry out intracellular biocatalysis. The porous shell can protect the encapsulated enzymes against proteolysis and attenuate immunological response. We developed a microemulsion-templating method for confining horseradish peroxidase (HRP) in the cavity of HSN. This simple one-pot enzyme encapsulation method allows entrapping of the enzyme, which retains high catalytic activity. Compared with HRP supported on solid silica spheres, HRP@HSN with thin porous silica shells displayed better enzyme activity. The small HRP@HSN (∼50 nm in diameter), giving satisfactory catalytic activity, can act as an intracellular catalyst for the oxidation of the prodrug indole-3-acetic acid to produce toxic free radicals for killing cancer cells. We envision this kind of hollow nanosystem could encapsulate multiple enzymes or other synergistic drugs and function as therapeutic nanoreactors.

The amine content of PEGylated chitosan Bombyx mori nanoparticles acts as a trigger for protein delivery

In modern medicine, effective protein therapy is a major challenge to which a significant contribution can be expected from nanoscience through the development of novel delivery systems. Here we present the effect of the amine content of nanoparticles based on PEGylated chitosan Bombyx mori (PEG-O-ChsBm) copolymers on the entrapment of molecules in a search for highly efficient nanocarriers. PEG-O-ChsBm copolymers were synthesized with amine contents from 1.12% to 0.70%, and nanoparticles were generated by self-assembly in dilute aqueous solutions. These nanoparticles successfully entrapped molecules with a wide range of sizes, the efficiency of which was dependent on their amine contents. While hydrophobic molecules were entrapped with high efficiency in all types of nanoparticle, hydrophilic molecules were entrapped only in those with low amine content. Bovine serum albumin, selected as a model protein, was entrapped in nanoparticles and efficiently released in acidic conditions. The triggered entrapment of molecules in PEG-O-ChsBm nanoparticles by selection of the appropriate amine content represents a straightforward way to modulate their delivery by fine changes in the properties of nanocarriers.

Aiding nature's organelles: artificial peroxisomes play their role

A major goal in medical research is to develop artificial organelles that can implant in cells to treat pathological conditions or to support the design of artificial cells. Several attempts have been made to encapsulate or entrap enzymes, proteins, or mimics in polymer compartments, but only few of these nanoreactors were active in cells, and none was proven to mimic a specific natural organelle. Here, we show the necessary steps for the development of an artificial organelle mimicking a natural organelle, the peroxisome. The system, based on two enzymes that work in tandem in polymer vesicles, with a membrane rendered permeable by inserted channel proteins was optimized in terms of natural peroxisome properties and function. The uptake, absence of toxicity, and in situ activity in cells exposed to oxidative stress demonstrated that the artificial peroxisomes detoxify superoxide radicals and H2O2 after endosomal escape. Our artificial peroxisome combats oxidative stress in cells, a factor in various pathologies (e.g., arthritis, Parkinson's, cancer, AIDS), and offers a versatile strategy to develop other "cell implants" for cell dysfunction.