Polymersomes as nanoreactors for preparative biocatalytic applications: current challenges and future perspectives

Nanomedicine in glaucoma treatment; Current challenges and future perspectives

Glaucoma presents a significant global health concern and affects millions of individuals worldwide and predicted a high increase in prevalence of about 111 million by 2040. The current standard treatment involves hypotensive eye drops; however, challenges such as patient adherence and limited drug bioavailability hinder the treatment effectiveness. Nanopharmaceuticals or nanomedicines offer promising solutions to overcome these obstacles. In this manuscript, we summarized the current limitations of conventional antiglaucoma treatment, role of nanomedicine in glaucoma treatment, rational design, factors effecting the performance of nanomedicine and different types of nanocarriers in designing of nanomedicine along with their applications in glaucoma treatment from recent literature. Current clinical challenges that hinder real-time application of antiglaucoma nanomedicine are highlighted. Lastly, future directions are identified for improving the therapeutic potential and translation of antiglaucoma nanomedicine into clinic.

Metal-Organic Framework Induced Stabilization of Proteins in Polymeric Nanoparticles

Developing protein confinement platforms is an attractive research area that not only promotes protein delivery but also can result in artificial environment mimicking of the cellular one, impacting both the controlled release of proteins and the fundamental protein biophysics. Polymeric nanoparticles (PNPs) are attractive platforms to confine proteins due to their superior biocompatibility, low cytotoxicity, and controllable release under external stimuli. However, loading proteins into PNPs can be challenging due to the potential protein structural perturbation upon contacting the interior of PNPs. In this work, we developed a novel approach to encapsulate proteins in PNPs with the assistance of the zeolitic imidazolate framework (ZIF). Here, ZIF offers an additional protection layer to the target protein by forming the protein@ZIF composite via aqueous-phase cocrystallization. We demonstrated our platform using a model protein, lysozyme, and a widely studied PNP composed of poly(ethylene glycol)-poly(lactic-co-glycolic acid) (PEG-PLGA). A comprehensive study via standard loading and release tests as well as various spectroscopic techniques was carried out on lysozyme loaded onto PEG-PLGA with and without ZIF protection. As compared with the direct protein encapsulation, an additional layer with ZIF prior to loading offered enhanced loading capacity, reduced leaching, especially in the initial stage, led to slower release kinetics, and reduced secondary structural perturbation. Meanwhile, the function, cytotoxicity, and cellular uptake of proteins encapsulated within the ZIF-bound systems are decent. Our results demonstrated the use of ZIF in assisting in protein encapsulation in PNPs and established the basis for developing more sophisticated protein encapsulation platforms using a combination of materials of diverse molecular architectures and disciplines. As such, we anticipate that the protein-encapsulated ZIF systems will serve as future polymer protein confinement and delivery platforms for both fundamental biophysics and biochemistry research and biomedical applications where protein delivery is needed to support therapeutics and/or nutrients.

Bioinspired photocatalytic systems towards compartmentalized artificial photosynthesis

Artificial photosynthesis aims to produce fuels and chemicals from simple building blocks (i.e. water and carbon dioxide) using sunlight as energy source. Achieving effective photocatalytic systems necessitates a comprehensive understanding of the underlying mechanisms and factors that control the reactivity. This review underscores the growing interest in utilizing bioinspired artificial vesicles to develop compartmentalized photocatalytic systems. Herein, we summarize different scaffolds employed to develop artificial vesicles, and discuss recent examples where such systems are used to study pivotal processes of artificial photosynthesis, including light harvesting, charge transfer, and fuel production. These systems offer valuable lessons regarding the appropriate choice of membrane scaffolds, reaction partners and spatial arrangement to enhance photocatalytic activity, selectivity and efficiency. These studies highlight the pivotal role of the membrane to increase the stability of the immobilized reaction partners, generate a suitable local environment, and force proximity between electron donor and acceptor molecules (or catalysts and photosensitizers) to increase electron transfer rates. Overall, these findings pave the way for further development of bioinspired photocatalytic systems for compartmentalized artificial photosynthesis.

Nanocarriers with Multiple Cargo Load-A Comprehensive Preparation Guideline Using Orthogonal Strategies

Multifunctional nanocarriers enhance the treatment efficacy for modern therapeutics and have gained increasing importance in biomedical research. Codelivery of multiple bioactive molecules enables synergistic therapies. Coencapsulation of cargo molecules into one nanocarrier system is challenging due to different physicochemical properties of the cargo molecules. Additionally, coencapsulation of multiple molecules simultaneously shall proceed with high control and efficiency. Orthogonal approaches for the preparation of nanocarriers are essential to encapsulate sensitive bioactive molecules while preserving their bioactivity. Preparation of nanocarriers by physical processes (i.e., self-assembly or coacervation) and chemical reactions (i.e., click reactions, polymerizations, etc.) are considered as orthogonal methods to most cargo molecules. This review shall act as a guideline to allow the reader to select a suitable preparation protocol for a desired nanocarrier system. This article helps to select for combinations of cargo molecules (hydrophilic-hydrophobic, small-macro, organic-inorganic) with nanocarrier material and synthesis protocols. The focus of this article lies on the coencapsulation of multiple cargo molecules into biocompatible and biodegradable nanocarriers prepared by orthogonal strategies. With this toolbox, the selection of a preparation method for a known set of cargo molecules to prepare the desired biodegradable and loaded nanocarrier shall be provided.

Recent advances in permeable polymersomes: fabrication, responsiveness, and applications

Polymersomes are vesicular nanostructures enclosed by a bilayer-membrane self-assembled from amphiphilic block copolymers, which exhibit higher stability compared with their biological analogues (e.g. liposomes). Due to their versatility, polymersomes have found various applications in different research fields such as drug delivery, nanomedicine, biological nanoreactors, and artificial cells. However, polymersomes prepared with high molecular weight components typically display low permeability to molecules and ions. It hence remains a major challenge to balance the opposing features of robustness and permeability of polymersomes. In this review, we focus on the design and strategies for fabricating permeable polymersomes, including polymersomes with intrinsic permeability, the formation of nanopores in the membrane bilayers by protein insertion, and the construction of stimuli-responsive polymersomes. Then, we highlight the applications of permeable polymersomes in the fields of biomimetic nanoreactors, artificial cells and organelles, and nanomedicine, to underline the challenges in the development of polymersomes as soft matter with biomedical utilities.

Biocatalytic Synthesis Using Self-Assembled Polymeric Nano- and Microreactors

Biocatalysis is increasingly being explored for the sustainable development of green industry. Though enzymes show great industrial potential with their high efficiency, specificity, and selectivity, they suffer from poor usability and stability under abiological conditions. To solve these problems, researchers have fabricated nano- and micro-sized biocatalytic reactors based on the self-assembly of various polymers, leading to highly stable, functional, and reusable biocatalytic systems. This Review highlights recent progress in self-assembled polymeric nano- and microreactors for biocatalytic synthesis, including polymersomes, reverse micelles, polymer emulsions, Pickering emulsions, and static emulsions. We categorize these reactors into monophasic and biphasic systems and discuss their structural characteristics and latest successes with representative examples. We also consider the challenges and potential solutions associated with the future development of this field.

Enzyme immobilization in hydrogels: A perfect liaison for efficient and sustainable biocatalysis

Biocatalysis is an established chemical synthesis technology that has by no means been restricted to research laboratories. The use of enzymes for organic synthesis has evolved greatly from early development to proof-of-concept - from small batch production to industrial scale. Different enzyme immobilization strategies contributed to this success story. Recently, the use of hydrogel materials for the immobilization of enzymes has been attracting great interest. Within this review, we pay special attention to recent developments in this key emerging field of research. Firstly, we will briefly introduce the concepts of both biocatalysis and hydrogel worlds. Then, we list recent interesting publications that link both concepts. Finally, we provide an outlook and comment on future perspectives of further exploration of enzyme immobilization strategies in hydrogels.

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.

Carboxy-Functionalized pH Responsive Capsule Polymer Particles Fabricated by Particulate Interfacial Photocrosslinking

pH-responsive capsule particles show promise for various applications, such as self-healing materials, micro/nanoreactors, and drug delivery systems. Herein, carboxy-functionalized capsule polymer particles possessing neutral-alkali pH responsive controlled release capability were...

Photo-responsive polymeric nanocarriers for target-specific and controlled drug delivery

Conventional drug delivery systems often have several pharmacodynamic and pharmacokinetic limitations related to their low efficacy and bad safety. It is because these traditional systems cannot always be selectively addressed to their therapeutic target sites. Currently, target-specific and controlled drug delivery is one of the foremost challenges in the biomedical field. In this context, stimuli-responsive polymeric nanomaterials have been recognized as a topic of intense research. They have gained immense attention in therapeutics - particularly in the drug delivery area - due to the ease of tailorable behavior in response to the surroundings. Light irradiation is of particular interest among externally triggered stimuli because it may be specifically localized in a contact-free manner. Light-human body interactions may sometimes be harmful due to photothermal and photomechanical reactions that lead to cell death by photo-toxicity and/or photosensitization. However, these limitations may also be overcome by the use of photo-responsive polymeric nanostructures. This review summarizes recent developments in photo-responsive polymeric nanocarriers used in the field of drug delivery systems, including nanoparticles, nanogels, micelles, nanofibers, dendrimers, and polymersomes, as well as their classification and mechanisms of drug release.

All-Peptide-Based Polyion Complex Vesicles: Facile Preparation and Encapsulation of the Protein in Active Form

The polyion complex vesicle (PICsome) is a promising platform for bioactive molecule delivery as well as nanoreactor systems. In addition to anionic and cationic charged blocks, a hydrophilic poly(ethylene glycol) (PEG) block is mostly employed for PICsome formation; however, the long-term safety of the PEG component in vivo is yet to be clarified. In this study, we developed novel PEG-free PICsome comprising all peptide components. Instead of the PEG block, we selected the sarcosine (Sar) oligomer as a hydrophilic block and fused it with anionic oligo(l-glutamic acid). Mixing the Sar-containing anionic peptide with cationic oligo(l-lysine) resulted in the formation of stable vesicles. The peptide-based PICsome was able to encapsulate a model protein in its hollow structure. After modification of the surface with a cell-penetrating peptide, the protein-encapsulated PICsome was successfully delivered into plant cells, indicating its promised for application as a biocompatible carrier for protein delivery.

Enzymatic Cascade Reactions Mediated by Highly Efficient Biomimetic Quasi Metal-Organic Frameworks

The integration of chemo- and enzymatic catalysis for effective multistep cascades has presented critical challenges for decades. In this work, the biomimetic quasi NH₂-MIL-101 (qNM) with highly efficient peroxidase-like activity was synthesized via a palmitic acid-induced strategy followed by pyrolysis. The effects of the amount of palmitic acid and calcination temperature on the synthesis of qNM were optimized. It was found that qNM was an excellent catalyst for oxidations of various peroxidase substrates, and a possible mechanism was proposed, i.e., the presence of Fe^II species in qNM was responsible for its excellent activity, which facilitated the transition between Fe^II and Fe^III species to produce more hydroxyl radicals by H₂O₂ decomposition. The qNM served as the potential matrix for enzyme immobilization through a cross-linking method, and kinetic studies revealed that the catalytic efficiency (k_cat/K_m) for the immobilized GOx (23.7 mM^-1 s^-1) is comparable to that of free GOx (26.9 mM^-1 s^-1). The immobilized GOx also showed improved stability against high temperatures and organic solvents compared to free GOx, and analysis of the secondary structure of GOx indicated that the improved stability resulted from enzyme rigidity by the intense covalent linkage with qNM. Furthermore, qNM contributed its biomimetic activity to cooperate with a single enzyme (GOx) or two enzymes (β-Gal and GOx) for the enzymatic cascade reactions. Compared with the mixture of each component in the solution, the combination of the single-enzyme system (GOx) or the two-enzyme system (β-Gal and GOx) in qNM achieved 2.67-fold and 1.83-fold enhancements in the activity of catalytic cascades, respectively. This study provides new insights into the construction of effective and synergistic cascade reactions by integrating biomimetic MOF with natural enzyme, which holds potential for applications in biotechnology and ecofriendly and biomimetic catalysis.

Nanomedicines for the treatment of glaucoma: Current status and future perspectives

Glaucoma is the global leading cause of irreversible blindness. It is a chronic progressive disorder and, therefore, often requires long-term management with drugs on patients' discretion. However, there is a shortage of antiglaucoma drugs in the current market due to their low bioavailability. This is because there are multiple biological barriers of the human eyes, thereby leading to increased demands for frequent dosage regimen per day of these drugs, which could result in concomitant side effects and eventually reduced patient compliance. Recently, nanomedicines have become optimized alternatives to conventional ophthalmic formulations due to advantages of improved barrier permeability, sustained drug release, tissue targeting, and lowered systemic absorption of instilled medications. These merits provide the active ingredients in these nanomedicines an effective manner to reach the ideal concentrations at sites of damaged nerves, offering a promising platform for neuroprotective treatment of these conditions. In this study, nanomedicines and nanomedicine-based novel strategies for pharmacotherapy of glaucoma were reviewed, including liposomes, niosomes, nanoparticles, and dendrimers. This article intends to offer a comprehensive review of frontier progresses as well as hotspots and issues that appeared in the field of nanomedicines, which may enable a practical flourish in the future. STATEMENT OF SIGNIFICANCE: Recent novel pharmaceutical strategies toward glaucoma, a chronic blinding ocular disease that currently requires frequent daily dosage regimen, based on nanomedicines and nanomaterials have been comprehensively reviewed in this manuscript. The collection of field hotspots and issues in the late years should offer a quick grasp of the general concept and up-to-date threads upon the refinement of existing treatment patterns for glaucoma. Meanwhile, the Conclusion and Future Perspective section given at the end of the text brings out the possible shortages and opinions in terms of ideal research direction, which hopefully could facilitate a future practical flourish in the area.

Polymeric Nanoreactors as Emerging Nanoplatforms for Cancer Precise Nanomedicine

How to precisely detect and effectively cure cancer which is defined as precise nanomedicine has drawn great attention worldwide. Polymeric nanoreactors which can in situ catalyze inert species into activated ones, can greatly increase imaging quality and enhance therapeutic effects along with decreased background interference and reduced serious side effects. After a brief introduction, the design and preparation of polymeric nanoreactors are discussed from the following aspects, that is, solvent-switch, pH-tuning, film rehydration, hard template, electrostatic interaction, and polymerization-induced self-assembly (PISA). Subsequently, the biomedical applications of these nanoreactors in the fields of cancer imaging, cancer therapy, and cancer theranostics are highlighted. The last but not least, conclusions and future perspectives about polymeric nanoreactors are given. It is believed that polymeric nanoreactors can bring a great opportunity for future fabrication and clinical translation of precise nanomedicine.

Silica Capsules Templated from Metal-Organic Frameworks for Enzyme Immobilization and Catalysis

Inspired by the unique biological microenvironments of eukaryotic cells, hollow capsules are promising to immobilize enzymes due to their advantages for physical protection and improved activity of enzymes. Herein, we report a facile method to fabricate silica (SiO₂) capsules using zeolitic imidazole framework-8 nanoparticles (ZIF-8 NPs) as templates for enzyme immobilization and catalysis. Enzyme-encapsulated SiO₂ capsules are obtained by encapsulation of enzymes in ZIF-8 NPs and subsequent coating of silica layers, followed by the removal of templates in a mild condition (i.e., ethylenediaminetetraacetic acid (EDTA) solution). The enzyme (i.e., horseradish peroxidase, HRP) activity in SiO₂ capsules is improved more than 15 times compared to that of enzyme-loaded ZIF-8 NPs. Enzymes in SiO₂ capsules maintain a high relative activity after being subjected to high temperature, enzymolysis, and recycling compared to free enzymes. In addition, multienzymes (e.g., glucose oxidase and HRP) can also be coencapsulated within SiO₂ capsules to show a reaction with a high cascade catalytic efficacy. This work provides a versatile strategy for enzyme immobilization and protection with potential applications in biocatalysis.

Peptide-Based Polyion Complex Vesicles That Deliver Enzymes into Intact Plants To Provide Antibiotic Resistance without Genetic Modification

Direct delivery of enzymes into intact plants using cell-penetrating peptides (CPPs) is an attractive approach for modifying plant functions without genetic modification. However, by conventional methods, it is difficult to maintain the enzyme activity for a long time because of proteolysis of the enzymes under physiological conditions. Here, we developed a novel enzyme delivery system using polyion complex vesicles (PICsomes) to protect the enzyme from proteases. We created PICsome-bearing reactive groups at the surface by mixing an anionic block copolymer, alkyne-TEG-P(Lys-COOH), and a cationic peptide, P(Lys). The PICsome encapsulated neomycin phosphotransferase II (NPTII), a kanamycin resistance enzyme, and protected NPTII from proteases in vitro. A CPP-modified PICsome delivered NPTII into the root hair cells of Arabidopsis thaliana seedlings and provided kanamycin resistance in the seedlings that lasted for 7 days. Thus, the PICsome-mediated enzyme delivery system is a promising method for imparting long-term transient traits to plants without genetic modification.

Photo-Responsive Polymersomes as Drug Delivery System for Potential Medical Applications

Due to a strong retardation effect of o-nitrobenzyl ester on polymerization, it is still a great challenge to prepare amphiphilic block copolymers for polymersomes with a o-nitrobenzyl ester-based hydrophobic block. Herein, we present one such solution to prepare amphiphilic block copolymers with pure poly (o-nitrobenzyl acrylate) (PNBA) as the hydrophobic block and poly (N,N'-dimethylacrylamide) (PDMA) as the hydrophilic block using bulk reversible addition-fragmentation chain transfer (RAFT) polymerization of o-nitrobenzyl acrylate using a PDMA macro-RAFT agent. The developed amphiphilic block copolymers have a suitable hydrophobic/hydrophilic ratio and can self-assemble into photoresponsive polymersomes for co-loading hydrophobic and hydrophilic cargos into hydrophobic membranes and aqueous compartments of the polymersomes. The polymersomes demonstrate a clear photo-responsive characteristic. Exposure to light irradiation at 365 nm can trigger a photocleavage reaction of o-nitrobenzyl groups, which results in dissociation of the polymersomes with simultaneous co-release of hydrophilic and hydrophobic cargoes on demand. Therefore, these polymersomes have great potential as a smart drug delivery nanocarrier for controllable loading and releasing of hydrophilic and hydrophobic drug molecules. Moreover, taking advantage of the conditional releasing of hydrophilic and hydrophobic drugs, the drug delivery system has potential use in medical applications such as cancer therapy.

The rise of bio-inspired polymer compartments responding to pathology-related signals

Self-organized nano- and microscale polymer compartments such as polymersomes, giant unilamellar vesicles (GUVs), polyion complex vesicles (PICsomes) and layer-by-layer (LbL) capsules have increasing potential in many sensing applications. Besides modifying the physicochemical properties of the corresponding polymer building blocks, the versatility of these compartments can be markedly expanded by biomolecules that endow the nanomaterials with specific molecular and cellular functions. In this review, we focus on polymer-based compartments that preserve their structure, and highlight the key role they play in the field of medical diagnostics: first, the self-assembling abilities that result in preferred architectures are presented for a broad range of polymers. In the following, we describe different strategies for sensing disease-related signals (pH-change, reductive conditions, and presence of ions or biomolecules) by polymer compartments that exhibit stimuli-responsiveness. In particular, we distinguish between the stimulus-sensitivity contributed by the polymer itself or by additional compounds embedded in the compartments in different sensing systems. We then address necessary properties of sensing polymeric compartments, such as the enhancement of their stability and biocompatibility, or the targeting ability, that open up new perspectives for diagnostic applications.

Towards compartmentalized photocatalysis: multihaem proteins as transmembrane molecular electron conduits

We show a proof-of-concept for using MtrCAB as a lipid membrane-spanning building block for compartmentalised photocatalysis that mimics photosynthesis.

Light-Driven Biocatalysis in Liposomes and Polymersomes: Where Are We Now?

The utilization of light energy to power organic-chemical transformations is a fundamental strategy of the terrestrial energy cycle. Inspired by the elegance of natural photosynthesis, much interdisciplinary research effort has been devoted to the construction of simplified cell mimics based on artificial vesicles to provide a novel tool for biocatalytic cascade reactions with energy-demanding steps. By inserting natural or even artificial photosynthetic systems into liposomes or polymersomes, the light-driven proton translocation and the resulting formation of electrochemical gradients have become possible. This is the basis for the conversion of photonic into chemical energy in form of energy-rich molecules such as adenosine triphosphate (ATP), which can be further utilized by energy-dependent biocatalytic reactions, e.g. carbon fixation. This review compares liposomes and polymersomes as artificial compartments and summarizes the types of light-driven proton pumps that have been employed in artificial photosynthesis so far. We give an overview over the methods affecting the orientation of the photosystems within the membranes to ensure a unidirectional transport of molecules and highlight recent examples of light-driven biocatalysis in artificial vesicles. Finally, we summarize the current achievements and discuss the next steps needed for the transition of this technology from the proof-of-concept status to preparative applications.

Olefin metathesis in air using latent ruthenium catalysts: imidazole substituted amphiphilic hydrogenated ROMP polymers providing nano-sized reaction spaces in water

Imidazole substituted hydrogenated amphiphilic ROMP polymers were used as both surfactants and ligand precursors for olefin metathesis reactions in water.