Engineering proteinaceous colloidosomes as enzyme carriers for efficient and recyclable Pickering interfacial biocatalysis

Natural shellac-based microcapsules as lipase carriers for recyclable efficient Pickering interfacial biocatalysis

Enzyme is an important class of catalyst. However, the efficiency of enzyme-catalyzed reactions is constrained by the limited contact between the enzyme and its substrate. In this study, to overcome this challenge, lipase-loaded microcapsules were prepared from natural shellac and nanoparticles using the emulsion template method. These microcapsules can perform dual roles as stabilizers and enzyme carriers to construct a water-in-oil Pickering interfacial biocatalytic system. The results showed that the hydrolytic conversion of the microcapsules could reach 90% within 20 min, which was significantly higher than that of the traditional biphasic system. The catalytic activity was influenced by the oil-to-water volume ratio and the microcapsule content. The microcapsules remained highly catalytic efficiency even after storage for three months or seven cycles of reuse. These microcapsules were prepared without the use of any cross-linkers or harsh solvents. This green and efficient catalytic system has great application prospects in the food industry.

Enzymatic interfacial conversion of acylglycerols in Pickering emulsions stabilized by hydrogel microparticles

HYPOTHESIS

A critical challenge in the enzymatic conversion of acylglycerols is the limited exposure of the enzyme dissolved in the aqueous solution to the hydrophobic substrate in the oil phase. Positioning the enzyme in a microenvironment with balanced hydrophobicity and hydrophilicity in Pickering emulsion will facilitate the acylglycerol-catalyzing reactions at the interface between the oil and liquid phases.

EXPERIMENTS

In this work, to overcome the challenge of biphasic catalysis, we report a method to immobilize enzymes in polyethylene glycol (PEG)-based hydrogel microparticles (HMPs) at the interface between the oil and water phases in Pickering emulsion to promote the enzymatic conversion of acylglycerols.

FINDINGS

3 wt% of HMPs can stabilize the oil-in-water Pickering emulsion for at least 14 days and increase the viscosity of emulsions. Lipase-HMP conjugates showed significantly higher hydrolytic activity in Pickering emulsion; HMP-immobilized lipase SMG1 showed an activity about three times that of free lipase SMG1. Co-immobilization of a lipase and a fatty acid photodecarboxylase from Chlorella variabilis (CvFAP) in Pickering emulsion enables light-driven cascade conversion of triacylglycerols to hydrocarbons, transforming waste oil to renewable biofuels in a green and sustainable approach. HMPs stabilize the Pickering emulsion and promote interfacial biocatalysis in converting acylglycerols to renewable biofuels.

Pickering emulsion biocatalysis: Bridging interfacial design with enzymatic reactions

Non-homogeneous enzyme-catalyzed systems are more widely used than homogeneous systems. Distinguished from the conventional biphasic approach, Pickering emulsion stabilized by ultrafine solid particles opens up an innovative platform for biocatalysis. Their vast specific surface area significantly enhances enzyme-substrate interactions, dramatically increasing catalytic efficiency. This review comprehensively explores various aspects of Pickering emulsion biocatalysis, provides insights into the multiple types and mechanisms of its catalysis, and offers strategies for material design, enzyme immobilization, emulsion formation control, and reactor design. Characterization methods are summarized for the determination of drop size, emulsion type, interface morphology, and emulsion potential. Furthermore, recent reports on the design of stimuli-responsive reaction systems are reviewed, enabling the simple control of demulsification. Moreover, the review explores applications of Pickering emulsion in single-step, cascade, and continuous flow reactions and outlines the challenges and future directions for the field. Overall, we provide a review focusing on Pickering emulsions catalysis, which can draw the attention of researchers in the field of catalytic system design, further empowering next-generation bioprocessing.

Pickering emulsion templated proteinaceous microparticles as glutathione-responsive carriers for endocytosis in tumor cells

The use of glucose oxidase (GOx) to disrupt glucose supply has been identified as a promising strategy in cancer starvation therapy. However, independent delivery of GOx is prone to degradation upon exposure to biological conditions and may cause damage to blood vessels and normal organs during transportation. Although some carriers can protect GOx from the surrounding environment, the harsh preparation conditions may compromise its activity. Moreover, the commonly used materials often exhibit poor biocompatibility and possess certain cytotoxicity. To address this issue, we developed a gentle and efficient method based on Pickering emulsion templates to synthesize protein-based microparticles using zein as the matrix material. These microparticles have high stability and can be tailored to efficiently encapsulate biomolecules while preserving their activity. Moreover, the zein-based microparticles can be triggered to release biomolecules in tumor cells under high glutathione levels, demonstrating excellent responsiveness, biocompatibility, and low cytotoxicity. Additionally, when loaded with GOx, these protein-based microparticles effectively deprive tumor cells of nutrients and induce apoptosis by generating high levels of H2O2, thereby exhibiting enhanced anticancer properties.

Proteinaceous Microsphere-Based Water-in-Oil Pickering Emulsions for Preservation of Chlorella Cells

Microalgae are highly regarded as ideal materials for the creation of liquid biofuels and have substantial potential for growth and utilization. However, traditional storage and culture methods for microalgae are plagued by challenges such as uncontrolled growth, bacterial contamination, and self-shading among algae. These issues severely impede the photosynthetic process and the efficient extraction of biomass energy. This study tackles these problems by utilizing magnetic hydrophobic protein particles to stabilize water-in-oil Pickering emulsions. This allows for the micro-compartment storage and magnetic transfer of algae. Additionally, the successful encapsulation of Chlorella cells in high-internal-phase water-in-oil Pickering emulsions effectively mitigates the settling problem of Chlorella cells in the liquid phase, thereby enabling the potential use of Pickering emulsions for the confined cultivation of microalgae.

Dual-responsive colloidosome-like microgels as the building blocks for phase inversion of Pickering emulsions

The intelligent regulation of microgel-stabilized Pickering emulsions with multi-responsiveness is presently constrained to the processes of emulsification and destabilization. However, the expansion of multi-control over Pickering emulsions to involve phase inversion and the investigation of the accompanying processes and mechanisms present a great challenge. In this study, a microgel with dual responsiveness to both pH and temperature was synthesized using an emulsion template. The resulting microgel exhibited a robust colloidosome-like structure, distinguished by the presence of monolayer-adsorbed silica nanoparticles. The regulation of the packing of surface-covered silica nanoparticles was easily achieved through the swelling of the microgel matrix. Furthermore, the wettability of the microgel can be adjusted between hydrophilic and hydrophobic intervals, allowing for the effective and dual-responsive phase inversion of Pickering emulsions. Moreover, it has been observed that colloidosome-like microgels can lead to unique interfacial structures during the emulsification process, thereby elucidating the fundamental mechanism governing emulsion phase inversion.

High Internal Phase Pickering Emulsion Stabilized by Lipase-Coated ZIF-8 Nanoparticles towards Recyclable Biphasic Biocatalyst

High internal phase Pickering emulsion (Pickering HIPE) stabilized by enzyme-decorated metal-organic frameworks (MOFs) nanoparticles is developed for biphasic biocatalysts to enhance lipase catalysis and recycling. Specifically, enzyme decorated nanoparticles are prepared via ZIF-8 physisorption of a model lipase Candida antarctica Lipase B (CALB), named ZIF-8@CALB, to be both Pickering stabilizer and catalytic sites. An oil-in-water (o/w) Pickering HIPE with oil/water volume ratio of 3 could then be fabricated by homogenizing p-nitrophenyl palmitate (p-NPP) n-heptane solution into the ZIF-8@CALB aqueous dispersion. The biocatalytic hydrolysis of p-NPP is conducted by just standing the biphasic system at room temperature. The Pickering HIPE system achieves a product conversion of up to 48.9% within 0.5 h, whereas the p-NPP n-heptane solution system containing free CALB only achieves a stable product conversion of 6.8% for the same time. Moreover, the ZIF@CALB could be recovered by a simple centrifugation at 800 rpm, and then reused in the next cycle. The hydrolysis equilibrium conversion rate of p-NPP keeps over 40% for all 8 cycles, reflecting the high catalytic efficiency and recyclability of the Pickering HIPE. This study provides a new opportunity in designing Enzyme-MOFs-based Pickering interfacial biocatalyst for practical applications.

A thermosensitive Pickering gel emulsion with a high oil-water ratio for long-term X-ray imaging and permanent embolization of arteries

Iodized oil has an excellent X-ray imaging effect, but it shows poor embolization performance. When used as an embolic agent, it is easily washed off by the blood flow and eliminated from the body. Therefore, it is essential to use iodized oil in combination with solid embolic agents such as gelatin sponge or to perform multiple embolization procedures to achieve the therapeutic effect. In the present study, a poly(N-isopropyl acrylamide)-co-acrylic acid (PNCAA) temperature-sensitive nanogel was synthesized by emulsion polymerization; the nanogel was then emulsified with iodized oil to prepare a thermosensitive iodized oil Pickering gel emulsion (TIPE). The oil-water (O/W) ratio of an O/W emulsion system can reach 4 : 6. When injected into the body, TIPE transforms into a nonflowing coagulated state at physiological temperature; the iodized oil is locked in the emulsion structure, thereby achieving local embolization and continuous imaging effects, which not only retain the X-ray imaging effect of the iodized oil but also improve its embolization effect. Subsequently, we further evaluated renal artery embolization in a normal rabbit renal artery model, and the results showed that TIPE shows a long-term conformal embolization performance and excellent long-term X-ray imaging ability.

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.

Lipase-Entrapped Colloidosomes with Tunable Positioning at the Oil-Water Interface for Pickering Emulsion-Enhanced Biocatalysis

Pickering interfacial biocatalysis (PIB) paves the way for efficient enzymatic catalysis in the biphasic system. However, the Pickering interfacial biocatalysts located on the oil-water interface still face the inevitable deactivation when one of the phases contains the reactant that inactivates the enzyme. Herein, the positioning of lipase-entrapped colloidosomes (LECs) at the emulsion interface is rationally designed by physically tuning the wettability, which allows LECs to protrude into the selected phase to protect the lipase away from the damage of the reactant. As a proof of concept, LECs with different positioning at the interface are used as Pickering interfacial biocatalysts to produce biodiesel by esterification of lauric acid and methanol. Impressively, the LECs that protrude into the oil phase possess an optimal catalytic performance to protect more lipases away from the damage of the reactant of short-chain alcohol, which shows an 8.18-fold enhancement in specific activity relative to the free lipase, reach a biodiesel yield of 80.37% after 8 h, and retain the 96.44% of relative activity after 10 cycles. This study provides a novel and robust platform for Pickering emulsion-enhanced biocatalysis.

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.

Key difference between transition state stabilization and ground state destabilization: increasing atomic charge densities before or during enzyme–substrate binding

The origin of the enormous catalytic power of enzymes has been extensively studied through experimental and computational approaches. Although precise mechanisms are still subject to much debate, enzymes are thought to catalyze reactions by stabilizing transition states (TSs) or destabilizing ground states (GSs). By exploring the catalysis of various types of enzyme–substrate noncovalent interactions, we found that catalysis by TS stabilization and the catalysis by GS destabilization share common features by reducing the free energy barriers (ΔG^‡s) of reactions, but are different in attaining the requirement for ΔG^‡ reduction. Irrespective of whether enzymes catalyze reactions by TS stabilization or GS destabilization, they reduce ΔG^‡s by enhancing the charge densities of catalytic atoms that experience a reduction in charge density between GSs and TSs. Notably, in TS stabilization, the charge density of catalytic atoms is enhanced prior to enzyme–substrate binding; whereas in GS destabilization, the charge density of catalytic atoms is enhanced during the enzyme–substrate binding. Results show that TS stabilization and GS destabilization are not contradictory to each other and are consistent in reducing the ΔG^‡s of reactions. The full mechanism of enzyme catalysis includes the mechanism of reducing ΔG^‡ and the mechanism of enhancing atomic charge densities. Our findings may help resolve the debate between TS stabilization and GS destabilization and assist our understanding of catalysis and the design of artificial enzymes.

Transition state stabilization and ground state destabilization utilize the same molecular mechanism when lowering the free energy barriers (ΔG^‡s) of reactions, but differ in achieving the requirement for ΔG^‡ reduction.

Inorganic reinforced poly(ionic liquid) microcapsules: confined cooling-assisted phase separation self-assembly and enhanced electro-responsive property

We report a simple preparation of inorganic reinforced poly(ionic liquid) (PIL) microcapsules by combining dispersion polymerization and confined cooling-assisted phase separation self-assembly. Silane coupling agent-modified PIL microbeads were first prepared by dispersion polymerization. Then, the microbeads were dissolved in a mixed solvent composed of good solvent and non-solvent to form hollow SiO_x microcapsules at a relatively high temperature. Finally, the solution was cooled to induce the nucleation and growth of dissolved PIL chains on the inner and outer surface of hollow SiO_x microcapsules to form inorganic reinforced microcapsules with asymmetric PIL/SiO_x /PIL sandwich-like shell. The morphology of microcapsules can be controlled by adjusting PIL concentration and cooling rate. The inorganic reinforced microcapsules show enhanced suspended stability and electro-responsive characteristic when used as the dispersed phase of smart suspensions. This article is protected by copyright. All rights reserved.