Biocatalytic Synthesis Using Self-Assembled Polymeric Nano- and Microreactors

A Supramolecular Approach to Engineering Living Cells with Enzymes for Adaptive and Recyclable Cascade Synthesis

Biocatalytic transformation in nature is inherently dynamic, spontaneous, and adaptive, enabling complex chemical synthesis and metabolism. These processes often involve supramolecular recognition among cells, enzymes, and biomacromolecules, far surpassing the capabilities of isolated cells and enzymes used in industrial synthesis. Inspired by nature, here we design a supramolecular approach to equip living cells with these capacities, enabling recyclable, efficient cascade reactions. Our two-step "plug-and-play" methodology begins by coating Escherichia coli cells with guest-containing polymers (SupraBAC) via supramolecular charge interactions, followed by the introduction of β-cyclodextrin-functionalized host enzymes through host-guest chemistry, creating a robust cell-enzyme complex. This supramolecular coating not only protects cells from various stresses, such as UV radiation, heat, and organic solvents, but also facilitates the overexpression of intracellular enzymes and the attachment of extracellular enzymes within and on SupraBAC. This combination results in efficient multienzyme cascade synthesis, enabling two- and three-step reactions in one pot. Importantly, the multienzyme system can be recycled up to five times without significant loss of activity. Our findings introduce a versatile, adaptive supramolecular coating for whole-cell catalysts, offering a sustainable and efficient solution for complex synthesis in both chemistry and industrial biotechnology.

Recent Advances of Stimuli-Responsive Liquid-Liquid Interfaces Stabilized by Nanoparticles

Liquid-liquid interfaces offer highly controlled, flexible, and adaptable platforms for precise molecular assemblies, enabling the construction of sophisticated functional materials. Interfacial assemblies of specific nanoparticles (NPs) and ligands can alter their physicochemical states under external stimuli, leading to macroscopic dynamic transformations at the interface. This Review summarizes and analyzes the recent advances of the assembly and disassembly behaviors of various stimuli-responsive nanoparticle surfactants (NPSs) at liquid-liquid interfaces, focusing on their responsive behaviors when exposed to external stimuli and the interaction forces between interfacial molecules. Additionally, we outline recent advancements in applications such as reconfigurable all-liquid devices, all-liquid 3D printing, and chemical reaction platforms. Finally, we discuss current challenges and future prospects for the development of applications in this rapidly evolving field.

Pharmacokinetics and fate of free and encapsulated IRD800CW-labelled human BChE intravenously administered in mice

Human butyrylcholinesterase (BChE) is an efficient bioscavenger of toxicants. Highly purified BChE was labelled with the near infrared fluorescent IRDye800CW. The goal was to determine the pharmacokinetics and fate of enzyme in mice. BChE-IRDye800CW was encapsulated in polyethylene glycol-polypropylene sulfide-based spherical polymersome nanoreactors with the following characteristics: 140 nm diameter, ξ = -6 mV, PDI ≤ 0.2, 1 year stability. Encapsulation did not alter the functional properties of BChE. Free and encapsulated enzyme were injected intravenously to CD-1 mice (single dose of enzyme 1.5 mg/kg and PEG-PPS polymersomes 25 mg/kg) and were analyzed for 8 days using an in vivo imaging system. Results showed that the pharmacokinetic distribution α-phase of encapsulated BChE (t1/2 = 17.6 h) was longer than for free enzyme (t1/2 = 6.6 h). The mean half-time for elimination β-phase was 2-time longer for encapsulated enzyme than for free enzyme (150 vs 72 h). Transient changes in infrared fluorescence in organs showed that BChE is eliminated from liver. However, free and encapsulated enzymes were cleared via different pathways. This first study of pharmacokinetics and fate of BChE encapsulated in polymersomes initiates research of new formulations of bioscavengers aimed at increasing the residence time of enzymes in the blood stream.

Oil-water interfaces of Pickering emulsions: microhabitats for living cell biocatalysis

Based on the size of bacterial cells and bacterial surface hydrophobicity, some bacteria meet the requirements of Pickering particles to stabilize Pickering emulsions. Here, we discuss the oil-water interfaces of bacteria-stabilized Pickering emulsions as microhabitats for microbial metabolism of oil-soluble chemicals. The correlation between living bacteria-stabilized Pickering emulsions and microhabitats of living bacteria at oil-water interfaces offers a new perspective to study bioprocess engineering at the mesoscale between the cell and reactor scales, which not only provides novel parameters to optimize the bioprocess engineering, but also unravels the paradox of some natural phenomena related to living cell biocatalysis.

Pickering Emulsion Promoted Interfacial Sequential Chemo-Biocatalytic Reaction for the Synthesis of Chiral Alcohols from Styrene

Chemo-biocatalytic cascades have emerged as a promising approach in the realm of advanced synthesis. However, reconciling the incompatible reaction conditions among distinct catalytic species presents a significant challenge. Herein, we introduce an innovative solution using an emulsion system stabilized by Janus silica nanoparticles, which serve as a bridge for both chemo-catalysts and biocatalysts at the interface. The chemo-catalyst is securely anchored within a hydrophobic polymer matrix, ensuring its residence in an organic environment. Meanwhile, the negatively charged E. coli cells containing enzymes are attracted to the aqueous phase at the interface, facilitating their optimal positioning. We demonstrate the efficacy of this system through a two-step cascade reaction. Initially, the oxidation of styrene to acetophenone using palladium as a chemocatalyst achieves a 6-fold increase in yield compared to the control system. Subsequently, the reduction of achiral acetophenone to its chiral alcohol derivative presents a 17-fold yield enhancement relative to that of the control reaction. Importantly, our system exhibits versatility, accommodating a wide range of substrates for both individual and sequential reactions. This work not only validates the concept but also paves the way for the integration of chemo- and biocatalysts in the synthesis of a broader array of high-value chemical compounds.

Amphiphilic Nanogels as Versatile Stabilizers for Pickering Emulsions

Pickering emulsions (PEs) are stabilized by particles at the water/oil interface and exhibit superior long-term stability compared to emulsions with molecular surfactants. Among colloidal stabilizers, nano/microgels facilitate emulsification and can introduce stimuli responsiveness. While increasing their hydrophobicity is connected to phase inversion from oil-in-water (O/W) to water-in-oil (W/O) emulsions, a predictive model to relate this phase inversion to the molecular structure of the nano/microgel network remains missing. Addressing this challenge, we developed a library of amphiphilic nanogels (ANGs) that enable adjusting their hydrophobicity while maintaining similar colloidal structures. This enabled us to systematically investigate the influence of network hydrophobicity on emulsion stabilization. We found that W/O emulsions are preferred with increasing ANG hydrophobicity, oil polarity, and oil/water ratio. For nonpolar oils, increasing emulsification temperature enabled the formation of W/O PEs that are metastable at room temperature. We connected this behavior to interfacial ANG adsorption kinetics and quantified ANG deformation and swelling in both phases via atomic force microscopy. Importantly, we developed a quantitative method to predict phase inversion by the difference in Flory-Huggins parameters between ANGs with water and oil (χwater - χoil). Overall, this study provides crucial structure-property relations to assist the design of nano/microgels for advanced PEs.

Crystalline Nanoflowers Derived from the Intramolecular Cyclization-Induced Self-Assembly of an Amorphous Poly(amic acid) at High Solid Content

The investigation of the amorphous to crystalline transformation and the corresponding influence on the self-assembly behavior of amphiphilic polymers are of significant interest in this field. Herein, we propose the concept of intramolecular cyclization-induced self-assembly (ICISA) to prepare crystalline nanoflowers at a high solid content of 15% on the basis of the amorphous to crystalline transformation of poly(amic acid) (PAA). Taking advantage of the reactive property of the PAA, rigid and crystalline polyimide (PI) segments are introduced to the backbone of the PAA to give P(AA-stat-I) induced by the intramolecular cyclization reaction upon thermal treatment, leading to the in situ formation of crystalline nanoflowers. Revealing the formation mechanism of the nanoflowers, we found that the nanosheets are formed at the early stage and then stacked to form the nanoflowers at high concentrations. The relationship between the degree of imidization and incubation temperature is quantitatively analyzed, and the effects of temperature on the morphology, degree of imidization, and crystallinity of the assemblies are also investigated. Furthermore, computer simulations demonstrate the optimized temperature of ICISA of 160 °C, which ensures the match between the intramolecular cyclization reaction rate, the self-assembly process, and the lowest energy state of the self-assembly system, resulting in the formation of nanoflowers with high crystallinity. Overall, a facile one-step strategy is proposed to prepare crystalline nanoflowers based on the in situ thermally triggered intramolecular cyclization reaction of a PAA, which may bring fresh insights into the dynamic amorphous to the crystalline transformation of polymers.

Pickering Emulsions Biocatalysis: Recent Developments and Emerging Trends

Biocatalysis within biphasic systems is gaining significant attention in the field of synthetic chemistry, primarily for its ability to solve the problem of incompatible solubilities between biocatalysts and organic compounds. By forming an emulsion from these two-phase systems, a larger surface area is created, which greatly improves the mass transfer of substrates to the biocatalysts. Among the various types of emulsions, Pickering emulsions stand out due to their excellent stability, compatibility with biological substances, and the ease with which they can be formed and separated. This makes them ideal for reusing both the emulsifiers and the biocatalysts. This review explores the latest developments in biocatalysis using Pickering emulsions. It covers the structural features, methods of creation, innovations in flow biocatalysis, and the role of interfaces in these processes. Additionally, the challenges and future directions are discussed in combining chemical and biological catalysts within Pickering emulsion frameworks to advance synthetic methodologies.

Pyridine-Bridged Covalent Organic Frameworks with Adjustable Band Gaps as Intelligent Artificial Enzymes for Light-Augmented Biocatalytic Sensing

One of the biggest challenges in biotechnology and medical diagnostics is finding extremely sensitive and adaptable biosensors. Since metal-based enzyme-mimetic biocatalysts may lead to biosafety concerns on accumulative toxicity, it is essential to synthesize metal-free enzyme-mimics with optimal biocatalytic activity and superior selectivity. Here, the pyridine-bridged covalent organic frameworks (COFs) with specific oxidase-like (OXD-like) activities as intelligent artificial enzymes for light-augmented biocatalytic sensing of biomarkers are disclosed. Because of the adjustable bandgaps of pyridine structures on the photocatalytic properties of the pristine COF structures, the pyridine-bridged COF exhibit efficient, selective, and light-responsive OXD-like biocatalytic activity. Moreover, the pyridine-bridged COF structures show tunable and light-augmented biocatalytic detection capabilities, which outperform the recently reported state-of-the-art OXD-mimics regarding biosensing efficiency. Notably, the pyridine-bridged COF exhibits efficient and multifaceted diagnostic activity, including the extremely low limit of detection (LOD), which enables visual assays for abundant reducibility biomarkers. It is believed that this design will offer unique metal-free biocatalysts for high-sensitive and low-cost colorimetric detection and also provide new insights to create highly efficient enzyme-like COF materials via linkage-modulation strategies for future biocatalytic applications.

Cutting-Edge Biomaterials in Intervertebral Disc Degeneration Tissue Engineering

Intervertebral disc degeneration (IVDD) stands as the foremost contributor to low back pain (LBP), imposing a substantial weight on the world economy. Traditional treatment modalities encompass both conservative approaches and surgical interventions; however, the former falls short in halting IVDD progression, while the latter carries inherent risks. Hence, the quest for an efficacious method to reverse IVDD onset is paramount. Biomaterial delivery systems, exemplified by hydrogels, microspheres, and microneedles, renowned for their exceptional biocompatibility, biodegradability, biological efficacy, and mechanical attributes, have found widespread application in bone, cartilage, and various tissue engineering endeavors. Consequently, IVD tissue engineering has emerged as a burgeoning field of interest. This paper succinctly introduces the intervertebral disc (IVD) structure and the pathophysiology of IVDD, meticulously classifies biomaterials for IVD repair, and reviews recent advances in the field. Particularly, the strengths and weaknesses of biomaterials in IVD tissue engineering are emphasized, and potential avenues for future research are suggested.

An In Vitro Hybrid Biocatalytic System Enabled by a Combination of Surface-Displayed, Purified, and Cell-Free Expressed Enzymes

Enzymatic cascades have become a green and sustainable approach for the synthesis of valuable chemicals and pharmaceuticals. Using sequential enzymes to construct a multienzyme complex is an effective way to enhance the overall performance of biosynthetic routes. Here we report the design of an efficient in vitro hybrid biocatalytic system by assembling three enzymes that can convert styrene to (S)-1-phenyl-1,2-ethanediol. Specifically, we prepared the three enzymes in different ways, which were cell surface-displayed, purified, and cell-free expressed. To assemble them, we fused two orthogonal peptide-protein pairs (i.e., SpyTag/SpyCatcher and SnoopTag/SnoopCatcher) to the three enzymes, allowing their spatial organization by covalent assembly. By doing this, we constructed a multienzyme complex, which could enhance the production of (S)-1-phenyl-1,2-ethanediol by 3 times compared to the free-floating enzyme system without assembly. After optimization of the reaction system, the final product yield reached 234.6 μM with a substrate conversion rate of 46.9% (based on 0.5 mM styrene). Taken together, our strategy integrates the merits of advanced biochemical engineering techniques, including cellular surface display, spatial enzyme organization, and cell-free expression, which offers a new solution for chemical biosynthesis by enzymatic cascade biotransformation. We, therefore, anticipate that our approach will hold great potential for designing and constructing highly efficient systems to synthesize chemicals of agricultural, industrial, and pharmaceutical significance.

Bottlebrush Block Copolymers at the Interface of Immiscible Liquids: Adsorption and Lateral Packing

Amphiphilic bottlebrush block copolymers (BBCPs), having a hydrophilic bottlebrush polymer (BP) linked covalently to a hydrophobic BP, were found to segregate to liquid-liquid interfaces to minimize the free energy of the system. The key parameter influencing the outcome of the experiments is the ratio between the degree of polymerization of the backbone (NBB) and that of the side-chain brushes (NSC). Specifically, a spherical, star-like configuration results when NBB < NSC, while a cylindrical, bottlebrush-like shape is preferred when NBB > NSC. Dynamic interfacial tension (γ) and fluorescence recovery after photobleaching (FRAP) measurements show that the BBCP configuration influences the areal density and in-plane diffusion at the fluid interface. The characteristic relaxation times associated with BBCP adsorption (τA) and reorganization (τR) were determined by fitting time-dependent interfacial tension measurements to a sum of two exponential relaxation functions. Both τA and τR initially increased with NBB up to 92 repeat units, due to the larger hydrodynamic radius in solution and slower in-plane diffusivity, attributed to a shorter cross-sectional diameter of the side-chains near the block junction. This trend reversed at NBB = 190, with shorter τA and τR attributed to increased segregation strength and exposure of the bare water/toluene interface due to tilting and/or wiggling of the backbone chains, respectively. The adsorption energy barrier decreased with higher NBB, due to a reduced BBCP packing density at the fluid interface. This study provides fundamental insights into macromolecular assembly at fluid interfaces, as it pertains to unique bottlebrush block architectures.

Integrating Enzymes with Supramolecular Polymers for Recyclable Photobiocatalytic Catalysis

Chemical modifications of enzymes excel in the realm of enzyme engineering due to its directness, robustness, and efficiency; however, challenges persist in devising versatile and effective strategies. In this study, we introduce a supramolecular modification methodology that amalgamates a supramolecular polymer with Candida antarctica lipase B (CalB) to create supramolecular enzymes (SupEnzyme). This approach features the straightforward preparation of a supramolecular amphiphilic polymer (β-CD@SMA), which was subsequently conjugated to the enzyme, resulting in a SupEnzyme capable of self-assembly into supramolecular nanoparticles. The resulting SupEnzyme nanoparticles can form micron-scale supramolecular aggregates through supramolecular and electrostatic interactions with guest entities, thus enhancing catalyst recycling. Remarkably, these aggregates maintain 80 % activity after seven cycles, outperforming Novozym 435. Additionally, they can effectively initiate photobiocatalytic cascade reactions using guest photocatalysts. As a consequence, our SupEnzyme methodology exhibits noteworthy adaptability in enzyme modification, presenting a versatile platform for various polymer, enzyme, and biocompatible catalyst pairings, with potential applications in the fields of chemistry and biology.

Reconfigurable droplet networks

Droplet networks stabilized by lipid interfacial bilayers or colloidal particles have been extensively investigated in recent years and are of great interest for compartmentalized reactions and biological functions. However, current design strategies are disadvantaged by complex preparations and limited droplet size. Here, by using the assembly and jamming of cucurbit[8]uril surfactants at the oil-water interface, we show a novel means of preparing droplet networks that are multi-responsive, reconfigurable, and internally connected over macroscopic distances. Openings between the droplets enable the exchange of matter, affording a platform for chemical reactions and material synthesis. Our work requires only a manual compression to construct complex patterns of droplet networks, underscoring the simplicity of this strategy and the range of potential applications.

Enzyme-Polymer-Conjugate-Based Pickering Emulsions for Cell-Free Expression and Cascade Biotransformation

In this study, we addressed the limitations of conventional enzyme-polymer-conjugate-based Pickering emulsions for interfacial biocatalysis, which traditionally suffer from nonspecific and uncontrollable conjugation positions that can impede catalytic performance. By introducing a non-canonical amino acid (ncAA) at a specific site on target enzymes, we enabled precise polymer-enzyme conjugation. These engineered conjugates then acted as biocatalytically active emulsifiers to stabilize Pickering emulsions, while encapsulating a cell-free protein synthesis (CFPS) system in the aqueous phase for targeted enzyme expression. The resulting cascade reaction system leveraged enzymes expressed in the aqueous phase and on the emulsion interface for optimized chemical biosynthesis. The use of the cell-free system eliminated the need for intact whole cells or purified enzymes, representing a significant advancement in biocatalysis. Remarkably, the integration of Pickering emulsion, precise enzyme-polymer conjugation, and CFPS resulted in a fivefold enhancement in catalytic performance as compared to traditional single-phase reactions. Therefore, our approach harnesses the combined strengths of advanced biochemical engineering techniques, offering an efficient and practical solution for the synthesis of value-added chemicals in various biocatalysis and biotransformation applications.

Tailoring the Inherent Properties of Biobased Nanoparticles for Nanomedicine

Biobased nanoparticles are at the leading edge of the rapidly developing field of nanomedicine and biotherapeutics. Their unique size, shape, and biophysical properties make them attractive tools for biomedical research, including vaccination, targeted drug delivery, and immune therapy. These nanoparticles are engineered to present native cell receptors and proteins on their surfaces, providing a biomimicking camouflage for therapeutic cargo to evade rapid degradation, immune rejection, inflammation, and clearance. Despite showing promising clinical relevance, commercial implementation of these biobased nanoparticles is yet to be fully realized. In this perspective, we discuss advanced biobased nanoparticle designs used in medical applications, such as cell membrane nanoparticles, exosomes, and synthetic lipid-derived nanoparticles, and highlight their benefits and potential challenges. Moreover, we critically assess the future of preparing such particles using artificial intelligence and machine learning. These advanced computational tools will be able to predict the functional composition and behavior of the proteins and cell receptors present on the nanoparticle surfaces. With more advancement in designing new biobased nanoparticles, this field of research could play a key role in dictating the future rational design of drug transporters, thereby ultimately improving overall therapeutic outcomes.

Multi-compartmental MOF microreactors derived from Pickering double emulsions for chemo-enzymatic cascade catalysis

Bioinspired multi-compartment architectures are desired in synthetic biology and metabolic engineering, as credited by their cell-like structures and intrinsic ability of assembling catalytic species for spatiotemporal control over cascade reactions like in living systems. Herein, we describe a general Pickering double emulsion-directed interfacial synthesis method for the fabrication of multicompartmental MOF microreactors. This approach employs multiple liquid-liquid interfaces as a controllable platform for the self-completing growth of dense MOF layers, enabling the microreactor with tailor-made inner architectures and selective permeability. Importantly, simultaneous encapsulation of incompatible functionalities, including hydrophilic enzyme and hydrophobic molecular catalyst, can be realized in a single MOF microreactor for operating chemo-enzymatic cascade reactions. As exemplified by the Grubb' catalyst/CALB lipase driven olefin metathesis/ transesterification cascade reaction and glucose oxidase (GOx)/Fe-porphyrin catalyzed oxidation reaction, the multicompartmental microreactor exhibits 2.24-5.81 folds enhancement in cascade reaction efficiency in comparison to the homogeneous counterparts or physical mixture of individual analogues, due to the restrained mutual inactivation and substrate channelling effects. Our study prompts further design of multicompartment systems and the development of artificial cells capable of complex cellular transformations.

Pickering Emulsion Droplet-Derived Multicompartmentalized Microspheres for Innovative Applications

Multicompartmentalized microspheres with multilevel and complex interior structures have great potential in practical applications due to their cell-like structures and microscale dimension. The Pickering emulsion droplet-confined synthesis route has been demonstrated to be a promising strategy for fabricating multicompartmentalized microspheres. Since Pickering emulsion-templated formation of hollow microspheres is an interface-directed process in which the growth of shells occurs at the oil/water interface and the confined space of Pickering emulsion droplet accommodates a variety of behaviors, such as surfactant-guided assembly growth, confined pyrolysis transformation, tritemplated growth, and bottom-up assembly, the independent and free regulation of the interface and internal structure of microspheres is allowed. In this Perspective, we highlight the recent progress in the synthesis of microparticles with tunable interior structures via the Pickering emulsion droplet-based approach. And we delve into the innovative applications of these multilevel-structured microparticles benefiting from their biomimetic multicompartments. Finally, some fundamental challenges and opportunities are identified for regulating the interior structure within microspheres and promoting practical applications by virtue of the Pickering emulsion droplet-confined synthesis pathway.

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.