Facile construction of multicompartment multienzyme system through layer-by-layer self-assembly and biomimetic mineralization

Supramolecular design of coordination bonding architecture on zein nanoparticles for pH-responsive anticancer drug delivery

A pH-responsive system by constructing a designable coordination bonding-based metal-tannic acid (TA) architecture on zein nanoparticles (NPs) has been investigated. Film formation was initiated by the adsorption of the polyphenol and directed by pH-dependent, multivalent coordination bonding. The prepared metal-TA coated zein NPs (zein-TA/metal NPs) demonstrated good stability to maintain particle size in cell culture medium at 37 °C. The microstructure of the NPs was revealed by transmission electron microscopy (TEM). To confirm the surface chemical information of the NPs, XPS analysis was performed. Furthermore, in vitro viability studies revealed that the zein-TA/metal NPs showed no significant cytotoxicity against HepG2 cells for 24h. Because of the pH-responsive coordination bonding between TA and metal ions, the functional property of the metal-TA films was tailored for drug delivery. Biocompatible AuNPs were produced using zein-TA/metal NPs as reducing and stabilizing agents which were promising in the photothermal therapy of cancers and other diseases.

Fabrication of pH sensitive microcapsules using soft templates and their application to drug release

The schematic depiction of the process preparing hollow microcapsules and drug loading via layer-by-layer assembly technique.

Facile preparation of porous magnetic polydopamine microspheres through an inverse replication strategy for efficient enzyme immobilization

Porous microspheres composed of biocompatible dopamine and magnetic Fe₃O₄ nanoparticles were fabricated by inverse replication of CaCO₃ templates.

Synthesis of organic–inorganic hybrid microcapsules through in situ generation of an inorganic layer on an adhesive layer with mineralization-inducing capability

A facile and efficient route is developed to prepare (PDA–PEI)/titania hybrid microcapsules by in situ generation of an inorganic layer on an adhesive layer with mineralization-inducing capability under mild conditions.

Compartmentalisation of enzymes for cascade reactions through biomimetic layer-by-layer mineralization

A biomineralisation-based method for compartmentalisation of multi-enzyme cascades has been developed, and design parameters governing a cascade's catalytic performance were elucidated.

Monodisperse hybrid microcapsules with an ultrathin shell of submicron thickness for rapid enzyme reactions

In this study, we report a facile approach for the fabrication of monodisperse hybrid alginate/protamine/silica (APSi) microcapsules with an ultrathin shell of submicron thickness as enzyme encapsulation systems for rapid enzymatic reactions. Monodisperse water-in-oil (W/O) emulsions, which have been generated in microfluidics, are used as templates for preparing APSi microcapsules via internal/external gelation and biosilicification. The microcapsules allow highly-efficient encapsulation of model actives bovine serum albumin (∼99%) during the fabrication process. The hybrid shell with an ultrathin thickness of ∼420 nm provides fast mass transfer for the encapsulated model enzyme laccase to undergo rapid reaction. Moreover, this rigid hybrid shell also endows the encapsulated laccase with excellent reusability and storage stability. These ultrathin-shelled APSi microcapsules show great potential as efficient encapsulation systems for enzymes and biomolecules for their rapid reactions, and as delivery systems for actives in biomedical applications.

Confined multiple enzymatic (cascade) reactions within poly(dopamine)-based capsosomes

The design of compartmentalized carriers as artificial cells is envisioned to be an efficient tool with potential applications in the biomedical field. The advent of this area has witnessed the assembly of functional, bioinspired systems attempting to tackle challenges in cell mimicry by encapsulating multiple compartments and performing controlled encapsulated enzymatic catalysis. Although capsosomes, which consist of liposomes embedded within a polymeric carrier capsule, are among the most advanced systems, they are still amazingly simple in their functionality and cumbersome in their assembly. We report on capsosomes by embedding liposomes within a poly(dopamine) (PDA) carrier shell created in a solution-based single-step procedure. We demonstrate for the first time the potential of PDA-based capsosomes to act as artificial cell mimics by performing a two-enzyme coupled reaction in parallel with a single-enzyme conversion by encapsulating three different enzymes into separated liposomal compartments. In the former case, the enzyme uricase converts uric acid into hydrogen peroxide, CO2 and allantoin, followed by the reaction of hydrogen peroxide with the reagent Amplex Ultra Red in the presence of the enzyme horseradish peroxidase to generate the fluorescent product resorufin. The parallel enzymatic catalysis employs the enzyme ascorbate oxidase to convert ascorbic acid into 2-L-dehydroascorbic acid.

Compartmentalized multilayer hydrogel formation using a stimulus-responsive self-assembling polysaccharide

Polymeric systems that self-assemble through strong noncovalent bonds form structures that are highly dependent on the spatiotemporal sequence of cues that trigger self-assembly. Here, we prepared capsules with a semipermeable alginate-chitosan polyelectrolyte membrane that encapsulates a solution of the pH-responsive self-assembling aminopolysaccharide chitosan. Immersion of these capsules in a basic solution triggers gelation of the capsule contents, and the details of the gel-inducing treatment dramatically affect the final structure of the gelled compartment. Specifically, we show that the sequential transfer of the capsules between the base and water can generate multilayer hydrogel structures, with the thickness of each layer being controlled by the base concentration and immersion times. We further demonstrate that these multilayer hydrogels can serve as templates for the synthesis of iron oxide particles with a complex internal structure (i.e., with a multilayer internal structure). This work demonstrates the ability to enlist the stimulus-responsive self-assembling properties of biological polymers to create materials with complex structures.

Hemin-block copolymer micelle as an artificial peroxidase and its applications in chromogenic detection and biocatalysis

Following an inspiration from the fine structure of natural peroxidases, such as horseradish peroxidase (HRP), an artificial peroxidase was constructed through the self-assembly of diblock copolymers and hemin, which formed a functional micelle with peroxidase-like activity. The pyridine moiety in block copolymer poly(ethylene glycol)-block-poly(4-vinylpyridine) (PEG-b-P4VP) can coordinate with hemin, and thus hemin is present in a five-coordinate complex with an open site for binding substrates, which mimics the microenvironment of heme in natural peroxidases. The amphiphilic core-shell structure of the micelle and the coordination interaction of the polymer to the hemin inhibit the formation of hemin μ-oxo dimers, and thereby enhance the stability of hemin in the water phase. Hemin-micelles exhibited excellent catalytic performance in the oxidation of phenolic and azo compounds by H2O2. In comparison with natural peroxidases, hemin-micelles have higher catalytic activity and better stability over wide temperature and pH ranges. Hemin-micelles can be used as a detection system for H2O2 with chromogenic substrates, and they anticipate the possibility of constructing new biocatalysts tailored to specific functions.

Cascade reactions in nanoreactors

In an attempt to mimic the biosynthetic efficiencies of nature and in a search for greener, more sustainable alternatives to nowadays ways of producing chemicals, one-pot cascade reactions have attracted a lot of attention in the past decade. Since most catalysts are not compatible with each other, compartmentalization techniques have often been applied to prevent catalyst inactivation. A various array of nanoreactors have been developed to meet the demand of having a site-isolated catalyst system, while maintaining the catalyst activity. Both multienzyme nanoreactors as well as enzyme/metal catalyst or organocatalyst systems have shown great potential in one-pot cascade reactions and hold promise for future developments in this field.

Incorporating mobile nanospheres in the lumen of hybrid microcapsules for enhanced enzymatic activity

Physical encapsulation of enzymes in microcapsules, as a mild, controllable method, has been widely utilized for enzyme immobilization. However, this method often suffers from the big mass transfer resistance from the capsule lumen. In this study, a novel biocatalysis system with enhanced catalytic activity is constructed through coencapsulating enzymes and nanospheres in the lumen of protamine/silica hybrid microcapsules, which are synthesized through the synergy of biomimetic silicification and layer-by-layer (LbL) assembly. When utilized as the host for catalase (CAT) encapsulation, the hybrid microcapsules maintain high mechanical stability, high enzyme loading, and low enzyme leaching. Particularly, because of the existence of mobile nanospheres, the mass transfer resistance in the microcapsules is significantly reduced because of the vigorous agitation, thus acquiring an enhanced catalytic activity. Our strategy may also find applications in drug delivery and biosensor fields.

Exploring the segregating and mineralization-inducing capacities of cationic hydrophilic polymers for preparation of robust, multifunctional mesoporous hybrid microcapsules

A facile approach to preparing mesoporous hybrid microcapsules is developed by exploring the segregating and mineralization-inducing capacities of cationic hydrophilic polymer. The preparation process contains four steps: segregation of cationic hydrophilic polymer during template formation, cross-linking of the segregated polymer, biomimetic mineralization within cross-linked polymer network, and removal of template to simultaneously generate capsule lumen and mesopores on the capsule wall. Poly(allylamine hydrochloride) (PAH) is chosen as the model polymer, its hydrophilicity renders the segregating capacity and spontaneous enrichment in the near-surface region of CaCO3 microspheres; its biopolyamine-mimic structure renders the mineralization-inducing capacity to produce titania from the water-soluble titanium(IV) precursor. Meanwhile, CaCO3 microspheres serve the dual templating functions in the formation of hollow lumen and mesoporous wall. The thickness of capsule wall can be controlled by changing the polymer segregating and cross-linking conditions, while the pore size on the capsule wall can be tuned by changing the template synthesizing conditions. The robust hybrid microcapsules exhibit desirable efficiency in enzymatic catalysis, wastewater treatment and drug delivery. This approach may open facile, generic, and efficient pathway to designing and preparing a variety of hybrid microcapsules with high and tunable permeability, good stability and multiple functionalities for a broad range of applications.

Responsive hybrid microcapsules by the one-step interfacial thiol-ene photopolymerization

We here demonstrated a general, convenient, and robust method to fabricate the hybrid microcapsules through the one-step thiol-ene photopolymerization at the interface between toluene and water. In the presence of amphiphilic polyhedral oligomeric silsesquioxane (POSS) containing thiol groups (PTPS) as reactive surfactants and trimethylolpropane triacrylate (TMPTA) as a cross-linker, the wall of hybrid microcapsules can be photo-cross-linked. The obtained hybrid microcapsules (HMCs) were well-characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and confocal laser scanning microscopy (CLSM). The results revealed that the obtained HMCs are uniform with the tunable size in diameter (2-4 μm) and wall thickness (55-120 nm). The size of HMCs increased with the increasing content of toluene. The wall thickness of HMCs decreased with the increasing content of toluene, while the wall thickness of HMCs increased with the increasing content of cross-linker TMPTA. Furthermore, HMCs are thermoresponsive in aqueous solution, can encapsulate both hydrophobic and dydrophilic dyes, and can be used in the controlled dispersion of dyes in different mediums. It is believed that this simple, robust, and general method to fabricate the hybrid microcapsules will extend the potential application fields of microcapsules, such as in the controlled dispersion and drug delivery.

Constructing spatially separated multienzyme system through bioadhesion-assisted bio-inspired mineralization for efficient carbon dioxide conversion

A facile and green bioadhesion-assisted bio-inspired mineralization (BABM) approach is proposed to construct spatially separated multienzyme system for conversion of carbon dioxide to formaldehyde. Specifically, formate dehydrogenase is entrapped accompanying the formation of titania nanoparticles (NPs) through bio-inspired titanification. After in situ surface functionalization of NPs with oligodopa, formaldehyde dehydrogenase is immobilized on the surface of NPs through amine-catechol adduct reaction. Compared to co-immobilized and free multienzyme system, the spatially separated multienzyme system exhibits significantly enhanced formaldehyde yield, selectivity and initial specific activity. The influence of particle size on the enzyme activity reveals that the formaldehyde yield (80.9%, 52.9%, 46.4%), selectivity (92.7%, 86.6%, 85.1%) and initial specific activity (1.87, 1.31, 0.29 U mg(-1)) all decreased as the NPs particle size increased from 75, 175 to 375 nm. After storing for 20 days at 4 °C, this multienzyme system retains as high as 70% of its initial activity.

Metal-organic coordination-enabled layer-by-layer self-assembly to prepare hybrid microcapsules for efficient enzyme immobilization

A novel layer-by-layer self-assembly approach enabled by metal-organic coordination was developed to prepare polymer-inorganic hybrid microcapsules. Alginate was first activated via N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxy succinimide (NHS) coupling chemistry, and subsequently reacted with dopamine. Afterward, the dopamine modified alginate (Alg-DA) and titanium(IV) bis(ammonium lactato) dihydroxide (Ti(IV)) were alternatively deposited onto CaCO3 templates. The coordination reaction between the catechol groups of Alg-DA and the Ti(IV) allowed the alternative assembly to form a series of multilayers. After removing the templates, the alginate-titanium hybrid microcapsules were obtained. The high mechanical stability of hybrid microcapsules was demonstrated by osmotic pressure experiment. Furthermore, the hybrid microcapsules displayed superior thermal stability due to Ti(IV) coordination. Catalase (CAT) was used as model enzyme, either encapsulated inside or covalently attached on the surface of the resultant microcapsules. No CAT leakage from the microcapsules was detected after incubation for 48 h. The encapsulated CAT, with a loading capacity of 450-500 mg g(-1) microcapsules, exhibited desirable long-term storage stability, whereas the covalently attached CAT, with a loading capacity of 100-150 mg g(-1) microcapsules, showed desirable operational stability.