Chen Yang

Polydopamine Microcapsules with Different Wall Structures Prepared by a Template-Mediated Method for Enzyme Immobilization

Microcapsules with diverse wall structures may exhibit different performance in specific applications. In the present study, three kinds of mussel-inspired polydopamine (PDA) microcapsules with different wall structures have been prepared by a template-mediated method. More specifically, three types of CaCO3 microspheres (poly(allylamine hydrochloride), (PAH)-doped CaCO3; pure-CaCO3; and poly(styrene sulfonate sodium), (PSS)-doped CaCO3) were synthesized as sacrificial templates, which were then treated by dopamine to obtain the corresponding PDA-CaCO3 microspheres. Through treating these microspheres with disodium ethylene diamine tetraacetic acid (EDTA-2Na) to remove CaCO3, three types of PDA microcapsules were acquired: that was (1) PAH-PDA microcapsule with a thick (∼600 nm) and highly porous capsule wall composed of interconnected networks, (2) pure-PDA microcapsule with a thick (∼600 nm) and less porous capsule wall, (3) PSS-PDA microcapsule with a thin (∼70 nm) and dense capsule wall. Several characterizations confirmed that a higher degree in porosity and interconnectivity of the capsule wall would lead to a higher mass transfer coefficient. When serving as the carrier for catalase (CAT) immobilization, these enzyme-encapsulated PDA microcapsules showed distinct structure-related activity and stability. In particular, PAH-PDA microcapsules with a wall of highly interconnected networks displayed several significant advantages, including increases in enzyme encapsulation efficiency and enzyme activity/stability and a decrease in enzyme leaching in comparison with other two types of PDA microcapsules. Besides, this hierarchically structured PAH-PDA microcapsule may find other promising applications in biocatalysis, biosensors, drug delivery, etc.

Facile One-Pot Preparation of Chitosan/Calcium Pyrophosphate Hybrid Microflowers

Flower-like chitosan/calcium pyrophosphate hybrid microparticles (microflowers) are prepared using a facile one-pot approach by combining ionotropic gelation with biomimetic mineralization. Chitosan-tripolyphosphate (CS-TPP) nanocomplexes are first synthesized through ionotropic gelation; meanwhile, excess TPP is partly hydrolyzed into pyrophosphate ions (P2O7(4-)). Upon addition of CaCl2, CS-TPP nanocomplexes serve as a versatile template, inducing in situ mineralization of Ca2P2O7 and directing its growth and assembly into microflowers. The whole preparation process can be completed within half an hour. The as-prepared microflowers are composed of 23.0% CS-TPP nanocomplexes and 77.0% Ca2P2O7 crystals. Mesopores (3.7 and 11.2 nm) and macropores coexist in the microflowers, indicating porous and hierarchical structures. The microflowers exhibit high efficiency in dye adsorption and enzymatic catalysis. Specifically, a high adsorption capacity of 520 mg g(-1) for Congo red is achieved. And the immobilized enzyme retains about 85% catalytic activity compared with that of the free enzyme. The facile one-pot preparation process ensures the broad applications of the porous hybrid microflowers.

Facile Method To Prepare Microcapsules Inspired by Polyphenol Chemistry for Efficient Enzyme Immobilization

In this study, a method inspired by polyphenol chemistry is developed for the facile preparation of microcapsules under mild conditions. Specifically, the preparation process includes four steps: formation of the sacrificial template, generation of the polyphenol coating on the template surface, cross-linking of the polyphenol coating by cationic polymers, and removal of the template. Tannic acid (TA) is chosen as a representative polyphenol coating precursor for the preparation of microcapsules. The strong interfacial affinity of TA contributes to the formation of polyphenol coating through oxidative oligomerization, while the high reactivity of TA is in charge of reacting/cross-linking with cationic polymer polyethylenimine (PEI) through Schiff base/Michael addition reaction. The chemical/topological structures of the resultant microcapsules are simultaneously characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier Transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), etc. The wall thickness of the microcapsules could be tailored from 257±20 nm to 486±46 nm through changing the TA concentration. The microcapsules are then utilized for encapsulating glucose oxidase (GOD), and the immobilized enzyme exhibits desired catalytic activity and enhanced pH and thermal stabilities. Owing to the structural diversity and functional versatility of polyphenols, this study may offer a facile and generic method to prepare microcapsules and other kinds of functional porous materials.

Coordination-Enabled One-Step Assembly of Ultrathin, Hybrid Microcapsules with Weak pH-Response

In this study, an ultrathin, hybrid microcapsule is prepared though coordination-enabled one-step assembly of tannic acid (TA) and titanium(IV) bis(ammonium lactate) dihydroxide (Ti-BALDH) upon a hard-templating method. Briefly, the PSS-doped CaCO3 microspheres with a diameter of 5-8 μm were synthesized and utilized as the sacrificial templates. Then, TA-Ti(IV) coatings were formed on the surface of the PSS-doped CaCO3 templates through soaking in TA and Ti-BALDH aqueous solutions under mild conditions. After removing the template by EDTA treatment, the TA-Ti(IV) microcapsules with a capsule wall thickness of 15 ± 3 nm were obtained. The strong coordination bond between polyphenol and Ti(IV) conferred the TA-Ti(IV) microcapsules high structural stability in the range of pH values 3.0-11.0. Accordingly, the enzyme-immobilized TA-Ti(IV) microcapsules exhibited superior pH and thermal stabilities. This study discloses the formation of TA-Ti(IV) microcapsules that are suitable for use as supports in catalysis due to their extensive pH and thermal stabilities.

Preparation and enzymatic application of flower-like hybrid microcapsules through a biomimetic mineralization approach

Fast and quantitative adsorption of molecules may confer hybrid microcapsules high performance in specific applications, such as biocatalysis, biosensing, drug delivery, and so on. Engineering the chemical/topological structures of the capsule wall renders great potential to achieve this goal. In the present study, flower-like microcapsules are prepared through a biomimetic mineralization approach. Briefly, protein-hybrid microflowers are firstly synthesized through enzyme-induced precipitation of Cu3(PO4)2, which are subsequently utilized as templates for alternative deposition of the protamine layer and the silica layer through biomimetic silicification assisted by layer-by-layer (LbL) assembly. After treatment with EDTA, the flower-like protamine/silica hybrid (FPSH) microcapsules are obtained. Additionally, the hybrid capsule wall also endows the FPSH microcapsules with desirable pH, temperature and storage stability. Hopefully, our approach may provide a promising alternative to increase the efficiency of catalysis, drug delivery, etc.

Merging of covalent cross-linking and biomimetic mineralization into an LBL self-assembly process for the construction of robust organic–inorganic hybrid microcapsules

A mild and efficient method for the construction of robust organic-inorganic hybrid microcapsules was developed by merging of covalent cross-linking and biomimetic mineralization into a layer-by-layer (LBL) self-assembly process. The diatom cell-inspired microcapsule structure had a biocompatible inner organic layer which could create a suitable microenvironment for biologically active substances inside the microcapsules and an inorganic layer which could function as a supporting membrane to maintain the intact morphology of the microcapsules. When in 40% PSS solution, only 5% of the hybrid microcapsules were deformed indicating that the hybrid microcapsule had a higher mechanical stability. The combination of the advantages of both the organic layer and the inorganic layer was applied for the immobilization of catalase (CAT). After being reused 7 times, the CAT in the hybrid microcapsules retained 78% of its initial activity. A buffering effect was created by the capsule wall and the immobilized CAT had a higher pH stability than the free CAT. After storing for 45 days, the CAT in the hybrid microcapsules retained 78% of its initial activity. It is envisaged that the as-prepared hybrid microcapsules can be extended to many applications such as biocatalysis, drug/gene delivery and biosensor fields.

MOF-templated rough, ultrathin inorganic microcapsules for enzyme immobilization

Ultrathin titania microcapsules with rough surfaces were prepared by using a metal-organic framework (ZIF-8) as one kind of hard template to mediate the structures of the microcapsule shell. Specifically, CaCO3 particles were first coated with tannic acid (TA) followed by the deposition of hydrophobic ZIF-8 and another TA layer, the obtained particles were then assembled with protamine/TiO2 bilayers through biomimetic mineralization. Finally, the microcapsules (Z-TiO2) were obtained after simultaneously removing CaCO3 and ZIF-8 templates using ethylenediaminetetraacetic acid (EDTA). The coordination interaction between TA and ZIF-8 ensured the robust templating which endowed the microcapsules with a rough surface and an ultrathin microcapsules shell (100 nm) with 4.4 nm pore size. Moreover, the surface roughness of microcapsules can be regulated by changing the size of ZIF-8 crystals. The microcapsules were then utilized to immobilize penicillin G acylase (PGA). And PGA@Z-TiO2 retained 69% activity of equivalent free PGA with a loading capacity of 160 mg g-1. The PGA@Z-TiO2 microcapsules exhibited superior reusability: after recycling 8 times, the conversion of the enzymatic reaction remained 36.0%, which was twice higher than that of PGA@TiO2 (14.7%). Moreover, compared with free PGA and PGA@TiO2 microcapsules, PGA@Z-TiO2 microcapsules exhibited higher thermal and storage stability. After storing for 60 days, the relative activity of PGA@Z-TiO2 remained 89.6%, which was higher than that of free PGA (34.5%) and PGA@TiO2 (73.6%). ZIF-8 can be envisioned to be a novel class of hard template for preparing a broad variety of microcapsules with different hierarchical structures.

Mask‐Like Symmetrical Microclusters through a Diffusion‐Limited Assembly Approach

A diffusion-limited assembly approach was explored to fabricate symmetrical [Cu(Succinate)]n microclusters with a different shape and size for the first time. The molecular structure of succinate and its coordination reaction capability towards copper(II) ions governed the one-dimensional growth of the nanofibers and the concomitant formation of the microclusters. In detail, a symmetrical concentration gradient was formed around the endpoints of the nanofibers caused by the diffusion-limited process at high reactant concentrations. The concentration gradient forced the nanofibers to grow divergently and further aggregate into open microcluster structure. The shape and size of the microclusters could be tuned by altering the concentration of the reactants. Particularly, mask-like double-hole symmetrical microclusters (MDHSMs) were obtained when the concentration of both reactants was as high as 140 mM. The resultant MDHSMs showed high selectivity in adsorption of dyes and proteins, and may find potential applications in water treatment, bioseparation, and immobilization of biomacromolecules.