Composite Microgels Research Articles

Facile preparation of graphene oxide/Poly (N‐Isopropylacrylamide‐co‐acrylic acid) composite thin film and its quartz crystal microbalance humidity sensing property

AbstractThe composite microgels were synthesized from N‐Isopropylacrylamide (NIPAM) and acrylic acid (AA) monomers in the presence of graphene oxide (GO) using an in situ radical copolymerization method. The successful preparation of these composite microgels was investigated through Fourier transform infrared spectroscopy (FTIR), ultraviolet visible absorption spectroscopy (UV–vis), and Raman spectroscopy. Due to the hydrophilic properties of GO and the microgels containing oxygenated groups (OH, COOH, and CONH2), quartz crystal microbalance (QCM) sensors can be fabricated by spraying the GO/P(NIPAM‐co‐AA) dispersion onto QCM sensors as sensitive coating materials. The results indicate a notable enhancement in the performance of GO/P(NIPAM‐co‐AA) modified QCM humidity sensor, compared to QCM sensors modified with either GO or P(NIPAM‐co‐AA) microgels alone. This improvement is mainly evidenced by higher sensitivity and reduced moisture hysteresis. The humidity sensing mechanism is based on the combined effect of GO and P(NIPAM‐co‐AA) microgels, which synergistically enhance the sensor's performance. Additionally, the results from water contact angle measurements, laser scanning confocal microscopy (LSCM), and scanning electron microscope (SEM) show that GO/P(NIPAM‐co‐AA) exhibits greater roughness and stronger hydrophilicity than either GO or P(NIPAM‐co‐AA) microgels alone. These properties make GO/P(NIPAM‐co‐AA) an effective moisture‐sensitive material for QCM sensors.

An injectable multicomponent integrated microgel promotes cardiomyocyte regeneration and heart function after ischemia reperfusion injury

Myocardial ischemia reperfusion (I/R) injury frequently impacts the outcome of patients with coronary heart disease and lacks effective therapeutic strategies. We have summarized the challenges in treating IR injury into three aspects, namely inflammatory reaction, fibrosis, and impaired proliferation ability of myocardial tissue. To address these issues, we have developed an injectable composite microgel called DMP@mgel by integrating three types of biomaterials: placental-derived mesenchymal stem cells loaded microgel, PEDOT:PSS loaded microgel, and siRNA-loaded carrier DP7-C. Upon injection into the injured area, DMP@mgel could regulate the inflammatory microenvironment, promote angiogenesis by the function of stem cells paracrine. Additionally, it enhances coupling between myocardial cells due to its high electrical conductivity. Moreover, DP7-C/siRNA complex can efficiently transfect into myocardial cells to inhibit Hippo pathway activity and promote cell proliferation. The electrostatic interaction enables DP7-C to combine all components into a stable delivery system. In vitro and in vivo experiments confirmed that each ingredient of DMP@mgel exhibits their respective functions such as neovascularization promotion, Hippo pathway inhibition, and antioxidation capability. Finally, administration of DMP@mgel in I/R injured rats significantly improved heart function while reducing fibrosis as evidenced by echocardiography results along with Evans blue staining and histological examination.

Surface lubrication with thermal- and pH-sensitive PNIPAM-co-PAA-(IF-MoS2/GO) composite microgels under YG8/TC4 contact

In this investigation, the surface tribological behavior of YG8/TC4 contacts under microgel lubrication was explored, utilizing thermal- and pH-sensitive PNIPAM-co-PAA-(IF-MoS2/GO) composite microgels as lubricant additives. Through the application of a ball-on-disk reciprocating tribometer, the study demonstrated the outstanding lubrication capabilities of the composite microgels. The lubrication process involving PNIPAM-co-PAA-(IF-MoS2/GO) composite microgels initiated a tribo-chemical reaction, leading to the generation of a larger quantity of TiS2 with exceptional lubricating properties on the friction surface compared to alternative lubrication conditions. The effective isolation of the friction pair by PNIPAM-co-PAA composite microgels contributed to the reduction in tribo-oxidation of the sliding surfaces , while the presence of IF-MoS2 facilitated the formation of TiS2. Furthermore, the facile sliding property of GO nanosheets played a crucial role in achieving overall excellent lubrication performance. The synergistic effects arising from the components in PNIPAM-co-PAA-(IF-MoS2/GO) composite microgels introduce a novel and effective strategy for controlling the friction and wear of YG8/TC4 contacts.

Efficient recovery of Cr(VI), Au(III), and Pd(II) using physically crosslinked aminoclay/polyvinyl alcohol composite microgels generated by microfluidics

Chemically crosslinked hydrogel adsorbents are typically produced using highly toxic agents for crosslinking, posing risks to both human health and the environment. In this study, we successfully demonstrated the fabrication of a physically crosslinked Fe–aminoclay (AC)/polyvinyl alcohol (PVA) composite microgel. This was achieved using a microfluidic approach to generate water-in-oil-in-water (W/O/W) double-emulsion droplets, eliminating the need for chemical crosslinkers. Compared to its chemically crosslinked counterpart, this physically crosslinked Fe–AC/PVA microgel showed superior performance in recovering the metals Cr(VI), Au(III), and Pd(II) from an aqueous solution. This enhanced capability was attributed to the abundance of free amine functional groups and a microgel structure that was conducive to metal ion adsorption. The physically crosslinked microgel demonstrated a maximum adsorption capacity of 203.7 mg/g for Cr(VI), 241.3 mg/g for Au(III), and 275.8 mg/g for Pd(II), compared to 144.3, 181.1, and 222.5 mg/g, respectively, for the chemically crosslinked microgel. The adsorption isotherms and kinetics for these metals conformed to the Sips isotherm and pseudo-second-order models, respectively, suggesting that chemical adsorption was the dominant mechanism. Furthermore, embedding magnetic nanoparticles in the Fe–AC/PVA microgel enabled straightforward separation and regeneration from an aqueous solution. The Fe–AC/PVA composite microgel also demonstrated excellent reusability, maintaining an adsorption efficiency of over 78 % across five consecutive cycles.

Preparation of CO2-Responsive Biobased Ternary Composite Microgel and Its Application in Reservoir Gas Channeling Plugging

Preparation of CO₂-Responsive Biobased Ternary Composite Microgel and Its Application in Reservoir Gas Channeling Plugging

Carboxylmethyl cellulose produced from wood sawdust for improving properties of sodium alginate hydrogel in dye adsorption

Cellulose-based materials have shown immense potential for diverse applications because of their attractive properties such as excellent mechanical properties, rich hydroxyl groups for modification, and natural properties with recyclability, nontoxicity, biocompatibility, biodegradability, and environmental friendliness. This study aimed to optimize cellulose extraction from wood sawdust using deep eutectic solution (DES) treatments for the preparation of carboxymethyl cellulose (CMC) and to evaluate the application of CMC in sodium alginate (SA) microgel for dye adsorption. Cellulose extractions were optimized in reduced chemical treatment conditions with high cellulose contents (88.19 %), and selectively increased lignin removal (87.23 %). The analyses by SEM, XRD, and FT-IR revealed that carboxymethylation has successfully transformed cellulose into CMC to facilitate the significantly improved water solubility and swelling ability. The TGA curve of CMC showed a higher thermal stability (residual weight of 52 % at 300 °C) compared to unmodified cellulose due to the decomposition of the amorphous regions during the carboxymethylation. The combined biodegradable SA and water-soluble CMC composite microgels were successfully fabricated via cross-linking with calcium chloride using a microfluidic approach. The incorporation of CMC into SA microgel had enhanced mechanical properties, adsorption capacities of 160.87 and 141.48 mg/g, and adsorption–desorption efficiencies of 96.84 % and 95.41 % for crystal violet and trypan blue respectively after five cycles. The adsorption processes of both dyes can be described by Sips adsorption isotherms and pseudo-second-order kinetic models, verifying the chemical interaction-assisted process. This simple green CMC/SA adsorbent has the potential to significantly enhance the adsorption capacity of dye removal from wastewater.

Impact of pH on the fabrication of egg white reinforced soy protein composite microgels for gastrointestinal delivery purposes.

Protein molecules such as soy protein isolate (SPI) and egg white (EW) are highly promising materials for developing hydrogels (especially micro/nanogels) for the encapsulation, protection and controlled release of bioactive substances. However, there are limited numbers of studies on the formulation and behavior of these two gelling materials as microgels. In our study, composite microgels of SPI and EW at various component ratios and pH conditions have been successfully prepared; the rheological behavior and structural properties of these composite microgels before, during and after in vitro digestion have been analyzed; and their performance in curcumin encapsulation and gastrointestinal delivery has also been investigated. It was concluded that the SPI-EW composites at a mass ratio of 50 : 50 showed the best gelling properties in terms of storage modulus. Composite microgels prepared at pH 4 had larger particle sizes with more compact structures than those prepared at pH 7, due to their acidic complex coacervation, and therefore were more resistant to gastrointestinal digestion. The results suggest that the SPI-EW composite microgel particles prepared at pH 4 could achieve better sustained-release of curcumin in the in vitro gastrointestinal tract, with preserved antioxidant activity. Our study shows promise for the utilization of protein-based composite micro/nanogels for oral delivery applications.

Composite Microgels Loaded with Doxorubicin-Conjugated Amine-Functionalized Zinc Ferrite Nanoparticles for Stimuli-Responsive Sustained Drug Release.

The purpose of this study is to address the need for efficient drug delivery with high drug encapsulation efficiency and sustained drug release. We aim to create nanoparticle-loaded microgels for potential applications in treatment development. We adopted the process of ionic gelation to generate microgels from sodium alginate and carboxymethyl cellulose. These microgels were loaded with doxorubicin-conjugated amine-functionalized zinc ferrite nanoparticles (AZnFe-NPs). The systems were characterized using various techniques. Toxicity was evaluated in MCF-7 cells. In vitro release studies were conducted at different pH levels at 37 oC, with the drug release kinetics being analyzed using various models. The drug encapsulation efficiency of the created carriers was as high as 70%. The nanoparticle-loaded microgels exhibited pH-responsive behavior and sustained drug release. Drug release from them was mediated via a non-Fickian type of diffusion. Given their high drug encapsulation efficiency, sustained drug release and pH-responsiveness, our nanoparticle-loaded microgels show promise as smart carriers for future treatment applications. Further development and research can significantly benefit the field of drug delivery and treatment development.

3D visualization reveals the cooling rate dependent crystallization near a wall in dense microgel systems.

Controlled crystallization, melting and vitrification are important fundamental processes in nature and technology. However, the microscopic details of these fundamental phenomena still lack understanding, in particular how the cooling rate and presence of a wall influence the crystal nucleation and glass formation. Thermoresponsive microgels provide the possibility to study phase transitions at the single-particle level, owing to the ability to tune the particle size with temperature. In this study, we employ composite microgels consisting of a hard core and a crosslinked poly(N-isopropyl acrylamide-co-methacrylic acid) shell to study the crystallization of dense suspensions of soft colloids near a wall using confocal microscopy. We investigate the effect of the cooling rate on the fluid-to-solid transition close to the sample wall. The structures formed during cooling range from glassy in the case of a rapid temperature quench to crystalline when a slow cooling rate is used. Detailed analysis of the final structure reveals that the cooling rate also sets the degree of alignment of the crystal domains with the wall as a result of a balance between homogeneous and heterogeneous crystal nucleation. The results presented here yield valuable insight into the microscopic details of temperature-controlled crystallization near a wall. This understanding will help pave the way towards optimal crystallization conditions for microgel applications.

Composite hydrogels formed from okara cellulose nanofibers and carrageenan: Fabrication and characterization

Currently, there is great interest in converting edible agro-waste, such as okara from soybean production, into value-added products. For this study, we focus on fabricating composite hydrogels from okara cellulose nanofibers (CNFs) and carrageenan (CA). We also examined the effects of TEMPO oxidation of the okara CNFs, as well as CA concentration, on the microstructure and physicochemical properties of the composite hydrogels. The water holding capacity, oil holding capacity, surface tension, gel strength, and viscoelasticity of the composite microgels increased with increasing CA concentration, and it was found that the highest values were obtained for TC-CA2 hydrogel: contact angle = 43.6° and surface tension = 45.12 mN/m, which was attributed to the formation of a more regular and dense three-dimensional gel network. All the CNF-CA microgels had highly anionic ζ-potential values (−38.8 to −50.1 mV), with the magnitude of the negative charge increasing with TEMPO oxidation and carrageenan concentration. These results suggest there would be strong electrostatic repulsion between the composite hydrogels. The composite microgels produced in our work may be useful functional materials for utilization within the food industry, thereby converting a waste product into a valuable commodity.

Microfluidic Fabrication of Monodisperse and Recyclable TiO2-Poly(ethylene glycol) Diacrylate Hybrid Microgels for Removal of Methylene Blue from Aqueous Medium.

Nearly monodisperse titanium oxide-polyethylene glycol diacrylate [TiO2-P(EGDA)] hybrid microbeads containing 0.5 wt % TiO2 nanoparticles entrapped within a P(EGDA) cross-linked polymeric network were synthesized using a modular Lego-inspired glass capillary microfluidic device. TiO2-P(EGDA) hybrid microgels were characterized by optical microscopy, scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, and thermogravimetric analysis. The fabricated TiO2-P(EGDA) hybrid microgel system showed 100% removal efficiency of methylene blue (MB) from its 1-3 ppm aqueous solutions after 4 h of UV light irradiation at 0.2 mW/cm2 at the loading of 25 g/L photocatalyst beads in the reaction mixture, corresponding to the loading of naked TiO2 of just 0.025 g/L. No decrease in photocatalytic efficiency was observed in 10 repeated runs with recycled photocatalyst using a fresh 1 ppm MB solution in each cycle. The rate of photocatalytic degradation was controlled by the UV light irradiance, catalyst loading, and the initial dye concentration. Physical adsorption of MB onto the surface of composite microgel was also observed. The adsorption data was best fitted with the Langmuir adsorption isotherm and the Elovich kinetic model. TiO2-P(EGDA) microgel beads are biocompatible, can be prepared with a tunable size in the microfluidic device, and can easily be separated from the reaction mixture by gravity settling. The TiO2-P(EGDA) system can be used for the removal of other toxic dyes and micropollutants from industrial wastewater.

Mineralized Microgels via Electrohydrodynamic Atomization: Optimization and In Vitro Model for Dentin-Pulp Complex.

There is growing interest in the use of micro-sized hydrogels, including bioactive signals, as efficient platforms for tissue regeneration because they are able to mimic cell niche structure and selected functionalities. Herein, it is proposed to optimize bioactive composite microgels via electrohydrodynamic atomization (EHDA) to regenerate the dentin-pulp complex. The addition of disodium phosphate (Na2HPO4) salts as mineral precursors triggered an in situ reaction with divalent ions in solution, thus promoting the encapsulation of different amounts of apatite-like phases. Morphological analysis via image analysis of optical images confirmed a narrow distribution of perfectly rounded particles, with an average diameter ranging from 223 ± 18 μm to 502 ± 64 μm as a function of mineral content and process parameters used. FTIR, TEM, and EDAX analyses confirmed the formation of calcium phosphates with a characteristic Ca/P ratio close to 1.67 and a needle-like crystal shape. In vitro studies-using dental pulp stem cells (DPSCs) in crown sections of natural teeth slices-showed an increase in cell viability until 14 days, recording a decay of proliferation at 21 days, independent on the mineral amount, suggesting that differentiation is started, as confirmed by the increase of ALP activity at 14 days. In this view, mineralized microgels could be successfully used to support in vitro osteogenesis, working as an interesting model to study dental tissue regeneration.

Early hydration characteristics and kinetics model of cement pastes containing internal curing materials with different absorption behaviors

Internal curing with superabsorbent polymer (SAP) has potential effect on the early deformation and hydration of cementitious material. However, there are few studies on the hydration kinetics and hydration characteristics of internal curing cementitious material. Here, the effects of microgel, composite microgel and commercial SAP with different dosage and absorption behaviors on the hydration characteristics of cement paste were studied by the hydration model proposed by Krstulović-Dabić and hydration heat. Results showed that the hydration reaction of paste containing internal curing materials increased as function of the dosage. When nano-silica(NS) incorporated into microgel, 24.5% and 5.6% increase in value of exothermic peak and cumulative heat were observed for paste. The hydration kinetic model showed that the composite microgel promoted the crystal growth and phase boundary reaction process, thus extending the transition point to the diffusion process. For commercial SAP with premature desorption behavior, the hydration rate of cement paste decreases and the appearance of conversion point at each process is delayed. Hydration characteristics are in good agreement with the kinetic model, suggesting that portlandite consumed by pozzolanic reaction promoted the development of hydration reaction and further refined the microstructure of paste.

Bactericidal and biocatalytic temperature responsive microgel based self-cleaning membranes for water purification

The present study focuses on creating an antimicrobial and biocatalytic smart gating membrane by synthesizing unique core–shell microgels. The core–shell microgels are synthesized by grafting short chains of poly(ethylenimine) (PEI) onto a poly((N-isopropyl acrylamide)–co-glycidyl methacrylate)) (P(NIPAm-co-GMA)) core. Subsequently, the produced microgels are utilized as a substrate for synthesizing and stabilizing silver nanoparticles (Ag NPs) through an in-situ approach. These Ag NPs immobilized microgels are then suction filtered over a polyethylene terephthalate (PET) track-etched support to create cross-linked composite microgel membranes (CMMs). After structural and permeation characterization of the prepared CMMs, the laccase enzyme is then covalently grafted to the surface of the membrane and tested for its effectiveness in degrading Reactive red-120 dye. The laccase immobilized biocatalytic CMMs show effective degradation of the Reactive red-120 by 71%, 48%, and 34% at pH 3, 4, and 5, respectively. Furthermore, the immobilized laccase enzyme showed better activity and stability in terms of thermal, pH, and storage compared to the free laccase, leading to increased reusability. The unique combination of Ag NPs and laccase on a thermoresponsive microgel support resulted in a responsive self-cleaning membrane with excellent antimicrobial and dye degradation capabilities for environmentally friendly separation technology.

Microstructure refinement and affected zone reinforcement for internal curing cement paste by composite microgel with nano silica

The introduction of superabsorbent polymers into cement increases the number of macroscopic pores, resulting in reduction of compressive strength. These limitations can be addressed by incorporated nano silica in polymer structure. Herein, a series of composite microgels containing nano silica were prepared and incorporated into cement paste. The effect of composite microgels on the hydration degree, compressive strength of cement paste was investigated. The microstructure and affected zone of cement paste were characterized by nitrogen adsorption desorption (NAD), backscattering (BSE), thermogravimetry (TGA) and microhardness techniques. The equilibrium absorptivity and water release rate of the composite microgels can be improved by proper crosslinking density and silica content. The addition of low crosslinking density composite microgels accelerated the formation of hydration products, which encouraged to filling formed voids. More dense arch structure was observed in vicinity of formed void. These further suggested that the reduction in the compressive strength of cement paste can be offset by composite microgels with proper crosslinking density, thus providing important application prospects in internal curing.

Dual (pH and thermal) stimuli-responsive Pickering emulsion stabilized by chitosan-carrageenan composite microgels

Formulation of water-in-oil (W/O) Pickering emulsion (PE) for food applications has been largely restricted by the limited choices of food-grade Pickering emulsifiers. In this study, composite microgels made of chitosan and carrageenan were explored as a dual (pH and thermal) stimuli-responsive Pickering emulsifier for the stabilization of W/O PE. The chitosan-carrageenan (CS-CRG) composite microgels not only exhibited pH- and thermo-responsiveness, but also displayed enhanced lipophilicity as compared to the discrete polymers. The stability of the CS-CRG-stabilized W/O PE system (CS-CRG PE) was governed by CS:CRG mass ratio and oil fractions used. The CS-CRG PE remained stable at acidic pH and at temperatures below 40 °C. The instability of CS-CRG composite microgels at alkaline pH and at temperatures above 40 °C rendered the demulsification of CS-CRG PE. This stimuli-responsive W/O PE could unlock new opportunities for the development of stimuli-responsive W/O PE using food-grade materials.

A home-made pipette droplet microfluidics rapid prototyping and training kit for digital PCR, microorganism/cell encapsulation and controlled microgel synthesis

Droplet microfluidics offers a platform from which new digital molecular assay, disease screening, wound healing and material synthesis technologies have been proposed. However, the current commercial droplet generation, assembly and imaging technologies are too expensive and rigid to permit rapid and broad-range tuning of droplet features/cargoes. This rapid prototyping bottleneck has limited further expansion of its application. Herein, an inexpensive home-made pipette droplet microfluidics kit is introduced. This kit includes elliptical pipette tips that can be fabricated with a simple DIY (Do-It-Yourself) tool, a unique tape-based or 3D printed shallow-center imaging chip that allows rapid monolayer droplet assembly/immobilization and imaging with a smart-phone camera or miniature microscope. The droplets are generated by manual or automatic pipetting without expensive and lab-bound microfluidic pumps. The droplet size and fluid viscosity/surface tension can be varied significantly because of our particular droplet generation, assembly and imaging designs. The versatility of this rapid prototyping kit is demonstrated with three representative applications that can benefit from a droplet microfluidic platform: (1) Droplets as microreactors for PCR reaction with reverse transcription to detect and quantify target RNAs. (2) Droplets as microcompartments for spirulina culturing and the optical color/turbidity changes in droplets with spirulina confirm successful photosynthetic culturing. (3) Droplets as templates/molds for controlled synthesis of gold-capped polyacrylamide/gold composite Janus microgels. The easily fabricated and user-friendly portable kit is hence ideally suited for design, training and educational labs.

Synthesis of Magneto-Controllable Polymer Nanocarrier Based on Poly(N-isopropylacrylamide-co-acrylic Acid) for Doxorubicin Immobilization.

In this work, the preparation procedure and properties of anionic magnetic microgels loaded with antitumor drug doxorubicin are described. The functional microgels were produced via the in situ formation of iron nanoparticles in an aqueous dispersion of polymer microgels based on poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM-PAA). The composition and morphology of the resulting composite microgels were studied by means of X-ray diffraction, Mössbauer spectroscopy, IR spectroscopy, scanning electron microscopy, atomic-force microscopy, laser microelectrophoresis, and static and dynamic light scattering. The forming nanoparticles were found to be β-FeO(OH). In physiological pH and ionic strength, the obtained composite microgels were shown to possess high colloid stability. The average size of the composites was 200 nm, while the zeta-potential was -27.5 mV. An optical tweezers study has demonstrated the possibility of manipulation with microgel using external magnetic fields. Loading of the composite microgel with doxorubicin did not lead to any change in particle size and colloidal stability. Magnetic-driven interaction of the drug-loaded microgel with model cell membranes was demonstrated by fluorescence microscopy. The described magnetic microgels demonstrate the potential for the controlled delivery of biologically active substances.

Highly efficient and selective removal of anionic dyes from aqueous solutions using magneto-responsive Fe-aminoclay/Fe2O3/polyvinyl alcohol composite microgels

In this study, magneto-responsive iron-aminoclay/iron oxide/polyvinyl alcohol (Fe-AC/Fe2O3/PVA) composite microgels were successfully fabricated via a Schiff-base and acetalization reactions using a microfluidic approach. The as-prepared Fe-AC/Fe2O3/PVA composite microgels were used as adsorbents to remove organic dyes from aqueous solutions. The chemical cross-linking and morphology of the prepared microgel particles were evaluated using Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, optical microscopy, Brunauer–Emmett–Teller surface area analysis, and scanning electron microscopy. The Fe-AC/Fe2O3/PVA microgels served as an effective adsorbent by exhibiting a remarkable adsorption capacity for anionic dyes such as methyl orange (MO), Congo red (CR), and methyl blue (MB) owing to their fast diffusion kinetics, porous structures, and numerous amino groups. The microgels had maximum adsorption capacities of 457.31 mg/g for MO, 352.88 mg/g for CR, and 566.98 mg/g for MB. The prepared microgels were systematically evaluated for their adsorption behavior toward the anionic dyes from aqueous solutions at various process parameters, such as pH, contact time, and dye concentration. The adsorption process for the anionic dyes fitted well with the pseudo-second-order kinetic model and Sips isotherm model, verifying that the sorption process was mainly governed by chemisorption. Furthermore, the Fe2O3 magnetic nanoparticle incorporation made it simple to separate the microgels from the aqueous solutions and reuse them. The microgels maintained an adsorption efficiency of above 80 % even after five adsorption–desorption cycles. These results demonstrate that the magneto-responsive Fe-AC/Fe2O3/PVA hybrid microgels are an effective and sustainable adsorbent for treating wastewater contaminated with anionic dyes.

Encapsulation of β-carotene in high internal phase Pickering emulsions stabilized by soy protein isolate – epigallocatechin-3-gallate covalent composite microgel particles

• Covalently conjugated SPI-EGCG microgel particles were used to stabilize HIPPEs. • EGCG addition improved the functional properties of β-carotene-loaded HIPPEs. • Thick particle layer and gel network jointly promoted the stability of HIPPEs. • Encapsulation of β-carotene enhanced the chemical stability and bioaccessibility. In the current study, soy protein isolate (SPI) and epigallocatechin-3-gallate (EGCG) covalent composite microgel particles with antioxidant capacity were prepared and the particles was used as β-carotene-loaded high internal phase Pickering emulsions (HIPPEs) stabilizers. The covalent binding of SPI-EGCG altered the structures of the SPI through an unfolding of the polypeptide chain. Moreover, compared to HIPPEs stabilized by SPI alone, HIPPEs stabilized by SPI-EGCG microgel particles showed smaller particle size, higher apparent viscosity, and better stability. Microstructure of the fabricated HIPPEs results revealed that SPI-EGCG covalent conjugates promoted the formation of a thick and dense protective layer on the surfaces of oil droplets. Furthermore, β-carotene-loaded HIPPEs stabilized by SPI-2% EGCG microgel particles exhibited a higher retention rate after 42 days of storage and better bioaccessibility (86.64 ± 0.27% and 54.43 ± 0.50%, respectively) compared to HIPPEs stabilized by SPI (75.80 ± 0.49% and 38.31 ± 0.93%, respectively). The current study illustrated that the design of HIPPEs stabilized with protein–polyphenol composite particles were of great importance for the delivery of lipophilic bioactive compounds.