Multiple pickering high internal phase emulsions stabilized by modified diatomite particles via one-step emulsification process

One-Step Formation of Pickering Double Emulsion Costabilized by Hydrophobic Silica Nanoparticles and Sodium Alginate

Pickering double emulsions exhibit higher stability and biocompatibility compared with surfactant-stabilized double emulsions. However, tailored synthesis of particle stabilizers with appropriate wettability is time consuming and complicated and usually limits their large-scale adoption. Using binary stabilizers may be a simple and scalable strategy for Pickering double emulsion formation. Herein, commercially available hydrophobic silica nanoparticles (SNPs) and sodium alginate (SA) as binary stabilizers are used to prepare O/W/O Pickering double emulsions in one-step emulsification. The influence of system composition on double emulsion preparation is identified by optical microscopy, confocal laser scanning microscopy, and interfacial tension and water contact angle analyses. The formation of the O/W/O Pickering double emulsion depends critically on the aqueous phase viscosity and occurrence of emulsion inversion. Both hydrophobic SNPs and SA adsorb at the droplet surface to provide a steric barrier, while SA also reduces interfacial tension and increases aqueous phase viscosity, giving double emulsion long-term stability. Their microstructure and stability are controlled by adjusting the SA concentration, water-oil volume ratio, concentration and wettability of the particle stabilizer, and oil type. As a demonstration, the middle layer of the as-prepared O/W/O Pickering double emulsions can be cross-linked in situ with calcium ions to produce calcium alginate porous microspheres. We believe that our strategy for double emulsion formation holds great potential for practical applications in food, cosmetics, or pharmaceuticals.

Preparation of a Porous Protein-Based Composite Material by In Situ Polymerization of Pickering High Internal Phase Emulsion for Adsorption of Lead Ions

The preparation of complex porous materials using a small molecular surfactant as the stabilizer of a high internal phase emulsion can result in harm to the environment. In this study, porous composites based on soy protein isolate with poly(acrylic acid) were prepared by in situ polymerization of a high internal phase monomer emulsion with an internal phase volume fraction of 80%. The material was prepared from acrylic acid and an N,N-methyl diacrylic acid monomer solution as the continuous phase, peanut oil as the dispersed phase, and soy protein isolate as the composite stabilizer. Scanning electron microscopy showed that porous composites exhibited a concave/convex three-dimensional interpenetrating pore structure. Fourier-transform infrared spectra revealed the existence of many active groups such as carboxyl, amino, hydroxyl, and sulfhydryl. The composite had a high adsorption capacity for lead ions, even at low concentration, with a removal rate of up to 95.7%. The adsorption process conformed to a two-stage model involving internal diffusion and Langmuir isothermal adsorption. The maximum saturated adsorption capacity was 36.71 mg/g when the initial solution concentration was 150 mg/L, the adsorbent concentration was 7.0 g/L, and the adsorption mechanism involved chemical interactions between the lead ions and the composite groups -COOH, -OH, and -SH.

A review of high internal phase Pickering emulsions: Stabilization, rheology, and 3D printing application

High internal phase Pickering emulsion (HIPPE) is renowned for its exceptionally high-volume fraction of internal phase, leading to flocculated yet deformed emulsion droplets and unique rheological behaviors such as shear-thinning property, viscoelasticity, and thixotropic recovery. Alongside the inherent features of regular emulsion systems, such as large interfacial area and well-mixture of two immiscible liquids, the HIPPEs have been emerging as building blocks to construct three-dimensional (3D) scaffolds with customized structures and programmable functions using an extrusion-based 3D printing technique, making 3D-printed HIPPE-based scaffolds attract widespread interest from various fields such as food science, biotechnology, environmental science, and energy transfer. Herein, the recent advances in preparing suitable HIPPEs as 3D printing inks for various applied fields are reviewed. This work begins with the stabilization mechanism of HIPPEs, followed by introducing the origin of their distinctive rheological behaviors and strategies to adjust the rheological behaviors to prepare more eligible HIPPEs as printing inks. Then, the compatibility between extrusion-based 3D printing and HIPPEs as building blocks was discussed, followed by a summary of the potential applications using 3D-printed HIPPE-based scaffolds. Finally, limitations and future perspectives on preparing HIPPE-based materials using extrusion-based 3D printing were presented.

One-Step Generation of O/W/O Double Pickering Emulsions Utilizing Biocompatible Gliadin/Ethyl Cellulose Complex Particles as the Exclusive Stabilizer

Double emulsions hold great potential for various applications due to their compartmentalized internal structures. However, achieving their long-term physical stability remains a challenging task. Here, we present a simple one-step method for producing stable oil-in-water-in-oil (O/W/O) double emulsions using biocompatible gliadin/ethyl cellulose complex particles as the sole stabilizer. The resulting O/W/O systems serve as effective platforms for encapsulating enzymes and as templates for synthesizing porous microspheres. We investigated the impact of particle concentration and water fraction on the properties of Pickering O/W/O emulsions. Our results demonstrate that the number and volume of inner oil droplets increased proportionally with both the water fraction and particle concentration after a 60-day storage period. Moreover, the catalytic reaction rate of the encapsulated lipase within the double emulsion exhibited a significant acceleration, achieving a substrate conversion of 80.9% within 15 min. Remarkably, the encapsulated enzyme showed excellent recyclability, enabling up to 10 cycles of reuse. Additionally, by utilizing the O/W/O systems as templates, we successfully obtained porous microspheres whose size can be controlled by the outer water droplet. These findings have significant implications for the future design of Pickering complex emulsion-based systems, opening avenues for extensive applications in pharmaceuticals, food, cosmetics, material synthesis, and (bio)catalysis.

Biopolymer-based pickering high internal phase emulsions: Intrinsic composition of matrix components, fundamental characteristics and perspective

Pickering HIPEs have received tremendous attention in recent years due to their superior stability and unique solid-like and rheological properties. Biopolymer-based colloidal particles derived from proteins, polysaccharides and polyphenols have been demonstrated to be safety stabilizers for the construction of Pickering HIPEs, which can meet the demands of consumers for "all-natural" products and provide "clean-label" foods. Furthermore, the functionality of these biopolymers can be further extended by forming composite, conjugated and multi-component colloidal particles, which can be used to modulate the properties of the interfacial layer, thereby adjusting the performance and stability of Pickering HIPEs. In this review, the factors affecting the interfacial behavior and adsorption characteristics of colloidal particles are discussed. The intrinsic composition of matrix components and fundamental characteristics of Pickering HIPEs are emphatically summarized, and the emerging applications of Pickering HIPEs in the food industry are reviewed. Inspired by these findings, future perspectives concerning this field are also put forward, including (1) the exploration of the interactions between biopolymers used to produce Pickering HIPEs and target food ingredients, and the influence of the added biopolymers on the flavor and mouthfeel of the products, (2) the investigation of the digestion properties of Pickering HIPEs under oral administration, and (3) the fabrication of stimulus-responsive or transparent Pickering HIPEs. This review will give a reference for exploring more natural biopolymers for Pickering HIPEs application development.

Recent Advances in Pickering Double Emulsions and Potential Applications in Functional Foods: A Perspective Paper

Double emulsions are complex emulsion systems with a wide range of applications across different fields, such as pharmaceutics, food and beverage, materials sciences, personal care, and dietary supplements. Conventionally, surfactants are required for the stabilization of double emulsions. However, due to the emerging need for more robust emulsion systems and the growing trends for biocompatible and biodegradable materials, Pickering double emulsions have attracted increasing interest. In comparison to double emulsions stabilized solely by surfactants, Pickering double emulsions possess enhanced stability due to the irreversible adsorption of colloidal particles at the oil/water interface, while adopting desired environmental-friendly properties. Such advantages have made Pickering double emulsions rigid templates for the preparation of various hierarchical structures and as potential encapsulation systems for the delivery of bioactive compounds. This article aims to provide an evaluation of the recent advances in Pickering double emulsions, with a special focus on the colloidal particles employed and the corresponding stabilization strategies. Emphasis is then devoted to the applications of Pickering double emulsions, from encapsulation and co-encapsulation of a wide range of active compounds to templates for the fabrication of hierarchical structures. The tailorable properties and the proposed applications of such hierarchical structures are also discussed. It is hoped that this perspective paper will serve as a useful reference on Pickering double emulsions and will provide insights toward future studies in the fabrication and applications of Pickering double emulsions.

Protein-Based High Internal Phase Pickering Emulsions: A Review of Their Fabrication, Composition and Future Perspectives in the Food Industry

Protein-based high internal phase Pickering emulsions (HIPEs) are emulsions using protein particles as a stabilizer in which the volume fraction of the dispersed phase exceeds 74%. Stabilizers are irreversibly adsorbed at the interface of the oil phase and water phase to maintain the droplet structure. Protein-based HIPEs have shown great potential for a variety of fields, including foods, due to the wide range of materials, simple preparation, and good biocompatibility. This review introduces the preparation routes of protein-based HIPEs and summarizes and classifies the preparation methods of protein stabilizers according to their formation mechanism. Further outlined are the types and properties of protein stabilizers used in the present studies, the composition of the oil phase, the encapsulating substances, and the properties of the constituted protein-based HIPEs. Finally, future development of protein-based HIPEs was explored, such as the development of protein-based stabilizers, the improvement of emulsification technology, and the quality control of stabilizers and protein-based HIPEs.

Microstructurally tunable pickering emulsions stabilized by poly(ethylene glycol)-b-poly(ε-caprolactone) diblock biodegradable copolymer micelles with predesigned polymer architecture

Poly(ethylene glycol)-b-poly(ε-caprolactone) diblock copolymers (PEG-b-PCL) with predesigned hydrophilic/hydrophobic block length ratios have been synthesized and self-assembled to form micelles, then used to emulsify medium-chain triglycerides with an aqueous phase. The morphologies and sizes of PEG-b-PCL copolymer micelles have been characterized by transmission electron microscopy and dynamic light scattering. Interfacial tension testing between micellar dispersions and oil, combined with water contact angle measurements, have been performed to assess the ability of these micelles to adjust interfacial tension and micellar hydrophobicity, respectively. Relationship between the wettability of PEG-b-PCL copolymer micelles and their emulsification properties has been proved through phase diagram, optical microscopic observation, droplet sizes evolution and phase separation behavior of Pickering emulsion samples. Results show that both oil-in-water and water-in-oil Pickering emulsions, as well as water-in-oil-in-water (W/O/W) double-Pickering emulsions, may be controllably prepared through one-step homogenization. Double microstructure of W/O/W Pickering emulsion has proved to be extremely stable during long-term storage.

Protein-polysaccharide interactions for the fabrication of bioactive-loaded nanocarriers: Chemical conjugates and physical complexes

As unique biopolymeric architectures, covalently and electrostatically protein-polysaccharide (PRO-POL) systems can be utilized for bioactive delivery by virtue of their featured structures and unique physicochemical attributes. PRO-POL systems (i. e, microscopic /nano-dimensional multipolymer particles, molecularly conjugated vehicles, hydrogels/nanogels/oleogels/emulgels, biofunctional films, multilayer emulsion-based delivery systems, particles for Pickering emulsions, and multilayer coated liposomal nanocarriers) possess a number of outstanding attributes, like biocompatibility, biodegradability, and bioavailability with low toxicity that qualify them as powerful agents for the delivery of different bioactive ingredients. To take benefits from these systems, an in-depth understanding of the chemical conjugates and physical complexes of the PRO-POL systems is crucial. In this review, we offer a comprehensive study concerning the unique properties of covalently/electrostatically PRO-POL systems and introduce emerging platforms to fabricate relevant nanocarriers for encapsulation of bioactive components along with a subsequent sustained/controlled release.

Construction of high internal phase Pickering emulsions stabilized by bamboo fungus protein gels with the effect of pH

This study is a contribution to explore natural protein sources as high internal phase Pickering emulsions (HIPPEs) stabilizers and to achieve full utilization of biological resources. Bamboo fungus proteins were obtained by alkaline extraction and subsequently transformed into protein gels by enzymatic cross-linking method. 1% (w/v) of bamboo protein gel particles (BGPs) were used to stabilize high HIPPEs (φ = 80%) using a one-step homogenization method. At pH 3, 9 and 11, BGPs could produce stable, gel-like oil/water HIPPEs with excellent storage stability. In contrast, at pH 5 and 7, stable HIPPEs could not be formed, which might be attributed to the variation of contact angle and electrostatic repulsion of BGPs. Structure analysis indicated that HIPPEs with gel-like structures were mainly stabilized by physical barriers and electrostatic repulsion. The present study is expected to provide new insight on comprehensive utilization of fungi sources.

Simple method for fabrication of high internal phase emulsions solely using novel pea protein isolate nanoparticles: Stability of ionic strength and temperature

The oil-in-water high internal phase emulsions (HIPEs) could be stabilized by pea protein isolate nanoparticles (PPINs) induced by potassium metabisulfite (K₂S₂O₅). Confocal laser scanning microscope proved that PPINs were attached on the oil-water interface, indicating characteristic of Pickering HIPEs. The HIPEs stabilized by PPINs of higher concentration had smaller droplet size, better storage and centrifugal stability than that of PPINs of low concentration because there were enough particles to constitute the thick interface film. The storage modulus was higher than loss modulus indicating that HIPEs exhibited gel-like structure. At different temperatures and ionic strengths, HIPEs exhibited flocculation but still maintained a stable gel-like structure. The strain curve of HIPEs showed Type III nonlinear behavior due to the flocculation of emulsion droplets. HIPEs stabilized by PPINs might be a potential alternative to partially hydrogenated oils to reduce intake of trans fatty acids.