Emulsions stabilized with solid nanoparticles: Pickering emulsions

Physicochemical properties and antibacterial property of pickering emulsion stabilized by smart Janus nanospheres

In this study, responsive Janus nanospheres were prepared by grafting LMA and DMAEMA monomers on both sides of SiO2 nanospheres using the Pickering emulsion stencil method and RAFT polymerization. The successful synthesis was verified through infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA), scanning electron microscopy (SEM) characterizations. Subsequently, Pickering emulsion was formulated using Janus nanospheres as emulsifiers. The particle size of the emulsion droplets was systematically investigated by manipulating factors such as pH, nanosphere dosage, water to oil ratio, and oil phase polarity. Notably, the Pickering emulsion exhibited responsive properties to pH, temperature, and CO2. Furthermore, Janus nanospheres exhibited excellent emulsification property for real oil phases, including canola oil, kerosene, gasoline, and diesel oil. Building upon this, a smart antibacterial Pickering emulsion was developed using Janus nanospheres, and its inhibition rate against E. coli could reach 100% within 4 h, which would be beneficial for its application in the food field.

Adsorption study on the formation of interfacial layers based on birch glucuronoxylans

Glucuronoxylans (GX), particularly crude fractions obtained by pressurized hot water extraction of birch wood, act as potent emulsifiers and stabilizers against physical separation and lipid oxidation. Herein, we studied the adsorption of GX on hydrophobic interfaces to correlate their multicomponent character towards the formation of interfacial layers in emulsions. Dynamic interfacial tension (DIFT) and quartz crystal microgravimetry with dissipation monitoring (QCM-D) were applied to various GX fractions and the results compared with those from cellulose-based emulsifiers. The roles of residual lignin and polysaccharides are discussed considering the formation of interfacial layers during emulsification. The DIFT of the different GXs reached quasi-equilibrium faster as the lignin concentration increased, implying a correlation between the rate of adsorption and the residual lignin content. The effect of NaCl addition was more pronounced in polysaccharide-rich fractions, indicating that the polysaccharide fraction modulated the effect of ionic strength. QCM-D showed that despite the fast adsorption exhibited by the lignin-rich GX extract in the DIFT curves, the adsorbed materials were lightweight, suggesting that the polysaccharide fraction built the bulk of the interfacial layer. These results provide a foundation towards understanding the role of GX in interfacial stabilization beyond traditional plant-based counterparts.

Hot-water soluble fraction of starch as particle-stabilizers of oil-in-water emulsions: Effect of dry heat modification

Dry heat treatment (DHT) ranging from 130 to 190 °C was employed to modify corn starch. The hot-water soluble fraction (HWS) of the DHT-modified starch was isolated, and its capacity and mechanism for stabilizing O/W emulsions were investigated. Corn starch underwent a significant structural transformation by DHT at 190 °C, characterized by a 7.3 % reduction in relative crystallinity, a tenfold decrease in weight-average molecular weight from 95.21 to 8.11 × 106 g/mol, and a degradation of over one-third of the extra-long chains of amylopectin (DP > 36) into short chains (DP 6-12). These structural modifications resulted in a substantial formation of soluble amylopectin, leading to a sharp increase in the HWS content of corn starch from 3.16 % to 85.06 %. This augmented HWS content surpassed the critical macromolecule concentration, prompting the formation of HWS nanoaggregates. These nanoaggregates, with an average particle size of 33 nm, functioned as particle stabilizers, ensuring the stability of the O/W emulsion through the Pickering mechanism. The O/W emulsion stabilized by HWS nanoaggregates exhibited noteworthy centrifugal and storage stability, with rheological properties remaining nearly unchanged over a storage period of 180 days. Given its straightforward preparation process, the HWS of DHT-modified starch could be a promising natural emulsifier.

Preparation of Geopolymers with Nanosilica and Water-in-Air Pickering Emulsion: Mechanisms Underlying Its Rheology, Polymerization, and Strength

Geopolymers are alkaline-activated aluminosilicate binders recognized as a promising alternative to traditional Portland cement due to their significantly lower greenhouse emissions, energy consumption, and carbon footprint. However, the challenge is meeting or exceeding the strength of Portland cement concrete while being prepared within a desired setting time and possessing workable rheology. A "water-in-air" Pickering emulsion, also called dry water, was prepared by stabilizing water droplets with hydrophobic nano silica and using them to control the geopolymer's strength, setting time, and workability. The mechanisms that underlie the effects of dry water on the rheology, setting, and strength were studied in detail through a combination of rheological, thermal, morphological, chemical, and microstructural assessments. A reduction in the viscosity and yield shear stress manifests in a higher flow diameter, principally due to the particle size coarsening in the precursor and the flowability of hydrophobic nano silica. There was a rapid rise in temperature during the setting process as the dry water temporarily increased the local alkalinity in the mixture, which boosted the dissolution of the precursor and, hence, the reaction. Outcomes from X-ray diffraction, thermogravimetric analysis, and Fourier-transform infrared confirm the highest degree of polycondensation for the principal N-A-S-H framework in mixtures containing dry water. These eventually correspond to a denser microstructure under scanning electron microscopy and, in turn, a superior mechanical strength. Depending on the unique combination of characteristics, including size coarsening, temporary water encapsulation, microfilling effect, and supplementary silica source, dry water resolves the "trade-off" between geopolymer's fresh and hardened properties when introducing nanoparticles.

Metal-Phenolic Network-Coated Nanoparticles as Stabilizers for the Engineering of Pickering Emulsions with Bioactivity

Pickering emulsions stabilized by functional nanoparticles (NPs) have received considerable attention for improving the physical stability and biological function of NPs. Herein, hydrophobic polyphenols were chosen as phenolic ligands to form metal-phenolic network (MPN) coatings on NPs (e.g., silica, polystyrene) mediated by the sono-Fenton reaction. The MPN coatings modulated the surface wettability and charges of NPs and achieved emulsification behavior for preparing Pickering emulsions with pH responsiveness and oxidation resistance. A series of polyphenols, including resveratrol, rutin, naringin, and curcumin, were used to form MPN coatings on NPs, which served as stabilizers for the engineering of functionalized oil-in-water (O/W) Pickering emulsions. This work provides a new avenue for the use of hydrophobic polyphenols to modulate NP emulsifiers, which broadens the application of polyphenols for constructing Pickering emulsions with antioxidant properties.

Topical pickering emulsion versus classical excipients: A study of the residual film on the human skin

The interest in Pickering emulsions is based on the possibility of replacing classical emulsifiers with solid particles. These emulsions are very attractive in the pharmaceutical field for their stability virtues and as a vehicle to deliver active ingredients. The study aimed to analyze the properties of the residual film of the Pickering emulsions on the human skin compared to conventional systems. For this project, three types of solid particles were used: titanium dioxide, zinc oxide and silicon dioxide. All of them are capable of stabilizing the oil/water interface and thus forming totally emulsified systems. To create an emulsion of reference, a classical surfactant was used as an excipient. Complementary systems containing both particles and the emulsifier were also analyzed. Then, a combined approach between physicochemical and biometrological in vivo analysis was employed. The study proved that Pickering emulsions stabilized by the metal oxides were distinct from the reference emulsion in terms of droplet sizes and organization, rheological and textural responses. Consequently, it impacted the properties of the residual film once the product was applied to the skin. The particle-stabilized emulsions formed a hydrophobic film counter to conventional excipients. Also, the Friction parameter (or the roughness of the film) was directly linked to the quantity of the particles used in the formulation and their perception on the skin surface. The use of the particles blurs the glossy effect of the oil phase. Finally, it was observed that the appearance of the residual film was impacted by the type of the particle, namely TiO2 and ZnO particles.

Effects of different solid particle sizes on oat protein isolate and pectin particle-stabilized Pickering emulsions and their use as delivery systems

Oat protein isolate (OPI)/high methoxyl pectin (HMP) complexes (OPP) were prepared to stabilized Pickering emulsions and applied as nutraceutical delivery systems. The different mass ratios and pH changed the interactions between OPI and HMP that caused the different size of OPP. Specifically, smaller particle size of OPP (125.7-297.6 nm) were formed when hydrophobic interactions along with electrostatic forces predominant in OPP (OPI:HMP = 3:1, pH 4, 5). Among these particles, OPP-2 could stabilize Pickering emulsion efficiently through formation of dense interfacial film, which exhibited the highest apparent viscosity and the smallest average droplet size (23.39 μm). Moreover, OPP-2 stabilized Pickering emulsions with superior stability not only exhibited higher encapsulation efficiency of 85.63%, but also could control curcumin release in simulated gastrointestinal fluids to improve curcumin's bioaccessibility. These results verified the possibility of OPP to be a Pickering emulsions stabilizer, and also identified its potential to be a stable delivery system for bioactive compounds.

Preparation of catechin-starch nanoparticles composites and its application as a Pickering emulsion stabilizer

Starch is a biopolymer commonly used for nanoparticle synthesis. Starch nanoparticles (SNPs) have potential as encapsulation agents and Pickering emulsion stabilizers. Here, we prepared SNPs by dry heating under mildly acidic conditions to encapsulate catechin. Catechin (30 mg) and SNPs (50-150 mg) were dispersed in distilled water and freeze-dried to prepare catechin-SNP composites. Isothermal titration calorimetry and Fourier-transform infrared spectroscopy revealed that the binding of catechin to SNP may involve spontaneous hydrogen bonding and hydrophobic interactions. SNPs exhibited encapsulation efficiency for catechin, with 100 % catechin retention when 150 mg of SNP was used to prepare the composites. The catechin-SNP composites had a particle size of 54.2-74.9 nm. X-ray diffraction analysis revealed the formation of small amounts of inclusion complexes in catechin-SNP composites. As the amount of SNPs added for encapsulation increased, the catechin encapsulated in the SNP composites exhibited higher water solubility and UV stability than the pure catechin. The catechin-SNP composite with 150 mg of catechin exhibited the highest contact angle (51.37°) and formed a stable emulsion without notable droplet size changes. Therefore, catechin-SNP composites improved the encapsulation efficiency, water-solubility, stability of catechins, and Pickering emulsion stability.

Plant gums in Pickering emulsions: A review of sources, properties, applications, and future perspectives

Recently, there has been an increasing research interest in the development of Pickering emulsions stabilized with naturally derived biopolymeric particles. In this regard, plant gums, obtained as plant exudates or from plant seeds, are considered promising candidates for the development of non-toxic, biocompatible, biodegradable and eco-friendly Pickering stabilizers. The main objective of this review article is to provide a detailed overview and assess the latest advances in the formulation of Pickering emulsions stabilized with plant gum-based particles. The plant gum sources, types and properties are outlined. Besides, the current methodologies used in the production of plant gum particles formed solely of plant gums, or through interactions of plant gums with proteins or other polysaccharides are highlighted and discussed. Furthermore, the work compiles and assesses the innovative applications of plant gum-based Pickering emulsions in areas such as encapsulation and delivery of drugs and active agents, along with the utilization of these Pickering emulsions in the development of active packaging films, plant-based products and low-fat food formulations. The last part of the review presents potential future research trends that are expected to motivate and direct research to areas related to other novel food applications, as well as tissue engineering and environmental applications.

General approaches to biopolymer-based Pickering emulsions

Pickering emulsion is a type of emulsion that uses solid particles or colloidal particles as emulsifiers rather than surfactants to adhere at oil-water interface. Pickering emulsions have gathered significant research attention recently due to their excellent stability and wide range of potential uses compared to traditional emulsions. Major advancements have been made in development of innovative Pickering emulsions using different colloidal particles by various techniques including homogenization, emulsification and ultrasonication. Use of biopolymer particles gives Pickering emulsions a more escalating possibilities. In this review paper, we seek to present a critical overview of development in food-grade particles that have been utilized to create Pickering emulsions with a focus on techniques and application of Pickering emulsions. Particularly, we have evaluated protein, lipid, polysaccharide-based particles and microalgal proteins that have emerged in recent years with respect to their potential to stabilize and add novel functionalities to Pickering emulsions. Some preparation methods of Pickering emulsions in brief, applications of Pickering emulsions are also highlighted. Encapsulation and delivery of bioactive compounds, fat substitutes, film formation and catalysis are potential applications of Pickering emulsions. Pickering double emulsions, nutraceutical and bioactive co-delivery, and preparation of porous materials are among research trends of food-grade Pickering emulsions.

Pickering emulsion biocatalysis: Bridging interfacial design with enzymatic reactions

Non-homogeneous enzyme-catalyzed systems are more widely used than homogeneous systems. Distinguished from the conventional biphasic approach, Pickering emulsion stabilized by ultrafine solid particles opens up an innovative platform for biocatalysis. Their vast specific surface area significantly enhances enzyme-substrate interactions, dramatically increasing catalytic efficiency. This review comprehensively explores various aspects of Pickering emulsion biocatalysis, provides insights into the multiple types and mechanisms of its catalysis, and offers strategies for material design, enzyme immobilization, emulsion formation control, and reactor design. Characterization methods are summarized for the determination of drop size, emulsion type, interface morphology, and emulsion potential. Furthermore, recent reports on the design of stimuli-responsive reaction systems are reviewed, enabling the simple control of demulsification. Moreover, the review explores applications of Pickering emulsion in single-step, cascade, and continuous flow reactions and outlines the challenges and future directions for the field. Overall, we provide a review focusing on Pickering emulsions catalysis, which can draw the attention of researchers in the field of catalytic system design, further empowering next-generation bioprocessing.

Fabrication and characterization of anthocyanin-loaded double Pickering emulsions stabilized by β-cyclodextrin

Anthocyanins, one of the important water-soluble pigments, are sensitive to environmental factors, which limits the application of anthocyanins in food field. In order to overcome this limitation, double Pickering emulsions stabilized by β-cyclodextrin were developed. The optimum preparation conditions of the emulsions were determined firstly and the performance and structure of emulsions were investigated. Results showed that the optimum preparation conditions of emulsions were the ratio of (W1/O): W2 = 6:4 and 4 % β-cyclodextrin concentration. Optical microscope and confocal laser scanning microscope results confirmed that β-cyclodextrin adsorbed onto the surface of droplets forming stable double Pickering emulsions structure. In vitro gastrointestinal digestion experiments proved that double Pickering emulsions played a controlled-release effect in the small intestine. Rheological analysis proved that the emulsions exhibited elastic properties and demonstrated shear thinning behavior. The emulsions showed excellent stability under centrifugation and thermal conditions. These findings will promote anthocyanins' application in daily diet.

Controllable Regulation of Diesel Oil-in-Water Pickering Emulsion Stability by Multiresponsive Recyclable Magnetic Polymer Brush Microvessels

To ensure safety and efficiency in the production and transportation of fuel oil, there is an urgent demand to develop intelligent emulsifiers to deal with this challenge. Fe3O4@PDA-P(NIPAM-b-MAA-b-LMA) (MNPDNML) microspheres were prepared by modifying polydopamine and the triblock polymer brush P(NIPAM-b-MAA-b-LMA) on the surface of Fe3O4 nanoparticles via oxidative autopolymerization and SI-RAFT polymerization. Therefore, the MNPDNML microspheres exhibited sensitive stimulus-responsive behavior to pH, temperature, near-infrared (NIR) laser radiation, and magnetic fields. The stability state of the emulsion could be modulated by changing pH, temperature, magnetic field, and NIR radiation, and the reversible switching of emulsification/breaking behavior could be reached at least 10 times. This "intelligent emulsifier" exhibited high emulsification efficiency, long-term stability, and on-demand emulsification/breaking properties. It was notable that MNPDNML microspheres showed excellent emulsification ability for olive oil, kerosene, gasoline, and crude oil, which allowed the material to be widely used in the controlled transportation and separation of fuel oil.

Lipid oxidation in emulsions: New insights from the past two decades

Lipid oxidation constitutes the main source of degradation of lipid-rich foods, including food emulsions. The complexity of the reactions at play combined with the increased demand from consumers for less processed and more natural foods result in additional challenges in controlling this phenomenon. This review provides an overview of the insights acquired over the past two decades on the understanding of lipid oxidation in oil-in-water (O/W) emulsions. After introducing the general structure of O/W emulsions and the classical mechanisms of lipid oxidation, the contribution of less studied oxidation products and the spatiotemporal resolution of these reactions will be discussed. We then highlight the impact of emulsion formulation on the mechanisms, taking into consideration the new trends in terms of emulsifiers as well as their own sensitivity to oxidation. Finally, novel antioxidant strategies that have emerged to meet the recent consumer's demand will be detailed. In an era defined by the pursuit of healthier, more natural, and sustainable food choices, a comprehensive understanding of lipid oxidation in emulsions is not only an academic quest, but also a crucial step towards meeting the evolving expectations of consumers and ensuring the quality and stability of lipid-rich food products.

Effects of Nanoparticle Wettability on the Meniscus Stability of Oil-Water Systems: A Coarse-Grained Modeling Approach

A coarse-grained modeling approach is employed to probe the effect of nanoparticles and their wettability on the stability of the interface between two immiscible fluids. In this study, pure oil (dodecane) and water are placed side by side in a nanochannel, forming a meniscus. Homogeneous hydrophilic nanoparticles, Janus particles, and homogeneous hydrophobic nanoparticles are placed at the oil-water interface, and their dynamics are studied as they rearrange at the oil-water interface. The results show that when the water is set in motion, two instabilities occur: the formation of fingers and the detachment of water from the channel wall. It is observed that the formation of fingers is affected by the wettability of the nanoparticles. The second instability may lead to the formation of a drop that propagates through the channel. However, it is found that the wetting properties of the nanoparticles do not affect the critical flow rate for the detachment of the water from the wall. Therefore, detachment occurs at the same three-phase contact angle regardless of the nanoparticle wetting properties. These findings can be important for industrial applications such as enhanced oil recovery, separation technologies, and microfluidic and nanofluidic technologies.

Physicochemical characterization and environmental stability of a curcumin-loaded Pickering nanoemulsion using a pea protein isolate-dextran conjugate via the Maillard reaction

This study investigated pea protein isolate (PPI) and dextran (DX) conjugates produced via the Maillard reaction as Pickering stabilizers for various food applications. The results found that as heating time increased (0-5 h), the grafting degree heightened. The PPI-DX conjugate exhibited a rough porous surface in contrast to native PPI, accompanied by changes in molecular weight and secondary structure. Additionally, the aggregation of low-solubility PPI was partially inhibited due to the contribution of increased solubility and reduced surface hydrophobicity by glycation. Curcumin-loaded Pickering nanoemulsions stabilized with PPI-DX had smaller droplets and higher curcumin encapsulation (greater than80 %) than PPI-stabilized nanoemulsions. PPI-DX adsorbed on the interface showed improved physical stability compared to PPI alone, even after various pH conditions and three heat treatments. The nanoemulsion stabilized with PPI-DX demonstrated improved apparent viscosity and dispersion stability. These findings highlight the effectiveness of PPI-DX conjugates as stabilizers for developing stable and functional Pickering nanoemulsions.

A Review on Use of Emulsified Acids for Matrix Acidizing in Carbonate Reservoirs

Almost 60% of oil and 40% of gas reserves worldwide are contained in carbonate reservoirs where acidizing stimulation is more challenging compared to sandstone reservoirs. Utilization of emulsified acids in matrix acidizing operations has been the most effective technique for more than half a century. This is due to the colloidal system's ability to generate deep, narrow conduits toward production zones under controlled retarded reactivity with the rock surface, along with the excellent sweep efficiency and corrosion inhibition of the well equipment. This Review attempts to review the various kinds of emulsified acids that are used for matrix acidizing of carbonate formations. The Review is trying to trace the innovations that have, gradually, been applied for enhancing the performance of emulsified acids for a variety of conditions, their limitations, and the developmental solutions such hybrid emulsifiers and pickering emulsions. In addition, the Review also discusses the parameters, characteristics, and measuring techniques required for the successful synthesis of a stable and quality emulsion while considering the environmental concerns raised toward the application of an emulsified acid system. From the reviewed publications, it can be summarized that macroemulsions are best suited for matrix acidizing applications over microemulsions due to low emulsifier concentrations and high acid volume retention; similarly, water in oil emulsions provide better retardation in a comparison to oil in water emulsions. The small droplet size of the emulsion yields high viscosity and stability. The compositional balance between each component present in the acidizing system is a crucial factor for optimum performance. Moreover, for future practice, much focus is required to design emulsified acids as ecofriendly systems that can leave the least amount of toxicity during and after implementation.

Using cryo-SEM and EDS to investigate the stabilisation of oil-water interfaces in mixed aqueous-and-oil foams

For multi-phase soft matter systems, optical microscopy is frequently employed to distinguish the different phases. Unfortunately, optical microscopy does not succeed in all cases. Consequently, researchers sometimes require more advanced imaging techniques with superior resolution or sample penetration capabilities. One such complex system is a mixed aqueous-and-oil foam stabilised by colloidal particles, which is composed of two immiscible foams organised as the dispersed and continuous phases of an emulsion. While its morphology has been extensively studied using fluorescence confocal microscopy, not all questions have been answered. While the aqueous phase bubble interfaces are stabilised by silica particles and the oil phase bubble interfaces are stabilised by fluorinated particles, it remains to be seen how the aqueous-oil interfaces are stabilised. Hence, to gain insights into the role of the different particles at the interfaces, we employ cryogenic scanning electron microscopy (Cryo-SEM) and energy-dispersive X-ray spectroscopy (EDS). We find that the hydrophobic silica particles reside at both the aqueous-air and aqueous-oil interfaces. In contrast, the fluorinated particles, which exhibit hydrophobic and oleophobic properties simultaneously, are exclusively found at the oil-air interfaces.

Starch-based particles as stabilizers for Pickering emulsions: modification, characteristics, stabilization, and applications

The potential utilization of starch as a particle-based emulsifier in the preparation of Pickering emulsions is gaining interest within the food industry. Starch is an affordable and abundant functional ingredient, which makes it an excellent candidate for the stabilization of Pickering emulsions. This review article focuses on the formation, stabilization, and properties of Pickering emulsions formulated using starch-based particles and their derivatives. First, methods of isolating and modifying starch-based particles are highlighted. The key parameters governing the properties of starch-stabilized Pickering emulsions are then discussed, including the concentration, size, morphology, charge, and wettability of the starch-based particles, as well as the type and size of the oil droplets. The physicochemical mechanisms underlying the ability of starch-based particles to form and stabilize Pickering emulsions are also discussed. Starch-based Pickering emulsions tend to be more resistant to coalescence than conventional emulsions, which is useful for some food applications. Potential applications of starch-stabilized Pickering emulsions are reviewed, as well as recent studies on their gastrointestinal fate. The information provided may stimulate the utilization of starch-based Pickering emulsions in food and other industries.

Analysis of instability of starch-based Pickering emulsion under acidic condition of pH < 4 and improvement of emulsion stability

Starch-based Pickering emulsions exhibit high interfacial stability in a certain range of mild pH environments. On the contrary, many studies have reported that when the pH value is <4, it often leads to different degrees of emulsion instability. In this paper, the microscopic state of starch granules in the emulsion and its effect on the stability of the emulsion were observed and analyzed by atomic force microscope (AFM) in tapping mode. At the same time, Pickering emulsions in acidic environment were prepared by using the gel properties of methyl cellulose (MC) in synergy with esterified high amylose maize starch (M-HAMS) granules. The results show that in the emulsion with pH 3, the excessive H + ion inhibits the swelling of M-HAMS granules and prevents it from forming a stable gel structure, which is the main cause of emulsion instability. The polarity of MC with water contact angle (WCA) of 81.8° is similar to that of M-HAMS granules with WCA of 80.1°, and a uniform and ordered micro-nanostructure is formed in the aqueous phase. The prepared acidic (pH 3-4) emulsion has good stability during the observation period of 30 days.

Thermocapillary migration of a drop with a thermally conducting stagnant cap

Hypothesis The thermocapillary migration of a spherical drop with a stagnant cap in the presence of a constant applied temperature gradient can be strongly affected by the finite thermal conductivity of the stagnant cap. Numerics The heat conduction of the stagnant cap is analytically modeled. The effects of the additional interfacial stresses generated by the disturbances to the local temperature field due to the presence of the cap at the fluid-fluid interface and the corresponding velocity of migration of the drop are evaluated by solving for the temperature and hydrodynamic field equations in and around the drop. An asymptotic model is derived to predict the terminal velocity in the presence of an infinitely conducting stagnant cap. Findings The effects of the surface conductivity and size of the stagnation region alongside the bulk thermal conductivities and viscosities of the drop and surrounding media are evaluated. The terminal velocity of the drop is shown to have a monotonic dependence on the conductivity of the stagnant cap. The bounds to the terminal velocity increment due to the stagnant cap are derived. These bounds can be of significance to multiphysics problems involving particle laden drops, Pickering emulsions and other multi-phase technologies where the conductivity of the surface adsorbents is non-negligible.

Polyoxometalate-loaded hyper-crosslinked nanoparticles as a Pickering interfacial catalyst for solvent-free epoxidation of allyl chloride under static conditions

Epoxidation of allyl chloride and hydrogen peroxide (H2O2) carried out in heterogeneous catalytic systems suffer from poor reaction efficiency due to their heavy mass transfer resistance present at the liquid-liquid interface. Pickering interfacial catalysis (PIC) provides an elegant solution by involving the design of amphiphilic heterogeneous catalysts, which can act as emulsifiers simultaneously. In this study, interface-active polyoxometalate-loaded hyper-crosslinked nanoparticles (HCNPs) were designed. The structural properties of materials were characterized in detail by elemental analysis, Zeta potential, ICP-OES, SEM, TEM, BET, FT-IR, TGA, and XPS. The prepared nanoparticles can build efficient W/O PIC systems with allyl chloride and H2O2. Systematic experiments indicate that catalysts' surface properties, catalyst dosage, and water/oil volume ratio significantly affect the PIC system's catalytic activity and emulsion properties. Moreover, this PIC system maintains high stability after the reaction and can be reused for at least 8 cycles. Excitingly, these interface-active HCNPs can also efficiently promote allyl chloride epoxidation in the absence of solvent and external stirring, illustrating that this approach holds great potential for developing catalytic systems suitable for multiphase reactions.

Characterization, interfacial rheology, and storage stability of Pickering emulsions stabilized by complex of whey protein isolate fiber and zein derived from micro-endosperm maize

In present study, we characterized the formation, interfacial rheology, and storage stability of emulsions stabilized by microendosperm maize-derived zein (M-Zein)/whey protein isolate fiber (WPIF) nanoparticles. Microendosperm maize is a newly developed, oleic acid-rich oilseed resource. Recent research has shown that M-Zein possesses unique hydrophobic properties. Combining it with WPIF may enhance its performance as a stabilizer. Optimization of weight ratios for M-Zein/WPIF composites, guided by particle size analysis, fluorescence spectroscopy, three-phase contact angle (θ), and interfacial rheological analysis, revealed that a 4: 6 mass ratio at pH 7 yielded favorable wettability (θ = 91.2°). Interfacial rheology analysis showed that the combination of WPIF reduced M-Zein's interfacial tension to 7.2 mN/m and 36.7 mN/m at oil-water and air-water interfaces, respectively. The M-Zein/WPIF complex exhibited an elastic protein layer at the oil-water interface. Further investigations into nanoparticle concentration, oil phase volume, and pH revealed that emulsions containing 3 % nanoparticles (w/w), 50 % oil phase volume, and pH 7 showed the best storage stability. This research highlights the development of M-Zein/WPIF composited nanoparticles with superior storage stability and interfacial rheology. Additionally, it introduces a novel application for M-Zein, which elevates the value proposition of microendosperm maize.

Proteinaceous Microsphere-Based Water-in-Oil Pickering Emulsions for Preservation of Chlorella Cells

Microalgae are highly regarded as ideal materials for the creation of liquid biofuels and have substantial potential for growth and utilization. However, traditional storage and culture methods for microalgae are plagued by challenges such as uncontrolled growth, bacterial contamination, and self-shading among algae. These issues severely impede the photosynthetic process and the efficient extraction of biomass energy. This study tackles these problems by utilizing magnetic hydrophobic protein particles to stabilize water-in-oil Pickering emulsions. This allows for the micro-compartment storage and magnetic transfer of algae. Additionally, the successful encapsulation of Chlorella cells in high-internal-phase water-in-oil Pickering emulsions effectively mitigates the settling problem of Chlorella cells in the liquid phase, thereby enabling the potential use of Pickering emulsions for the confined cultivation of microalgae.

Pickering Emulsion Stabilized by Hordein-Whey Protein Isolate Complex: Delivery System of Quercetin

As a lipophilic flavonol, quercetin has low bioavailability, which limits its application in foods. This work aimed to prepare a hordein-based system to deliver quercetin. We constructed hordein-whey isolate protein fibril (WPIF) complexes (H-Ws) by anti-solvent precipitation method at pH 2.5. The TEM results of the complexes showed that spherical-like hordein particles were wrapped in WPIF clusters to form an interconnected network structure. FTIR spectra revealed that hydrogen bonds and hydrophobic interactions were the main driving forces for the complex formation. H-W1 (the mass ratio of hordein to WPIF was 1:1) with a three-phase contact angle of 70.2° was chosen to stabilize Pickering emulsions with oil volume fractions (φ) of 40-70%. CLSM images confirmed that the oil droplets were gradually embedded in the three-dimensional network structure of H-W1 with the increase in oil volume fraction. The emulsion with φ = 70% showed a tight gel structure. Furthermore, this emulsion exhibited high encapsulation efficiency (97.8%) and a loading capacity of 0.2%, demonstrating the potential to deliver hydrophobic bioactive substances. Compared with free quercetin, the bioaccessibility of the encapsulated quercetin (35%) was significantly improved. This study effectively promoted the application of hordein-based delivery systems in the food industry.

Review on demulsification techniques for oil/water emulsion: Comparison of recyclable and irretrievable approaches

Since the establishment of the first global refinery in 1856, crude oil has remained one of the most lucrative natural resources worldwide. However, during the extraction process from reservoirs, crude oil gets contaminated with sediments, water, and other impurities. The presence of pressure, shear forces, and surface-active compounds in crude oil leads to the formation of unwanted oil/water emulsions. These emulsions can take the form of water-in-oil (W/O) emulsions, where water droplets disperse continuously in crude oil, or oil-in-water (O/W) emulsions, where crude oil droplets are suspended in water. To prevent the spread of water and inorganic salts, these emulsions need to be treated and eliminated. In existing literature, different demulsification procedures have shown varying outcomes in effectively treating oil/water emulsions. The observed discrepancies have been attributed to various factors such as temperature, salinity, pH, droplet size, and emulsifier concentrations. It is crucial to identify the most effective demulsification approach for oil/water separation while adhering to environmental regulations and minimizing costs for the petroleum sector. Therefore, this study aims to explore and review recent advancements in two popular demulsification techniques: chemical demulsification and magnetic nanoparticles-based (MNP) demulsification. The advantages and disadvantages of each technique are assessed, with the magnetic approach emerging as the most promising due to its desirable efficiency and compliance with environmental and economic concerns. The findings of this report are expected to have a significant impact on the overall process of separating oil and water, benefiting the oil and gas industry, as well as other relevant sectors in achieving the circular economy.

Self-Healing Composite Coating Fabricated with a Cystamine Cross-Linked Cellulose Nanocrystal-Stabilized Pickering Emulsion

A gelled Pickering emulsion system was fabricated by first stabilizing linseed oil droplets in water with dialdehyde cellulose nanocrystals (DACNCs) and then cross-linking with cystamine. Cross-linking of the DACNCs was shown to occur by a reaction between the amine groups on cystamine and the aldehyde groups on the CNCs, causing gelation of the nanocellulose suspension. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to characterize the cystamine-cross-linked CNCs (cysCNCs), demonstrating their presence. Transmission electron microscopy images evidenced that cross-linking between cysCNCs took place. This cross-linking was utilized in a linseed oil-in-water Pickering emulsion system, creating a novel gelled Pickering emulsion system. The rheological properties of both DACNC suspensions and nanocellulose-stabilized Pickering emulsions were monitored during the cross-linking reaction. Dynamic light scattering and confocal laser scanning microscopy (CLSM) of the Pickering emulsion before gelling imaged CNC-stabilized oil droplets along with isolated CNC rods and CNC clusters, which had not been adsorbed to the oil droplet surfaces. Atomic force microscopy imaging of the air-dried gelled Pickering emulsion also demonstrated the presence of free CNCs alongside the oil droplets and the cross-linked CNC network directly at the oil-water interface on the oil droplet surfaces. Finally, these gelled Pickering emulsions were mixed with poly(vinyl alcohol) solutions and fabricated into self-healing composite coating systems. These self-healing composite coatings were then scratched and viewed under both an optical microscope and a scanning electron microscope before and after self-healing. The linseed oil was demonstrated to leak into the scratches, healing the gap automatically and giving a practical approach for a variety of potential applications.

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.

Incorporation of fucoxanthin into 3D printed Pickering emulsion gels stabilized by salmon by-product protein/pectin complexes

The remarkable performance of fucoxanthin (FX) in antioxidant and weight loss applications has generated considerable interest. However, the application of fucoxanthin in the food and pharmaceutical industries is limited due to its highly unsaturated structure. This research aimed to investigate the synergistic mechanism of a unique Pickering emulsion gel stabilized by salmon byproduct protein (SP)-pectin (PE) aggregates and evaluate its ability to enhance the stability and bioavailability of FX. Various analytical techniques, including fluorescence spectroscopy, contact angle testing, turbidity analysis, and cryo-field scanning electron microscopy, were used to demonstrate that electrostatic and hydrophobic interactions between SP and PE contribute to the exceptional stability and wettability of the Pickering emulsion gels. Rheological analysis revealed that increasing the concentration of SP-PEs resulted in shear-thinning behavior, excellent thixotropic recovery performance, higher viscoelasticity, and good thermal stability of the Pickering emulsion gels stabilized by SP-PEs(SEGs). Furthermore, encapsulation of FX in the gels showed protected release under simulated oral and gastric conditions, with the subsequent controlled release in the intestine. Compared to free FX and the control group without PE (SEG-0), SEG-4 exhibited a 1.92-fold and 1.37-fold increase in the total bioavailable fraction of FX, respectively. Notably, during the study, it was observed that SEGs have the potential to serve as cake decoration for 3D printing to replace traditional cream under lower oil phase conditions (50%). These findings suggest that SP-PEs-stabilized Pickering emulsion gels hold promise as carriers for delivering bioactive compounds, offering the potential for various innovative food applications.

Bio-based Pickering emulsifier from mangosteen residues-derived sodium caseinate grafted spherical cellulose nanocrystals: Stability, rheological properties and microstructure studies

This study focuses on the preparation of mangosteen rind-derived nanocellulose via green ascorbic acid hydrolysis. Subsequently, milk protein-grafted nanocellulose particles were developed as a renewable Pickering emulsifier for water-oil stabilization. The stabilizing efficiency of modified nanocellulose (NC-S) at different caseinate (milk protein) concentrations (1.5, 3.0, and 4.0 % w/v) was tested in a water-in-oil emulsion (W/O ratio of 40:60). At a concentration 3.0 % w/v of caseinate (3.0NC-S), the emulsion exhibited a stronger network of adsorption between water, Pickering emulsifier, and oil. This resulted in reduced oil droplet flocculation, increased stability over a longer period, and favorable emulsifying properties, as depicted in the creaming index profile, oil droplet distribution, and rheology analysis. Since 3.0NC-S demonstrated the best colloidal stability, further focus will be placed on its microstructural properties, comparing them with those of mangosteen rind (MG), cellulose, and nanocellulose (NC-L). The XRD profile indicated that both NC-L and NC-S possessed a cellulose nanocrystal structure characterized as type I beta with a high crystallinity index above 60 %. Morphology investigation shown that the NC-L present in the spherical shape of particles with nanosized ranging at diameters of 11.27 ± 0.50 nm and length 11.76 ± 0.46 nm, while modified NC-S showed increase sized at 14.26 ± 4.60 nm and length 14.96 ± 4.94 nm. The increment of particle sizes from NC-L to NC-S indicated 2.82 × 10-15 mg/m2 of surface protein coverage by caseinate functional groups.

Physicochemical properties of Pickering emulsion fabricated with polysaccharides/pea protein isolate complex and its application in plant-based patty

Incorporation of structured liquid oil within plant-based patties can be achieved through the utilization of food-grade Pickering emulsion (PE). Therefore, the aim of this study was to evaluate the quality characteristics of PE and its application in plant-based patty. The PEs were formulated using sunflower oil (SO), polysaccharides and protein, and the specific ratios employed were as following: methylcellulose (MC) 2 % only (MP0); MC 1.5 % + pea protein isolate (PPI) 0.5 % (MP1); MC 1 % + PPI 1 % (MP2); xanthan gum (XG) 2 % only (XP0); XG 1.5 % + PPI 0.5 % (XP1); XG 1 % + PPI 1 % (XP2). MP0 and MP1 were unstable as PEs, whereas MP2 and XP groups (XP0, XP1, and XP2) exhibited stability as a PE. In addition, MP2 and all XP groups showed increased oil binding capacity, hydrophobic interaction, thermal stability, crystallization, rheological properties, and oxidative stability, compared to MP0 and MP1. In PE-applied plant-based patties, MP2 and all XP groups had significantly lower cooking loss and higher emulsion stability than SO. Particularly, MP2-employed plant-based patties exhibited significantly improved textural and sensory properties. Therefore, our data suggest that PEs with methylcellulose and pea protein isolate could be an effective replacement of plant oil in plant-based meat analogs.

Modulating digestibility and stability of Pickering emulsions based on cellulose nanofibers

Cellulose nanofibers (CNF) have been widely studied for their biodegradability and for their unique advantages as a stabilizer in Pickering-type emulsions. However, it is challenging to produce cellulose nanofibers from agroindustry waste with good techno-functional properties, without the use of harsh process conditions. Green alternatives (eco-friendly) have been studied to obtain nanofibers, such as enzymatic hydrolysis and/or application of mechanical processes. In this work, we used acid hydrolysis (as a control and example of an efficient method), enzymatic hydrolysis and a mechanical process (ultrasound) to obtain cellulose nanofibers. We also evaluated the effect of the presence of ethyl groups in the cellulosic matrix (ethylcellulose) on the stabilizing mechanism of emulsions. All cellulose nanofibers were able to produce Pickering emulsions at concentrations of 0.01-0.05% (w/w), although showing differences in emulsion stability and digestibility. Morphology of the different cellulose nanofibers affected the viscosity of the aqueous suspensions used as continuous phase. Emulsions with nanofibers obtained from cassava peel (without the presence of ethyl groups) were stabilized only by the Pickering-type mechanism, while ethylcellulose nanofibers also showed surface activity that contributed to the stability of the emulsion. Furthermore, these latter emulsions showed greater release of free fatty acids in in vitro digestion compared to emulsions stabilized by cellulose nanofibers. Despite these differences, in vitro digestion showed the potential of applying cellulose-stabilized emulsions to control the rate of lipid digestion, due to the low amount of free fatty acids released (<20%).

Enhanced Biphasic Reactions in Amphiphilic Silica Mesopores

In this study, we investigated the effect of the pore volume and mesopore size of surface-active catalytic organosilicas on the genesis of particle-stabilized (Pickering) emulsions for the dodecanal/ethylene glycol system and their reactivity for the acid-catalyzed biphasic acetalization reaction. To this aim, we functionalized a series of fumed silica superparticles (size 100-300 nm) displaying an average mesopore size in the range of 11-14 nm and variable mesopore volume, with a similar surface density of octyl and propylsulfonic acid groups. The modified silica superparticles were characterized in detail using different techniques, including acid-base titration, thermogravimetric analysis, TEM, and dynamic light scattering. The pore volume of the particles impacts their self-assembly and coverage at the dodecanal/ethylene glycol (DA/EG) interface. This affects the stability and the average droplet size of emulsions and conditions of the available interfacial surface area for reaction. The maximum DA-EG productivity is observed for A200 super-SiNPs with a pore volume of 0.39 cm3·g-1 with an interfacial coverage by particles lower than 1 (i.e., submonolayer). Using dissipative particle dynamics and all-atom grand canonical Monte Carlo simulations, we unveil a stabilizing role of the pore volume of porous silica superparticles for generating emulsions and local micromixing of immiscible dodecanal and ethylene glycol, allowing fast and efficient solvent-free acetalization in the presence of Pickering emulsions. The micromixing level is interrelated to the adsorption energy of self-assembled particles at the DA/EG interface.

Interfacial Activity of Janus Particle: Unity of Molecular Surfactant and Homogeneous Particle

Janus particles with different compositions and properties segmented to different regions on the surface of one objector provide more opportunities for interfacial engineering. As a novel interfacial active material, Janus particles integrate the amphiphilic properties of molecular surfactants and the Pickering effect of homogeneous particles. In this research, the outstanding properties of Janus particles on various interfaces are examined from both theoretical and practical perspectives, and the advantages of Janus particles over molecular surfactants and homogeneous particle surfactants are analyzed. We believe that Janus particles are ideal tools for interface regulation and functionalization in the future.

Effect of surface acetylation of chitin nanocrystals on the preparation and viscoelasticity of sunflower seed oil-in-water Pickering emulsions

Acetylated chitin nanocrystals (ChNCs) were used as stabilizer in this work to prepare sunflower seed oil-in-water emulsions for the morphological and rheological studies. The results revealed that the acetylation with moderate degree of substitution (0.38) reduced hydrophilicity and increased surface charge level of rod-like ChNCs, and as a result, significantly improved the emulsifying ability of ChNCs. At the same oil/water ratio and particle loading, the emulsions stabilized with the acetylated ChNCs had far smaller droplet size (∼3 μm) as compared to the emulsions stabilized with the pristine ChNCs (5-7 μm). The increased droplets numbers and improved surface coating level resulted in the enhanced viscous resistance and yield stress level, which improved the physical stability of the acetylated ChNC-stabilized emulsions as a result. In addition, the droplet clusters easily formed in this system, contributing to weak strain overshoot and decreased large-deformation sensitivity during dynamic shear flow. Therefore, the acetylated ChNC-stabilized system showed enhanced transient stress overshoot during startup flow and weakened thixotropy during cyclic ramp shear flow as compared to the pristine ChNC-stabilized system. The relationships between surface acetylation of ChNCs and flow behavior of emulsions were then established, which provide valuable information on the modulation of the ChNC-stabilized Pickering emulsions.

Pickering emulsions as an effective route for the preparation of bioactive composites: A study of nanocellulose/polyaniline particles with immunomodulatory effect

Several studies have reported on application of cellulose particles for stabilizing Pickering emulsions (PE). Here we employ an original approach that involves using these particles as a part of advanced composite colloids made of conducting polymer polyaniline (PANI) and cellulose nanocrystals (CNC) or nanofibrils (CNF). PANI/cellulose particles were prepared using oxidative polymerization of aniline in situ in the presence of CNC or CNF. The type and amount of celluloses (CNC vs CNF) and concentration of precursors (aniline monomer and oxidant) used in the reaction determined properties of the colloidal particles, such as size, morphology and content of PANI. The particles demonstrated intriguing biological characteristics, including no cytotoxicity, antibacterial activity against Staphylococcus aureus and Escherichia coli, antioxidant activity and related immunomodulatory activity. For the first time, such composites were used to successfully stabilize oil-in-water PE with undecane or capric/caprylic triglyceride oils. The properties of the emulsions were determined by the PANI/cellulose particles and oil used. The key finding of the study is the demonstrated ability of PANI/cellulose particles to stabilize PE, as well as the excellent antioxidant activity and ROS scavenging action originating from PANI presence, indicating potential of such systems for use in biomedicine, particularly for wound healing.

Co-loading of Temozolomide with Oleuropein or rutin into polylactic acid core-shell nanofiber webs inhibit glioblastoma cell by controlled release

Glioblastoma (GB) has susceptibility to post-surgical recurrence. Therefore, local treatment methods are required against recurrent GB cells in the post-surgical area. In this study, we developed a nanofiber-based local therapy against GB cells using Oleuropein (OL), and rutin and their combinations with Temozolomide (TMZ). The polylactic acid (PLA) core-shell nanofiber webs were encapsulated with OL (PLAOL), rutin (PLArutin), and TMZ (PLATMZ) by an electrospinning process. A SEM visualized the morphology and the total immersion method determined the release characteristics of PLA webs. Real-time cell tracking analysis for cell growth, dual Acridine Orange/Propidium Iodide staining for cell viability, a scratch wound healing assay for migration capacity, and a sphere formation assay for tumor spheroid aggressiveness were used. All polymeric nanofiber webs had core-shell structures with an average diameter between 133 ± 30.7-139 ± 20.5 nm. All PLA webs promoted apoptotic cell death, suppressed cell migration, and spheres growth (p < 0.0001). PLAOL and PLATMZ suppressed GB cell viability with a controlled release that increased over 120 h, while PLArutin caused rapid cell inhibition (p < 0.0001). Collectively, our findings suggest that core-shell nano-webs could be a novel and effective therapeutic tool for the controlled release of OL and TMZ against recurrent GB cells.

Comparative study of rheological properties and Pickering emulsion stabilizing capacity of nonenyl succinic anhydride and octenyl succinic anhydride modified amaranth starches

Functional properties and ability to stabilize Pickering emulsions of amaranth starch with the novel nonenyl succinic anhydride (NSA) modification and the widely used octenyl succinic anhydride (OSA) modification were compared. The NSA modification was more effective in altering the rheological properties of amaranth starches. NSA-modified amaranth starch showed significantly higher peak viscosity (7.13 Pa·s at DS of 0.02209) than the OSA-modified amaranth starch (6.10 Pa·s at DS of 0.03042). The gelatinization temperature, gelatinization enthalpy, and relative crystallinity of amaranth starch were more affected by the OSA than the NSA. The Pickering emulsions stabilized with NSA-modified starches had higher stability than those with the OSA-modified starches as characterized by particle size distribution, morphological, and rheological approaches. A lower degree of substitution by NSA than by OSA is needed to achieve a similar emulsification capacity. Thus, the NSA modification could be an efficient alternative to OSA modification in tailoring physicochemical and rheological functions, as well as stabilizing Pickering emulsions.

The influence of α and α' subunits on SPI Pickering emulsions based on natural hybrid breeding varieties

In this study, food-grade protein nanoparticles (Wild-NPs, α-lack-NPs, α'-lack-NPs, and (α + α')-lack-NPs) were organized as emulsion stabilizers via thermal induction. The effects of α and α' subunits in soybean protein isolate (SPI) on Wild nanoparticle Pickering emulsion (Wild-NPPEs), α-lack nanoparticle Pickering emulsion (α-lack-NPPEs), α'-lack nanoparticle Pickering emulsion (α'-lack-NPPEs) and (α + α')-lack nanoparticle Pickering emulsion ((α + α')-lack-NPPEs) were investigated. The Pickering emulsion stabilization mechanism indicated that the α'-lack-NPs particle size, surface hydrophobicity, and contact angle were mostly comparatively large. Therefore, the absence of the α' subunit made the desorption of protein nanoparticles at the oil and water interface require higher energy. Through the hydrophobic interaction between molecules, the structure and properties of the emulsion were improved, showing good stability. The existence of α'-lack-NPPEs leads to the formation of a gel-like network in the emulsion, which increases the viscosity of the emulsion and makes the network structure of the emulsion more uniform and denser.

Hydroxyapatite nanoparticle-modified porous bone grafts with improved cell attachment

Emulsion-templated foams have displayed promise as injectable bone grafts; however, the use of a surfactant as an emulsifier resulted in relatively small pores and impedes cell attachment. Hydroxyapatite nanoparticles were explored as an alternative stabilizer to address these limitations. To this end, hydroxyapatite nanoparticles were first modified with myristic acid to generate the appropriate balance of hydrophobicity to stabilize a water-in-oil emulsion of neopentyl glycol diacrylate and 1,4-butanedithiol. In situ surface modification of the resulting foam with hydroxyapatite was confirmed with elemental mapping and transmission electron microscopy. Nanoparticle-stabilized foams displayed improved human mesenchymal stem cell viability (91 ± 5%) over surfactant-stabilized foams (23 ± 11%). Although the pore size was appropriate for bone grafting applications (115 ± 71 μm), the foams lacked the interconnected architecture necessary for cell infiltration. We hypothesized that a co-stabilization approach with both surfactant and nanoparticles could be used to achieve interconnected pores while maintaining improved cell attachment and larger pore sizes. A range of hydroxyapatite nanoparticle and surfactant concentrations were investigated to determine the effects on microarchitecture and cell behavior. By balancing these interactions, a co-stabilized foam was identified that possessed large, interconnected pores (108 ± 67 μm) and improved cell viability and attachment. The co-stabilized foam was then evaluated as an injectable bone graft including network formation, microscale integration with bone, push out strength, and compressive properties. Overall, this work demonstrated that in situ surface modification with nHA improved cell attachment while retaining desirable bone grafting features and injectability.

Low-Frequency Ultrasound Effects on Cellulose Nanocrystals for Potential Application in Stabilizing Pickering Emulsions

Cellulose, in the form of cellulose nanocrystals (CNCs), is a promising biomaterial for stabilizing Pickering emulsions (PEs). PEs are commonly formed using low-frequency ultrasound (LFU) treatment and impact CNC properties. The present study investigated the specific effects of LFU treatment on CNCs' chemical and physical properties. CNCs were characterized using dynamic light scattering, ζ;-potential determination, Fourier transform infrared spectroscopy, X-ray diffraction, and contact angle measurement. CNC suspensions were studied using rheological analysis and static multiple light scattering. LFU treatment broke CNC aggregates and modified the rheological behavior of CNC suspensions but did not affect the CNCs' chemical or crystallographic structures, surface charge, or hydrophilic properties. During the storage of CNC suspensions and PEs, liquid crystal formation was observed with cross-polarized light. Hypotheses related to the impact of liquid crystal CNCs on PE stability were proposed.

Temperature sensitive nanogel-stabilized pickering emulsion of fluoroalkane for ultrasound guiding vascular embolization therapy

Various X-ray imaging technologies like computed tomography (CT) and digital subtraction angiography (DSA) are widely used in transcatheter arterial embolization (TAE) therapy for treating hepatocellular cancer (HCC) patients. Although they display high-contrast imaging, they have a few disadvantages, such as complex operation and exposure to ionizing radiation. Thus, ultrasound (US) imaging plays an important role in medical diagnosis because of its advantages, like simple and fast operation, no ionizing radiation exposure, and accurate real-time imaging. Subsequently, Poly N-isopropylacrylamide-co-2,2,3,4,4,4-Hexafluorobutyl methacrylate (PNF) nanogels were synthesized for stabilizing TGFPE, the Pickering emulsions of 2H, 3H-decafluoropentane (HDFP). These emulsions displayed dual abilities of thermosensitive sol-gel transition and long-term US imaging in vitro. Thus, it was concluded that these emulsions could achieve vascular embolization and long-term US imaging in vivo as per the TAE animal model results. The emulsion droplets' flow and accumulation were visualized under the US imaging guidance. In summary, the Pickering emulsions have the potential to be used as US-guided embolization material for mediating TAE surgeries.

Antibacterial and angiogenic potential of iron oxide nanoparticles-stabilized acrylate-based scaffolds for bone tissue engineering applications

Pickering emulsion polymerization, stabilized by inorganic nanoparticles such as iron oxide nanoparticles (IONPs), can be used to fabricate scaffolds with the desired porosity and pore size. These nanoparticles create stable emulsions that can be processed under harsh polymerization conditions. IONPs, apart from serving as an emulsifier, impart beneficial bioactivities such as antibacterial and pro-angiogenic activity. Here, we coated IONPs with three different weights of oleic acid (5.0 g, 7.5 g, and 10.0 g) to synthesize oleic acid-IONPs (OA-IONPs) that possess the desired hydrophobicity (contact angle > 100°). Next, glycidyl methacrylate and trimethylolpropane triacrylate were polymerized using the Pickering emulsion polymerization technique stabilized by the OA-IONPs. The physicochemical properties of the resulting porous scaffolds were thoroughly characterized using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometry (VSM), and a universal testing machine (UTM). The SEM images confirmed the formation of a porous scaffold. The IONPs content, measured using inductively coupled plasma mass spectrometry (ICP-MS), was in the range of 22-26 µg/mg of the scaffold. The mechanical strengths of the scaffolds were in the range of cancellous bone. The degradation profile of the scaffolds varied between 29% and 41% degradation over 30 days. In vitro cytotoxicity studies conducted using the fibroblast (L929) and osteosarcoma (MG-63) cell lines proved that these scaffolds were non-toxic. SEM images showed that the MG-63 cells adhered firmly to the scaffolds and exhibited a well-spread morphology. The antibacterial activity was confirmed by percentage inhibition studies, SEM analysis of bacterial membrane distortion, and reactive oxygen species (ROS) generation in the bacteria. Chick chorioallantoic membrane assay showed that the total vessel length and branch points were significantly increased in the presence of the scaffolds. These results confirm the pro-angiogenic potential of the fabricated scaffolds. The physicochemical, mechanical, and biological properties of the material suggest that the developed scaffolds would be suitable for bone tissue engineering applications.

Smart Emulsions Stabilized by a Multi-headgroup Surfactant Tolerant to High Concentrations of Acids and Salts

Retaining emulsions stable at high acidity and salinity is still a great challenge. Here, we report a novel multi-headgroup surfactant (C3 H7 -NH+ (C10 COOH)2 , di-UAPAc) which can be reversibly transformed among cationic, anionic and zwitterionic forms upon pH variation. Stable oil-in-dispersion (OID) emulsions in strong acidity (pH=2) can be co-stabilized by low concentrations of di-UAPAc and silica nanoparticles. High salinity at pH=2 improves the adsorption of di-UAPAc on silica particles through hydrogen bonding, resulting in the transformation of OID emulsions into Pickering emulsions. Moreover, emulsification/demulsification and interconversion between OID and Pickering emulsions together with control of the viscosity and droplet size can be triggered by pH. The present work provides a new protocol for designing surfactants for various applications in harsh aqueous media, such as strong acidity and high salinity, involved in oil recovery and sewerage treatments.

Cellulose Nanofibril Stabilized Pickering Emulsion Templated Aerogel with High Oil Absorption Capacity

Nanocellulose-based aerogels, featuring a three-dimensional porous structure, are considered as a desirable green absorbent because of their exceptional absorption performance as well as the abundance and renewability of the raw material. However, these aerogels often require hydrophobic modification or carbonization, which is often environmentally harmful and energy-intensive. In this study, we introduce a Pickering-emulsion-templating approach to fabricate a cellulose nanofibril (CNF) aerogel with a hierarchical pore structure, allowing for high oil absorption capacity. n-Hexane-CNF oil-in-water Pickering emulsions are prepared as an emulsion template, which is further lyophilized to create a hollow microcapsule-based CNF (HM-CNF) aerogel with a density ranging from 1.3 to 6.1 mg/cm3 and a porosity of ≥99.6%. Scanning electron microscopy and Brunauer-Emmett-Teller analyses reveal the HM-CNF aerogel's hierarchical pore structure, originating from the CNF Pickering emulsion template, and also confirm the aerogel's very high surface area of 216.6 m2/g with an average pore diameter of 8.6 nm. Furthermore, the aerogel exhibits a maximum absorption capacity of 354 g/g and 166 g/g for chloroform and n-hexadecane, respectively, without requiring any surface modification or chemical treatment. These combined findings highlight the potential of the Pickering-emulsion-templated CNF aerogel as an environmentally sustainable and high-performance oil absorbent.

Promising application of probiotic microorganisms as Pickering emulsions stabilizers

The purpose of this work was to study the ability of nineteen food-grade microorganisms as Pickering emulsion (PE) stabilizers. Medium-chain triacylglycerol (MCT) oil-in-water (50:50) PEs were fabricated by 10 wt% or 15 wt% of thermally-inactivated yeast, cocci, Bacillus spp. and lactobacilli cells. The characteristics of microorganisms related to "Pickering stabilization" including morphology, surface charge, interfacial tension, and "contact angle" were firstly studied. After that, the cells-stabilized PEs were characterized from both kinetic and thermodynamic viewpoints, microstructure and rheological properties. The interfacial tension and "contact angle" values of various microorganisms ranged from 16.33 to 38.31 mN/m, and from 15° to 106°, respectively. The mean droplet size of PEs ranged from 11.51 to 57.69 µm. Generally, the physical stability of cell-stabilized PEs followed this order: lactobacilli > Bacillus spp. > cocci > yeast. These variations were attributed to the morphology and cell wall composition. Increasing the microorganism concentration significantly increased the physical stability of PEs from a maximum of 12 days at 10 wt% to 35 days at 15 wt% as a result of better interface coverage. Shear-thinning and dominant elastic behaviors were observed in PEs. Physical stability was affected by the free energy of detachment. Therefore, food-grade microorganisms are suggested for stabilizing PEs.

Adding nanoparticles to improve emulsion efficiency and enhance microbial degradation in Pickering emulsions

Interfacial microbial degradation of alkane in Pickering emulsions stabilized by hydrophobic bacterial cells is a new mechanism for microbial degradation of water-insoluble chemicals, where both water-insoluble chemicals in the oil phase and water-soluble nutrients (such as nitrogen and phosphorus) in the water phase are bio-accessible to living microorganisms anchoring onto the oil-water interfaces. In the present work, super-hydrophobic Mycobacterium sp. (contact angle 168.6°) degradation of tetradecane was set up as a model. Addition of fumed SiO2 particles (Aerosil® R974) as a new strategy was developed to enhance tetradecane degradation where the biodegradation rate (based on the accumulated biomass) increased by approximately 80%. The enhanced effect of SiO2 particles on the tetradecane degradation attributed to the synergistic effect of SiO2 particles on the emulsion efficiency of Pickering emulsions stabilized by bacterial cells and then on the enhancement of interfacial microbial degradation in Pickering emulsions. KEY POINTS: • Interfacial microbial degradation in bacterial cells stabilized Pickering emulsions. • Adding fumed SiO2 particles to enhance microbial degradation of tetradecane. • Correlation relationship between emulsion efficiency and interfacial microbial degradation.

Thymol-loaded Zein-pectin composite nanoparticles as stabilizer to fabricate Pickering emulsion of star anise essential oil for improved stability and antimicrobial activity

The aim of the present study was to prepare a new antimicrobial Pickering emulsion of which the star anise essential oil was added to the oil phase, and to investigate the effect of stabilization by bio-based active nanoparticles consisting of zein and pectin loaded with thymol. First, the thymol-loaded zein/pectin composite nanoparticles (ZTNPs) were fabricated as uniformly distributed spherical nanoparticles with an average diameter of 200 nm through antisolvent precipitation. Second, the effects of nanoparticles' concentration, oil phase ratio, and storage time on the stability of emulsions were explored according to particle size potential, interfacial tension, rheology, and micromorphology. Finally, the antibacterial results showed that Pickering emulsion inhibited Escherichia coli and Staphylococcus aureus compared to the control group by nearly 7 log colony-forming unit/g at 36 h, which was twice as much as the inhibition by thymol or star anise essential oils and ZTNPs. Therefore, the proposed Pickering emulsion with star anise essential oil could be used as a green and safe plant-derived antimicrobial agent in the food industry.

Preparation of lauric acid esterified starch by ethanol solvothermal process and its Pickering emulsion

In this paper, the esterification modification of different kinds of starches such as waxy maize, normal maize, high-amylose maize, cassava and potato in high temperature closed system were studied by solvothermal method. The oil-in-water Pickering emulsion were prepared with esterified starches as granule stabilizer. The microscopic state of granules in the emulsion and the physical and oxidation stability of emulsion were studied. The results show that starches are not gelatinized and can be esterified at a temperature (100 °C) much higher than that of gelatinization, and the granule morphology is almost unchanged. DS (degree of substitution) values of esterified starches range from 0.0333 to 0.0512. Pickering emulsion with 50 vol% oil volume fraction prepared with 3.0 wt% granule concentration did not show any instability such as oil-water separation after storage at room temperature for 30 days. Atomic force microscope (AFM) analysis showed that all esterified starch granules had the characteristics of granular cold-water swelling starch (GCWSS). The granules completely swelled into a dense molecular chain in the emulsion, and this three-dimensional network structure improved the stability of emulsion. Therefore, the preparation of esterified starch granules by ethanol solvothermal method is a simple and effective method.

Liquid-Liquid Interfacial Nanoarchitectonics

Science in the small world has become a crucial key that has the potential to revolutionize materials technology. This trend is embodied in the postnanotechnology concept of nanoarchitectonics. The goal of nanoarchitectonics is to create bio-like functional structures, in which self-organized and hierarchical structures are working efficiently. Liquid-liquid interface like environments such as cell membrane surface are indispensable for the expression of biological functions through the accumulation and organization of functional materials. From this viewpoint, it is necessary to reconsider the liquid-liquid interface as a medium where nanoarchitectonics can play an active role. In this review, liquid-liquid interfacial nanoarchitectonics is classified by component materials such as organic, inorganic, carbon, and bio, and recent research examples are discussed. Examples discussed in this paper include molecular aggregates, supramolecular polymers, conductive polymers film, crystal-like capsules, block copolymer assemblies, covalent organic framework (COF) films, complex crystals, inorganic nanosheets, colloidosomes, fullerene assemblies, all-carbon π-conjugated graphite nanosheets, carbon nanoskins and fullerphene thin films at liquid-liquid interfaces. Furthermore, at the liquid-liquid interface using perfluorocarbons and aqueous phases, cell differentiation controls are discussed with the self-assembled structure of biomaterials. The significance of liquid-liquid interfacial nanoarchitectonics in the future development of materials will then be discussed.