Chitosan nanoparticles as particular emulsifier for preparation of novel pH-responsive Pickering emulsions and PLGA microcapsules

Fabrication and stability of Pickering nanoemulsion stabilized by self-aggregated chitosan nanoparticles

The fabrication of Pickering nanoemulsions, specifically food-grade ones, is challenging due to the limited availability of particles with appropriate amphiphilic wettability and sufficiently small particle size. Chitosan nanoparticles offer a promising solution due to their adjustable size and amphiphilic properties. The study investigated the effects of pH, oil phase volume fraction, chitosan concentration, and ultrasonic intensity on the formation of chitosan Pickering nanoemulsions. Nanoemulsions with droplet size of approximately 300 nm were achieved under optimal conditions of pH 6.5, oil phase volume fraction of 1 %, chitosan concentration of 1.0 wt%, and 455 W ultrasonic power for 360 min. Stability tests indicated that the nanoemulsions had good pH (2-6), ionic strength (100-500 mM), thermal (60-90 °C), freeze-thaw (3 times) and storage stabilities (0-60 days). The findings highlight the potential of chitosan nanoparticles as effective stabilizers for Pickering nanoemulsions, providing valuable insights for the development of food-grade Pickering nanoemulsions.

Recent developments in chitosan based microgels and their hybrids

Chitosan based microgels have gained great attention because of their chemical stability, biocompatibility, easy functionalization and potential uses in numerous fields. Production, properties, characterization and applications of chitosan based microgels have been systematically reviewed in this article. Some of these systems exhibit responsive behavior towards external stimuli like pH, light, temperature, glucose, etc. in terms of swelling/deswelling in an aqueous medium depending upon the functionalities present in the network which makes them a potential candidate for various applications in the fields of biomedicine, agriculture, catalysis, sensing and nanotechnology. Current research development and critical overview in this field accompanying by future possibilities is presented. The discussion is concluded with recommended possible future works for further progress in this field.

Molybdate and Phosphate Cross-Linked Chitosan Films for Corrosion Protection of Hot-Dip Galvanized Steel

Environmentally friendly and sustainable methods to protect hot-dip galvanized (HDG) steel from corrosion are extensively studied. Films of the biopolymer polyelectrolyte chitosan were ionically cross-linked in this work with the well-known corrosion inhibitors phosphate and molybdate. Layers on this basis are presented as components in a protective system and could, e.g., be applied in pretreatments similar to a conversion coating. For the preparation of the chitosan-based films, a procedure involving sol-gel chemistry and wet-wet application was utilized. Homogeneous films of few micrometers thickness were obtained on HDG steel substrates after thermal curing. Properties of chitosan-molybdate and chitosan-phosphate films were compared with purely passive epoxysilane-cross-linked chitosan, and pure chitosan. Delamination behavior of a poly(vinyl butyral) (PVB) weak model top coating studied by scanning Kelvin probe (SKP) showed an almost linear time dependence over >10 h on all systems. Delamination rates were 0.28 mm h^-1 (chitosan-molybdate) and 0.19 mm h^-1 (chitosan-phosphate), ca. 5% of a non-cross-linked chitosan reference and slightly higher than of the epoxsyilane cross-linked chitosan. Immersion of the treated zinc samples over 40 h in 5% NaCl solution yielded a 5-fold increase of the resistance in the chitosan-molybdate system, as evidenced by electrochemical impedance spectroscopy (EIS). Ion exchange of electrolyte anions with molybdate and phosphate triggers corrosion inhibition, presumably by reaction with the HDG surface as well described in the literature for these inhibitors. Thus, such surface treatments have potential for application, e.g., in temporary corrosion protection.

Food-Grade Oil-in-Water (O/W) Pickering Emulsions Stabilized by Agri-Food Byproduct Particles

In recent years, emulsions stabilized by solid particles (known as Pickering emulsions) have gained considerable attention due to their excellent stability and for being environmentally friendly compared to the emulsions stabilized by synthetic surfactants. In this context, edible Pickering stabilizers from agri-food byproducts have attracted much interest because of their noteworthy benefits, such as easy preparation, excellent biocompatibility, and unique interfacial properties. Consequently, different food-grade particles have been reported in recent publications with distinct raw materials and preparation methods. Moreover, emulsions stabilized by solid particles can be applied in a wide range of industrial fields, such as food, biomedicine, cosmetics, and fine chemical synthesis. Therefore, this review aims to provide a comprehensive overview of Pickering emulsions stabilized by a diverse range of edible solid particles, specifically agri-food byproducts, including legumes, oil seeds, and fruit byproducts. Moreover, this review summarizes some aspects related to the factors that influence the stabilization and physicochemical properties of Pickering emulsions. In addition, the current research trends in applications of edible Pickering emulsions are documented. Consequently, this review will detail the latest progress and new trends in the field of edible Pickering emulsions for readers.

Chitosan nanocarriers containing essential oils as a green strategy to improve the functional properties of chitosan: A review

Large amounts of agricultural waste, especially marine product waste, are produced annually. These wastes can be used to produce compounds with high-added value. Chitosan is one such valuable product that can be obtained from crustacean wastes. Various biological activities of chitosan and its derivatives, especially antimicrobial, antioxidant, and anticancer properties, have been confirmed by many studies. The unique characteristics of chitosan, especially chitosan nanocarriers, have led to the expansion of using chitosan in various sectors, especially in biomedical sciences and food industries. On the other hand, essential oils, known as volatile and aromatic compounds of plants, have attracted the attention of researchers in recent years. Like chitosan, essential oils have various biological activities, including antimicrobial, antioxidant, and anticancer. In recent years, one of the ways to improve the biological properties of chitosan is to use essential oils encapsulated in chitosan nanocarriers. Among the various biological activities of chitosan nanocarriers containing essential oils, most studies conducted in recent years have been in the field of antimicrobial activity. It was documented that the antimicrobial activity was increased by reducing the size of chitosan particles in the nanoscale. In addition, the antimicrobial activity was intensified when essential oils were in the structure of chitosan nanoparticles. Essential oils can increase the antimicrobial activity of chitosan nanoparticles with synergistic effects. Using essential oils in the structure of chitosan nanocarriers can also improve the other biological properties (antioxidant and anticancer activities) of chitosan and increase the application fields of chitosan. Of course, using essential oils in chitosan nanocarriers for commercial use requires more studies, including stability during storage and effectiveness in real environments. This review aims to overview recent studies on the biological effects of essential oils encapsulated in chitosan nanocarriers, with notes on their biological mechanisms.

Recent developments in improving the emulsifying properties of chitosan

Chitosan is one of the valuable products obtained from crustacean waste. The unique characteristics of chitosan (antimicrobial, antioxidant, anticancer, and anti-inflammatory) have increased its application in various sectors. Besides unique biological properties, chitosan or chitosan-based compounds can stabilize emulsions. Nevertheless, studies have shown that chitosan cannot be used as an efficient stabilizer because of its high hydrophilicity. Hence, this review aims to provide an overview of recent studies dealing with improving the emulsifying properties of chitosan. In general, two different approaches have been reported to improve the emulsifying properties of chitosan. The first approach tries to improve the stabilization property of chitosan by modifying its structure. The second one uses compounds such as polysaccharides, proteins, surfactants, essential oils, and polyphenols with more wettability and emulsifying properties than chitosan's particles in combination with chitosan to create complex particles. The tendency to use chitosan-based particles to stabilize Pickering emulsions has recently increased. For this reason, more studies have been conducted in recent years to improve the stabilizing properties of chitosan-based particles, especially using the electrostatic interaction method. In the electrostatic interaction method, numerous research has been conducted on using proteins and polysaccharides to increase the stabilizing property of chitosan.

Capsules templated from water-in-oil Pickering emulsions for enzyme encapsulation

HYPOTHESIS

Encapsulation of sensitive water-soluble bioactive materials such as fragrances, polyphenols and enzymes poses an immense challenge with capsules templated from water-in-oil (w/o) emulsions. Generation of radicals, heating, and extreme pH that are necessary for shell formation through interfacial reactions may have undesired influences on the active ingredients and thus lower their activity.

EXPERIMENTS

To overcome these limitations, we present a method to encapsulate sensitive ingredients, whereby capsules are templated from a w/o Pickering emulsion stabilized by binary particles of different hydrophilicity levels; the particles assembled at the water/oil interface are then crosslinked by polydiisocyanate (PHDI) at room temperature and neutral pH. Zein and casein nanoparticles were used as hydrophilic stabilizers and lipase was chosen as a model sensitive biomolecule that was encapsulated in the water core.

FINDINGS

Our results indicated that the enzymes encapsulated in colloid capsules had higher activity than those encapsulated in traditional w/o Pickering emulsion without shell crosslinking. The capsule structure effectively protected enzymes from the outer environment. This method is well suited for the encapsulation and protection of sensitive ingredients and shows great application in food, drug, and cosmetic industries.

Physicochemical, Thermal, and Morphological Properties of Chitosan Nanoparticles Produced by Ionic Gelation

Chitosan nanoparticles (CSNPs) can be widely used in the food, pharmaceutical, and cosmetic sectors due to their high performance, unique properties, and high surface area. In this research, CSNPs were produced by the ionic gelation method and using sodium tripolyphosphate (STPP) as an appropriate technique compared to the conventional methods. To evaluate the effects of various factors on the size, zeta potential (ZP), and optimal synthesis conditions, different concentrations of CS (1, 3, and 5 mg/mL), STPP (0.5, 0.75, and 1 mg/mL), and CS to STPP ratio (1:1, 3:1, and 5:1) were applied and optimized using the response surface methodology. The size of CSNPs was increased by using higher concentrations of CS, STPP, and CS/STPP ratios. The value of ZP was determined positive and it increased with increasing CS concentrations and CS/STPP ratios. ATR-FTIR spectra revealed interactions between CS and STPP. The DSC thermogram of CSNPs showed a double sharp endothermic peak at about 74.5 °C (ΔH = 122.00 J/g); further, the TGA thermograms indicated the total weight loss of STPP, CS, and CSNPs as nearly 3.30%, 63.60%, and 52.00%, respectively. The XRD data also revealed a greater chain alignment in the CSNPs. Optimized, the CSNPs can be used as promising carriers for bioactive compounds where they also act as efficient stabilizers in Pickering emulsions.

Chitosan Nanoparticle Encapsulation of Antibacterial Essential Oils

Chitosan is the most suitable encapsulation polymer because of its natural abundance, biodegradability, and surface functional groups in the form of free NH₂ groups. The presence of NH₂ groups allows for the facile grafting of functionalized molecules onto the chitosan surface, resulting in multifunctional materialistic applications. Quaternization of chitosan's free amino is one of the typical chemical modifications commonly achieved under acidic conditions. This quaternization improves its ionic character, making it ready for ionic-ionic surface modification. Although the cationic nature of chitosan alone exhibits antibacterial activity because of its interaction with negatively-charged bacterial membranes, the nanoscale size of chitosan further amplifies its antibiofilm activity. Additionally, the researcher used chitosan nanoparticles as polymeric materials to encapsulate antibiofilm agents (such as antibiotics and natural phytochemicals), serving as an excellent strategy to combat biofilm-based secondary infections. This paper provided a summary of available carbohydrate-based biopolymers as antibiofilm materials. Furthermore, the paper focuses on chitosan nanoparticle-based encapsulation of basil essential oil (Ocimum basilicum), mandarin essential oil (Citrus reticulata), Carum copticum essential oil ("Ajwain"), dill plant seed essential oil (Anethum graveolens), peppermint oil (Mentha piperita), green tea oil (Camellia sinensis), cardamom essential oil, clove essential oil (Eugenia caryophyllata), cumin seed essential oil (Cuminum cyminum), lemongrass essential oil (Cymbopogon commutatus), summer savory essential oil (Satureja hortensis), thyme essential oil, cinnamomum essential oil (Cinnamomum zeylanicum), and nettle essential oil (Urtica dioica). Additionally, chitosan nanoparticles are used for the encapsulation of the major essential components carvacrol and cinnamaldehyde, the encapsulation of an oil-in-water nanoemulsion of eucalyptus oil (Eucalyptus globulus), the encapsulation of a mandarin essential oil nanoemulsion, and the electrospinning nanofiber of collagen hydrolysate-chitosan with lemon balm (Melissa officinalis) and dill (Anethum graveolens) essential oil.

Optimization of Emulsification and Microencapsulation of Balangu (Lallemantia royleana) Seed Oil by Surface Response Methodology

Balangu (Lallemantia royleana) seed oil is a valuable source of omega-6 fatty acids that reduces the risk of cardiovascular diseases. Due to the high sensitivity of this oil to environmental factors, microencapsulation has been recommended to preserve valuable compounds of oils and prevent adverse environmental effects. In this study, the oil of balangu seeds was extracted using a combination of ultrasound and shaking incubation and was microencapsulated using an emulsification method. The process was optimized using the response surface methodology (RSM). For this purpose, the effect of three independent variables such as chitosan concentration (0–1.5%), sodium alginate concentration (0–4.5%), and pH (3–7) on emulsification and microencapsulation condition was analyzed. The results showed that the optimal conditions for emulsification and microencapsulation included 0.30% chitosan, 0.14% sodium alginate, and pH 3. Scanning electron microscopy (SEM) showed that the structure of the optimal sample was smooth, spherical, and without cracks, which confirms the success of emulsification and microencapsulation processes.

Biosourced Polymeric Emulsifiers for Miniemulsion Copolymerization of Myrcene and Styrene: Toward Biobased Waterborne Latex as Pickering Emulsion Stabilizer

Biobased waterborne latexes were synthesized by miniemulsion radical copolymerization of a biosourced β-myrcene (My) terpenic monomer and styrene (S). Biobased amphiphilic copolymers were designed to act as stabilizers of the initial monomer droplets and the polymer colloids dispersed in the water phase. Two types of hydrophilic polymer backbones were hydrophobically modified by terpene molecules to synthesize two series of amphiphilic copolymers with various degrees of substitution. The first series consists of poly(acrylic acid) modified with tetrahydrogeraniol moieties (PAA-g-THG) and the second series is based on the polysaccharide carboxymethylpullulan amino-functionalized with dihydromyrcenol moieties (CMP-g-(NH-DHM)). The produced waterborne latexes with diameters between 160 and 300 nm and were composed of polymers with varying glass transition temperatures (T_g, PMy = -60 °C, T_{g, P(My-co-S)} = -14 °C, T_g, PS = 105 °C) depending on the molar fraction of biobased β-myrcene (f_My,0 = 0, 0.43, or 1). The latexes successfully stabilized dodecane-in-water and water-in-dodecane emulsions for months at all compositions. The waterborne latexes composed of low T_g poly(β-myrcene) caused interesting different behavior during drying of the emulsions compared to polystyrene latexes.

Solid Lipid Microspheres Decorated Nanoparticles As Drug Carriers

While Pickering emulsions have been known since 1906, where oil droplets are dispersed in aqueous media owing to nanoparticles decorating each oil droplet, no solid lipid microparticles decorated with nanoparticles have been described. These Solid-Pickering microparticles are surfactant-free micro-scale spherical active agent carriers composed of beeswax as a natural solid lipid with chitosan and starch nanoparticles embedded in the surface. Microparticles of this type were made by dispersing molten lipid in hot aqueous media containing dispersed nanoparticles to create microdroplets. Once the droplets are cooled below the melting point of the lipid, the microparticles of spherical form are obtained. The novel system allows encapsulation of active agents within a solid lipid core which is slowly released over time. It has been demonstrated through encapsulation of Ibuprofen and Lidocaine as a model poorly water-soluble drugs and an extended-release profile (for at least a week) was achieved. These Solid Pickering microparticles can be used in food, medicine, agriculture, and personal care products.

A green initiative for oiled sand cleanup using chitosan/rhamnolipid complex dispersion with pH-stimulus response

The released oil can affect the vulnerable shoreline environment if the oil spills happen in coastal waters. The stranded oil on shorelines is persistent, posing a long-term influence on the intertidal ecosystem after weathering. Therefore, shoreline cleanup techniques are required to remove the oil from the shoreline environment. In this study, a new shoreline cleanup initiative using chitosan/rhamnolipid (CS/RL) complex dispersion with pH-stimulus response was developed for oiled sand cleanup. The results of factorial and single-factor design revealed that the CS/RL complex dispersion maintained high removal efficiency for oiled sand with different levels of oil content in comparison to using rhamnolipid alone. However, the increase of salinity negatively affected the removal efficiency. The electrostatic screening effect of high ionic strength can hinder the formation of the CS/RL complex, and thus reduce removal efficiency. The pH-responsive characteristic of chitosan allows the easy separation of water and oil in washing effluent. The chitosan polyelectrolytes aggregated and precipitated due to the deprotonation of amino groups by adjusting the pH of the washing effluent to above 8. The microscope image demonstrated that the chitosan aggregates wrapped around the oil droplets and settled to the bottom together, thus achieving oil-water separation. Such pH-stimulus response may help achieve an easy oil-water separation after washing. These findings have important implications for developing the new strategies of oil spill response.

Curcumin, a potent therapeutic nutraceutical and its enhanced delivery and bioaccessibility by pickering emulsions

Curcumin is a biomolecule with functional moieties, which contribute to its anti-inflammatory, anticancer, and antioxidant properties. It has shown several therapeutic effects on treating inflammatory and neurodegenerative diseases and contributes to the reduction of oxidative stress and damage to body tissues. However, its low solubility and fast metabolism limit its absorption in the gastrointestinal (GI) tract and lead to its low bioavailability. Preparation of Pickering emulsions stabilized with mineral or biopolymer-based nanoparticles can be an effective strategy for enhancing the stability of curcumin against degradation, increasing its bioaccessibility in the GI tract, and achieving its controlled release at various locations based on changes in environmental conditions. Various nanoparticles prepared from minerals, proteins, and polysaccharides show potential for stabilizing the curcumin-loaded emulsions, and their wettability can be altered through complexation and formation of hybrid nanoparticles. Stabilization of Pickering emulsions with polysaccharide-based nanoparticles and their complexes can enhance the stability of the curcumin against degradation. Moreover, various protein-based nanoparticles and their conjugated forms with other proteins or polysaccharides can enable the preparation of high internal phase Pickering emulsions (HIPEs) with concomitant higher loading and bioaccessibility of the curcumin molecule. In light of the several therapeutic properties of curcumin, this review article aims to highlight recent studies and the strategies used for the preparation of curcumin Pickering emulsions stabilized by various nanoparticles for enhancing its bioaccessibility during metabolism. These may be useful in pharmaceutical and food industries for drug development and delivery and fortification of food products with this nutraceutical component.

The effect of chitosan molecular weight on CO2-triggered switching between emulsification and demulsification

The role of molecular weight as a key physical property of macromolecules in determining the CO₂-triggered switching characteristics of responsive emulsions prepared using CO₂-switchable macromolecules has not been studied and is the focus of the current study. In this work, CO₂-switchable chitosan of four different molecular weights is used to investigate the effect of molecular weight on CO₂-triggered switching of CO₂-responsive emulsions. The molecular weight of chitosan is shown to have an opposite effect on emulsification and demulsification by the CO₂ trigger. Before bubbling of CO₂, chitosan of higher molecular weight forms a more stable three-dimensional network structure in the continuous phase of oil-in-water (O/W) emulsions, which leads to the formation of a more stable emulsion. After bubbling of CO₂, the chitosan of higher molecular weight makes the continuous phase more viscous, which leads to an incomplete demulsification as compared with the chitosan of lower molecular weight. Experimental evidence from the measurement of conductivity, interfacial tension and rheological properties is provided to support the proposed mechanism. This work is of great significance in guiding the selection of desirable CO₂-switchable polymers for switchable emulsions of desired switching characteristics.

Recent progress on Pickering emulsions stabilized by polysaccharides-based micro/nanoparticles

Pickering emulsions stabilized by micro/nanoparticles have attracted considerable attention owing to their great potential in various applications ranging from cosmetic and food industries to catalysis, tissue engineering and drug delivery. There is a growing demand to design "green" micro/nanoparticles for constructing stable Pickering emulsions. Micro/nanoparticles derived from the naturally occurring polysaccharides including cellulose, chitin, chitosan and starch are capable of assembling at oil/water interfaces and are promising green candidates because of their excellent biodegradability and renewability. The physicochemical properties of the micro/nanoparticles, which are determined by the fabricating approaches and/or post-modification methods, have a significant effect on the characteristics of the final Pickering emulsions and their applications. Herein, recent advances on Pickering emulsions stabilized by polysaccharides-based micro/nanoparticles and the construction of functional materials including porous foams, microcapsules and latex particles from these emulsions as templates, are reviewed. In particular, the effects of micro/nanoparticles properties on the characteristics of the Pickering emulsions and their applications are discussed. Furthermore, the obstacles that hinder the practical applications of polysaccharides-based micro/nanoparticles and Pickering emulsions as well as the prospects for the future development, are discussed.

Polysaccharides as Stabilizers for Polymeric Microcarriers Fabrication

Biodegradable polymeric microparticles are widely used in drug delivery systems with prolonged-release profiles and/or cell microcarriers. Their fabrication via the oil/water emulsion solvent evaporation technique has normally required emulsifiers in the aqueous phase. The present work aims to evaluate the effectiveness of various polysaccharides, such as chitosan, hyaluronic acid, cellulose, arabinogalactan, guar and their derivatives, as an alternative to synthetic surfactants for polylactide microparticle stabilization during their fabrication. Targeted modification of the biopolymer’s chemical structure was also tested as a tool to enhance polysaccharides’ emulsifying ability. The transformation of biomacromolecules into a form of nanoparticle via bottom-up or top-down methods and their subsequent application for microparticle fabrication via the Pickering emulsion solvent evaporation technique was useful as a one-step approach towards the preparation of core/shell microparticles. The effect of polysaccharides’ chemical structure and the form of their application on the polylactide microparticles’ total yield, size distribution and morphology was evaluated. The application of polysaccharides has great potential in terms of the development of green chemistry and the biocompatibility of the formed microparticles, which is especially important in biomedicine application.

The Role of Ultrasound in the Preparation of Zein Nanoparticles/Flaxseed Gum Complexes for the Stabilization of Pickering Emulsion

Ultrasound is one of the most commonly used methods to prepare Pickering emulsions. In the study, zein nanoparticles-flaxseed gum (ZNP-FSG) complexes were fabricated through various preparation routes. Firstly, the ZNP-FSG complexes were prepared either through direct homogenization/ultrasonication of the zein and flaxseed gum mixture or through pretreatment of zein and/or flaxseed gum solutions by ultrasonication before homogenization. The Pickering emulsions were then produced with the various ZNP-FSG complexes prepared. ZNP-FSG complexes and the final emulsions were then characterized. We found that the complex prepared by ultrasonication of zein as pretreatment followed by homogenization of the ZNP with FSG ((ZNP_U-FSG)H) exhibited the smallest turbidity, highest absolute potential value, relatively small particle size, and formed the most stable complex particles. Meanwhile, complex prepared through direct ultrasonication plus homogenization on the mixture ((ZNP-FSG)HU) showed significantly decreased emulsifying properties and stability. Compared with the complex without ultrasonic treatment, the complex and emulsion, which prepared by ultrasonicated FSG were extremely unstable, and the phase separation phenomenon of the emulsion was observed 30 min after preparation. The above conclusions are also in line with the findings obtained from the properties of the corresponding emulsions, such as the droplets size, microstructure, freeze-thaw stability, and storage stability. It is, therefore, clear that to produce stable Pickering emulsion, ultrasonication should be avoided to apply together at the end of ZNP-FGS complex preparation. It is worth noticing that the emulsions prepared by complex with ultrasonicated zein (ZNP_U-FSG)H are smaller, distributed more uniformly, and are able to encapsulate oil droplets well. It was found that the emulsions prepared with ZNP_U-FSG remained stable without serum phase for 14 days and exhibited improved stability at low-temperature storage. The current study will provide guidance for the preparation of protein–polysaccharide complexes and Pickering emulsions for future work.

Influence of molecular interactions on structure, controlled release and cytotoxicity of curcumin encapsulated chitosan - Silica nanostructured microspheres

Curcumin possesses numerous medicinal benefits including anti-cancer and anti-viral properties. However, its wide scale use as a drug is often hindered owing to the dearth of suitable drug-delivery systems which can solubilise it for long-term sustained-release and safeguard its beneficial properties. In this work, a fast, one-step method, employing evaporation induced assembly of colloids, has been employed for the synthesis of curcumin encapsulated organic-inorganic hybrid micron-sized spheres. Detailed physical properties of the microspheres, with scaffolds of silica nanoparticles (∼8.5 nm) cross linked by chitosan, are studied to trace the underlying mechanism of structural assembly in such systems, by tuning the polymer matrix with solubilizing agents, DMSO and Tween 20. A systematic modification in the hydrogen bonding network, conformations and interactions between macromolecules is revealed upon tuning the organic matrix. This in turn is found to control the assembly vis-à-vis the granular morphology, drug entrapment and packing fraction of nanoparticles in the microspheres, which have direct influence on the biological properties. Consequently, the microspheres are found to follow a first order drug release kinetics with a tunable rate constant which follows the ordering of packing fraction of silica nanoparticles in the micro-granules. A sustained curcumin release for a period extending up to 24 h has been achieved. Further studies using human lung and cervical cancer cell lines assert good anti-cancer properties of these nanostructured microspheres in cancer cells, while showing no toxicity towards normal cells. Thus, such hybrid organic-inorganic formulations achieved using multi-component colloidal assembly approach, with enhanced stability against degradation, are promising candidates for future clinical applications of water-insoluble drugs.

Pickering Emulsions Based on the pH-Responsive Assembly of Food-Grade Chitosan

Few natural, biocompatible, and inexpensive emulsifiers are available because such emulsifiers must satisfy severe requirements, be produced synthetically rather than naturally, be nontoxic, and require minimal effort to produce. Therefore, the synthesis of food-grade and biocompatible nanoparticles as an alternative to surfactants has recently received attention in the industry. However, many previous efforts involved chemical modification of materials or the introduction of secondary cocomponents for emulsion formation. To achieve the goal of simple preparation, we consider here chitosan nanoparticles to prepare Pickering emulsions of food-grade oil through the control of pH, without further chemical modification or extra additives. A mild process can prepare nanoparticles from chitosan by simply increasing the pH from 3.0 to 6.0. The results showed that the average radius of chitosan at pH 6.0 was 170 nm, while large aggregates were formed at pH 6.5. These nanoparticles were utilized to prepare the Pickering emulsion. The average size of emulsion droplets decreased upon increasing the pH from 3.0 to 6.0. Moreover, Pickering emulsions at different oil fractions and nanoparticle concentrations were stable and showed a low creaming index for 45 days. The emulsions were stable against coalescence and flocculation and behaved rheologically as gel-like, shear-thinning fluids (G' > G″). Pickering emulsion prevents the growth of the microorganism (Staphylococcus aureus) at different pH values and chitosan concentrations. These results demonstrate that chitosan nanoparticles could be a cost-effective and biocompatible emulsifier for the food or pharmaceutical industry for encapsulation and bioactive compounds, and Pickering emulsions have promising antibacterial effects for further applications.

Fabrication and antibacterial evaluation of peppermint oil-loaded composite microcapsules by chitosan-decorated silica nanoparticles stabilized Pickering emulsion templating

Novel peppermint oil (PO)-loaded composite microcapsules (CM) with hydroxypropyl methyl cellulose (HPMC)/chitosan/silica shells were effectively fabricated by PO Pickering emulsion, which were stabilized with chitosan-decorated silica nanoparticles (CSN). The surface modification of chitosan could improve the hydrophobicity of silica nanoparticles and favor their adsorption at the oil-water interface of PO Pickering emulsions. The microcapsule composite shells were formed dependent on the electrostatic adsorption of HPMC and CSN, and further subjected to spray-drying. The peppermint oil-loaded composite microcapsules with 100% HPMC as wall material (PO-CM@100%HPMC) seemed to be optimum formulation based on the prolonged release, acceptable entrapment efficiency (89.1%) and drug loading (25.5%). The PO-CM@100%HPMC could remarkably prolong the stability of PO. Moreover, the PO-CM@100%HPMC had a long-term antimicrobial activity (85.4%) against S. aureus and E. coli even after storage for 60 days. Therefore, the Pickering emulsions based microcapsules seemed to be a promising strategy for antibacterial application for PO.

Recyclable magnetic chitosan microspheres with good ability of removing cationic dyes from aqueous solutions

Sr_3.8Fe_25.7O_70.4-chitosan magnetic microparticles (Sr_3.8Fe_25.7O_70.4-CMNs) with a core-shell structure were synthesized, characterized and applied for the removal of two model cationic dyes. The results showed that these magnetic microparticles possess fast adsorption rate and high adsorption efficiency for both crystal violet (CV) and basic red 9 (BR9) at a temperature ranging 30 °C to 40 °C and suitable pH range (pH ≥ 7). The maximum removal efficiency for CV and BR9 attained to 94.5% and 97.5% in 30 min, which was significantly faster and higher than that of chitosan (<50% in 60 min) (P<0.01). And its maximum adsorption capacity for CV and BR9 reached 29.46 mg/g and 32.16 mg/g, respectively. The adsorption process of Sr_3.8Fe_25.7O_70.4-CMNs follows the Langmuir isotherm with a high correlation coefficient (R² > 0.97) and the pseudo-second-order model. Additionally, the synthesized Sr_3.8Fe_25.7O_70.4-CMNs were easy to regeneration and reuse, and the removal rate remained above 90% after 5 recycle times. This study would provide a new more environmental friendly material and method for the treatment of wastewater containing toxic dyes.

Engineered Multilayer Microcapsules Based on Polysaccharides Nanomaterials

The preparation of microcapsules composed by natural materials have received great attention, as they represent promising systems for the fabrication of micro-containers for controlled loading and release of active compounds, and for other applications. Using polysaccharides as the main materials is receiving increasing interest, as they constitute the main components of the plant cell wall, which represent an ideal platform to mimic for creating biocompatible systems with specific responsive properties. Several researchers have recently described methods for the preparation of microcapsules with various sizes and properties using cell wall polysaccharide nanomaterials. Researchers have focused mostly in using cellulose nanomaterials as structural components in a bio-mimetic approach, as cellulose constitutes the main structural component of the plant cell wall. In this review, we describe the microcapsules systems presented in the literature, focusing on the works where polysaccharide nanomaterials were used as the main structural components. We present the methods and the principles behind the preparation of these systems, and the interactions involved in stabilizing the structures. We show the specific and stimuli-responsive properties of the reported microcapsules, and we describe how these characteristics can be exploited for specific applications.

Pickering/Non-Pickering Emulsions of Nanostructured Sulfonated Lignin Derivatives

Sulfoethylated lignin (SEKL) polymeric surfactant and sulfoethylated lignin nanoparticles (N-SEKL) with a size of 750±50 nm are produced by using a facile green process involving a solvent-free reaction and acidification-based fractionation. SEKL forms a liquid-like conventional emulsion with low viscosity that has temporary stability (5 h) at pH 7. However, N-SEKL forms a gel-like, motionless, and ultra-stable Pickering emulsion through a network of interactions between N-SEKL particles, which creates steric hindrance among the oil droplets at pH 3. The deposition of SEKL and N-SEKL on the oil surface is monitored by a using a quartz crystal microbalance. Experimentally, the formation of emulsions at pH 7 is found to be reversible owing to the low adsorption energy ΔE of SEKL on the oil droplet (ΔE≈15 k_B T), which is determined with the help of three-phase contact-angle measurements. However, the high desorption energy (ΔE≈6.0×10⁵  k_B T) of N-SEKL makes it irreversibly adsorb on the oil droplets. SEKL is too hydrophilic to attach to the oil interface (ΔE≈0) and thus does not facilitate emulsion formation at pH 11. Therefore, it is feasible to apply SEKL for the formulation of Pickering or non-Pickering emulsions in the form of nanoparticles or polymeric surfactants, depending on the targeted application.

Capture of Perfluorooctanoic Acid Using Oil-Filled Graphene Oxide-Silica Hybrid Capsules

Fluorinated hydrocarbon (FHC) contamination has attracted global attention recently because of persistence within the environment and ecosystems of many types of FHC. The surfactant perfluorooctanoic acid (PFOA) is particularly commonly found in contaminated sites, and thus, urgent action is needed for its removal from the environment. In this study, water dispersible hybrid capsules were successfully prepared from an oil-in-water emulsion stabilized by graphene oxide and including a silicate precursor to grow a strong, mesoporous capsule shell surrounding the droplets. These capsules were decorated with amine groups to present a positively charged outer corona that attracts negative PFOA molecules. The aminated capsules were effectively applied as a novel technology to adsorb and sequester PFOA contamination in water. It was confirmed that PFOA removal by the capsules was pH and PFOA concentration dependent, with adsorption efficiencies of >60 mg g^-1 under ideal conditions. PFOA removal kinetics followed using high-performance liquid chromatography and liquid chromatography-mass spectrometry showed that capture of PFOA by the capsules reached a maximum of >99.9% in 2-3 days.

Self-Assembled Egg Yolk Peptide Micellar Nanoparticles as a Versatile Emulsifier for Food-Grade Oil-in-Water Pickering Nanoemulsions

Pickering emulsions stabilized by food-grade particles have garnered increasing interest in recent years due to their promising applications in biorelated fields such as foods, cosmetics, and drug delivery. However, it remains a big challenge to formulate nanoscale Pickering emulsions from these edible particles. Herein we show that a new Pickering nanoemulsion that is stable, monodisperse, and controllable can be produced by employing the spherical micellar nanoparticles (EYPNs), self-assembled from the food-derived, amphiphilic egg yolk peptides, as an edible particulate emulsifier. As natural peptide-based nanoparticles, the EYPNs have a small particle size, intermediate wettability, high surface activity, and deformability at the interface, which enable the formation of stable Pickering nanodroplets with a mean dynamic light scattering diameter below 200 nm and a polydispersity index below 0.2. This nanoparticle system is versatile for different oil phases with various polarities and demonstrates the easy control of nanodroplet size through tuning the microfluidization conditions or the ratio of EYPNs to oil phase. These food-grade Pickering nanoemulsions, obtained when the internal phase is an edible vegetable oil, have superior stability during long-term storage and spray-drying based on the irreversible and compact adsorption of intact EYPNs at the nanodroplet surface. This is the first finding of a natural edible nano-Pickering emulsifier that can be used solely to make stable food Pickering nanoemulsions with the qualities of simplicity, versatility, low cost, and the possibility of controllable and mass production, which make them viable for many sustainable applications.

Millimeter-Size Pickering Emulsions Stabilized with Janus Microparticles

The ability to make stable water-in-oil and oil-in-water millimeter-size Pickering emulsions is demonstrated using Janus particles-particles with distinct surface chemistries. The use of a highly cross-linked hydrophobic polymer network and the excellent water-wetting nature of a hydrogel as the hydrophobic and hydrophilic sides, respectively, permit distinct wettability on the Janus particle. Glass capillary microfluidics allows the synthesis of Janus particles with controlled sizes between 128 and 440 μm and control over the hydrophilic-to-hydrophobic domain volume ratio of the particle from 0.36 to 12.77 for a given size. It is shown that the Janus particle size controls the size of the emulsion drops, thus providing the ability to tune the structure and stability of the resulting emulsions. Stability investigations using centrifugation reveal that particles with the smallest size and a balanced hydrophilic-to-hydrophobic volume ratio (Janus ratio) form emulsions with the greatest stability against coalescence. Particles eventually jam at the interface to form nonspherical droplets. This effect is more pronounced as the hydrogel volume is increased. The large Janus particles permit facile visualization of particle-stabilized emulsions, which result in a better understanding of particle stabilization mechanisms of formed emulsions.

Synthesis of Mesoporous/Macroporous Microparticles Using Three-Dimensional Assembly of Chitosan-Functionalized Halloysite Nanotubes and Their Performance in the Adsorptive Removal of Oil Droplets from Water

Halloysite nanotubes (HNTs) were assembled into mesoporous/macroporous microparticles (c-g-HNTs MPs) using Pickering template-assisted approach. To unravel the stabilization mechanism in Pickering emulsion form, several emulsions and microparticles were prepared at various conditions and visualized using confocal laser scanning microscopy. The prepared c-g-HNTs MPs were used to treat emulsified oil solutions resulting in a maximum removal efficiency of 94.47%. The kinetics data of oil adsorption onto c-g-HNTs MPs was best fitted by the pseudo-second-order kinetic model ( R² = 0.9983). The maximum monolayer adsorption capacity of oil onto c-g-HNTs MPs as predicted by the multilayer Brunauer-Emmett-Teller model was found to be 788 mg/g. Compared with pristine HNTs, c-g-HNTs MPs exhibited higher self-settleability rates in aqueous solutions as well as in emulsified oil solutions, demonstrating their candidacy for practical water treatment applications. The c-g-HNTs MPs were repeatedly used for five adsorption-desorption cycles with minimal losses noticed in their performance.