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

Spontaneous Hollow Coacervate Transition of Silk Fibroin via Dilution and Its Transition to Microcapsules

Polymeric microcapsules are useful for drug delivery, microreactors, and cargo transport, but traditional fabrication methods require complex processes and harsh conditions. Coacervates, formed by liquid-liquid phase separation (LLPS), offer a promising alternative for microcapsule fabrication. Recent studies have shown that coacervates can spontaneously form hollow cavities under specific conditions. Here, we investigate the spontaneous hollow coacervate transition of silk fibroin (SF). SF coacervates, induced by mixing SF with dextran, calcium ions, and copper ions, transition to hollow coacervates upon dilution. Adding ethylenediaminetetraacetic acid (EDTA) further transforms them into vesicle-like capsule coacervates, which solidify into microcapsules. As a proof-of-concept, we successfully loaded a high-molecular-weight polymer cargo into the hollow cavity and bioactive enzyme cargo into the capsule layer by simply mixing the cargo with the coacervate solution. Our results demonstrate a facile, organic-solvent-free approach for fabricating SF-based microcapsules and provide insight into the mechanisms driving hollow coacervate formation.

Microscale Delivery Systems for Hydrophilic Active Ingredients in Functional Consumer Goods

Hydrophilic active ingredients play a crucial role in formulated consumer products, encompassing antioxidants, flavoring substances, and pharmaceuticals. Yet, their susceptibility to environmental factors, such as light, pH, temperature, and humidity, poses challenges to their stability and sustained release. Microencapsulation offers a promising avenue to address these challenges, facilitating stabilization, targeted delivery, and enhanced efficacy of hydrophilic actives. However, despite significant advancements in the field, microencapsulation of hydrophilic actives remains at the forefront of innovation. This is primarily due to the intrinsic characteristics of hydrophilic actives, including small molecular weight and thus high permeability through many microcarriers (e.g., shells), which often necessitate complex and costly technologies to be developed. Moreover, in light of escalating regulatory frameworks, the pursuit of biodegradable and other compliant materials suitable for the entrapment of hydrophilic ingredients is gaining momentum. These advancements aim to provide alternatives to currently used non-degradable synthetic polymer materials. Research is currently pushing towards meeting these regulatory constraints via cutting-edge technologies to engineer novel microscale delivery systems for hydrophilic active ingredients, including microcapsules, microspheres, microneedles, and micropatches. Although still in its infancy, this approach holds true potential for revolutionizing the future of formulated consumer goods.

Encapsulation of Oil Droplets Using Film-Forming Janus Nanoparticles

Polymer Janus nanoparticles with one hard cross-linked polystyrene lobe and one soft film-forming poly(methyl methacrylate-co-butyl acrylate) lobe were synthesized by reversible addition-fragmentation chain transfer (RAFT)-mediated emulsion polymerization. The Janus nanoparticles adsorbed to oil/water and air/water interfaces, where the soft lobes coalesced, forming films of thickness between 25 and 250 nm; droplets of silicone oil could be stably encapsulated in polymer in this way. When prepared by mechanical mixing without additives, capsules of diameter 5-500 μm could be prepared, and with additives and application of heat, capsules of diameter around 5 μm were achieved, even with highly viscous silicone oil (20,000 cSt). In a microfluidic device, monodisperse capsules of diameter 180 μm could be formed. The particles were weakly surface-active and spontaneously assembled themselves at air/water interfaces. When added into a paint formula, the oil capsules improved the stain resistance of paint films. Silicone oil leakage from the capsules could be mitigated by incubating the capsules with silica nanoparticles, on which silicone oil reacts, creating grafted layers.

Design and Synthesis of Multi-compartment Microcapsules via Pickering Emulsion Polymerization for Infrared Stealth and Adaptive Camouflage Applications

High-performance color-changing compounds, recognized as prominent smart materials, dynamically alter their color in response to external environmental stimuli. However, existing compounds exhibit limited responsiveness and color diversity, presenting challenges in the development of textiles responsive to multiple stimuli. This research introduces a novel design for dual-responsive color-changing microcapsules, employing a Pickering emulsion template method. The larger compartment encloses photosensitive dyes, whereas the smaller one contains thermochromic phase-change colorants. Adjusting the density of nanocapsules in the smaller compartment on the microcapsule surface enables a spectrum of colors, including red, yellow, blue, and green, triggered by light and heat. When incorporated into textiles, these microcapsules bestow adaptive color-changing attributes and infrared stealth capabilities onto the fabrics. Additionally, by modulating the color via surface micro/nanostructures, textile surfaces can exhibit hydrophobic and oleophobic properties. Such enhancements extend the textiles' potential applications in areas like anti-counterfeiting and military operations.

Strong self-association of chitosan microgels at interface mediated high stabilities in Pickering emulsion

The spontaneous self-organization of naturally-occurring polysaccharide particles into a thick and robust gel network at interface in Pickering emulsion is challenging. Inspired by the phenomenon that chitosan microgels (CSMs) with a certain size could self-associate into a solidified gel phase upon freezing, here we tentatively used CSMs to construct a highly-stable Pickering emulsion. CSMs can form a stable Langmuir's layer at the water/oil interface through the network deformation and re-arrangement of dangling chains, while the subsequent negative polymer coating can avoid the bridging resulting from the cross-association for CSMs on different emulsion droplets upon freezing. The experimental results indicated that the emulsion showed excellent features, including the wide pH range stability (3-12), long-term storage stability (> 3 months), thermal stability (121 °C, 30 min). Moreover, CSMs could self-associate into a reliable gel layer around the oil droplet in freezing, leading to the better freeze-thaw stability (1-3 cycles). The negative coating not only facilitates the formation of interfacial gel network around each emulsion droplet, but also produces huge steric hindrance and electrostatic repulsion to suppress the coalescence. This work provides a different way to modulate the interfacial structure, thus developing a more stable polysaccharide-based Pickering emulsion.

High precision acoustofluidic synthesis of stable, biocompatible water-in-water emulsions

Water-in-water (w/w) emulsions, comprising aqueous droplets within another continuous aqueous phase, rely on a low interfacial tension for stability. Thus far, it has been challenging to control their size and stability without the use of stabilizers. In this study, we introduce a microfluidic technique that addresses these challenges, producing stable w/w emulsions with precisely controlled size and uniformity. Results shows that using an acoustically actuated microfluidic mixer, PEG, Dextran, and alginate solutions (84.66 mPa.s viscosity difference) were homogenized rapidly, forming uniformly distributed w/w emulsions stabilized in alginate gels. The emulsion size, uniformity, and shear sensitivity can be tuned by modifying the alginate concentration. Biocompatibility was evaluated by monitoring the viability of kidney cells in the presence of emulsions and gels. In conclusion, this study not only showed emulsion formation with a high mixing efficiency exceeding 90 % for all viscosities, actuated at an optimized frequency of 1.064 MHz, but also demonstrated that an aqueous, solvent, and emulsifier-free composition exhibited remarkable biocompatibility, holding promise for precise drug delivery, cosmetics, and food applications.

Pickering emulsions stabilized by prolamin-based proteins as innovative carriers of bioactive compounds

Pickering emulsions (PEs) can be used as efficient carriers for encapsulation and controlled release of different bioactive compounds. Recent research has revealed the potential of prolamins in development of nanoparticle- and emulsion-based carriers which can improve the stability and bioavailability of bioactive compounds. Prolamin-based particles have been effectively used as stabilizers of various PEs including single PEs, high internal phase PEs, multiple PEs, novel triphasic PEs, and PE gels due to their tunable self-assembly behaviors. Prolamin particles can be fabricated via different techniques including anti-solvent precipitation, dissolution followed by pH adjustment, heating, and ion induced aggregation. Particles fabricated from prolamins alone or in combination with other hydrocolloids or polyphenols have also been used for stabilization of different PEs which were shown to be effective carriers for food bioactives, providing improved stability and functionality. This article covers the recent advances in various PEs stabilized by prolamin particles as innovative carriers for bioactive ingredients. Strategies applied for fabrication of prolamin particles and prolamin-based carriers are discussed. Emerging techno-functional applications of prolamin-based PEs and possible challenges are also highlighted.

Redox-Responsive Nanopesticides Based on Natural Polymers for Environmentally Safe Delivery of Pesticides with Enhanced Foliar Dispersion and Washout Resistance

Based on the modified cross-linking of the degradable natural polymers chitosan oligosaccharides (COS) and gelatin (GEL) via introduction of a functional bridge 3,3'-dithiodipropionic acid, this study constructed an environmentally responsive dinotefuran (DNF) delivery system (DNF@COS-SS-GEL). The introduction of the disulfide bond (-S-S-) endowed DNF@COS-SS-GEL with redox-responsive properties, allowing for the rapid release of pesticides when stimulated by glutathione (GSH) in the simulated insect. Compared with commercial DNF suspension concentrate (DNF-SC), DNF@COS-SS-GEL showed superior wet spreading and retention performance on cabbage leaves with a reduced contact angle (57°) at 180 s and 4-fold increased retention capacity after rainfall washout. Nanoencapsulation effectively improved the UV-photostability with only a 31.4% decomposition rate of DNF@COS-SS-GEL at 96 h. The small scale and large specific surface area resulted in excellent uptake and transportation properties in plants as well as higher bioactivity against Plutella xylostella larvae. This study will help promote sustainable agricultural development by reducing environmental pollution through improved pesticide utilization.

Facile Preparation of Silica/Tannic Acid/Zein Microcapsules Templated from Non-Aqueous Pickering Emulsions and their Application in Cargo Protection

Microcapsules have attracted significant attention in academia and industry due to their unique properties for protecting and controlling the release of active substances. However, based on water-insoluble biopolymers, developing a straightforward approach to prepare microcapsules with improved biocompatibility and functional shells remains a great challenge. In this study, zein, a water-insoluble protein, is employed to prepare robust microcapsules facilely using oil-in-aqueous ethanol Pickering emulsions as templates. First, the emulsion template is stabilized by hydrophobic silica nanoparticles with in situ surface modification of tannic acid. The zein is then precipitated at the interface in a controlled manner using antisolvent approach to obtain silica/tannic acid/zein (STZ) microcapsules. It is found that the concentration of zein and the presence of tannic acid played a significant role in the formation of STZ microcapsules with well-defined morphology and a robust shell. The uniform deposition of zein on the surface of template droplets is facilitated by the interactions between tannic acid and zein via hydrogen bond and electrostatic force. Finally, the resulting STZ microcapsules showed super resistance to ultraviolet (UV) radiation and high temperature for the unstable, lipophilic, and active substance of β-carotene.

Pickering emulsion co-delivery system: Stimuli-responsive biomineralized particles act as particulate emulsifiers and bioactive carriers

Pickering emulsions provide a promising platform for the efficient delivery of bioactive. However, co-delivery of fragile bioactives with different physicochemical properties for comprehensive effects still faces practical challenges due to the limited protection for bioactives and the lack of stimuli-responsive property for on-demand release. Herein, a stimuli-responsive co-delivery system is developed based on biomineralized particles stabilized Pickering emulsions. In this tailor co-delivery system, hydrophilic bioactive (pepsin) with the fragile structure is encapsulated and immobilized by biomineralization, the obtained biomineralized particles (PPS@CaCO3) are further utilized as emulsifiers to form O/W Pickering emulsions, in which the hydrophobic oxidizable bioactive (curcumin) is stably trapped into the dispersed phase. The results show that two bioactives are successfully co-encapsulated in Pickering emulsions, and benefiting from the protection capacities of biomineralization and Pickering emulsions, the activity of pepsin and curcumin shows a 7.33-fold and 144.83-fold enhancement compared to the free state, respectively. Moreover, In vitro study demonstrates that Pickering emulsions enable to co-release of two bioactives with high activity retention by the acid-induced hydrolyzation of biomineralized particles. This work provides a powerful stimuli-responsive platform for the co-delivery of multiple bioactive compounds, enabling high activity of bioactives for the comprehensive health effects.

Nanoparticle-Empowered Core-Shell Microcapsules: From Architecture Design to Fabrication and Functions

Compartmentalization is a powerful concept to integrate multiscale components with diverse functionalities into miniature architectures. Inspired by evolution-optimized cell compartments, synthetic core-shell capsules enable storage of actives and on-demand delivery of programmed functions, driving scientific progress across various fields including adaptive materials, sustainable electronics, soft robotics, and precision medicine. To simultaneously maximize structural stability and environmental sensitivity, which are the two most critical characteristics dictating performance, diverse nanoparticles are incorporated into microcapsules with a dense shell and a liquid core. Recent studies have revealed that these nano-additives not only enhance the intrinsic properties of capsules including mechanical robustness, optical behaviors, and thermal conductivity, but also empower dynamic features such as triggered release, deformable structures, and fueled mobility. In this review, the physicochemical principles that govern nanoparticle assembly during microencapsulation are examined in detail and the architecture-controlled functionalities are outlined. Through the analysis of how each primary method implants nanoparticles into microcapsules, their distinct spatial organizations within the core-shell structures are highlighted. Following a detailed discussion of the specialized functions enabled by specific nanoparticles, the vision of the required fundamental insights and experimental studies for this class of microcarriers to fulfill its potential are sketched.

Microencapsulation of multi-component traditional Chinese herbs extracts and its application to traditional Chinese medicines loaded textiles

Extracts of traditional Chinese herbs (TCH) contain a variety of anti-allergic, anti-inflammatory and other bioactive factors. However, the defect of easy degradation or loss of active ingredients limits its application in traditional Chinese medicines (TCM) loaded textiles. In this work, TCH extracts containing different active ingredients were innovatively proposed as the core material of microcapsules. The feasibility of microencapsulation of multi-component TCH extracts in the essential oil state was initially demonstrated. Polyacrylate was also used as a binder to load the microcapsules onto the fabric to improve the durability and wash resistance of the treated fabric. Modeling the oil release of microcapsules for controlled release under different conditions may provide new possible uses for the materials. Results show that the constructed microcapsule has a smooth surface without depression and can be continuously released for over 30 days. The release behavior of microcapsules follows different release mechanisms and can be modulated by temperature and water molecules. The incorporation of microcapsules and polyacrylate does not significantly change the fabric's air permeability, water vapor transmission and hydrophilicity. The washing durability and friction properties of the microcapsule-based fabric are greatly improved, and it can withstand 30 washing tests and 200 friction tests. Moreover, the results of methyl thiazolyl tetrazolium (MTT) release assay using human dermal papilla cells (HDP) as an in vitro template confirm that the microcapsule has no toxic effects on human cells. Therefore, the successful microencapsulation of multi-component TCH extracts indicates their potential application in the field of TCM-loaded textiles.

Body temperature responsive capsules templated from Pickering emulsion for thermally triggered release of β-carotene

In recent years, functional foods with lipophilic nutraceutical ingredients are gaining more and more attention because of its potential healthy and commercial value, and developing of various bioderived food-grade particles for use in fabrication of Pickering emulsion has attracted great attentions. Herein, the bio-originated sodium caseinate-lysozyme (Cas-Lyz) complex particles were firstly designed to be used as a novel interfacial emulsifier for Pickering emulsions. Pickering emulsions of various food oils were all successfully stabilized by the Cas-Lyz particles without addition of any synthetic surfactants, while the fluorescence microscopy and SEM characterizations clearly evidenced Cas-Lyz particles were attached on the surface of emulsion droplets. Additionally, the Cas-Lyz particles stabilized emulsion can also be used to encapsulate the β-carotene-loaded soybean oil, suggestion a potential method to carry lipophilic bioactive ingredients in an aqueous formulation for food, cosmetic and medical industry. At last, we present a Pickering emulsion strategy that utilizes biocompatible, edible and body temperature-responsive lard oil as the core material in microcapsules, which can achieve hermetic sealing and physiological temperature-triggered release of model nutraceutical ingredient (β-carotene).

Pickering emulsion templated proteinaceous microparticles as glutathione-responsive carriers for endocytosis in tumor cells

The use of glucose oxidase (GOx) to disrupt glucose supply has been identified as a promising strategy in cancer starvation therapy. However, independent delivery of GOx is prone to degradation upon exposure to biological conditions and may cause damage to blood vessels and normal organs during transportation. Although some carriers can protect GOx from the surrounding environment, the harsh preparation conditions may compromise its activity. Moreover, the commonly used materials often exhibit poor biocompatibility and possess certain cytotoxicity. To address this issue, we developed a gentle and efficient method based on Pickering emulsion templates to synthesize protein-based microparticles using zein as the matrix material. These microparticles have high stability and can be tailored to efficiently encapsulate biomolecules while preserving their activity. Moreover, the zein-based microparticles can be triggered to release biomolecules in tumor cells under high glutathione levels, demonstrating excellent responsiveness, biocompatibility, and low cytotoxicity. Additionally, when loaded with GOx, these protein-based microparticles effectively deprive tumor cells of nutrients and induce apoptosis by generating high levels of H2O2, thereby exhibiting enhanced anticancer properties.

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.

Panax Notoginseng polysaccharide stabilized gel-like Pickering emulsions: Stability and mechanism

In this work, the polysaccharide from Panax Notoginseng (SPNP), a traditional herb in China, was used as an outstanding Pickering stabilizer to fabricate Pickering emulsions. The SPNP was characterized to be a porous network structure with a rough surface surrounded by some nanoparticles. Rheological measurement of the obtained Pickering emulsions demonstrated the formation of emulsion gels. Moreover, the emulsions exhibited excellent storage (14 days), pH (1.0-11.0), ionic strength (0-500 mM), and temperature (4-50 °C) stabilities. In addition, the Pickering emulsions showed a freeze-thaw stability, which is beneficial in food, cosmetic or biomedical applications when they may require freezing for storage and melting before use. Confocal laser scanning microscope (CLSM) and cryo-scanning electron microscopy (cryo-SEM) results showed that SPNPs effectively adsorbed at the oil-water interface by forming a compact three-dimensional (3D) network structure and multilayer anchoring on the surface of the emulsion droplets, thus inhibiting the droplet coalescence and flocculation. This study provides a kind of Pickering emulsions applicable in food, biomedical and cosmetic industries.