Preparation of core-shell CaCO3 capsules via Pickering emulsion templates

Advancing Inorganic Microcapsule Fabrication through Frozen-Assisted Interfacial Reactions Utilizing Liquid Marbles

Inorganic microcapsules (IMs) have gained significant attention as versatile platforms for delivering functional agents in various fields. Traditional template-dependent methods employing hard templates often involve complex and harsh template removal processes. Achieving IMs with diverse composition and structure remains challenging with current preparation strategies. Therefore, in this work, we have for the first time demonstrated an extremely facile and efficient liquid-marbles-based template approach for fabricating pure inorganic microcapsules via interfacial reaction in a mild aqueous solution. The water-water reaction interface is created by changing the wettability of the liquid marble (LM) surface through the icing-melting process. The composition and function of the inorganic shell could be easily adjusted by varying the inorganic reagent species of the interfacial reaction, the hydrophobic particle of the shell, and the reaction environment according to the specific requirements of the application field. Such an approach provides a flexible platform for material preparation.

Pickering Emulsions Based in Inorganic Solid Particles: From Product Development to Food Applications

Pickering emulsions (PEs) have attracted attention in different fields, such as food, pharmaceuticals and cosmetics, mainly due to their good physical stability. PEs are a promising strategy to develop functional products since the particles’ oil and water phases can act as carriers of active compounds, providing multiple combinations potentiating synergistic effects. Moreover, they can answer the sustainable and green chemistry issues arising from using conventional emulsifier-based systems. In this context, this review focuses on the applicability of safe inorganic solid particles as emulsion stabilisers, discussing the main stabilisation mechanisms of oil–water interfaces. In particular, it provides evidence for hydroxyapatite (HAp) particles as Pickering stabilisers, discussing the latest advances. The main technologies used to produce PEs are also presented. From an industrial perspective, an effort was made to list new productive technologies at the laboratory scale and discuss their feasibility for scale-up. Finally, the advantages and potential applications of PEs in the food industry are also described. Overall, this review gathers recent developments in the formulation, production and properties of food-grade PEs based on safe inorganic solid particles.

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.

Pickering emulsions as an alternative to traditional polymers: trends and applications

Pickering emulsions have gained increasing interest because of their unique features, including easy preparation and stability. In contrast to classical emulsions, in Pickering emulsions, the stabilisers are solid micro/nanoparticles that accumulate on the surfaces of liquid phases. In addition to their stability, Pickering emulsions are less toxic and responsive to external stimuli, which make them versatile material that can be flexibly designed for specific applications, e.g., catalysis, pharmaceuticals and new materials. The potential toxicity and adverse impact on the environment of classic emulsions is related to the extractable nature of the water emulsifier. The impacts of some emulsifiers are related to not only their chemical natures but also their stabilities; after base or acid hydrolysis, some emulsifiers can be turned into sulphates and fatty alcohols, which are dangerous to aquatic life. In this paper, recent research on Pickering emulsion preparations is reviewed, with a focus on styrene as one of the main emulsion components. Moreover, the effects of the particle type and morphology and the critical parameters of the emulsion production process on emulsion properties and applications are discussed. Furthermore, the current and prospective applications of Pickering emulsion, such as in lithium-ion batteries and new vaccines, are presented.

Stimulus responsive microcapsules and their aromatic applications

Fragrances and essential oils are promising for a wide range of applications due to their pleasant odors and diverse effects. However, direct addition to consumer products has the disadvantages of short retention time and easy deterioration of odor. At the same time, releasing a large amount of odor in a short time may be an unpleasant experience, which severely limits the practical application of aromatic substances. Microencapsulation perfectly solves these problems. Stimuli-responsive microcapsules, which combine environmental stimulation with microencapsulation, can not only effectively prevent the rapid decomposition and evaporation of aroma components, but also realize the "on-off" intelligent release of aroma substances to environmental changes, which have great promise in the field of fragrances. In this review, the application of stimuli-responsive microcapsules in fragrances is highlighted. Firstly, various encapsulation materials used to prepare stimuli-responsive aromatic microcapsules are described, mainly including some natural polymers, synthetic polymers, and inorganic materials. Subsequently, there is a detailed description of the common release mechanisms of stimuli-responsive aromatic microcapsules are described in detail. Finally, the application and future research directions are given for stimuli-responsive aromatic microcapsules in new textiles, food, paper, and leather.

Progress in Colloid Delivery Systems for Protection and Delivery of Phenolic Bioactive Compounds: Two Study Cases—Hydroxytyrosol and Curcumin

Insufficient intake of beneficial food components into the human body is a major issue for many people. Among the strategies proposed to overcome this complication, colloid systems have been proven to offer successful solutions in many cases. The scientific community agrees that the production of colloid delivery systems is a good way to adequately protect and deliver nutritional components. In this review, we present the recent advances on bioactive phenolic compounds delivery mediated by colloid systems. As we are aware that this field is constantly evolving, we have focused our attention on the progress made in recent years in this specific field. To achieve this goal, structural and dynamic aspects of different colloid delivery systems, and the various interactions with two bioactive constituents, are presented and discussed. The choice of the appropriate delivery system for a given molecule depends on whether the drug is incorporated in an aqueous or hydrophobic environment. With this in mind, the aim of this evaluation was focused on two case studies, one representative of hydrophobic phenolic compounds and the other of hydrophilic ones. In particular, hydroxytyrosol was selected as a bioactive phenol with a hydrophilic character, while curcumin was selected as typical representative hydrophobic molecules.

Preparation of Multicore Colloidosomes: Nanoparticle-Assembled Capsules with Adjustable Size, Internal Structure, and Functionalities for Oil Encapsulation

Colloidosomes, also known as Pickering emulsion capsules, have attracted attention for encapsulation of hydrophilic and hydrophobic actives. However, current preparation methods are limited to single core structures and require the use of modified/engineered nanoparticles for forming the shell. Here, we report a fast, simple, and versatile method for producing multi-oil core silica colloidosomes via salt-driven assembly of purely hydrophilic commercial nanoparticles dispersed within an oil-in-water-in-oil (O/W/O) double emulsion template. The internal structure and overall diameter of the capsules can be adjusted by altering the primary and secondary emulsification conditions. With this approach, 7-35 μm diameter multicore colloidosomes containing 0.9-4.2 μm large oil cores were produced. The capsules can easily be functionalized depending on the type of nanoparticles used in the preparation process. Here, metal oxide nanoparticles, such as Fe₃O₄, TiO₂, and ZnO, were successfully incorporated within the structure, conferring specific functional properties (i.e., magnetism and photocatalysis) to the final microcapsules. These capsules can also be ruptured by using ultrasound, enabling easy access to the internal core environments. Therefore, we believe this work offers a promising approach for producing multicore colloidosomes with adjustable structure and functionalities for the encapsulation of hydrophobic actives.

Incorporation of nanogels within calcite single crystals for the storage, protection and controlled release of active compounds

Nanocarriers have tremendous potential for the encapsulation, storage and delivery of active compounds. However, current formulations often employ open structures that achieve efficient loading of active agents, but that suffer undesired leakage and instability of the payloads over time. Here, a straightforward strategy that overcomes these issues is presented, in which protein nanogels are encapsulated within single crystals of calcite (CaCO3). Demonstrating our approach with bovine serum albumin (BSA) nanogels loaded with (bio)active compounds, including doxorubicin (a chemotherapeutic drug) and lysozyme (an antibacterial enzyme), we show that these nanogels can be occluded within calcite host crystals at levels of up to 45 vol%. Encapsulated within the dense mineral, the active compounds are stable against harsh conditions such as high temperature and pH, and controlled release can be triggered by a simple reduction of the pH. Comparisons with analogous systems - amorphous calcium carbonate, mesoporous vaterite (CaCO3) polycrystals, and calcite crystals containing polymer vesicles - demonstrate the superior encapsulation performance of the nanogel/calcite system. This opens the door to encapsulating a broad range of existing nanocarrier systems within single crystal hosts for the efficient storage, transport and controlled release of various active guest species.

Stabilization and Release of Palm Tocotrienol Emulsion Fabricated Using pH-Sensitive Calcium Carbonate

Calcium carbonate (CaCO3) has been utilized as a pH-responsive component in various products. In this present work, palm tocotrienols-rich fraction (TRF) was successfully entrapped in a self-assembled oil-in-water (O/W) emulsion system by using CaCO3 as the stabilizer. The emulsion droplet size, viscosity and tocotrienols entrapment efficiency (EE) were strongly affected by varying the processing (homogenization speed and time) and formulation (CaCO3 and TRF concentrations) parameters. Our findings indicated that the combination of 5000 rpm homogenization speed, 15 min homogenization time, 0.75% CaCO3 concentration and 2% TRF concentration resulted in a high EE of tocotrienols (92.59-99.16%) and small droplet size (18.83 ± 1.36 µm). The resulting emulsion system readily released the entrapped tocotrienols across the pH range tested (pH 1-9); with relatively the highest release observed at pH 3. The current study presents a potential pH-sensitive emulsion system for the entrapment and delivery of palm tocotrienols.

Textured Microcapsules through Crystallization

This work demonstrates the fabrication of surface-textured microcapsules formed from emulsion droplets, which are stabilized by an interlocking mesh of needle-like crystals. Crystals of the small-organic-compound decane-1,10-bis(cyclohexyl carbamate) are formed within the geometric confinement of the droplets, through precipitation from a binary-solvent-dispersed phase. This binary mixture consists of a volatile solvent and nonvolatile carrier oil. Crystallization is facilitated upon supersaturation due to evaporation of the volatile solvent. Microcapsule diameter can be easily tuned using microfluidics. This approach also proves to be scalable when using conventional mixers, yielding spikey microcapsules with diameters in the range of 10-50 μm. It is highlighted that the capsule shape can be molded and arrested by jamming using recrystallization in geometric confinement. Moreover, it is shown that these textured microcapsules show a promising enhanced deposition onto a range of fabric fibers.

Carbonate biomineralization differentially induced by two psychrophilic Pseudomonas psychrophila strains isolated from an alpine travertine landform

Besides geography and climate, biological factors play an important role in shaping travertine landforms, but the biochemical mechanisms of microbial processes in travertine formation have been rarely studied. Two psychrophilic bacterial strains, A20-18 and B21-3 of Pseudomonas psychrophila, isolated from travertine pools of Huanglong, a typical alpine travertine landform, were investigated for their roles in calcium carbonate mineralization, including the deposition process and products. X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy were used to characterize the crystal phase and morphology of CaCO₃ precipitation. The results showed that there were no significant differences between the two strains in CaCO₃ deposition rate. Extracellular polymeric substances (EPS)-free cells significantly inhibited calcification, compared with a control. Irregular crystals and polyhedral structures are common to all treatments using the two strains. These complex polycrystals were the result of the synergistic effect of homogeneous nucleation and heterogeneous nucleation. EPS and cells of strain B21-3 formed ring-like structures of calcium carbonate, which was possibly from the amphiphilic polymer forming a circular arrangement in water. These results are significant for understanding the microbial factor in Huanglong travertine deposition and providing new insights into the morphological control of the biomineralization mechanism at low temperatures.

Calcium carbonate crystals induced by two Pseudomonas psychrophila strains and their organic compounds were studied.

Liquid–Solid Core-Shell Microcapsules of Calcium Carbonate Coated Emulsions and Liposomes

Micron-sized core-shell particles consisting of a calcium carbonate (CaCO3) mineral shell and a fluidic core were generated using a biomimetic approach, for the purpose of use as biodegradable microcapsules for release of active agents. Dinoflagellate cysts, unicellular organisms which deposit a protective hard mineral shell around their soft and fluidic cellular interior, served as our inspiration. Using the biomimetic polymer-induced liquid-precursor (PILP) mineralization process, calcium carbonate coatings were deposited on charged emulsion droplets and liposomes. Light microscopy, scanning electron microscopy, polarized light microscopy, X-ray diffraction, and confocal fluorescence microscopy were used to demonstrate that smooth CaCO3 mineral coatings can be deposited onto the high curvature surfaces of emulsions and liposomes to yield micron-sized microcapsules for the effective entrapment of both hydrophobic and hydrophilic active agents. These biodegradable and biocompatible CaCO3 microcapsules are novel systems for producing a powdered form of fluid-containing capsules for storage and transport of pharma/chemical agents. They may be used in lieu of, or in conjunction with, existing microcapsule delivery approaches, as well as providing a convenient foundation for which polymeric coatings could be further applied, allowing for more complex targeting and/or chemical-release control.

Pickering emulsion approach for fabrication of waterborne cross-linkable polydimethylsiloxane coatings with high mechanical performance

HYPOTHESIS

The Pickering emulsion approach has been frequently employed to fabricate various emulsions. However, the direct formation of cross-linked polymer films from Pickering emulsions and double functions (emulsified and mechanical reinforcement) of Pickering agents have not been sufficiently reported.

EXPERIMENTS

Fumed silica was co-modified with vinyltrimethoxysilane (VTMS) and hexamethyl disilylamine (HMDS) and was further adopted to emulsify vinyl or hydrogen dimethicone. The as-obtained Pickering emulsions were mixed with Karstedt catalyst capsules to produce one-component waterborne cross-linkable polydimethylsiloxane (PDMS) coatings that were subsequently transformed into elastic films after drying at ambient temperature.

FINDINGS

The co-modification of fumed silica with VTMS/HMDS is shown to balance the Pickering emulsion effect and film-forming ability of the coatings. Greater amounts of grafted VTMS/HMDS or higher modified silica dosages demonstrated better Pickering emulsion effects. Nevertheless, because Pickering agents hinder the coalescence of silicone oil droplets, the appropriate modified silica concentration is crucial for achieving the highest cross-link density and thus the highest mechanical strength. The grafted CC groups can endow the modified silica with hydrosilylation reactivity and can thus additionally contribute to the mechanical performance of PDMS film. In addition, the Pickering emulsion approach is shown to be superior to the traditional emulsion approach for acquiring waterborne coatings with high mechanical performance.

Slow-Release and Nontoxic Pickering Emulsion Platform for Antimicrobial Peptide

The resistance in microorganisms against many conventional antibiotics has become a serious global health problem. However, antibacterial drug delivery materials are still limited in toxicity, short efficacy and reducing inflammation. The novel and natural Pickering emulsions stabilized by antimicrobial peptide nanoparticles were tested as promising platforms to control bacterial resistance development. The parasin I interacted or conjugated with lecithin or chitosan and formed nanoparticles encapsulated by Pickering emulsion. The protonation and deprotonation of amino groups in chitosan and parasin I resulted in nanoparticles in different aggregate states and changed emulsion stability. Moreover, the Pickering emulsion could induce severe bacterial agglomeration on both Gram-positive and Gram-negative bacteria than parasin I through the membrane disintegration mechanism. Furthermore, the Pickering emulsion could alleviate the cytotoxicity of human liver cells and hemolytic activity in rat blood cells. In combination with the lack of acute cytotoxicity in Kunming mice and milder, more effective anti-inflammatory effect in peritonitis demonstrated for these Pickering emulsions, especially chitosan peptide-embedded nanoparticles Pickering emulsion, a potential role in combating multidrug resistant bacteria in biomedical applications.

Synthesis of Methyl-Capped TiO2-SiO2 Janus Pickering Emulsifiers for Selective Photodegradation of Water-Soluble Dyes

Recently, Pickering emulsion stabilized by Janus particles has received considerable attention for interfacial reactions and droplet manipulation. However, its potential interests have been rarely explored because of the difficulties in designing and fabricating Janus particles for Pickering emulsion with suitable applications. Also, photocatalytic materials are scarcely applied as emulsifiers in Pickering emulsions because of their photogenerated hydrophilicity. This work reports the synthesis of methyl-capped Janus TiO₂-SiO₂ particles (MJTSs), which can be used as a novel emulsifier and photocatalyst simultaneously. The MJTSs, composed of an anatase TiO₂ sphere and silica rod, are prepared by inverse emulsion-based step-by-step growth. We demonstrate that the Pickering emulsion stabilized by MJTSs represents extraordinary ability of emulsification, excellent stability, and tunable emulsion type (water in oil or oil in water). In addition, the MJTSs exhibit photocatalytic activity in decomposition of pollutants in the water phase while maintaining the stability of the Pickering emulsion.

Gelatin Hydrolysate Hybrid Nanoparticles as Soft Edible Pickering Stabilizers for Oil-In-Water Emulsions

The aim of this study was to fabricate edible gelatin enzymic digest (GED) based gel particles that can stabilize oil-in-water (O/W) microemulsions. The gel particles were generated by covalent crosslinking, with genipin, the individual protein molecules within tannic acid-induced gelatin hydrolysate (GED-TA) particles. The ability of the genipin-treated GED-TA (GP-GED-TA) to stabilize emulsions was evaluated by Turbiscan analysis and droplet-size changes. For comparison, gelatin hydrolysate (GE) and tannic acid-induced gelatin hydrolysate particles (GED-TA) were used as controls. The mean diameters of GED, GED-TA, and GP-GED-TA particles were 0.68 ± 0.1 nm, 66.2 ± 8.4 nm, and 66.9 ± 7.2 nm, respectively. Nanomechanic analysis using atomic force microscopy(AFM) indicated the average Young’s modulu of the GP-GED-TA particles was 760.8 ± 112.0 Mpa, indicating the GP-GED-TA were soft particles. The Turbiscan stability indexes (lower values indicate a more stable emulsion) of the emulsions stabilized with GED, GED-TA, and GP-GED-TA, after storage for three days, were 28.6 ± 1.5, 19.3 ± 4.8, and 4.4 ± 1.3, respectively. After one, or 60 days of storage, the volume-weighted mean diameters (D_[4,3]) of oil droplets stabilized by GP-GED-TA were 1.19 ± 0.11 μm and 1.18 ± 0.1 µm, respectively. The D_[4,3] of oil droplets stabilized by GED-TA, however, increased from 108.3 ± 5.1 μm to 164.3 ± 19.1 μm during the storage. Overall, the GP-GED-TA gel particles have considerable potential for stabilization of O/W emulsions in food products.

Natural Shape-Retaining Microcapsules With Shells Made of Chitosan-Coated Colloidal Lignin Particles

Thin film coating of charged nanoparticles with oppositely charged polymers is an efficient and straightforward way for surface modification, but synthetic polyelectrolytes should be replaced by abundant biopolymers. In this study a thin film of chitosan was adsorbed onto colloidal lignin particles (CLPs) that were then systematically studied for olive oil stabilization with an objective to develop shape-retaining microcapsules that comprised of only renewable biomaterials. Full surface coverage was achieved with merely 5 wt% of chitosan relative to the dry weight of CLPs, reversing their surface charge from negative to positive. Such modification rendered the chitosan-coated particles excellent stabilizers for forming Pickering emulsions with olive oil. The emulsion droplets could be further stabilized by sodium triphosphate that provided ionic intra- and inter-particle cross-linking of the chitosan corona on the CLPs. Following the optimum conditions, the non-cross-linked microcapsules exhibited a strong stability against coalescence and the electrostatically stabilized ones additionally retained their shape upon drying and rewetting. Non-cross-linked microcapsules were used to demonstrate encapsulation and rapid release of ciprofloxacin as a model lipophilic drug in aqueous media. Overall, the combination of antimicrobial chitosan and antioxidative lignin nanoparticles hold unprecedented opportunities as biocompatible and biodegradable materials for controlled drug delivery.

Natural Shape-Retaining Microcapsules With Shells Made of Chitosan-Coated Colloidal Lignin Particles

Thin film coating of charged nanoparticles with oppositely charged polymers is an efficient and straightforward way for surface modification, but synthetic polyelectrolytes should be replaced by abundant biopolymers. In this study a thin film of chitosan was adsorbed onto colloidal lignin particles (CLPs) that were then systematically studied for olive oil stabilization with an objective to develop shape-retaining microcapsules that comprised of only renewable biomaterials. Full surface coverage was achieved with merely 5 wt% of chitosan relative to the dry weight of CLPs, reversing their surface charge from negative to positive. Such modification rendered the chitosan-coated particles excellent stabilizers for forming Pickering emulsions with olive oil. The emulsion droplets could be further stabilized by sodium triphosphate that provided ionic intra- and inter-particle cross-linking of the chitosan corona on the CLPs. Following the optimum conditions, the non-cross-linked microcapsules exhibited a strong stability against coalescence and the electrostatically stabilized ones additionally retained their shape upon drying and rewetting. Non-cross-linked microcapsules were used to demonstrate encapsulation and rapid release of ciprofloxacin as a model lipophilic drug in aqueous media. Overall, the combination of antimicrobial chitosan and antioxidative lignin nanoparticles hold unprecedented opportunities as biocompatible and biodegradable materials for controlled drug delivery.

Fabrication of Hybrid Capsules via CaCO3 Crystallization on Degradable Coacervate Droplets

Organic-inorganic CaCO₃ capsules were prepared by crystallization of CaCO₃ on Pickering emulsion prepared using coacervate droplets made from thermoresponsive and degradable poly(2-methylene-1,3-dioxepane- co-2-hydroxyethyl acrylate) (poly(MDO- co-HEA)) in sole aqueous medium. The diameters of CaCO₃-based Pickering emulsion could be controlled by varying several parameters: diameter of CaCO₃ powders, initial polymer concentration, and copolymer composition. The CaCO₃ Pickering emulsion was able to load low-molecular-weight hydrophobic substances at temperatures above the lower critical solution temperature (LCST) due to formation of polymer-concentrated phases, i.e., coacervate droplets. The diameter of CaCO₃ capsules prepared by crystallization also depended on the diameter of the CaCO₃ Pickering emulsion. The CaCO₃ shell was composed of calcite-type crystals, the most stable polymorph among known CaCO₃ crystals. The facially prepared CaCO₃ capsules are valuable for use in functional biomaterials, such as drug delivery carriers and cell culture scaffolds for noninvasive bone-regenerative medicine.

Preparation and application of flavor and fragrance capsules

The preparation methods and applications of flavor and fragrance capsules based on polymeric, inorganic and polymeric–inorganic wall materials are summarized.

Novel polystyrene sulfonate–silica microspheres as a carrier of a water soluble inorganic salt (KCl) for its sustained release, via a dual-release mechanism

Polystyrene sulfonate and silica microspheres with potassium chloride encapsulated show a dual-release mechanism of K⁺ in an aqueous environment.

Bifunctional ultraviolet/ultrasound responsive composite TiO2/polyelectrolyte microcapsules

Designing and fabricating multifunctional microcapsules are of considerable interest in both academic and industrial research aspects. This work reports an innovative approach to fabricate composite capsules with high UV and ultrasound responsive functionalities that can be used as external triggers for controlled release, yet with enhanced mechanical strength that can make them survive in a harsh environment. Needle-like TiO2 nanoparticles (NPs) were produced in situ into layer-by-layer (LbL) polyelectrolyte (PE) shells through the hydrolysis of titanium butoxide (TIBO). These rigid TiO2 NPs yielded the formed capsules with excellent mechanical strength, showing a free standing structure. A possible mechanism is proposed for the special morphology formation of the TiO2 NPs and their reinforcing effects. Synergistically, their response to UV and ultrasound was visualized via SEM, with the results showing an irreversible shell rapture upon exposure to either UV or ultrasound irradiation. As expected, the release studies revealed that the dextran release from the TiO2/PE capsules was both UV-dependent and ultrasound-dependent. Besides, the biocompatibility of the capsules with the incorporation of amorphous TiO2 NPs was confirmed by an MTT assay experiment. All these pieces of evidence suggested a considerable potential medicinal application of TiO2/PE capsules for controlled drug delivery.

Inorganic/organic hybrid microcapsules: melamine formaldehyde-coated Laponite-based Pickering emulsions

A facile synthesis route to novel inorganic/organic hybrid microcapsules is reported. Laponite nanoparticles are surface-modified via electrostatic adsorption of Magnafloc, an amine-based polyelectrolyte allowing the formation of stable oil-in-water Pickering emulsions. Hybrid microcapsules can be subsequently prepared by coating these Pickering emulsion precursors with dense melamine formaldehyde (MF) shells. Employing a water-soluble polymeric stabiliser, poly(acrylamide-co-sodium acrylate) leads to stable hybrid microcapsules that survive an alcohol challenge and the ultrahigh vacuum conditions required for SEM studies. Unfortunately, the presence of this copolymer also leads to secondary nucleation of excess MF latex particles in the aqueous continuous phase. However, since the Magnafloc is utilised at submonolayer coverage when coating the Laponite particles, the nascent cationic MF nanoparticles can deposit onto anionic surface sites on the Laponite, which removes the requirement for the poly(acrylamide-co-sodium acrylate) component. Following this electrostatic adsorption, the secondary amine groups on the Magnafloc chains can react with the MF, leading to highly robust cross-linked MF shells. The absence of the copolymer leads to minimal secondary nucleation of MF latex particles, ensuring more efficient deposition at the surface of the emulsion droplets. However, the MF shells appear to become more brittle, as SEM studies reveal cracking on addition of ethanol.

Inorganic microcapsules mineralized at the interface of water droplets in ethanol solution and their application as drug carriers

A crystallization – dissolution – interface mineralization (CDIM) method was reported to synthesize pH biocompatible and sensitive calcium carbonate (CaC) and calcium phosphate (CaP) inorganic microcapsules with potential on drug delivery.

Templated synthesis of nanostructured materials

Templating is one of the most important techniques for the controlled synthesis of nanostructured materials. This powerful tool uses a pre-existing guide with desired nanoscale features to direct the formation of nanomaterials into forms that are otherwise difficult to obtain. As a result, templated synthesis is capable of producing nanostructures with unique structures, morphologies and properties. In this review, we summarize the general principles of templated synthesis and cover recent developments in this area. As a wide variety of synthesis techniques are utilized to produce nanomaterials using template-based methods, the discussion is organized around the various types of common templates. We examine the use of both physical and chemical hard colloidal templates, soft templates, and other non-colloidal templates, followed by our perspective on the state of the field and potential future directions.