Stimulus responsive microcapsules and their aromatic applications

Dual-mode regulatory cross-linked chitosan nanocapsules for pH-responsive and controllable sustained release in textiles

Stimuli-responsive microcapsules enable controlled release of core materials in response to environmental triggers, offering greater application potential than conventional systems, particularly in smart textiles and drug delivery. However, challenges persist in enhancing encapsulation efficiency, stability, and achieving sustained, controllable release under specific environmental conditions. In this study, dual cross-linked chitosan nanocapsules (DC) encapsulating Lavender essential oils were synthesized through a combination of electrostatic interactions between chitosan and sodium tripolyphosphate and Schiff base reactions between chitosan and glutaraldehyde. The resulting nanocapsules, approximately 50 nm in size, exhibited an encapsulation efficiency of 93.18 % and a loading capacity of 14.54 %. They demonstrated sustained release, retaining 77.11 % of their content after 36 days at room temperature, as well as notable thermal stability. Additionally, under alkaline conditions (pH = 10), the nanocapsules showed enhanced release rates, confirming their pH-responsive behavior. When loaded onto cotton fabrics via electrostatic adsorption, the functionalized fabrics exhibited slow-release properties. These findings highlight the potential of dual cross-linked chitosan nanocapsules as multifunctional and innovative delivery systems for diverse applications.

Biochar-based composite microspheres embedded with zero-valent iron and soybean oil efficiently remove 1,1,1-trichloroethane and reshape microbial community in simulated groundwater

The increasing contamination of global groundwater by organic chlorine solvents poses a major threat to environmental and human health; however, there is a lack of structurally stable and effective materials for removing organic chlorine pollutants. In this study, biochar-based composite microspheres embedded with zero-valent iron (ZVI) and soybean oil were prepared and their effects on 1,1,1-trichloroethane (1,1,1-TCA) removal and the microbial community in simulated groundwater system were investigated. The composite microspheres achieved a remarkable 85.79% removal rate of 1,1,1-TCA after 360 h in groundwater, which was 1.63 times higher than that of ZVI + biochar microspheres (52.69%) and 1.33 times higher than that of soybean oil + biochar microspheres (64.50%). The composite microspheres also significantly reduced the oxidation-reduction potential to - 248.52 mV and maintained a neutral pH range of 6.8-7.2, thereby creating favorable conditions for long-term reductive dechlorination. The surface morphology of the composite was stable during degradation, reflecting its potential for long-term usage. The rich network structure of microspheres and the micropore structure of the biochar were conducive to the capturing of pollutants, safety of microorganisms, and slow release of organic carbon. 16S rDNA sequencing demonstrated that the composite significantly affected the diversity and stability of the microbial community, especially promoting the growth and interaction of dechlorinating and fermentative microorganisms in the groundwater and composite microspheres. The preliminary removal mechanisms included biochar-induced adsorption and ZVI-induced chemical reduction in the early stage and biochemical coupling of dechlorination in the middle and last stages. The biochar-based composite microspheres significantly enhanced the effectiveness and consistency of 1,1,1-TCA removal, potentially being applied to in situ enhanced reductive dechlorination of organochlorine solvents in site groundwater. Moreover, considering the abundant porous structure and easy availability of biochar, it can effectively promote the sustainability and cost-efficiency of the microspheres during application.

Dual cross-linking with tannic acid and transglutaminase improves microcapsule stability and encapsulates lemon essential oil for food preservation

The microencapsulation of essential oils by complex coacervation technology has attracted considerable attention. This paper deals with the preparation of gelatin-chitosan microcapsules through dual cross-linking using transglutaminase (TGase) and tannic acid (TA). Lemon essential oil (LEO) was successfully encapsulated with 82.5 % encapsulation efficiency. Compared to single cross-linking microcapsules (TG), dual cross-linking microcapsules (TG-TA) exhibit superior thermal stability and swell stability. In vitro release studies demonstrated that TG-TA exhibited better controlled-release behavior with a longer duration of action. Meanwhile, the lipid oxidation of TG-TA was 1.45 mg MDA/kg that of control group was 2.23 mg MDA/kg which showed their excellent antioxidant effects. Moreover TG-TA have higher antibacterial rate, more inhibition zone diameters and better effect for preventing the growth of total viable count than TG and LEO. This study has theoretical implications for the use of TG-TA ideal carriers for protecting various active substances, thus facilitating their applications in food preservation.

Progress in the Preparation and Applications of Microcapsules for Protective Coatings Against Corrosion

The annual economic loss caused by corrosion accounts for about 2%~4% of GDP, which exceeds the sum of losses caused by fires, floods, droughts, typhoons, and other disasters. Coating is one of the most effective methods to delay metal corrosion. With the development of technology and the intersection of disciplines, functional microcapsules have been applied to anticorrosive coatings, but microcapsules are still being updated. To understand the application progress of microcapsules in anticorrosive coatings, the future development trend of microcapsules is analyzed. The preparation methods, physical and chemical properties, functional characteristics, and development trends of organic, inorganic, and organic-inorganic hybrid microcapsules are described, respectively, from the perspective of material and molecular characteristics. Simultaneously, the influence of microcapsules of different materials on the properties of organic coatings is proved by examples. In addition, the research status and future development trends of microcapsule composite coating are introduced in detail. Finally, the great advantages of organic-inorganic hybrid microcapsules modified by functional materials based on natural inorganic materials in improving the utilization efficiency of loaded active substances and prolonging the life of coatings are foreseen.

Prodrug Self-Assemblies Based on Plant Volatile Aldehydes with Improved Stability and Antimicrobial Activity Against Plant Pathogens

Plant volatile aldehydes (PVAs) such as cinnamaldehyde (Cin), citral (Cit), citronellal (Citr), and perillaldehyde (Per) have broad-spectrum antimicrobial activity and show great potential in agricultural sustainable production. However, most PVAs not only have very high volatility but also are easily degradable in environment, which seriously restricts their wide application. To address the inherent problems with PVAs, four prodrugs based on PVAs are fabricated by conjugating individually Cin, Cit, Citr, and Per to sodium bisulfite (Sod) through a simple addition reaction and subsequently self-assembled into nanoparticles (prodrug self-assemblies) in aqueous solutions. The results showed that pH of 7 and temperature of 35 °C are the optimal conditions for the formation of the prodrug self-assemblies with the highest self-assembly rates. The prepared prodrug self-assemblies are spherical nanoparticles with average particle sizes of 100-200 nm, almost no volatilization, and high surface activity and stability, and can respond to acidic and redox microenvironments to release PVAs. The prodrug self-assemblies showed synergistic antimicrobial activities against Sclerotinia sclerotiorum and Penicillium digitatum, and good biological safety to plants. Therefore, these findings have important implications for the efficient utilization of PVAs in agriculture, ensuring the safety of the ecological environment and realizing the sustainable development of agriculture.

Hairpin aptamer and ROS-sensitive microcapsule-mediated glycoprotein determination for the prognosis of colorectal cancer

A novel glycoprotein assay was developed by integrating the hairpin aptamer (H-APT)-mediated glycoprotein recognition and the reactive oxygen species-sensitive microcapsule (ROS-MC)-induced signal amplification. The analyzing process begins with the transfer of the target glycoprotein to a chlorin e6 (Ce6)-labeled DNA sequence via H-APT-mediated DNA displacement. Subsequently, the Ce6-labeled DNA was used to induce the disassembly of fluorophore-loaded ROS-MC under 650-nm light irradiation. Leveraging the rapid release of the fluorophore and the high loading capacity of the MC, this glycoprotein assay is capable of quantifying glycoprotein content in native biofluids within 2.5 h, achieving a detection limit of 0.034 ng/mL. We applied this assay to determine the glycoprotein composition in plasma samples of colorectal cancer patients, revealing a significant increase in glycoprotein content for those with a poor prognosis. In summary, we have developed an innovative method for glycoprotein determination that shows potential for clinical translation.

Microstructure induction of quaternary ammonium chitosan microcapsules based on magnetic field and study of their aroma release

Traditional pressure-sensitive microcapsules used in textiles face challenges of insufficient environmental friendliness in the production process and uncontrollable fragrance release. To address this issue, this study utilized quaternary ammonium chitosan and silica as wall materials to develop a magnetic aromatic microcapsule. The microstructure of the microcapsules was controlled by magnetic field induction, and its evolution pattern was investigated. After magnetic field induction, the microcapsules exhibited a trend of evolving from spherical to asymmetrical shapes, accompanied by significant changes in mechanical properties. Asymmetrical microcapsules showed higher adhesion and lower stiffness. When applied to cotton textiles, the cotton textiles treated with asymmetrical microcapsules released 63.40 % of lavender essential oil after 200 friction cycles, representing an 11.3 % improvement in release efficiency compared to regular microcapsules, indicating better mechanical stimulus responsiveness. Additionally, in antibacterial tests, aromatic cotton exhibited a 96.52 % inhibition ratio against Escherichia coli. In summary, this study explores methods to adjust the mechanical properties of microcapsules and the relationship between mechanical properties and microstructure, providing a new approach for functional textiles.

Current Challenges in Microcapsule Designs and Microencapsulation Processes: A Review

Microencapsulation is an advanced methodology for the protection, preservation, and/or delivery of active materials in a wide range of industrial sectors, such as pharmaceuticals, cosmetics, fragrances, paints, coatings, detergents, food products, and agrochemicals. Polymeric materials have been extensively used as microcapsule shells to provide appropriate barrier properties to achieve controlled release of the encapsulated active ingredient. However, significant limitations are associated with such capsules, including undesired leaching and the nonbiodegradable nature of the typically used polymers. In addition, the energy cost of manufacturing microcapsules is an important factor to be considered when designing microcapsule systems and the corresponding production processes. Recent factors linked to UN sustainability goals are modifying how such microencapsulation systems should be designed in pursuit of "ideal" microcapsules that are efficient, safe, cost-effective and environmentally friendly. This review provides an overview of advances in microencapsulation, with emphasis on sustainable microcapsule designs. The key evaluation techniques to assess the biodegradability of microcapsules, in compliance with recently evolving European Union requirements, are also described. Moreover, the most common methodologies for the fabrication of microcapsules are presented within the framework of their energy demand. Recent promising microcapsule designs are also highlighted for their suitability toward meeting current design requirements and stringent regulations, tackling the ongoing challenges, limitations, and opportunities.

Preparation and sustained-release of chitosan-alginate bilayer microcapsules containing aromatic compounds with different functional groups

This study investigated the release of aromatic compounds with distinct functional groups within bilayer microcapsules. Bilayer microcapsules of four distinctive core materials (benzyl alcohol, eugenol, cinnamaldehyde, and benzoic acid) were synthesized via freeze-drying. Chitosan (CS) and sodium alginate (ALG) were used as wall materials. CS concentration, using orthogonal experiments with the loading ratio as a metric. Under optimal conditions, three other types of microcapsules (cinnamic aldehyde, benzoic acid, and benzyl alcohol) were obtained. The four types of microcapsules were characterized using Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscope (TEM), and thermogravimetric analysis (TGA), and their sustained release characteristics were evaluated. The optimal conditions were: CS dosage, 1.2 %; CS-to-eugenol mass ratio, 1:2; and CS-to-ALG mass ratio, 1:1. By comparing the IR spectra of the four types of microcapsules, wall material, and core material, the core materials were revealed to be encapsulated within the wall material. SEM results revealed that the granular protuberances on the surface of the microcapsules were closely aligned and persistent when magnified 2000×. The TEM results indicated that all four microcapsules had a spherical and bilayer structure. The thermal stability and sustained release results showed that the four microcapsules were more resilient and less volatile than the four core materials. The release conformed to first-order kinetics, and the release ratios of the four microcapsules were as follows: benzyl alcohol microcapsules ˃ eugenol microcapsules ˃ cinnamaldehyde microcapsules ˃ benzoic acid microcapsules. The prepared bilayer microcapsules encapsulated four different core materials with good sustained release properties.

Pore engineering of micro/mesoporous nanomaterials for encapsulation, controlled release and variegated applications of essential oils

Essential oils have become increasingly popular in fields of medical, food and agriculture, owing to their strongly antimicrobial, anti-inflammation and antioxidant effects, greatly meeting demand from consumers for healthy and safe natural products. However, the easy volatility and/or chemical instability of active ingredients of essential oils (EAIs) can result in the loss of activity before realizing their functions, which have greatly hindered the widely applications of EAIs. As an emerging trend, micro/mesoporous nanomaterials (MNs) have drawn great attention for encapsulation and controlled release of EAIs, owing to their tunable pore structural characteristics. In this review, we briefly discuss the recent advances of MNs that widely used in the controlled release of EAIs, including zeolites, metal-organic frameworks (MOFs), mesoporous silica nanomaterials (MSNs), and provide a comprehensive summary focusing on the pore engineering strategies of MNs that affect their controlled-release or triggered-release for EAIs, including tailorable pore structure properties (e.g., pore size, pore surface area, pore volume, pore geometry, and framework compositions) and surface properties (surface modification and surface functionalization). Finally, the variegated applications and potential challenges are also given for MNs based delivery strategies for EAIs in the fields of healthcare, food and agriculture. These will provide considerable instructions for the rational design of MNs for controlled release of EAIs.

Encapsulation of Fragrances in Micro- and Nano-Capsules, Polymeric Micelles, and Polymersomes

Fragrances are ubiquitously and extensively used in everyday life and several industrial applications, including perfumes, textiles, laundry formulations, hygiene household products, and food products. However, the intrinsic volatility of these small organic molecules leaves them particularly susceptible to fast depletion from a product or from the surface they have been applied to. Encapsulation is a very effective method to limit the loss of fragrance during their use and to sustain their release. This review gives an overview of the different materials and techniques used for the encapsulation of fragrances, scents, and aromas, as well as the methods used to characterize the resulting encapsulation systems, with a particular focus on cyclodextrins, polymer microcapsules, inorganic microcapsules, block copolymer micelles, and polymersomes for fragrance encapsulation, sustained release, and controlled release.

Stabilization and Sustained Release of Fragrances Using Silk-PEG Microspheres

Fragrances, which are commonly used in food, textiles, consumer products, and medical supplies, are volatile compounds that require stabilization and controlled release due to their sensitivity to environmental conditions such as light, oxygen, temperature, and humidity. Encapsulation in various material matrices is a desired technique for these purposes, and there is a growing interest in using sustainable natural materials to reduce environmental impact. In this study, fragrance encapsulation in microspheres made from silk fibroin (SF) was investigated. Fragrance-loaded silk fibroin microspheres (Fr-SFMSs) were prepared by adding fragrance/surfactant emulsions to silk solutions, followed by mixing them with polyethylene glycol under ambient conditions. The study investigated eight different fragrances, where citral, beta-ionone, and eugenol showed higher binding affinities to silk than the other five fragrances, resulting in better microsphere formation with uniform sizes and higher fragrance loading (10-30%). Citral-SFMSs showed characteristic crystalline β-sheet structures of SF, high thermal stability (initial weight loss at 255 °C), long shelf life at 37 °C (>60 days), and sustained release (∼30% of citral remained after incubation at 60 °C for 24 h). When citral-SFMSs with different sizes were used to treat cotton fabrics, about 80% of the fragrance remained on the fabrics after one wash, and the duration of release from the treated fabrics was significantly longer than that of control samples treated with citral alone (no microspheres). This method of preparing Fr-SFMSs has potential applications in textile finishing, cosmetics, and the food industry.

Near-Infrared Light Responsive Surface with Switchable Wettability in Microstructure and Surface Chemistry

Intelligent surfaces with reversibly switchable wettability have recently drawn considerable attention. One typical strategy to obtain such a surface is to change the surface chemistry or the microstructure. Herein, we report a new smart surface for which the wettability was controlled by both the surface chemistry and microstructure. Various wetting states were reversibly and precisely controlled through heating, pressing, NIR irradiation, and oxygen plasma treatment. The excellent shape memory characteristics of shape memory polyurethane (SMPU) and the controlled release of hydrophobic/hydrophilic oxygen-containing functional groups contributed to this ability. Microcapsules were used to design these smart surfaces. They controlled the release of a fluorinated alkyl silane (FAS) through shell melting, changed the surface composition, and played a decisive role in protecting the FAS against hydrolysis and evaporation to ensure that the surface's wettability is recyclable. Controlling of the surface chemistry or microstructure was repeated for at least 19 or 16 cycles, respectively, which indicated excellent repeatability compared to other smart surfaces. Based on the excellent controllability, the surface exhibited multiple functions, such as liquid directional transport and coefficient of friction control. In addition, it maintained this extraordinary ability under harsh environments owing to the great stability of the SMPU and adequate protection of the FAS by the microcapsules. With switchable wettability based on the surface chemistry and microstructure, this work provides a new principle for designing smart surfaces with wettability controlled in two ways.

Release of Volatile Cyclopentanone Derivatives from Imidazolidin-4-One Profragrances in a Fabric Softener Application

Imidazolidin-4-ones were investigated as hydrolytically cleavable profragrances to increase the long-lastingness of perfume perception in a fabric softener application. The reaction of different amino acid amides with 2-alkyl- or 2-alkenylcyclopentanones as the model fragrances to be released afforded the corresponding bi- or tricyclic imidazolidin-4-ones as mixtures of diastereoisomers, which were separated by column chromatography. In polar solution, the different stereoisomers equilibrated under thermodynamic conditions to form mixtures with constant isomeric distributions, as shown by NMR spectroscopy. Dynamic headspace analysis on dry cotton demonstrated the controlled fragrance release from the precursors in practical application. Under non-equilibrium conditions (continuous evaporation of the fragrance) and depending on the structure and stereochemistry of the profragrances, the recorded headspace concentrations of the fragrance released from the precursors increased by a factor of 2 up to 100 with respect to the unmodified reference. Prolinamide-based precursors released the highest amount of fragrance and were thus found to be particularly suitable for prolonging the evaporation of cyclopentanone-derived fragrances on a dry cotton surface.