Formation Of Microcapsules Research Articles

High Catalytic Activity of Lipase from Yarrowia lipolytica Immobilized by Microencapsulation.

Microencapsulation of lipase from Yarrowia lipolytica IMUFRJ 50682 was performed by ionotropic gelation with sodium alginate. Sodium alginate, calcium chloride and chitosan concentrations as well as complexation time were evaluated through experimental designs to increase immobilization yield (IY) and immobilized lipase activity (ImLipA) using p-nitrophenyl laurate as substrate. To adjust both parameters (IY and ImLipA), the desirability function showed that microcapsule formation with 3.1%(w/v) sodium alginate, 0.19%(w/v) chitosan, 0.14 M calcium chloride, and 1 min complexation time are ideal for maximal immobilization yield and immobilized lipase activity. A nearly twofold enhancement in Immobilization yield and an increase up to 280 U/g of the lipase activity of the microcapsules were achieved using the experimental design optimization tool. Chitosan was vital for the high activity of this new biocatalyst, which could be reused a second time with about 50% of initial activity and for four more times with about 20% of activity.

Synthesis and optimization of polyurethane microcapsules containing [BMIm]PF6 ionic liquid lubricant

Polyurethane (PU) microcapsules containing [BMIm]PF6 as a lubricant have been fabricated by interfacial polymerization. The stabilizing effect of 10 kinds of emulsifiers towards [BMIm]PF6 ionic liquid have been delineated. A Pickering emulsion stabilized by lignin showed the best emulsification effect on highly viscous [BMIm]PF6. The types and reactivities of monomers have an important influence on the formation of microcapsules. Three kinds of isocyanate (IPDI, MDI, TDI) were reacted with diamines or diols to prepare the PU microcapsules in this work. The optiaml [BMIm]PF6@PU microcapsules were obtained when using IPDI and TETA as monomers, under conditions of 5,000 rpm emulsifying rate, 0.5 wt% concentration of lignin Pickering emulsion, and a 3:1 mass ratio of [BMIm]PF6/IPDI. The synthesized microcapsules have a regular and compact spherical structure, smooth outer, and inner surfaces with a mean diameter of 43 ± 15 µm, and a thickness of 3.8 µm. The core content of [BMIm]PF6@PU microcapsules was determined as >70%, and the initial decomposition temperature was 300 °C. The [BMIm]PF6 ionic liquid shown excellent lubricating property, ultralow friction coefficient (decreased by 72.7%) and wear rate (decreased by 160 times) were obtained by embedding 30 wt% microcapsules into epoxy compared with pure epoxy.

Microfluidic fabrication of microcapsules tailored for self-healing in cementitious materials

Autonomic self-healing in cement-based infrastructure materials has recently emerged as a promising strategy for extending the service life of concrete infrastructure. Amongst the various self-healing systems being developed, the use of microcapsules has received significant attention partly because of its ease implementation. Up to date, microcapsules for self-healing applications have been mainly manufactured using bulk emulsifications polymerisation techniques. However this methodology raises concerns regarding shell dimensions and interfacial bonding. This study proposes for the first time the fabrication of microcapsules with tailored characteristics for mechanically triggered self-healing action in cement-based composites. For this, a microfluidic device was used to produce a double emulsion template for the formation of microcapsules, containing both aqueous and organic liquid core. In addition, a novel method has been proposed to functionalize the microcapsules' surface with hydrophilic groups in order to increase the interfacial bond with the cementitious host matrix. The core retention was studied using EDX and TGA, and their mechanical triggering was investigated via SEM of the microcapsules embedded in the cement paste. The results demonstrated the capability of microfluidics to produce microcapsules with liquid organic core, thin shell, hydrophilic surface and appropriate fracture strength for use in mechanically triggered self-healing of cementitious materials.

Metal-Organic Framework Based Microcapsules.

MOFs are a type of ideal crystalline material with rigid reticular structures whereas microcapsules are usually prepared from soft mater, such as polymers or supramolecules. The synthesis of MOF-based microcapsules with novel nanostructures at the molecular scale remains a great challenge. Herein, we develop a competitive coordination strategy to synthesize MOF-based microcapsules with novel bowl-like structures. During the competitive coordination process, the infinite structures of MOFs are partially broken by the competitive reagents, thus flexibility is introduced into the rigid skeletons and results in the formation of bowl-like microcapsules. Owing to the unique structure and composition of these nano-structures, the microcapsules exhibit excellent performance and stability in adsorbing and removing iodine for both vapor and solution. This work describes new opportunities in designing MOF-based microcapsules with novel structures.

Microencapsulation of energy conversion photochromic materials with epoxy resin shell by interfacial polymerization

In this study, a novel type of photochromic spirooxazine microcapsule was prepared by interfacial polymerization between epoxy resin and polyamine compound. The effects of different process parameters on the formation, microstructure and performance of microcapsules, such as curing reaction temperature, emulsification shear rate and the addition of silica nanoparticles were studied in this paper. The morphology, microstructure, diameter and distribution, as well as the thermal stability of microencapsulated photochromic spirooxazine were also investigated by field emission scanning electron microscope, laser particle size analyzer and thermogravimetric analysis systematically. In addition, the photochromic performance of microcapsule was studied as well.

Formation of microcapsules by ultrasound stimulation for use in remote-controlled drug-eluting stents

Coronary Heart Disease (CHD) is the leading cause of death globally. The placement of drug-eluting stents (DESs) in diseased coronary arteries is the most successful minimally-invasive intervention to treat CHD. The key limitations of such interventional therapy are the risk of in-stent restenosis (ISR) and late stent thrombosis. This paper investigates a new drug-release system by formatting nanoparticles as drug carriers, which are later subjected to an external ultrasonic stimulus for controlled drug release remotely for DESs. The drug delivery could delay smooth muscle cell growth whilst enabling effective regeneration of a functional endothelium. Microcapsules were produced by employing a layer-by-layer technique, encapsulated with Rhodamine 6G dye used in place of anti-restenotic drugs. Gold nanoparticles were employed as a shell in the microcapsules. The presence of gold nanoparticles significantly enhanced the efficiency of the ultrasonically induced dye release from the microcapsules and increased the sensitivity of the microcapsules to ultrasonic stimulation compared to those without gold nanoparticles.

Electrospraying assisted by pressurized gas as an innovative high-throughput process for the microencapsulation and stabilization of docosahexaenoic acid-enriched fish oil in zein prolamine

Zein, a prolamine obtained from maize, was employed to encapsulate a fish oil highly enriched with docosahexaenoic acid (DHA) by an innovative process termed electrospraying assisted by pressurized gas (EAPG). This technology combines high electric voltage with pneumatic spray to yield a high-throughput encapsulation process. Semi-spherical zein flowable capsules with mean sizes of 1.4 μm containing the DHA-enriched fish oil were produced by EAPG from inert ethanol solutions at room conditions, presenting a high encapsulation efficiency. The oxidative stability tests carried out in the zein microcapsules obtained by EAPG showed that the DHA-enriched fish oil was efficiently protected over storage time. Sensory tests were also performed on fortified reconstituted milk with the freshly prepared zein/DHA-enriched fish oil microcapsules, suggesting negligible oxidation effects after 45 days. The results described herein indicate that EAPG is a promising innovative high-throughput electrospraying-based methodology for the encapsulation of bioactives and, therefore, the resultant DHA-enriched fish oil containing microcapsules can be industrially applied for the formulation of fortified foods. An innovative process, termed electrospraying assisted by pressurized gas (EAPG), is herein originally presented as a novel encapsulation methodology. This technology is based on the combination of high voltage and pneumatic spray, allowing the formation of microcapsules at room temperature conditions. Thus, EAPG shows a great deal of potential to encapsulate nutraceuticals and other bioactives that are sensitive to thermal degradation and/or oxidation. The resultant bioactive-containing capsules can be, thereafter, applied to develop novel fortified food products.

Production and characterization of palm oil microcapsules obtained by complex coacervation in gelatin/gum Arabic

AbstractPalm oil is a carotenoid‐rich natural compound, whose microencapsulation by complex coacervation may protect it against adverse conditions, allowing applications in food formulations for nutritional enrichment and natural pigmentation. Besides, since the coacervates are insoluble in acid pH of stomach, this undigested lipid is delivered slowly in the intestinal tract, which can help treatment of metabolic disturbs. Accordingly, this study intended to optimize palm oil microencapsulation by complex coacervation using gelatin and gum Arabic as wall materials. For this purpose, the effects of wall material concentration (WM) (2.5, 5.0, and 7.5% w/v), gelatin:gum Arabic ratio (G:GA) (1:2; 1:1; 2:1), and core:wall material ratio (C:WM) (75, 100, and 125%) on the encapsulation efficiency, particle morphology, and size distribution of microcapsules were investigated. Microencapsulation assays followed a factorial central design and, after coacervation, the microcapsules were freeze‐dried. The highest values of encapsulation efficiency were obtained using G:GA = 1:1 or 2:1 with C:WM = 100%, whereas the WM concentration could vary from 2.5 to 7.5%. High concentrations of WM (7.5%) and G:GA = 2:1 hampered the formation of spherical or oval microcapsules. Microcapsules showed average diameter (D[4.3]) between 97 and 690 µm, with increasing concentration of WM and higher C:WM ratio contributing to formation of larger microcapsules. The G:GA ratio showed the highest influence on the particle size, with the 1:2 ratio resulting in smaller microcapsules.Practical applicationsPalm oil is a significant source of antioxidants and other phytonutrients, and its microencapsulation may protect these bioactive compounds, enabling its use to nutritional enrichment of dry food formulations, at the same time as functioning as a natural pigment given the intense reddish‐orange color of the oil. In addition, the microcapsules may slow down palm oil release in the gastrointestinal tract, since the coacervates are insoluble in acid pH of stomach, allowing this nutrient to achieve the ileum before being digested and help treatment of metabolic disturbs. Accordingly, microencapsulation of palm oil can be of great interest for food and pharmaceutical industries to develop controlled‐delivery systems to encapsulate and slow down digestion of lipids, inducing modulation of satiety response.

Ultrasonically synthesized organic liquid-filled chitosan microcapsules: part 1: tuning physical & functional properties.

This study reports the synthesis of tetradecane-filled chitosan microcapsules in acetic acid aqueous solutions using high intensity ultrasound at 20 kHz. The size, size distribution, and stability of microcapsules were tuned by varying the concentration of acetic acid from 0.2% to 25% v/v. After long-time storage at room temperature (more than 3 months), the microcapsules maintained their shell-core structure where the volume of the microcapsules at 0.2% acetic acid concentration increased by 8.3% due to leaking and coalescence. Microcapsules were consistently spherical and had a smooth shell surface, however, their shell thickness varied with acetic acid concentration. The relaxation behavior of individual microcapsules to an applied constant stress was measured by atomic force microscopy (AFM) to probe the shell strength and extent of crosslinking. The effect of acetic acid on the relative viscosity of chitosan aqueous solutions played a major role in microcapsule size control at low acid concentrations. With constant addition of acetic acid, amino groups in chitosan chains were acetylated partially under ultrasonic irradiation. This reduced the amphiphilicity of the shell material and therefore influenced the size, size distribution, stability and mechanical strength of the microcapsules. Apart from the acetylation effect, the counter-ion effect and the formation of covalent bond crosslinks also made contributions to the formation of stable chitosan microcapsules.

Encapsulation of Theophylline in Gelatin A-Pectin Complex Coacervates.

The present study aims at synthesizing gelatin A-pectin complex coacervates and encapsulation of theophylline in the polymer system. Variation and optimization of different reaction parameters such as pH, ratio between the polymers and cross-linker concentration was carried out to attain higher product yield. Relative viscosity, turbidity and UV-visible measurements were done for optimization. The optimum ratio between gelatin A-pectin was fixed at weight ratio 42:8 and pH=3.5. It was further observed that adhesion between the microcapsules decreased by the use of sodium carboxymethyl cellulose (SCMC) to the coacervate. The synthesized microcapsules were characterized by using spectroscopic techniques to assess their formation, drug loading and chemical interaction between theophylline and coacervate. Scanning electron microscopy (SEM) revealed the formation of microcapsules. Study relating to the encapsulation efficiency and swelling of the complex coacervates were also carried out.

<b>Use of milk protein and maltodextrin in the microencapsulation of <i>Lactobacillus acidophilus<i>: a model approach

The microcapsules containing the Lactobacillus acidophilus La-5 probiotic were obtained by spray drying technique, using maltodextrin and milk powder concentrate as encapsulating agents, whose conditions were optimized using Central Composite Rotatable Design (CCRD), obtaining maximum performance with yield 87,59 ± 0,27% employing the inlet air temperature of 100 to 106°C and maltodextrin concentration between 21 to 23.7% (w v -1 ). The microcapsules revealed by optical microscopy as spherical and homogeneous particles with varying diameters. The results in differential scanning calorimetry corroborate with the optical microscopy for the formation of microcapsules.

Standardization of microencapsulation process of volatile oil of Azadirachta indica

Neem oil microcapsule gel was successfully prepared with wall material including gelatin and gum Arabic using coacervation technique by the researcher as an outcome of standardization of microencapsulation process of volatile oil of Azadirachta indica . An essential oil is the volatile lipophilic component extracted from plants. The use of medicinal plants is a universal phenomenon. The plant Neem belongs to the big mahogany family of Meliaceae and the genus Azadirachta of A. indica . The diverse biological activities of Neem essential oils can be applied on a large scale as antioxidant, antimicrobial agents comprising many important benefits including their volatility, lower level of risk to the environment than with synthetic ones. Findings of the study revealed that best results of microcapsules formation using Neem oil were obtained when the ratio of oil:gum:gelatin was kept 2:4:4, at optimized 50°C temperature having initial pH 4.5 and final pH 9.5.

Microfluidic-assisted Formation of Highly Monodisperse and Mesoporous Silica Soft Microcapsules

The fabrication of mesoporous silica microcapsules with a highly controlled particle size ranging in the micrometer size presents a major challenge in many academic and industrial research areas, such as for the developement of smart drug delivery systems with a well controlled loading and release of (bio)active molecules. Many studies based on the solvent evaporation or solvent diffusion methods have been developed during the last two decades in order to control the particle size, which is often found to range at a sub-micrometer scale. Droplet-based microfluidics proved during the last decade a powerful tool to produce highly monodisperse and mesoporous silica solid microspheres with a controllable size in the micrometer range. We show in the present study, in contrast with previous microfluidic-assisted approaches, that a better control of the diffusion of the silica precursor sol in a surrounding perfluorinated oil phase during the silica formation process allows for the formation of highly monodisperse mesoporous silica microcapsules with a diameter ranging in the 10 micrometer range. We show also, using optical, scanning and transmission electron microscopies, small angle x-ray diffraction and BET measurements, that the synthesized mesoporous silica microcapsules exhibit a soft-like thin shell with a thickness of about 1 μm, across which 5.9 nm sized mesopores form a well-ordered hexagonal 2D network. We suggest and validate experimentally a model where the formation of such microcapsules is controlled by the solvent evaporation process at the droplet-air interface.

Electrodeposited Poly(thieno[3,2-b]thiophene) Films for the Templateless Formation of Porous Structures by Galvanostatic and Pulse Deposition.

The formation of porous nanostructures by using a templateless electropolymerization process with thieno[3,2-b]thiophene as a monomer and two different deposition methods (galvanostatic and pulse potentiostatic deposition) has been studied. The wettability, roughness, and morphology of the surfaces are reported. The surfaces prepared by galvanostatic deposition show hydrophilic behavior (θw ≈80°) that is highly dependent on the roughness. Nanoseeds were formed in the first instances followed by the formation of large microcapsules and hollow spheres. Indeed, as the deposition time and current density increase, the size and amount of structures also increase. By pulse deposition, the surfaces are hydrophobic (θw ≈100°) and only show a roughness dependence if the mean surface roughness is >1.5 μm. The surfaces are formed from nanodomes and nanospheres, but they are less structured than that of surfaces produced by the galvanostatic method. The formation of these structures is directly related to the amount of gas released from trace water in situ during electropolymerization, which is highly dependent on the electrochemical method chosen. The formation of new seeds is highly favored by the galvanostatic method, whereas their growth is favored by the pulse deposition method. This is the first study on the use of galvanostatic and pulse deposition methods, with potential applications in surface chemistry. Thieno[3,2-b]thiophene proved to be very versatile to form different structures with potential applications as water harvesting and separation membranes.

Influence of Biotechnological Processes, Speed of Formulation Flow and Cellular Concurrent Stream-Integration on Insulin Production from β-cells as a Result of Co-Encapsulation with a Highly Lipophilic Bile Acid.

We have shown that incorporation of the hydrophilic bile acid, ursodeoxycholic acid, into β-cell microcapsules exerted positive effects on microcapsules' morphology and size, but these effects were excipient and method dependent. Cell viability remained low which suggests low octane-water solubility and formation of highly hydrophilic dispersion, which resulted in low lipophilicity dispersion and compromised cellular permeation of the incorporated bile acid. Thus, this study aimed at investigating various microencapsulating methodologies using highly lipophilic bile acid (LPBA), in order to optimise viability and functions of microencapsulated β-cells. Four different types of microcapsules were produced with (test) and without (control) LPBA, totalling eight different microcapsules. Microencapsulating methodologies were screened for best microcapsule-cell functions and microencapsulating processes were examined in terms of frequency, formulation flow, total bath-gelation time and cellular concurrent stream-integration rate, cell-viability, insulin production and inflammatory profile. Optimum biotechnological processes include formation frequency (Hz) of 2350, formulation flow (ml/min) of 1.2, total gelation time (min) of 18 and cellular concurrent stream-integration rate (ml/min) of 0.7. In all formulations, LPBA consistently improved cell viability, insulin production, mitochondrial activities and ameliorated inflammation. The deployed biotechnological processes and LPBA optimised formation and functions of β-cell microcapsules, which suggests potential applications in diabetes mellitus via the creation of more stable β-cell microcapsules capable of delivering adequate levels of insulin to control glycaemia and potentially curing diabetes.

Preparation of aroma microcapsules with sodium alginate and tetradecylallyldimethylammonium bromide (TADAB) and its potential applications in cosmetics

AbstractThe formation of apple aroma microcapsules was achieved by sodium alginate (SA) and tetradecylallydimethylammonium bromide (TADAB) as shells based on complex coacervation‐emulsion polymerization. Alkyl alcohol polyoxyethylene ether was employed as emulsifier. Pentaerythritol tetraacrylate (PETRA) was used as a crosslinking agent and methyl methacrylate (MMA) was applied as comonomer to copolymerize with TADAB. The aroma microcapsules were characterized by scanning electron microscopy (SEM). Results showed that the aroma microcapsules prepared under optimal conditions were core‐shell structure. The aroma microcapsules were sphere‐like shape with particle size between 20 to 50 μm. FT‐IR analysis results showed that the electrostatic interactions and polymerization occurred assuredly. TG‐DTA study indicated that the thermal stability of the aroma microcapsules crosslinked with MMA shell was improved, and the thermal resistant temperature was up to 110°C. Moreover, the encapsulation efficiency of aroma microcapsules was measured by ultraviolet–visible near‐infrared spectrophotometer. In the surfactant solution, the release of aroma was quick during the first 8 hours, losing ca. 10.8% aroma encapsulated, however, there was no more else aroma dissolving out from the 9th hour. In open conditions, the encapsulation efficiency of the aroma microcapsules kept 66.57% after 48 hours, compared with the encapsulation efficiency going down alone if the microcapsules were milled.

High-Throughput Platform for Synthesis of Melamine-Formaldehyde Microcapsules.

The synthesis of microcapsules via in situ polymerization is a labor-intensive and time-consuming process, where many composition and process factors affect the microcapsule formation and its morphology. Herein, we report a novel combinatorial technique for the preparation of melamine-formaldehyde microcapsules, using a custom-made and automated high-throughput platform (HTP). After performing validation experiments for ensuring the accuracy and reproducibility of the novel platform, a design of experiment study was performed. The influence of different encapsulation parameters was investigated, such as the effect of the surfactant, surfactant type, surfactant concentration and core/shell ratio. As a result, this HTP-platform is suitable to be used for the synthesis of different types of microcapsules in an automated and controlled way, allowing the screening of different reaction parameters in a shorter time compared to the manual synthetic techniques.

Microencapsulation of reactive amine by interfacially engineered epoxy microcapsules for smart applications

The most common approach for incorporation of extrinsic self-healing functionality relies on introducing healant-loaded micro-containers in the polymeric formulation. In this context, a healing system based on encapsulated epoxy resin and amine hardener appears to be one of the most economically viable solutions, in view of the chemical as well as mechanical compatibility with the matrix. Encapsulation of epoxy resins has been extensively studied while the high reactivity of the amine hardener renders its encapsulation rather difficult and has been attempted with only modest success. The purpose of the present work is to adopt an interfacial polymerization approach for the preparation of epoxy microcapsules encapsulating a reactive amine hardener (triethylene tetramine). The effects of experimental parameters, including reaction temperature, stirring speed and epoxy/amine concentration ratio on the microcapsule formation were investigated. A polymeric surfactant was used to stabilize the suspension to modulate the particle size distribution of the resultant microcapsules. The highest encapsulation efficiencies were obtained when the reaction medium was maintained at 70 °C under stirring (600 rpm) at epoxy/amine ratio of 10/3.2. The microcapsule dimensions and core content could be tailored, following this encapsulation approach of interfacial polymerisation. Under optimal conditions, spherical microcapsules with 100% yield and 12% core content were obtained.

Effect of double alginate microencapsulation on in vitro digestibility and thermal tolerance of Lactobacillus plantarum NCDC201 and L. casei NCDC297

This study was undertaken for the microencapsulation of Lactobacillus plantarum NCDC201 and L. casei NCDC297 into double alginate coatings. Microencapsulated probiotics showed significant improvement in their survivability after simulated gastrointestinal passage and exposure to heat treatments. The resistance in simulated gastric juice (SGJ) (120 min) was 47.50% and 45.82% higher as compared to free cells of L. plantarum NCDC201 and L. casei NCDC297, respectively. After incubation in simulated intestinal juice (SIJ) (120 min), the viable probiotic population was 6.34 log CFU/ml and 6.92 log CFU/ml for microencapsulated L. plantarum NCDC201 and L. casei NCDC297, respectively. Similarly, microencapsulated probiotics showed relevant counts at higher heat exposure (75 °C for 1 and 10 min). SEM results indicated the absence of free bacteria confirming the formation of microcapsules, with spherical morphology, continuous and compact surfaces. ATR-FTIR analysis confirmed the cross linking of the microcapsules by calcium chloride and successful immobilization of the probiotics into the polymer microcapsules. DSC suggested the formation of cross-linking and structure of “egg box” and increase in the melting temperature of microcapsules. This study has concluded that double alginate coating technique enhanced the stability of probiotics at high temperature (75 ± 1 °C) and in simulated gastric and intestinal conditions.

Optimization of Ziziphora clinopodiodes essential oil microencapsulation by whey protein isolate and pectin: A comparative study

The performance of whey protein isolate (WPI) and pectin as wall materials in encapsulation of Ziziphora clinopodiodes essential oil by ultrasonication method was compared. In this regard, using the response surface methodology, the influence of ultrasonication (US) power (50–150W) and core-coating ratio (10–100%) on the properties of microcapsules was evaluated. Increasing US power and core-coating ratio, caused to increase and decrease the particle size, respectively. The polydispersity index (PDI) of WPI coated microcapsules was increased by increasing of US power. The Zeta potential values were increased by increasing of core-coating ratio. Also, the effect of core-coating ratio on encapsulation efficiency was more than US power. Morphological studies by SEM on optimized microcapsules showed regular spherical shapes. X-ray diffraction analysis revealed that the type of the wall material had no effect on the structural properties of the microparticles. FT-IR analysis confirmed the pronounced effect of electrostatic interactions in the formation of microcapsules.