Structure Of Microcapsules Research Articles

Encapsulation of caffeine into starch matrices: Bitterness evaluation and suppression mechanism

In this study, caffeine (CA) was encapsulated into food-grade starch matrices, including swelled starch (SS), porous starch (PS), and V-type starch (VS). The bitterness of the microcapsules and suppression mechanisms were investigated using an electronic tongue, molecular dynamics (MD) simulation and the in vitro release kinetics of CA. All the CA-loaded microcapsules showed a lower bitterness intensity than the control. The MD results proved that the weak interactions between starch and CA resulted in a moderate CA release rate for SS-CA microcapsules. The PS-CA microcapsule presented the longest CA release, up to 40 min, whereas the VS-CA microcapsule completely released CA in 9 min. The CA release rate was found to be related to the microcapsule structure and rehydration properties. A low CA bitterness intensity could be attributed to a delay in the CA release rate and resistance to erosion of the microcapsules. The results of this work are valuable for improving starch-based microcapsules (oral-targeted drug-delivery systems) by suppressing the bitterness of alkaloid compounds.

Microencapsulation May Preserve the Viability of Probiotic Bacteria During a Baking Process and Digestion: A Case Study with Bifidobacterium animalis Subsp. lactis in Bread.

The high sensitivity of probiotic bacteria (PB) to many environmental factors limits the number of food products where they can be incorporated. This study aimed to examine the capability of a unique three-layered microcapsule structure to protect PB against extremely elevated temperatures and low pHs to allow their incorporation into bakery goods. The microcapsules were prepared first by granulation of a Bifidobacterium lactis (BL) strain, as a model PB, to form a core, and then coating the core with three consecutive protective layers. The physical features and the shape of the microcapsules obtained from three sequential preparations were characterized using various methods. A viable cell count was utilized to evaluate the efficiency of the microcapsule structure to protect the bacteria during a bread-baking process carried out at 180°C for 40min and also during the exposure to simulated gastric fluid (pH 1.2) for up to 1h. The results showed that whereas the free bacteria (unprotected BL) encountered a significant viability loss under these conditions, the microencapsulated BL presented superior resistance.

Backgrounds of Computer-Aided Assessment of Morphological Structure in Polymer Drugs-Delivery Microcapsules

Microcapsules are widely used as one of the drug delivery means. The paper presents the backgrounds of a method of microcapsules size and shape assessment by computer-aided analysis of microscope images of microcapsules’ cross-sections. The method has been elaborated and is practically used to the microcapsules quality control at the Nalecz Institute of Biocybernetics and Biomedical Engineering PAS in Warsaw. Mathematical definitions of parameters describing the size, shape and inner structure of microcapsules are described in the paper. A general scheme of a computer-aided microcapsules quality assessment procedure is presented. Remarks about the limitations of the applicability of the described microcapsules assessment method are also given. On this basis, directions of future works aimed at improvement of the described microcapsules quality assessment method are suggested.

Analysis of the microcapsule structure based on machine learning algorithm

For the microcapsules preparation process, the mechanism is estimated by structure reformation during the preparation process since diameter and wall thickness drastically changed. Microstructures are recently studied by machine learning techniques. The Hough transformation algorithm is used by other researchers for the preparation of the microcapsules but it is difficult to determine the mechanism by using only a diameter change of the microcapsules. Therefore, one additional way to establish the mechanism is the analysis of the formation of the microcapsule structure. In this study, The Hough transformation algorithm was used for the image segmentation, the simple feature extractions were checked and the support vector machine and the k-nearest neighbors algorithm were used as classifiers in order to analyze the structure of the microcapsules which were prepared by solvent evaporation method from a solid in oil in water, S/O/W, emulsion system. The structural distribution was analyzed by the developed detection method. The microcapsules had a specific structural distribution which are monocore, multicore, and other aggregated structures. The structural distribution was changed by the preparation condition. The monocore structure was dominant by increasing in the amount of water soluble solid particles added in the organic phase.

Clinicopathological features and differential diagnosis of eosionphilic chromophobe renal cell carcinoma

Objective: To investigate the clinicopathological characteristics of eosionphilic Chromophobe renal cell carcinoma (eChRCC), and differences in morphology, immunophenotype and clinical prognosis betweeneChRCC, renal oncocytoma(RO) and classic Chromophobe renal cell carcinoma (cChRCC). Methods: The clinicopathologic data of 17 patients diagnosed as eChRCC from the Affiliated Hospital of Qingdao University (13 cases) and 971 Hospital of PLA Navy (4 cases) from October 2006 to February 2019 were collected. Immunohistochemical analysis was carried out to compare the immunophenotypes between 17 cases with ChRCC, 27 cases with RO and 30 cases with cChRCC. Resuls: Among the 17 patients, seven were males and ten were females, and the age ranged from 40 to 75 years (median 54 years). Clinically, 15 cases of 17 were found accidentally by physical examination. The tumor size ranged from 1.8 cm to 10.0 cm (average 5.7 cm) and the cut surface of 15 cases were solid, one case was solicl and cystic, and one was cystic. Most showed gray to red, and partially soft, gray to yellow appearances. Microscopically, most tumors presented solid growth pattern with vary number of alveolar structures (12 cases). Some were predominately characterized by cystic structure (3 cases), alveolar structure(1 case) and microcapsule structure (1 case). There were boundaries with varying degrees of clarity between tumor cells in 16 cases. The cytoplasm of tumor cells was eosinophilic and the nuclei were small round or irregular with focal perinuclear haloes in 14 cases. Large polygonal cells with light-stained cytoplasm appeared focally in 9 cases, and edematous areas with scarce tumor cells were found in 4 cases. Among 7 cases, 4 cases focally invaded peripheral renal parenchyma, 2 cases invaded adipose tissues outside the renal capsule, and 1 case presented invasion of renal sinus. Immunohistochemically, all cases were moderate to strong positive for EMA and claudin-7. CK7, CD117 and Ksp-cad were highly expressed with the expression rates of 12/17, 15/17, 14/17, respectively. Cyclin D1, AMACR, CD10, S100A1, and RCC were rarely expressed with the expression rates of 4/17, 3/17, 4/17, 1/17 and 1/17, respectively. On the contrary, all cases were negative for vimentin, CAⅨ, HMB45 and Melan A. The Ki-67 proliferation index of the 17 cases was 1%‒5%. Follow-up data were available for all 17 patients from 7 to 154 months. Among them, 15 patients were alive without tumor recurrence or metastasis, one patient died of pulmonary metastasis after 31 months of surgery and one patient died of hepatic metastasis after 38 months of surgery. Conclusion: eChRCC has overlapping morphology and immunophenotype with RO. eChRCC is characterized by solid nest or alveolar structure, distinct border between tumor cells, perinuclear halos and lacking of interstitial looseness and edema. Scattered large polygonal cells with light-stained cytoplasm in tumor tissue play a significant role in the diagnosis of eChRCC. The positive expression of CK7, CD117, claudin-7 and Ksp-cad, and negative expression of cyclin D1, S100A1 are helpful to the diagnosis and differential diagnosis of eChRCC. The prognosis of eChRCC after complete surgical resection is excellent and few cases may have long-term metastasis. There is no significant difference in prognosis between eChRCC and cChRCC, but eChRCC shows better outcome than RO.

Biodegradability Evaluation of Hydroxyethylcellulose-based Microcapsules by 1H Nuclear Magnetic Resonance Spectroscopy

This study introduces a robust synthetic method of fabricating co-assembled biodegradable microcapsules composed mainly of representative natural sugar polymers, hydroxyethylcellulose (HEC), alginate, and sorbitol. We propose a facile enzymatic method evaluating initial biodegradation processes of the microcapsules utilizing a linewidth analysis on 1H nuclear magnetic resonance (NMR) spectroscopy. Linewidth analysis on the 1H resonance signals represents that broad resonance signals of the sugar-based microcapsules are changed to relatively narrower signals as an association of cellulase enzyme. This phenomenon explains co-assembled and cross-linked microcapsule structures are destroyed or/and loosened by the enzymatic breakdowns of ester bonds in the microcapsules. Moreover, closer inspection indicates that co-assembled sorbitol molecules are released from the main networked microcapsules, additionally supporting the biodegradation properties of the microcapsules. Considering the unique features of this method, the proposed study provides valuable information about the initial biodegradation processes and mechanisms of various microcapsules.

Microencapsulation of zinc by spray-drying: Characterisation and fortification

Zinc sulphate heptahydrate was microencapsulated by spray-drying using maltodextrin, HI-CAP® 100 and whey protein isolate as wall materials. Spray-drying conditions were optimised using Taguchi orthogonal array design with encapsulation efficiency and bulk density as responses. The influences of wall material, wall material to zinc ratio and inlet air temperature were evaluated. Microcapsules prepared with HI-CAP® 100 in 20:1 loading ratio at 185 °C had maximum encapsulation efficiency (92.65%), whereas 10:1 ratio yielded maximum bulk density (541.2 kg/m3). SEM micrographs revealed the spherical structure of microcapsules, while EDX confirmed the presence of zinc in the microcapsules. SEM micrographs, FTIR and XRD analyses showed that zinc was successfully encapsulated as microcapsules. The tapped, bulk and particle densities of zinc microcapsules were in the range of 586.15–698.15, 437.40–541.20 and 1263.25–1436.50 kg/m3, respectively, while flowability was ‘fair' to ‘passable’. The adsorption isotherm of microcapsules was sigmoidal, and was described by GAB model. Fortification of milk with zinc microcapsules did not affect its inherent organoleptic qualities.

Synthesis of Melamine‐Formaldehyde Microcapsules Containing Polyfluorene for Fluorescent Detection of Picric Acid in Aqueous Medium

To detect nitroaromatic picric acid (PA) in water, polyfluorene (PF) encapsulated melamine‐formaldehyde microcapsules (PF@MFMs) were fabricated via in situ polymerizations. Because of the microcapsule structure, PF@MFMs were uniformly dispersed in water maintaining the blue fluorescence of PF in the capsules. The fluorescence intensity of PF@MFMs linearly decreased with increase in the PA concentrations with high limit of detection of 3.0 × 10−6 M. The addition of other nitroaromatic derivatives, which had structure similar to PA, or various ions did not affect the fluorescence of PF@MFMs, showing high specificity of the microcapsules toward PA.

Preparation, characterization and foaming performance of thermally expandable microspheres

Thermal expansion microcapsules (TEMs) are widely used in various fields due to their unique structures. In recent years, TEMs have attracted much attention and have broad market application prospects. In this study, thermally expandable microcapsules with a core–shell structure were prepared by suspension polymerization using acrylonitrile (AN), methyl methacrylate (MMA), and methyl acrylate (MA) as monomers and low-boiling alkane as the core material. Through particle size analysis, morphology test, thermal analysis and other methods, the effects of core material types, single core material and mixed core material, dispersion system on the microcapsule structure, particle size distribution, and expansion properties were compared. Moreover, the core material with a content of 35% can make the expansion ratio of the microcapsules up to 4 times. The expansion performance of the microcapsules with a mixture of isopentane and isooctane (ratio 1:1) as the core material was increased by 27% compared with that of a single core material. In addition, comparing with colloidal SO2/PVP dispersant, the expansion ratio of the microcapsules with magnesium hydroxide as the dispersant was increased by 20%. Finally, the optimized method for preparing thermally expandable microcapsules was obtained.

Polyamine microcapsules featured with high storage stability used for one‐component epoxy adhesive

AbstractOne‐component epoxy adhesives have great promising prospects in industrial applications. However, it faces the challenge to reduce the activity of curing agents for achieving long‐term storage and controlled release. Microencapsulation is a feasible and effective solution. In this paper, multi‐polyaniline (MPAN) was successfully encapsulated with polyetherimide (PEI), a thermoplastic resin, as the shell material by using solvent evaporation method with dichloromethane (DCM) as solvent. The impacts of different preparation parameters on the structure and properties of microcapsules were investigated by single variable control method. It is found that the resulted microcapsules under the optimal process parameters, namely PVA concentration 1 wt%, core/shell mass ratio 1:1 and stirring rate 700 rpm, exhibits a smooth and dense spherical surface with an average particle size concentrated around 17.8 μm. Compared with the pure curing agent, the encapsulated curing agent effectively prolonged the shelf life of the epoxy adhesive at 40°C for at least 60 days, indicating excellent storage stability. The microencapsulated MPAN curing agent prepared in our research is of potential applications in the fields of electronic component bonding, potting and circuit board sealing due to its high storage stability and encapsulation efficiency (74%).

Structural regulation of poly(urea-formaldehyde) microcapsules containing lube base oil and their thermal properties

Regulating the micro-structure of microcapsules containing lubricant is paramount to their properties and the subsequent self-lubrication performance of the composites. In this study, poly(urea-formaldehyde) (PUF) microcapsules containing lube base oil as lubricant have been fabricated by in-situ polymerization technology. The structure and properties of PUF microcapsules are investigated by altering the emulsifier content, homogenization time, oil viscosity and synthetic method. The content of sodium lignosulfonate, an environment-friendly emulsifier, has important regulation effect on the regularity and core content of PUF microcapsules. The homogenization time and oil viscosity directly affect the particle size and distribution of PUF microcapsules. Moreover, the oil viscosity plays an important role in regulating the morphology and thermal behavior of PUF microcapsules. Specifically, by adding low content of emulsifier (0.2 wt %), well-dispersed spherical microcapsules are obtained. Adopting 15# oil as core material and 0.2 wt % emulsifier, high core content of up to 89.2 wt % is achieved. When using lube base oil (32#, 46# oil) with high viscosity, the microcapsules show compact spherical structure and high thermal stability, with the initial decomposition temperature of up to 251.8 °C. This research can provide guidance for fabricating PUF microcapsules with suitable structures and performances for improving the tribological properties of different polymers.

Mechanical and Optical Properties of Thermochromic Reversible Waterborne Primer Film on Tilia europaea with 1,2-Benzo-6-diethylaminofluorane Based Microcapsules.

A waterborne thermochromic primer film containing thermochromic reversible microcapsules on the surface of Tilia europaea was prepared. The influences of different microcapsule concentrations on the reversible thermochromic, optical, mechanical and liquid resistance properties of the primer films were investigated. Not only were the morphology and structure of microcapsules and films observed, but also the chemical compositions of the microcapsules and films were analyzed. The results showed that for the primer film with microcapsules, the microcapsule concentration had a more significant influence on color difference. The primer film with microcapsules can achieve thermochromic reversibility. The temperature of color change was 32 °C and it had a good color recovery. The film gloss was negatively correlated with the microcapsule concentration, and the film with 5.0%–15.0% concentration had the best gloss. Adding an appropriate concentration of microcapsules can effectively improve the mechanical properties of the film. The film with 0–15.0% microcapsules had better liquid resistance to detergent, i.e., grade 1. The bonding form between the primer film added with microcapsules and Tilia europaea was physical bonding. This study provides a technical reference for the development of modern intelligent discoloration wood products.

Microencapsulation of tris(dimethylaminomethyl)phenol using polystyrene shell for self-healing materials

The self-healing function of the polymer material has been realized by the microencapsulation technology of the healing agent. A novel microcapsule contained tris(dimethylaminomethyl)phenol (DMP-30) with polystyrene as shell material was prepared via solvent evaporation technique in a W/O/W emulsion. Two key strategies were implemented to prepare the microcapsules successfully. First, a small amount of deionized water was added into DMP-30 to form a complex, and a stable W/O emulsion was successfully prepared. The second one is to form a stable W/O/W emulsion system with the high viscosity aqueous solution added with Arabia gum and surfactants as the third phase. In addition, the influencing factors of microcapsules preparation were investigated systematically. The chemical structure of DMP-30 microcapsule was investigated by Fourier transform infrared. The morphology and shell thickness of the microcapsules were observed by optical microscope and scanning electron microscope. The reactivity of the core material was studied by differential scanning calorimetry. The thermal properties of microcapsules were studied by thermogravimetric analysis. The environmental resistance of microcapsules was verified by the isothermal aging test. Results showed that DMP-30 was successfully coated by polystyrene and the microcapsule size was in the range of 2–40 μm. The synthesized microcapsules were thermally stable below 50 °C.

Preparation and Characterization of Paraffin@CLPS/MS Phase Change Microcapsules for Thermal Energy Storage

AbstractIn this study, a series of encapsulated micro phase change material (EMPCM) based on industrial paraffin and inorganic‐organic hybrid shell was reported. The microcapsules (28#P@CLPS/MS) were synthesized with 28#paraffin (28#P) as phase change material (PCM), crosslinked polystyrene (CLPS) as flexible organic shell and modified nano SiO2(MS) as rigid inorganic shell, via a Pickering emulsion polymerization method. MS reduces the interfacial tension of water and plays a good emulsification effect. Secondly, after polymerization, the mechanical stability of the microcapsule shell can be enhanced, and the thermal reliability of the phase change microcapsules can be improved. The morphology, thermal energy storage capacity, and structure of microcapsules were characterized and analyzed. Besides, the grafting ratio of nano SiO2on the heat storage properties of microcapsules was investigated. When the graft ratio of nano‐SiO2was 4.2 %, the prepared microcapsules with highst paraffin content (54.37 %) and encapsulation efficiency (95.15 %). The synthesized microcapsules with regular spherical shape and size range of 1–5 μm, latent heat capacity (Tm28.20 °C, 86.35 J/g) and good thermal stability. Besides, the chemical composition of the microcapsules did not change after 500 cycles, and the latent heat did not decrease. Our research shows that Pickering emulsion polymerization is a convenient, economical and green method for the preparation of highly stable energy storage microcapsules.

Effect of starch film containing thyme essential oil microcapsules on physicochemical activity of mango

Essential oils are natural antibacterial substances with potential applications in packaging; however, due to their volatile and oxidizable properties, these materials have a low utilization rate. In this study, starch films containing thyme essential oil microcapsules (TEO-M) were prepared using the casting method, and the effect of the films on the quality and physicochemical properties of mango was evaluated. Scanning electron microscopy (SEM) image analysis showed that the structure of microcapsules presented higher integrity in starch films. The TEO-M starch film thermal stability was decreased compared to the stability of starch film alone. Fourier transform infrared (FT-IR) spectroscopy analysis revealed that TEO-M interacted effectively with starch films via hydrogen bonding. Furthermore, the TEO-M starch films showed an inhibitory effect against Botryodiplodia theobromae Pat and Colletotrichum gloeosporioides Penz. The addition of TEO-M to starch films increased the opacity, thickness, tensile strength and water solubility. Additionally, the TEO-M starch films presented lower elongation, moisture content and water vapor permeability. TEO-M starch films showed a better preservation effect compared with that of starch film alone. The shelf-life of mangoes treated with TEO-M starch films was 10 days at 25 °C. These results demonstrate the potential of developing TEO-M starch films for mango preservation.

Characteristics of lactobacillus plantarum LIP-1 microcapsules prepared using an aqueous phase separation method

The emulsification method (EM) is popular for microencapsulating probiotics with lactoprotein as the wall material. We have developed an aqueous phase separation method (APSM) based on this technique by replacing emulsification with fermentation. Compared with the EM microcapsules, the electrophoresis results showed that the wall materials of the microcapsules prepared using the APSM consisted of more protein fragments after fermentation. Plate-counting results revealed porliferation of the core material —Lactobacillus plantarum LIP-1). Microencapsulation efficiency of the APSM microcapsules of 82 ± 5%, particle size of 80 ± 5 μm, survival rate in simulated gastric fluid of 85 ± 5%, survival rate after freeze-drying of 88.4%, and prolonged shelf-life. These characteristics were all significantly better than those of the EM microcapsules (P < 0.05). Scanning electron microscopy showed that the surface structure of the APSM microcapsules was more compact, which helped improve the resistance of the probiotics to adverse environments. The APSM overcame the disadvantages of the EM and produced microcapsules with superior characteristics; thus, it has broad prospects in industrial development.

One‐step building of molecularly imprinted polymer microcapsules with multicore structure by Pickering emulsion polymerization

AbstractNovel molecularly imprinted polymer (MIP) microcapsules with multicore structure were prepared through one step Pickering emulsion polymerization combined with the polymerization driven phase separation. Bisphenol A (BPA) is found to play the part of heterogeneous nuclei besides template molecule, which offers opportunity for the building of the multicore structure inside of MIP microcapsules. The internal structure of MIP microcapsules could be regulated by choosing different kinds of template molecules. Rebinding experiments showed that the MIP with multicore structure possessed excellent binding properties toward BPA. The imprinting factor of MIP toward BPA is 1.96. The binding could reach equilibrium within 30 min. The fast rebinding kinetics was attributed to the unique multicore structure which reduced largely the mass transfer resistance of BPA in the MIP.

The study on the mechanical properties of PU/MF double shell self-healing microcapsules

The self-healing microcapsules can be buried in the coating to improve the anticorrosive ability. In this paper, self-healing microcapsules of polyurea (PU)/melamine resin (MF) double shell were prepared by in-situ polymerization and interfacial polymerization with isocyanate as the core material. Scanning electron microscope was used to observe the microcapsule morphology. The structures of microcapsules prepared with different chain extenders were characterized by Fourier transform infrared spectroscopy. The micromanipulation system was used to loading–holding, loading–unloading and loading to rupture individual microcapsules, so as to explore the mechanical properties of microcapsules. The Young's modulus corresponding to microcapsules was calculated by mathematical model fitting. The self-healing properties of microcapsule coating were characterized by optical microscope. The experimental results showed that the microcapsule shell prepared under optimized conditions had a complete morphology and good mechanical properties. The microcapsule was in the elastic deformation stage under small deformation, and the plastic deformation stage under large deformation. The Young's modulus range of microcapsules was 9.29–14.51 MPa, and the corresponding Young's modulus could be prepared by adjusting the process. The surface crack of the coating containing microcapsule could heal itself after 48 h in a humid environment.

Modeling and optimization of tea polyphenol-alginate/chitosan magnetic microcapsules

New preparation condition of magnetic microcapsule was designed and optimized by response surface methodology(RSM) in this study. The optimal formula was as follows: the concentration of chitosan(CTS), magnetofluid(MHD), calcium chloride(CaCl2) and sodium alginate solution(ALG) were 10.4(g/L),4.83(g/L), 5.625(g/L), and 28(g/L),respectively. The optimized magnetic microcapsules had good slow release effect, and the release time of magnetic microcapsule was up to 100 h. The chemical structure of magnetic microcapsules was determined by Fourier transform infrared(FT-IR) spectrometer. Meanwhile, the chemical composition of the magnetic microcapsule was determined by X-ray diffraction(XRD) instrument.Thermogravimetric analysis(TGA) was used to detect the thermal properties. The properties of anti-oxidation and drug release of the magnetic microcapsules were further analyzed. Most importantly, magnetic microcapsules had superparamagnetism with extremely low magnetic retention and coercivity, which could be used as a good microcapsule embolization agent for tumor endovascular embolization therapy.

Photochromic microcapsules by coacervation and in situ polymerization methods for product-marking applications

Photochromic materials can change their colour quickly and reversibly when exposed to light of certain wavelengths. These materials have recently been of great interest for intelligent and functional textile applications. In this study, two different photochromic dyes, including 1′,3′-dihydro-1′,3′,3′-trimethyl-6-nitro-spiro[2H-1-benzopyran-2,2′-(2H)-indole] and 1′,3′-dihydro-8-methoxy-1′,3′,3′-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2′-(2H)-indole], were microencapsulated by coacervation and in situ polymerization methods. Ethyl cellulose and melamine–urea–formaldehyde were used as polymers. The Fourier transform infrared spectroscopy, particle size and size distribution analysis, scanning electron microscopy, and ultraviolet spectrophotometry evaluations were utilized to characterize the structure, morphology, size distribution, and absorbance maxima of the photochromic microcapsules. The results indicated that photochromic microcapsules were in spherical shape, smooth, and homogeneous characteristics. These microcapsules were applied successfully onto cotton fabric using printing technique. Then, the activities of photochromic microcapsules on the fabrics were analysed by colour analysis under different light sources, fatigue resistance, washing, and rubbing fastness tests. After printing, the colours of the fabrics changed very quickly under different light sources. At the same time, these fabrics showed a reversible photochromic response and good fatigue resistance. Mechanical and physical properties of the fabrics such as thickness, air permeability and tensile and tear strength were also investigated. It can be concluded that photochromic microcapsules are well appropriate for brand protection and prevention of imitation in textile materials.