Preparation and characterization of melamine-formaldehyde resin microcapsules containing fragrant oil

In this study, melamine-formaldehyde microcapsules were prepared viain situ polymerization using peppermint oil as a core material, melamine-formaldehyde as the wall material, Tween 20 as the emulsifier, and poly (vinyl alcohol) as a protective colloid. The melamine-formaldehyde microcapsules prepared in this study were then evaluated with regard to their structures, thermal properties, particle size distributions, morphologies, and release behaviors.     

Preparation and characterization of microencapsulated proteinase inhibitor aprotinin.

Preparation of microcapsules through interfacial cross-linking of soluble starch/hydroxyethyl starch and bovine serum albumin (BSA) with terephthaloyl chloride is described. The proteinase inhibitor aprotinin, either native or active site protected, was microencapsulated, being incorporated in the aqueous phase. The influence of aqueous phase pH, BSA, and terephthaloyl chloride concentrations as well as stirring rate on microcapsule morphology and size was studied. The polycondensation pH was shown to be the determining factor for tough microcapsule production with a high encapsulation yield. The size of the microcapsules ranged between 10-30 and 50-100 microm at stirring speed 1500 and 500 rpm, respectively. Fourier transform infrared spectroscopic studies were performed on microcapsules prepared under various conditions. A correlation was established between spectral changes and microcapsule morphology and size. The optimal conditions for microcapsule degradation by alpha-amylase were found. Active site-protected aprotinin was shown to fully retain its activity after microencapsulation.     

Preparation and Thermal Energy Storage of Carboxymethyl Cellulose-Modified Nanocapsules

A series of nanocapsules with carboxymethyl cellulose (CMC)-modified melamine-formaldehyde as the shell material and phase change paraffin as the core material were prepared by in situ polymerization. The modified capsules were examined using Fourier transform infrared spectra, scanning electronic microscope, differential scanning calorimeter, and optical microscopy, and two factors that influence paraffin emulsion preparation (emulsifier type and stirring rate) were investigated. The effects of the synthesis conditions used for the prepolymer on the surface morphology of the capsules were also studied. We found that phase change capsules prepared with both anionic and nonionic emulsifiers were superior to those prepared with a simple emulsifier. The best performance of the paraffin emulsion was obtained when the emulsion was stirred at 8,000 rpm during preparation. The optimal prepolymer reaction conditions to give smooth capsules with good dispersibility and complete morphology were reaction temperature 72.5 °C, reaction time 75 min, and pH?8.5. The CMC-modified nanocapsules have a phase change enthalpy of 83.46 J/g, are fully encased, and are uniform, with an average particle size of 50 nm.     

Microencapsulation of alpha-tocopherol using sodium alginate and its controlled release properties

Response surface methodology (RSM) was used to optimize microencapsulation yield (MY) using three independent variables; the ratio of coating material to core material (w/w, X1), the emulsifier concentration (%, v/v, X2), and the CaCl2 concentration (%, w/v, X3). In the preparation of sodium alginate (SA) microcapsule, the regression model equation for the MY was predicted as follows; MY(%) = 56.02 + 3.64X2 + 3.18X1X2 - 3.74X2(2). The optimal conditions for the SA microcapsule were obtained at the [SA]/[alpha-TP] ratio of 6.6:3.4 (w/w), [emulsifier] of 1.35% (v/v), and [CaCl2] of 4.3% (w/v), and the predicted MY in this condition was of 57.2%. In vitro alpha-TP releasing test of the SA-based microcapsules was performed. The SA microcapsule released 28.8% of alpha-TP when exposed in the simulated gastric fluid (SGF, pH 1.2) for 24 h. In the simulated intestinal fluid (SIF, pH 7.4), the amount of released alpha-TP (81.5%) was significantly greater than that in the SGF. The duration time required for releasing 50 (T50%) and 70% (T70%) of alpha-TP from the SA-microcapsule were calculated to be 3.8 and 12.3 h, respectively. From these results, it was suggested that SA microcapsule would be structurally resistant against acidic environment, and it would rapidly release core material under mild alkali condition.     

CHO immobilization in alginate/poly-l-lysine microcapsules: an understanding of potential and limitations

Microencapsulation offers a unique potential for high cell density, high productivity mammalian cell cultures. However, for successful exploitation there is the need for microcapsules of defined size, properties and mechanical stability. Four types of alginate/poly-l-Lysine microcapsules, containing recombinant CHO cells, have been investigated: (a) 800 μm liquid core microcapsules, (b) 500 μm liquid core microcapsules, (c) 880 μm liquid core microcapsules with a double PLL membrane and (d) 740 μm semi-liquid core microcapsules. With encapsulated cells a reduced growth rate was observed, however this was accompanied by a 2–3 fold higher specific production rate of the recombinant protein. Interestingly, the maximal intracapsular cell concentration was only 8.7 × 10⁷ cell mL^-1, corresponding to a colonization of 20% of the microcapsule volume. The low level of colonization is unlikely to be due to diffusional limitations since reduction of microcapsule size had no effect. Measurement of cell leaching and mechanical properties showed that liquid core microcapsules are not suitable for continuous long-term cultures (>1 month). By contrast semi-liquid core microcapsules were stable over long periods with a constant level of cell colonization (ϕ = 3%). This indicates that the alginate in the core plays a predominant role in determining the level of microcapsule colonization. This was confirmed by experiments showing reduced growth rates of batch suspension cultures of CHO cells in medium containing dissolved alginate. Removal of this alginate would therefore be expected to increase microcapsule colonization.     

响应面法优化火麻仁油微胶囊喷雾干燥工艺的研究

为了制备包埋率高、稳定性好的火麻仁油微胶囊,拓展其在食品领域的应用范围,以火麻仁油为芯材、单双脂肪酸甘油酯为乳化剂、酪蛋白酸钠为壁材、固体玉米糖浆为填充剂、柠檬酸钠为缓冲盐、抗坏血酸棕榈酸钠为抗氧化剂,通过喷雾干燥法制备60%载油率的火麻仁油微胶囊,以微胶囊包埋率为响应值,在单因素实验的基础上,以干物浓度、进风温度、出风温度为实验因素,采用Box-Behnken响应面分析法进行优化。随后通过扫描电镜观察火麻仁油微胶囊表面形态结构,以确定包埋效果。并利用油脂氧化分析仪检测火麻仁油微胶囊的氧化稳定性。研究确定微胶囊的最佳工艺条件为：干物浓度42%、进风温度168 ℃、出风温度74 ℃,在此条件下制备得到的火麻仁油微胶囊包埋率可达92.15%。通过扫描电镜观察到火麻仁油微胶囊表面圆滑无裂痕,表明火麻仁油微胶囊包埋效果比较理想。经油脂氧化分析仪测定,与对照组（火麻仁油）相比,试验组（火麻仁油微胶囊）的氧化诱导期时间较长,能够达到30 h以上,说明通过对火麻仁油进行微胶囊包埋可以较大程度地提高油脂的稳定性。研究结果为火麻仁油在食品工业领域的开发和应用提供了理论支持。     

Scalable encapsulation of hepatocytes by electrostatic spraying

Encapsulating cells by polyelectrolyte complex coacervation can be accomplished at physiological temperature and buffer conditions. One of the oppositely charged polyelectrolytes in the microcapsule core can be collagen or any other natural extra-cellular matrices suitable for cellular support while the other polyelectrolyte forms the ultra-thin shell to ensure efficient mass transfer. These microcapsules with ultra-thin shell are difficult to produce in large quantities due to their fragility. In this study, electrostatic spraying technique was used to achieve a scalable production of one such type of microcapsules formed by complex coacervation between the cationic methylated collagen and anionic terpolymer of hydroxylethyl methacrylate, methyl methacrylate and methylacrylic acid (HEMA-MMA-MAA). It was found that the microcapsule sizes were dependent on several important operational parameters, such as the diameter of the spraying needle, the flow rate of the hepatocytes-collagen mixture and the voltage of the electrical field. The microcapsules with diameters of 200-800 microm and a narrow size distribution (standard deviation of 5-28%) were successfully produced. The above parameters also influenced the hepatocyte viability and functions. With a practical encapsulation rate of up to 55 ml/h per orifice required in bio-artificial liver-assisted device applications, we have produced large quantities of microcapsules maintaining comparable cell viability (>87%), mechanical stability and bio-functions to the manually extruded microcapsules.     

Measurement of particle diameter of <Emphasis Type="Italic">Lactobacillus acidophilus</Emphasis> microcapsule by spray drying and analysis on its microstructure

Lactobacillus acidophilus, as a probiotic, is widely used in many functional food products. Microencapsulation not only increases the survival rate of L. acidophilus during storage and extends the shelf-life of its products, but also optimal size microcapsule makes L. acidophilus have an excellent dispersability in final products. In this paper, L. acidophilus was microencapsulated using spray drying (inlet air temperature of 170°C; outlet air temperature of 85–90°C). The wall materials used in this study were β-cyclodextrin and acacia gum in the proportion of 9:1 (w/w), and microcapsules were prepared at four levels of wall materials (15, 20, 25 and 30% [w/v]) with a core material concentration of 6% (v/v). The microcapsule diameters were measured by Malvern’s Mastersizer-2000 particle size analyzer. The results showed that the particle diameters of microcapsule were mostly within 6.607 μm and 60.256 μm and varied with 2.884–120.226 μm (the standard smaller microcapsule designated as <350 μm). Through comparison of microcapsule size and uniformity with different concentration of wall materials, we concluded that the optimal concentration of wall material was 20% (w/v), which gave microcapsule with a relatively uniform size (averaging 22.153 μm), and the number of surviving encapsulated L. acidophilus was 1.50 × 10⁹ c.f.u./ml. After 8 weeks storage at 4°C, the live bacterial number was above 10⁷ c.f.u./ml, compared with unencapsulated L. acidophilus, 10⁴–10⁵ c.f.u./ml. Through the observation of scanning electron microscopy, we found that the shapes of microcapsule were round and oval, and L. acidophilus cells located in the centre of microcapsule.     

Physical modeling of animal cell damage by hydrodynamic forces in suspension cultures

Physical damage of animal cells in suspension culture, due to stirring and sparging, is coupled with complex metabolic responses. Nylon microcapsules, therefore, were used as a physical model to study the mechanisms of damage in a stirred bioreactor and in a bubble column. Microcapsule breaskage folowed first-order kinetices in all experiments Entrainment of bubbles into the liquid phase in the stirred bioreactor gave more microcapsule breakage. In the bubble column, the bubble bursting zone at gas-liquid interface was primarilu responsible for microcapsule breakage. The forces on the microcapsules were equivalent to an external pressure of approximately 4 x 10(4) N . m(-2), based on the critical microcapsule diameter for survival of 190 mum. A stable foam layer, however, was found to be effective in protecting microcapsules from damage. The microcapsule transport to the gas-liquid interface and entrainment into the foam phase was consistent with flotation by air bubbles. This result implies that additives and operation of bioreactors should be selected to minimize flotation of cells. (c) 1992 John Wiley & Sons, Inc.     

以聚γ-谷氨酸为材质研制微胶囊的工艺

微胶囊制剂能够利用壁材将囊芯物质包裹起来,减少外界环境的不良因素对其造成的影响,但存在产品残效期和速效性的矛盾、成本过高等问题。聚γ-谷氨酸具有成膜性,可生物降解。本文通过自制的枯草芽胞杆菌聚γ-谷氨酸,对开发聚γ-谷氨酸微胶囊的工艺展开研究。对壁材浓度、搅拌转速、反应温度、聚γ-谷氨酸∶明胶质量比、菌悬液体积和甲醛的用量进行优化,建立了聚γ-谷氨酸微胶囊制备工艺,微胶囊对枯草芽胞杆菌的包埋率达到94.2%。同时考察了微胶囊制剂对热、紫外线和极端pH的抗逆性,结果表明聚γ-谷氨酸-明胶微胶囊能赋予微生物细胞更强的抗紫外能力和耐热性。在极端pH条件下热处理,聚γ-谷氨酸-明胶微胶囊剂中枯草芽胞杆菌的存活率也显著提高。     

Influence of microenvironmental conditions on hybridoma cell growth inside the alginate-poly-l-lysine microcapsule

A mathematical model was formulated to describe hybridoma cell growth within the alginate-poly-l-lysine (alginate-PLL) microcapsules during air-lift bioreactor cultivation. Model development was based on experimentally obtained data concerning the hybridoma cell counts, monoclonal antibody (mAb) production and the distribution of hybridoma cell growth within the microcapsules. The cell growth was modeled using a mean field approach expressed as Langevin class of equations for two different regions of alginate-PLL microcapsules, the alginate microcapsule core and the annular region between microcapsule core and membrane. In this paper we propose an influence of microenvironmental conditions on cell growth. The osmotic pressure changes in the Na-alginate liquefied annular region, as well as, the resistance effects of Ca-alginate hydrogel in the core region during the cell growth were incorporated into the model. Good agreement between the experimental data and model prediction values was obtained. The proposed model successfully predicted the impact of various microenvironmental restriction effects on the dynamics of cell growth and appears useful for further optimization of microcapsule design in order to achieve higher intra-capsule cell concentrations resulting in higher amounts of mAb produced.     

Optimization and oxidative stability of the microencapsulated conjugated linoleic acid

We used response surface methodology to optimize the preparation conditions of conjugated linoleic acid (CLA) microcapsules for maximum entrapment efficiency. Three independent variables were used: the ratio of CLA core material to agar and waxy corn starch wall material (X₁), the temperature of dispersion fluid (X₂), and the concentration of emulsifier (X₃). The optimized values of X₁, X₂, and X₃ were found to be 3.82:6.18, 19.97 °C, and 0.34%, respectively. The CLA oxidation stability was significantly protected by microencapsulation. These results suggest that CLA-loaded microcapsules can be used as a means to enhance not only the entrapment efficiency but also the oxidative stability of CLA.     

Competing two enzymatic reactions realizing one‐step preparation of cell‐enclosing duplex microcapsules

The usefulness of cell‐enclosing microcapsules in biomedical and biopharmaceutical fields is widely recognized. In this study, we developed a method enabling the preparation of microcapsules with a liquid core in one step using two enzymatic reactions, both of which consume H₂O₂ competitively. The microcapsule membrane prepared in this study is composed of the hydrogel obtained from an alginate derivative possessing phenolic hydroxyl moieties (Alg‐Ph). The cell‐enclosing microcapsules with a hollow core were obtained by extruding an aqueous solution of Alg‐Ph containing horseradish peroxidase (HRP), catalase, and cells into a co‐flowing stream of liquid paraffin containing H₂O₂. Formation of the microcapsule membrane progressed from the surface of the droplets through HRP‐catalyzed cross‐linking of Ph moieties by consuming H₂O₂ supplied from the ambient liquid paraffin. A hollow core structure was induced by catalase‐catalyzed decomposition of H₂O₂ resulting in the center region being at an insufficient level of H₂O₂. The viability of HeLa cells was 93.1% immediately after encapsulation in the microcapsules with about 250 µm diameter obtained from an aqueous solution of 2.5% (w/v) Alg‐Ph, 100 units mL^?1 HRP, 9.1 × 10⁴ units mL^?1 catalase. The enclosed cells grew much faster than those in the microparticles with a solid core. In addition, the thickness of microcapsule membrane could be controlled by changing the concentrations of HRP and catalase in the range of 13–48 µm. The proposed method could be versatile for preparing the microcapsules from the other polymer derivatives of carboxymetylcellulose and gelatin. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:1528–1534, 2013     

Use of encapsulated live microalgae to investigate pre-ingestive selection in the oyster Crassostrea gigas

The involvement of algal chemical cues in the pre-ingestive selection of food particles in Crassostrea gigas was studied using a new approach. Live cells of two microalgal species, Nitzschia closterium and Tetraselmis suesica, were separately entrapped in small alginate microcapsules using an emulsification/internal gelation method. Microcapsule size was adjusted to be within the range of particles ingested by oysters. Using this technique, about 80% of microcapsules had a diameter ranging from 21 to 100 μm. The monitoring of entrapped algae showed that phytoplankton cells remained alive and maintained an active growth for at least 24 days. In particle selection bioassays, adult C. gigas were fed a mixture of microcapsules containing the above algae species as well as control empty alginate microcapsules. The comparison of the proportions of each microcapsule type in the diet and in pseudofeces revealed that those containing T. suesica were significantly ingested while those containing N. closterium were preferentially rejected. Since microcapsule material (alginate matrix) prevented physical contacts between algae cells and oyster feeding organs, this study clearly demonstrate that extracellular metabolites produced by microalgae play a crucial role in the pre-ingestive selection of particles in suspension-feeding bivalves.     

Synthesis of amidic alginate derivatives and their application in microencapsulation of λ-cyhalothrin

1-Octyl amine was covalently coupled to sodium alginate(NaAlg) in an aqueous-phase reaction via acidamide functions using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC-HCl) as a coupling reagent to provide octyl-grafted amphiphilic alginate-amide derivative(OAAD) for subsequent use in λ-cyhalothrin (LCH) microcapsule application. The structure of OAAD was confirmed by FT-IR and (1)H NMR spectroscopies. The new alginate-amide derivative was used for fabricating microcapsule that can effectively encapsulate LCH by emulsification-gelation technique. The microcapsules were characterized by optical microscopy (OM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and laser particle size analysis. The encapsulation efficiency and drug release behavior of LCH from the microcapsules were investigated. Results showed that the microcapsules were in spherical form with diameter mostly in the range of 0.5-10 μm and possessed a structure with LCH as core and OAAD as shell. The encapsulation efficiency and the release performance of the microcapsules were influenced by DS of OAAD and amount of CaCl(2). The mechanism of LCH release was found to vary from anomalous to Fickian to quasi-Fickian transport with the DS of OAAD varied from 10.8 to 30.3 and the CaCl(2)/emulsion ratios varied from 0.09 to 0.03%.     

海藻酸钠漂浮微囊的制备以及载药应用研究

目的:本文研究了一种海藻酸钠漂浮微囊的制备方法用以实现胃部持续给药。方法:采用微胶囊发生器制备海藻酸钠漂浮微囊,壁材为海藻酸钠,芯材为食用油的漂浮微囊,衡量不同的制备参数对微囊的理化特性影响;采用克拉霉素作为模型脂溶性药物,测量漂浮药物递送系统的控制释放性质、以及微囊载药特性和小鼠体内漂浮验证。结果:成功制备出了具有漂浮特性的海藻酸钠微囊,其中泵送速度对微囊性质的影响最大。制备出的微囊具有低细胞毒性,可以实现90%的药物包埋率。此外,微囊可以在小鼠的胃中保存超过6小时,具有良好的漂浮特性。结论:海藻酸钠漂浮微囊是一种有效的胃部药物递送系统,可明显延长药物在胃部的滞留时间。     

Shear breakage of nylon membrane microcapsules in a turbine reactor

The breakage of nylon membrane microcapsules is proposed as a new method to study and quantify shear effects in biological systems. A critique of this method shows that a narrower particle size distribution may be an important improvement in the breakage study as well as breakage control in many bioreactor and biotechnological applications. In a turbine reactor, it was shown that the primary process which determines the microcapsule breakage is the shear effect. The breakage kinetics are first order with regard to the microcapsule concentration. The breakage kinetic constant was ob served to be dependent on the temperature and the particle size, and proportional to the average shear rate and the third power of the turbine angular velocity. Decrease of the breakage kinetic constant with temperature can be explained by a decrease of fluid viscosity and a change in nylon membrane properties. An increase in the breakage kinetic constant with the microcapsule diameter can be due to a lowering of internal pressure and a reduction of the membrane resistance with size. Proportionality between the breakage kinetic constant and the shear rate shows that shear is the main process which leads to microcapsule breakage. The additional intervention in the shear rate expression of the turbine angular speed in the form of the turbine and particle velocities, results in the dependence of the breakage kinetic constant on the third power of the angular velocity.     

Polyelectrolyte microcapsules as the systems for delivery of biologically active substances

Based on the method of the layer-by-layer (LbL) adsorption of oppositely charged polyelectrolytes, sodium alginate (Alg) and poly-L-lysine (PLL), novel biodegradable microcapsules have been prepared for delivery of biological active substances (BAS). Porous spherical CaCO₃ microparticles were used as templates. The template cores were coated with several layers of oppositely charged polyelectrolytes forming shell on the core surface. The core-shell microparticles were converted into hollow microcapsules by means of core dissolution with EDTA. Mild conditions for microcapsules preparation allow to perform incorporation of various biomolecules maintaining their bioactivity. Biocompatibility and biodegradability of the polyelectrolytes give a possibility to use the microcapsules as the target delivery systems. Chymotrypsin entrapped into the microcapsules was used as a model enzyme. The immobilized enzyme retained about 86% of the activity compared to a native chymotrypsin. The resultant microcapsules were stable in acidic medium and could be easily decomposed by trypsin treatment in slightly alkaline medium. Chymotrypsin was shown to be active after its release from the microcapsules decomposed by the trypsin treatment. Thus, the microcapsules prepared by the LbL technique can be used for the development of new type of BAS delivery systems in humans and animals.     

Development of hydrocortisone succinic acid/and 5-fluorouracil/chitosan microcapsules for oral and topical drug deliveries

Recently, we demonstrated the safety use of calendula oil/chitosan microcapsules as a carrier for both oral and topical deliveries. We also reported the improved biological activity towards skin cells and Staphylococcus aureus of phyllanthin containing chitosan microcapsules. However, the possibility of both oral and topical applications was still necessary to be further studied. Here we investigated that both oral and topical applications of chitosan-based microcapsules were tested using hydrocortisone succinic acid (HSA) and 5-fluorouracil (5-FU), respectively. The drug loading efficiency, particle size, surface morphology and chemical compositions of both drug loaded microcapsules were confirmed by UV-vis spectrophotometer, particle size analyzer, scanning electron microscope and Fourier transform infrared spectroscopy. The in vitro release studies revealed that both HSA and 5-FU could be released form chitosan microcapsules. The mean adrenocorticotropic hormone concentration in HSA loaded microcapsule mice plasma was detected to be lower than that of water control. One hundred micrograms per milliliter of 5-FU containing microcapsules exhibited a stronger growth inhibition towards skin keratinocytes than that of free 5-FU. In vitro drug delivery model demonstrated the delivery of 5-FU from microcapsule treated textiles into nude mice skin. Further uses of the drug loaded microcapsules may provide an efficiency deliverable tool for both oral and topical applications.     

Reducing the microcapsule diameter by micro-emulsion to improve the insecticidal activity of Bacillus thuringiensis encapsulated formulations

The emulsion/internal gelation method is highly effective to produce microcapsules of Bacillus thuringiensis (Bt) in a short time; however, it has the limitation to produce microcapsules within a wide range of diameters (1–1000?µm). The aim of this study was to reduce the range of small microcapsule diameters by using a water/corn-oil (W/CO) micro-emulsion as the dispersing medium and the mixture Tween 80–Span 80 as the surfactant. It involved the development of the W/CO micro-emulsion and the determination of the suitable agitation time to disperse the gelling medium (sodium alginate) through the micro-emulsion. A micro-emulsion formulation that allowed reduction of the microcapsule diameter was composed of 82% corn oil, 12% alginate solution and 6% surfactant mixture Tween80–Span80 (31:69). Evaluation of four dispersing times showed that 45 min was suitable to produce 75% of microcapsules of an average diameter of 3.1?±?1?µm containing the spore–protein complex (SPC) produced by Bt. Bioassays carried out at low concentrations of microencapsulated formulations of cry proteins allowed determination of how its insecticidal effect increased if the range of microcapsule diameters was reduced in the range 1–9?µm. Furthermore, the SPC formulation in alginate microcapsules showed high resistance to extreme irradiation (2.9?±?0.5?×?10⁸ erg) of a long wavelength (365?nm), which made the microencapsulated formulation profitable and of high yield since repeated applications of the biopesticide during the same harvest period may not be necessary.