Rotor-stator Homogenizer Research Articles

Rheological properties and physical stability of ecological emulsions stabilized by a surfactant derived from cocoa oil and high pressure homogenization

The goal of this work was to investigate the influence of the emulsification method on the rheological properties, droplet size distribution and physical stability of O/W green emulsions formulated with an eco-friendly surfactant derived from cocoa oil. The methodology used can be applied to other emulsions. Polyoxyethylene glycerol esters are non-ionic surfactants obtained from a renewable source which fulfill the environmental and toxicological requirements to be used as eco-friendly emulsifying agents. In the same way, N,NDimethyloctanamide and α-Pinene (solvents used as oil phase) could be considered green solvents. Emulsions with submicron mean diameters and slight shear thinning behavior were obtained regardless of the homogenizer, pressure or number of passes used. All emulsions exhibited destabilization by creaming and a further coalescence process which was applied to the coarse emulsion prepared with a rotor-stator homogenizer. The emulsion obtained with high pressure at 15000 psi and 1-pass was the most stable.

Emulsification using tubular metallic membranes

Tubular metallic membranes with pore diameters of 5 and 10 μm have been used in a cross-flow unit to prepare monodisperse oil-in-water emulsions (O/W) with span values as low as 0.67, significantly lower than for emulsions prepared with a rotor–stator homogenizer. The influence of typical operating parameters (continuous phase flow rate and transmembrane pressure) on droplet size distribution was studied. The smallest droplets were obtained at low transmembrane pressures and high continuous phase flow rates. The droplet production with tubular metallic membranes was higher than with other types of tubular membranes, such as SPG or ceramic. Experimental results were compared with those obtained in a stirred tank unit operating under similar conditions and using flat metallic membranes with the same pore diameter. Droplet size prediction models based on simple force balances were applied to compare theoretical and experimental droplet diameters. The droplet formation regime (dripping, jetting) was also studied for both types of membranes.

SiO 2 纳米颗粒与聚氧乙烯对Pickering乳液的协同稳定作用

研究了聚氧乙烯(PEO)与SiO 2 纳米颗粒对水/二甲苯体系Pickering乳液的协同稳定作用. 实验发现，PEO的存在减小了乳液液滴的平均直径，抑制了乳液的相反转，有效阻止了乳液的熟化，使乳液具有更好的稳定性. 进一步对纳米颗粒膜的流变性质进行研究，结果表明，PEO高分子促进了纳米颗粒形成更大尺寸的聚集结构，提高了其在界面上的吸附性，增强了颗粒膜的力学性能，在较小颗粒用量条件下使得Gibbs稳定性判据得到满足.

Measurement and analysis of bimodal drop size distribution in a rotor–stator homogenizer

Rotor–stator homogenizers are widely used to manufacture liquid–liquid emulsions, but little emphasis has been placed on understanding the processing principles of these devices. In this study, a systematic series of experiments have been performed to investigate and quantify the effects of process parameters and formulation variables on the drop size distribution (DSD) and relative sizes of oil-in-water emulsions manufactured in a Rotor–stator homogenizer. The effects of rotor speed, the dispersed phase viscosity and the dispersed phase volume fraction were studied. The DSDs by volume were predominantly bimodal, and the smaller drop size peak appeared at 1μm for most of the oil-in-water emulsions in our experiment. Furthermore, the relationship between the Sauter mean diameter and the maximum stable drop diameter was found to be linear in emulsions with a bimodal volume distribution, and the proportionality constant somewhat decreases as the viscosity of the dispersed phase increases. Compared with the normal and log-normal function, the Frechet function, which is usually proposed to describe the extreme value problem, can describe the monomodal number DSD very well. The experiments also show that the low-viscosity droplets are stabilized by a combination of interfacial tension and viscous forces, while viscous forces primarily prevent breakage in high viscosity droplets. A modified version of Calabrese's model has been developed for combining the effect of the dispersed phase viscosity and volume fraction on drop size, which represents the experimental data well.

Stirred tank membrane emulsification using flat metallic membranes: A dimensional analysis

The performance of a membrane emulsification unit, using flat membranes in a stirred tank, has been examined by dimensional analysis. The dimensionless numbers were defined in terms of shear and membrane pore size. Dimensionless droplet size prediction models based on simple force balances were used to select the most representative dimensionless numbers including operating parameters. Oil-in-water emulsions were produced with tailor-made metallic membranes with pore sizes of 30 and 50μm. Results showed that monodisperse emulsions were produced with span values around 0.5, significantly lower than when a rotor-stator homogenizer is used. The influence of the selected operating parameters (impeller rotational speed, continuous phase viscosity and dispersed phase flux) on droplet size distribution was studied and experimental results were compared with droplet size prediction models. Impeller rotational speed and membrane pore size were the key parameters influencing emulsion droplet size and monodispersity. A correlation based on the Euler dimensionless number, including all the operating parameters is proposed.

Preparation and characterization of water-in-oil emulsions loaded with high concentration of l-ascorbic acid

The present study was conducted to encapsulate higher concentration of l-ascorbic acid up to (30 g 100 mL−1) in the dispersed phase of water-in-oil (W/O) emulsions. Their continuous phase contained refined soybean oil or Moringa oleifera oil and a food-grade hydrophobic emulsifier. The volume fraction of the dispersed phase was fixed as to 30%. W/O emulsions with l-ascorbic acid retention greater than 95% were prepared using rotor–stator homogenizer at 7000 rpm for 5 min. The prepared W/O emulsions under this operating conditions had average droplet diameter of 2.0–3.0 μm and coefficients of variation of 13%–22%. All the W/O emulsions were stable for more than 30 days at 4 °C or 25 °C with slight increase in average droplet diameter and without phase separation. Their l-ascorbic acid retentions were 50 g 100 g−1 at 4 °C and 30 g 100 g−1 at 25 °C after 30 days of storage. l-ascorbic acid retention ratio of the prepared W/O emulsions followed first-order kinetics with a good fit.

Fish Oil Microcapsules from O/W Emulsions Produced by Premix Membrane Emulsification

Fish oil microcapsules were prepared by combining a low-energy emulsification method (premix membrane emulsification) with spray drying. Oil-in-water (O/W) emulsions were prepared using a two-step emulsification method that used a rotor–stator homogenizer followed by membrane emulsification. The influence of the emulsification method (mechanical stirring or membrane emulsification), the emulsification conditions (membrane and emulsifier type), and the amount of wall material on the physicochemical characteristics of the microcapsules was studied. The results show that the emulsification method and the type and amount of emulsifier and wall material affect the final amount of encapsulated oil. Microcapsules produced by membrane emulsification and stabilized with 2 % Tween-20 or 10 % whey protein presented the highest values (higher than 50 %) of oil encapsulation efficiency (OEE). It has been found that the OEE increases when decreasing the droplet size of the emulsions as well as with the increase of the amount of wall material employed during drying. Morphology analysis showed that the microcapsules obtained from O/W emulsions produced by premix membrane emulsification were rounder in shape, without visible cracks on the surface and no vacuoles on the inside. Oxidation stability tests performed on some selected samples indicate that the microcapsules with higher stability are the ones produced with a higher amount of wall material and have less surface oil.

Effect of homogenization conditions on properties of gelatin–olive oil composite films

Gelatin–olive oil composite films were prepared through emulsification to improve water barrier ability of gelatin-based films. The effects of homogenization conditions of film-forming dispersions (FFD) on lipid droplets distributions in the FFD and films were evaluated and compared. Some selected physical properties, e.g., water vapor permeability (WVP), microstructure of the films were also evaluated. The rotor–stator homogenizer provided a lower energy input and so the largest particles were observed in the related FFD and films. These films exhibited excellent water barrier ability, but poor mechanical resistance, extensibility and transparency. The microfluidizer provided the FFD with lower and narrower particle size distributions, promoting mechanical resistance, extensibility and transparency of the films. The physical properties of the emulsified films were dependent on the special microfluidization pressure or cycle used, e.g., the WVP of the films decreased upon increasing microfluidization pressure or cycle. The present results indicated that the microfluidizer can be used to modulate lipid droplets in the FFD, thus films’ properties.

Hexosamine Biosynthetic Pathway Mutations Cause Neuromuscular Transmission Defect

Neuromuscular junctions (NMJs) are synapses that transmit impulses from motor neurons to skeletal muscle fibers leading to muscle contraction. Study of hereditary disorders of neuromuscular transmission, termed congenital myasthenic syndromes (CMS), has helped elucidate fundamental processes influencing development and function of the nerve-muscle synapse. Using genetic linkage, we find 18 different biallelic mutations in the gene encoding glutamine-fructose-6-phosphate transaminase 1 (GFPT1) in 13 unrelated families with an autosomal recessive CMS. Consistent with these data, downregulation of the GFPT1 ortholog gfpt1 in zebrafish embryos altered muscle fiber morphology and impaired neuromuscular junction development. GFPT1 is the key enzyme of the hexosamine pathway yielding the amino sugar UDP-N-acetylglucosamine, an essential substrate for protein glycosylation. Our findings provide further impetus to study the glycobiology of NMJ and synapses in general.

Optimization of the emulsification and solvent displacement method for the preparation of solid lipid nanoparticles

Objective: The essential aim of this article is to prepare solid lipid nanoparticles (SLNs) by emulsification and solvent displacement method and to determine the best process conditions to obtain submicron particles. Methods: The emulsification and solvent displacement method is a modification of the well-known emulsification–diffusion method, but without dilution of the system. The extraction of the partially water-miscible solvent from the emulsion globules is carried out under reduced pressure, which causes the diffusion of the solvent toward the external phase, with subsequent lipid aggregation in particles whose size will depend on the process conditions. The critical variables affecting the process, such as stirring rate, the proportion of phases in the emulsion, and the amount of stabilizer and lipid, were evaluated and optimized. Results: By this method, it was possible to obtain a high yield of solids in the dispersion for the lipids evaluated (Compritol® ATO 888, Geleol®, Gelucire® 44/14, and stearic acid). SLNs of up to ∼20 mg/mL were obtained for all lipids evaluated. A marked reduction in size, between 500 and 2500 rpm, was seen, and a transition from micro- to nanometric size was observed. The smaller particle sizes obtained were 113 nm for Compritol® ATO 888, 70 nm for Gelucire® 44/14, 210 nm for Geleol®, and 527 nm for stearic acid, using a rotor–stator homogenizer (Ultra-Turrax®) at 16,000 rpm. The best phase ratio (organic/aqueous) was 1 : 2. Conclusions: The process proposed in this study is a new alternative to prepare SLNs with technological potential.

Neuronal Nogo-A Modulates Growth Cone Motility via Rho-GTP/LIMK1/Cofilin in the Unlesioned Adult Nervous System

Nogo-A has been extensively studied as a myelin-associated neurite outgrowth inhibitor in the lesioned adult central nervous system. However, its role in the intact central nervous system has not yet been clarified. Analysis of the intact adult nervous system of C57BL/6 Nogo-A knock-out (KO) versus wild-type (WT) mice by a combined two-dimensional gel electrophoresis and isotope-coded affinity tagging approach revealed regulation of cytoskeleton-, transport-, and signaling growth-related proteins, pointing to regulation of the actin cytoskeleton, the neuronal growth machinery, and in particular the Rho-GTPase/LIMK1/cofilin pathway. Nogo-A KO adult neurons showed enlarged, more motile growth cones compared with WT neurons. The phenotype was reproduced by acute in vitro neutralization of neuronal Nogo-A. LIMK1 phosphorylation was increased in Nogo-A KO growth cones, and its reduction caused the decrease of KO growth cone motility to WT levels. Our study suggests that in the unlesioned adult nervous system, neuronal Nogo-A can restrict neuronal growth through negative modulation of growth cone motility.

Characterization of an Alternative Splice Variant of LKB1

LKB1 is an upstream activating kinase for the AMP-activated protein kinase (AMPK) and at least 12 other AMPK-related kinases. LKB1 therefore acts as a master kinase regulating the activity of a wide range of downstream kinases, which themselves have diverse physiological roles. Here we identify a second form of LKB1 generated by alternative splicing of the LKB1 gene. The two LKB1 proteins have different C-terminal sequences generating a 50-kDa form (termed LKB1L) and a 48-kDa form (LKB1S). LKB1L is widely expressed in mouse tissues, whereas LKB1S has a restricted tissue distribution with predominant expression in the testis. LKB1S, like LKB1L, forms a complex with MO25 and STRAD, and phosphorylates and activates AMPK both in vitro and in intact cells. A phosphorylation site (serine 431 in mouse) and a farnesylation site (cysteine 433 in mouse) within LKB1L are not conserved in LKB1S raising the possibility that these sites might be involved in differential regulation and/or localization of the two forms of LKB1. However, we show that phosphorylation of serine 431 has no effect on LKB1L activity and that both LKB1L and LKB1S have similar patterns of subcellular localization. These results indicate that the physiological significance of the different forms of LKB1 is not related directly to differences in the C-terminal sequences but may be due to their differential patterns of tissue distribution.

Analysis of gene expression in human tendon pathology

Chronic tendon pain is extremely common but little is known about the pathology of early stages of the disease, mainly due to the lack of human tendon biopsy material. Most chronic tendinopathy (tendinitis) involves changes in collagen composition, such as an increase in collagen type III compared to collagen type I, consistent with an attempt by the tenocytes to repair minor matrix damage (Riley et al. 1994). There is also evidence for increased collagen turnover associated with changes in the relative activities of interstitial collagenase (MMP-1) and its inhibitor (TIMP) (Riley et al. 1997). Growth factors and cytokines such as transforming growth factor beta (TGFb) and IL-1 are involved in matrix repair after injury and are likely to have a role in the regulation of tendon metabolism, although their activity in chronic tendinopathy is currently not known. Ultrasound-guided needle biopsies have recently been used to investigate tendon pathology (Movin et al. 1997) providing valuable material from relatively early stages of tendon disease, prior to rupture. However such tissue samples are very small — sometimes less than 5 mg wet weight — and present particular difficulties for molecular and biochemical analysis. The aims of this project are to: develop and optimize a method for the extraction of RNA and protein from very small tendon tissue samples; use this RNA in a quantitative RT-PCR-based method to measure levels of mRNA of proteins such as the collagens, MMP-1, TIMP, TGFβ, IL-1 and GAPDH; compare mRNA and protein levels in the same specimens, using semiquantitative immunoblotting. Materials and methods RNA was extracted using either Trizol reagent or a modification of ‘TriSpin’ method (Reno et al. 1997). A rotor-stator homogenizer was used to disrupt tendon tissue samples in Trizol or in a home-made monophasic reagent containing phenol, isoamyl alcohol, guanidinium isothiocyanate and beta-mercaptoethanol (PIG-B) (Weber et al. 1994). After addition of chloroform and phase separation, RNA was extracted from the aqueous phase of the Trizol reagent by alcohol precipitation or from the aqueous phase of PIG-B by using commercially available spin columns. Total RNA was used in a quantitative RT-PCR-based method which used an external standard curve generated by coamplification of increasing amounts of in vitro transcribed wild-type mRNA with constant amount of competitor mimic mRNA which had an internal deletion (Ravaggi et al. 1994). Primers for TGFb and IL-1 were purchased from Stratagene. Other primer sequences were taken from published data (Wagget et al. 1998) or designed using GCG software. Protein was extracted from the organic phase of the extraction reagents by alcohol precipitation, separated by SDS-PAGE, transferred to PVDF for immunoblotting with antibodies to MMP-1, TIMP-1, collagen I and collagen III and detected using a chemiluminescent detection system (ECL plus, Amersham).

Influence of the primary emulsification procedure on the characteristics of small protein-loaded PLGA microparticles for antigen delivery

Microparticles prepared from poly(lactic-co-glycolic acid) (PLGA) using a W1/O/W2 double emulsion solvent evaporation method are suitable vehicles for the delivery of proteins to antigen presenting cells, e.g. dendritic cells. In this study, the influence of different techniques for the preparation of the primary W1/O emulsion was investigated with respect to the protein localization within the microparticles, morphological characteristics of these particles, protein burst release and the native state of the released protein. Bovine serum albumin bearing fluorescein isothiocyanate (FITC-BSA) was used as model protein. A static micromixer was applied for the preparation of the W1/O/W2 double emulsion. Employing a rotor-stator homogenizer (Ultra-Turrax®) for primary emulsification, microcapsules with a high burst release were produced, because nearly all FITC-BSA was attached to the outside of the particle wall. Using a high pressure homogenizer or an ultrasonic procedure resulted in the formation of microspheres with homogeneous protein distribution and a reduced burst release.

Preparation of Suspension Polymerized Color Toners and Correlation Between Ingredients and Rheological Behavior

Syntheses and technology for preparation of cyan toner for dual component development by means of a suspension polymerization method is described. In this study, the organic phase, containing styrene monomer, n-butylacrylate, divinylbenzene, azo-bis-diisobutyronitrile, paraffin and Phthalocyanine Blue, was first dispersed into the aqueous phase, containing polyvinyl alcohol and sodium dodecylsulfate as suspension dispersants. Then dispersion was performed by a rotor-stator homogenizer, and subsequently the dispersion system was transferred to a three-orifice flask with a paddle stirring blade, where the polymerization reaction occurred. Correlations between amount of crosslinking agent and molecular weight of insoluble proportion in toners, and between gel content and some rheological behavior, such as viscous ? ow temperature, and melt index are discussed. Effects of Phthalocyanine Blue on charge-to-mass ratio and the interaction between resin in toners and Phthalocyanine Blue were studied. It was suggested that gel formation rather than increasing the molecular weight of the insoluble portion of the toner resulted in a change in rheological behavior according to the measured data of gel content, GPC, DSC, softening point and melt index. The Phthalocyanine Blue cause a notable increase in charge-to-mass ratio. The related infrared spectra suggested that the interactions between Phthalocyanine Blue T and resin mainly involved physical forces.

Interfacial polymerization encapsulation of a viscous pigment mix: emulsification conditions and particle size distribution.

A viscous organic phase, containing up to 65 per cent solid pigment, was dispersed into water with an emulsifier by a rotor-stator homogenizer and the droplets formed were encapsulated by interfacial polymerization. Microcapsules with volume median diameters d50 ranging from 10 to 25 microns and geometric standard deviation (GSD), from 1.25 to 1.65, were obtained depending on emulsification conditions. Larger impellers gave smaller d50 and slightly narrowed GSD; d50 decreased and GSD increased as volume fraction of dispersed phase is decreased. Higher homogenizer speed and emulsifier concentration decreased d50 but slightly increased GSD. Increasing pigment content in dispersed phase decreased d50 but had little effect on GSD. These effects were assessed quantitatively by fitting an empirical model to the data.