Rotating Membrane Emulsification Research Articles

The performance of rotating membrane emulsification in the presence of baffles: Insights from flux experiments, microstructural analysis, and positron emission particle tracking

Rotating Membrane Emulsification (RME) is a bottom-up emulsification technique developed to circumvent the significant energy requirements of conventional methods; however, its implementation has been hindered by low emulsion throughputs. This work presents a novel baffled-RME setup and investigates the potential improvement to emulsion throughput and droplet microstructure, whilst employing both surface-active and Pickering particle emulsifiers to assess whether any advantages are emulsifier-specific. Overall, baffle addition improves emulsion throughputs, however the droplet microstructure was positively influenced only when using surfactant-based emulsifiers. Positron Emission Particle Tracking (PEPT) was utilised to demonstrate that these advantages result from improved hydrodynamic conditions instigated by the break-up of streamlines, inducing higher turbulence near the membrane surface, and by increasing the transmembrane pressure drop and drag force through flow restrictions. Overall, by detailing the first baffled-RME setup and first application PEPT analysis to such equipment, this work lays the foundation for further optimisation of bottom-up emulsification approaches.

Preparation of Alginate Microspheres by Rotating Membrane Emulsification

Preparation of Alginate Microspheres by Rotating Membrane Emulsification

Application of Square and Oblong Pore Shapes in Rotating Membrane Emulsification to Produce Novel Particulate Products

Rotating membrane emulsification (RMR) has been intensively developed and applied for producing emulsion as well as particulate products such as microcapsules. Polyurea microcapsules were generally prepared by interfacial polycondensation polymerisation with addition of modifier to produce more stable microcapsules. In this research, development of the RMR was applied for producing polymer particles stabilised by nanoparticle without any addition of surfactant or modifier. Two types of membrane pores, the square (Type-A) with hydraulic diameter (Dh) of 84 mm and oblong pores with an aspect ratio of 0.33 (Type-B) having Dh of 69 mm was investigated. For the membranes designed in this research, pore shape A membrane could produce good uniformity in both polyurea microcapsule and polymer particle. In the polymer stabilised particle, this membrane type obtained a narrower size distribution than the usage for o/w emulsification. Reasonable uniform particles at high membrane rotation speed could also be achieved with the use of Type-A membrane. The uniformity confirmed that there was only minor breakup of products during operation at high membrane rotation. This attractive feature was significant in the production of fragile or shear-sensitive particulate products since the delicate structure of these products is possibly easy to destroy at high membrane rotation speed. Keywords: polyurea microcapsules; particles stabilised nanoparticles; slotted pore

Magnetic navigation helps PLGA drug loaded magnetic microspheres achieve precise chemoembolization and hyperthermia

The poly-(lactic-co-glycolic acid) drug loaded magnetic microspheres (PLGA-DMMs) containing anti-tumor drug PTX with well-controlled sizes have been prepared by novel rotating membrane emulsification technique. Scanning electron microscopy and EDS showed that the as-prepared microspheres had regular shape while the C, O and Fe elements were observed distribution on the surface uniformly. The in vitro cytotoxicity and magnetically induced heating evaluation certified their well biocompatibility and excellent heating performance, respectively. The HPLC confirmed these as-prepared microspheres with fine drug loading coefficient 8.1 % along with 94.6 % encapsulation efficiency. In particular, PTX release behavior revealed that temperature had played a decisive role to affect the drug release during 90 days. We subsequently introduced the gradient magnetic field analysis system to simulate magnetic navigation embolization and help understanding the dynamic behavior of microspheres during this process. We believe that this work can not only enrich the fabrication of drug loaded magnetic microspheres with high performance, but also provide a valuable reference for achieving precise chemoembolization and hyperthermia via magnetic navigation in the future.

Pickering particle and emulsifier co-stabilised emulsions produced via rotating membrane emulsification

Producing stable particle-stabilised emulsions of small droplet sizes and high monodispersity via membrane emulsification approaches is hindered by the poor mixing environment during processing and the low diffusivity and minimal interfacial tension lowering capacity of colloidal particles. The present study investigates the co-stabilisation (particles and emulsifiers) of O/W emulsions formed by rotating membrane emulsification. Formulation aspects of the employed co-stabilisation strategy (type/concentration of emulsifiers and type/size of particles) were assessed at a fixed trans-membrane pressure (10 kPa) and rotational velocity (2000 rpm). Emulsion microstructure was shown to be affected by the occurrence of emulsifier/particle interactions. In formulations where these interactions are synergistic and emulsifier content is low, interfacial stabilisation is carried out by both species and resulting emulsions possess smaller droplet sizes, higher monodispersity indices and enhanced stability against coalescence, compared to systems stabilised by either of the two components alone. This work concludes that a carefully controlled co-stabilisation strategy can overcome the current challenges associated with the production of particle-stabilised emulsions via membrane emulsification methods.

Rotating Membrane Emulsification for Producing Single and Multiple Emulsions

Membrane emulsification is a technique utilising a novel concept of generating droplet ‘drop by drop’ to produce emulsions. The technique has several distinctive advantages over the conventional emulsification techniques.This paper concerns on the development of membrane emulsification (Rotating Membrane Reactor, RMR) which utilizes rotating tubular membrane to initiate droplet detachments. The RMR uses a rotating stainless steel tubular membrane with laser drilled pores (100 μm pore diameter) and a syringe pump to drive the dispersed phase through the membrane at a given flow rate. O/W formulations were prepared with low viscosity of paraffin wax, two types of emulsifiers, different membrane rotation rate and dispersed phase flow rate. The emulsion droplets exhibited a coefficient of variation of 9% and 81μm droplet size. In this research, the pore size/droplet size ratio could achieve 0.8. This value was below than other membrane emulsification processes. The effects of principal system operating parameters on both the average droplet diameter and droplet uniformity were discussed. In addition, a multiple (W/O/W) emulsion formulation was investigated as well.

High-Performance Poly(lactic-co-glycolic acid)-Magnetic Microspheres Prepared by Rotating Membrane Emulsification for Transcatheter Arterial Embolization and Magnetic Ablation in VX2 Liver Tumors.

Interventional embolization is a popular minimally invasive vascular therapeutic technique and has been widely applied for hepatocellular carcinoma (HCC) therapy. However, harmful effects caused by transcatheter arterial chemoembolization (TACE) and radioembolization, such as the toxicity of chemotherapy or excessive radiation damage, are serious disadvantages and significantly reduce the therapeutic efficacy. Here, a synergistic therapeutic strategy combined transcatheter arterial embolization and magnetic ablation (TAEMA) by using poly(lactic-co-glycolic acid) (PLGA)-magnetic microspheres (MMs) has been successfully applied to orthotopic VX2 liver tumors of rabbits. These MMs fabricated by novel rotating membrane emulsification system with well-controlled sizes (100-1000 μm) exhibited extremely low hemolysis ratio and excellent biocompatibility with HepG2 cells and L02 cells. Moreover, experimental results demonstrated that, while exposed to alternating magnetic field (AMF) after TAE, the tumor edge could be heated up by more than 15 °C both in vivo and in vitro, whereas only a negligible increase of temperature was observed in the normal hepatic parenchyma (NHP) nearby. Sufficient temperature increase induces apoptosis of tumor cells. This can further inhibit the tumor angiogenesis and results in necrosis compared to the rabbits only treated with TAE. In stark contrast, tumors rapidly grow and subtotal metastasis occurs in the lungs or kidneys, causing severe complications for rabbits only irradiated under AMF. Importantly, the results from the biochemical examination and the gene expression of relative HCC markers further confirmed that the treatment protocol using PLGA-MMs could achieve good biosafety and excellent therapeutic efficacy, which are promising for liver cancer therapy.

Analysis of rotating membrane emulsification performance for oil droplet production based on the Taylor vortices approach

ABSTRACTMembrane emulsification processes generally employ a cross flow of the continuous phase in order to produce shear stress. Modification of membrane emulsification for the o/w emulsion using the rotating system has been introduced such as the use of stirred cells or a rotating tubular membrane in a stationary liquid. This paper presents an examination of membrane rotation speed on droplet characteristics. The performance of rotating membrane emulsification on o/w droplet size, the coefficient of variation, and size distribution was investigated. In addition, the operated flow regime in the rotating membrane emulsification is addressed. It has been found that overall the droplet size decreased with the increase of membrane rotation speed. The droplet size below the pore size could be produced when operating at a high rotation speed (1500 rpm). The decrease of droplet size was believed due to the action of Taylor vortices on droplet detachment. Analysis of membrane rotation speed proposed that action of Taylor vortices facilitates droplet detachment. Calculation of Taylor numbers (having a value of 0–629) confirmed that the rotating membrane emulsification produced laminar flow with vortices.

The effects of membrane composition and morphology on the rotating membrane emulsification technique for food grade emulsions

The effects of using different membrane materials and morphologies in the membrane emulsification process were observed using similar operating parameters and system geometry, allowing a direct comparison of not only the membranes themselves but also between both a stationary cross-flow membrane emulsification device and a rotated membrane emulsification device. Each membrane type tested had distinct characteristics, and the droplet sizes produced responded differently to changes in operating conditions.The rotating membrane produced similar droplet sizes to the cross flow membrane system, but at a much lower shear rate. This suggests that the detachment of the droplets occurs sooner due to the additional centrifugal force and system vibration. The Shirasu porous glass (SPG) membrane produced the smallest droplet sizes (<1µm from a 1µm membrane), however the stainless steel membrane produced the lowest droplet size to pore size ratio (~0.5:1) due to its cylindrical pore geometry as opposed to the tortuous geometries of the other membranes used. The droplet sizes produced at different pressures are similar between rotated and cross-flow membrane emulsification, with increases in pressure increasing droplet size and size distribution. The viscosity of the continuous phase has an effect on the droplet size; increasing the viscosity decreases the droplet size by increasing the applied shear, allowing fine tailoring of the size produced, with a more viscous continuous phase reducing the droplet size from ~4µm to ~1µm with an increase in viscosity of 100mPas.Rotating membrane emulsification has properties with potential to produce shear sensitive emulsion microstructures with small droplet sizes. Emulsion microstructures such as duplex emulsions, core/shell structures beads etc. can be used in the production of novel food structures.

Process optimisation of rotating membrane emulsification through the study of surfactant dispersions

In this study, a rotating membrane emulsification setup incorporating a 6.1μm pore diameter Shirasu porous glass membrane was used to produce oil-in-water emulsions. The processing conditions varied between 0.2 and 1.5bar for the transmembrane pressure and shear rates at the membrane surface between 0.6s−1 and 104.6s−1 were generated. All emulsions consisted of 10vol.% of sunflower oil stabilised by one of four different surfactants (Tween 20, Brij 97, lecithin and sodium dodecyl sulphate) of either 0.1wt.% or 1wt.% concentration. A novel approach for emulsification processing was introduced which incorporates high hydrophilic–lypophilic balance, non-ionic surfactants within the dispersed phase rather than the continuous phase. A reduction in droplet size by at least a factor of 3 for the same formulation can be achieved without significant hindrance on disperse phase flux. This therefore suggests a possible strategy for further process optimisation.

Processing effects during rotating membrane emulsification

In this study, a rotating membrane emulsification setup incorporating a 6.1μm pore diameter SPG membrane was used to produce O/W emulsions of average droplet sizes between 23.4 and 216.6μm. All emulsions consisted of 10vol% of sunflower oil or silicone oil stabilised by 1wt% Tween 20. The transmembrane pressure (0.1–1.8bar), rotational speeds (100–2000RPM) annular gap width (5–45mm), dispersed and continuous phase viscosity were all investigated as to their effect on emulsion droplet size and dispersed phase flux. Modification of the dispersed phase flow properties alters the droplet size with four regions being suggested; a decrease in size (as droplet coalescence is minimised), a plateau (size-stable zone), a gradual increase in size (due to transfer of mass via droplet neck) and then a rapid increase (due to jetting). The importance of Taylor vortices development was seen with larger droplets formed in their absence; typically at low rotational speeds, narrow vessel diameters and more viscous continuous phases. It was concluded that the flow behaviour of each phase requires careful consideration to understand the likely formation mechanism(s) during operation. Across the pressure and viscosity ranges investigated, the dispersed phase flux ranged between 50 and 12,500Lm−2h−1 and pore activity was within the range of 0.5–2.7%.

Production of solid-stabilised emulsions through rotational membrane emulsification: influence of particle adsorption kinetics

There is currently a significant interest in the production of stable emulsions using particulate emulsifiers. A key design and manufacturing challenge in such systems is the production of emulsions with controlled droplet sizes and narrow polydispersity; one candidate production technique is membrane emulsification. In this study we demonstrate that under optimal conditions, highly stable near monodisperse tricaprylin droplets stabilised with 800 nm silica colloids can be achieved using Rotating Membrane Emulsification (RME). We report the influence of various mechanical and chemical parameters on the droplet sizes and size distributions. The optimal conditions for highly stable emulsions with narrow size distributions using the RME approach are described. Investigating the rotational speed and particle concentration in particular highlights the importance of particle adsorption kinetics onto a growing droplet on the detachment of that droplet from the membrane. The data clearly show that if the particles attach and adsorb to the interface before a critical droplet detachment time, stable monodisperse droplets are produced. However, if the adsorption time takes longer than this critical value, the partially stabilized droplets can coalesce and we observe a wider size distribution.

Performance of slotted pores in particle manufacture using rotating membrane emulsification

This paper addresses the use of different slotted pores in rotating membrane emulsification technology. Pores of square and rectangular shapes were studied to understand the effect of aspect ratio (1–3.5) and their orientation on oil droplet formation. Increasing the membrane rotation speed decreased the droplet size, and the oil droplets produced were more uniform using slotted pores as compared to circular geometry. At a given rotation speed, the droplet size was mainly determined by the pore size and the fluid velocity of oil through the pore (pore fluid velocity). The ratio of droplet diameter to the equivalent diameter of the slotted pore increased with the pore fluid velocity. At a given pore fluid velocity and rotation speed, pore orientation significantly influences the droplet formation rate: horizontally disposed pores (with their longer side perpendicular to the membrane axis) generate droplets at double the rate of vertically disposed pores. This work indicates practical benefits in the use of slotted membranes over conventional methods.

Manufacture of controlled emulsions and particulates using membrane emulsification

Crossflow and rotating membrane emulsification techniques were used for making oil-in-water (O/W) emulsions. The emulsions produced from a variety of oils and monomers (viscosity 7–528 mPas) exhibited narrow size distributions over a wide droplet size range, with the average droplet size ranging from less than 1 μm up to 500 μm. The monomer emulsions were further encapsulated to produce microcapsules through subsequent polymerisation reactions. The monodispersity feature of the primary emulsions was retained after the encapsulation. In comparison with other homogenisation methods, our experimental results demonstrated that the membrane emulsification technique is not only superior in emulsion droplet size controls, but also advantageous in energy efficiency and industrial-scale productions.

Performance of rotating membrane emulsification for o/w production

The conventional process for emulsificationbased on rotor–stator system, high pressurehomogenizer and ultrasonic waves use dropletbreak-up as dispersing mechanism and usuallycouple with considerably input and high shearstress [1]. In order to so lve the limitation of con-ventional production of emulsion, a new methodcalled membrane emulsification has been devel-oped [2]. This new method has been proven as asuperior technique for producing emulsion [3,4].A new development of membrane emulsifica-tion that is called rotating membrane reactor(RMR) is introduced [5]. The membrane hasbeen modified to rotate or through the use ofspinning membrane tube. It is expected that themembrane rotation can increase the productivityof membrane emulsification and well suited tothe production of solids and capsules.

Manufacture of large uniform droplets using rotating membrane emulsification

A new rotating membrane emulsification system using a stainless steel membrane with 100 μm laser drilled pores was used to produce oil/water emulsions consisting of 2 wt% Tween 20 as emulsifier, paraffin wax as dispersed oil phase and 0.01–0.25 wt% Carbomer (Carbopol ETD 2050) as stabilizer. The membrane tube, 1 cm in diameter, was rotated inside a stationary glass cylinder, diameter of 3 cm, at a constant speed in the range 50–1500 rpm. The oil phase was introduced inside the membrane tube and permeated through the porous wall moving radially into the continuous phase in the form of individual droplets. Increasing the membrane rotational speed increased the wall shear stress which resulted in a smaller average droplet diameter being produced. For a constant rotational speed, the average droplet diameter increased as the stabilizer content in the continuous phase was lowered. The optimal conditions for producing uniform emulsion droplets were a Carbomer content of 0.1–0.25 wt% and a membrane rotational speed of 350 rpm, under which the average droplet diameter was 105–107 μm and very narrow coefficients of variation of 4.8–4.9%. A model describing the operation is presented and it is concluded that the methodology holds potential as a manufacturing protocol for both coarse and fine droplets and capsules.