Scientific Papers

Hanga, MP and Holdich, RG (2014) Membrane emulsification for the production of uniform poly-N-isopropylacrylamide-coated alginate particles using internal gelation, Chemical Engineering Research and Design, 92(9), pp.1664-1673, DOI: 10.1016/j.cherd.2013.12.010.

Alginate particles, crosslinked by calcium ions, have a number of potential biopharmaceutical industry applications due to the biocompatibility of the materials used and formed. One such use is as microcarriers for cell attachment, growth and then detachment without the use of proteolytic enzymes. A straightforward and reproducible method for producing uniform calcium alginate particles with controllable median diameters which employs membrane emulsification and internal gelation (solid particles contained in the dispersed phase) is demonstrated, as well as functionalisation of the resulting beads with amine terminated poly N-isopropylacrylamide (pNIPAM) to form temperature responsive particles, by taking advantage of the electrostatic interaction between the carboxyl groups of the alginate and amino groups of the modified pNIPAM. Cell attachment, growth and detachment capabilities of these core–shell structures were assessed and successfully demonstrated by using phase contrast microscopy and fluorescent staining with calcein-AM and ethidium homodimer-1.

The formulation used for the alginate particles avoided non-GRAS chemicals by only using food grade and pharmaceutical grade reagents. The median particle size was controllable within the range between 55 μm and 690 μm and the size distributions produced were very narrow: ‘span’ values as low as 0.2. When using a membrane pore size of 20 μm no membrane blockage by the suspended calcium carbonate necessary for internal gelation of the alginate particles was observed. Membrane pore openings with diameters of 5 and 10 μm were also tested, but blocked with the 2.3 μm median diameter calcium carbonate solids.

Laura Carballido, Miriam Dabrowski, Friederike Dehli, Lukas Koch, Cosima Stubenrauch*
Institute of Physical Chemistry
Pfaffenwaldring 55, 70569 Stuttgart, Germany
*cosima.stubenrauch@ipc.uni-stuttgart.de, 0049 711 685-64470​

Xiaolu Pu, Bettina Wolf, Marijana Dragosavac Journal of Food Engineering
Volume 247, April 2019, Pages 178-187

This study has for the first time shown that complex food emulsifiers such as starch and protein can be applied to produce stable w/o/w emulsions with the membrane emulsification technology. Using a microporous metal membrane with a 20 μm pore size, 2% of polyoxyethylene (20) sorbitan monolaurate (Tween 20), 4% of octenyl succinic anhydride (OSA) starch or 1.5% of pea protein isolate (PPI) in the external water phase respectively was the minimum concentration necessary to stabilise the w/o/w droplets. Uniform with a span as low as 0.45 and for at least 13-day stable w/o/w emulsions of droplets between 35 and 320 μm were obtained. The release of a magnesium tracer from the internal water phase of xanthan gum-thickened w/o/w emulsions, when OSA starch and PPI were used, was found to be limited to around 3% after 13-day storage. However, w/o/w emulsions stabilised with Tween 20 were less stable with magnesium showing a release of 27% on day 13.

Xiaolu Pu, Robert Linforth,M. M. Dragosavac, and Bettina Wolf
J. Agric. Food Chem.2019

In-vitro dynamic aroma release over oil-in-water (o/w) and water-in-oil-in-water (w/o/w) emulsions stabilised with Tween 20 or octenyl succinic anhydride (OSA) starch as a hydrophilic emulsifier and polyglycerol polyricinoleate (PGPR) as a hydrophobic emulsifier was investigated. The equal-molecular-weight hydrophilic aroma diacetyl (2,3-butanedione) or relatively-more-hydrophobic 3-pentanone was added to the emulsions prepared by high speed mixing, or membrane emulsification followed by thickened with xanthan gum removing droplet size distribution and creaming as variables affecting dynamic release. Results showed the differences of w/o/w emulsions in the dynamic release compared to o/w emulsions mainly depended on aroma hydrophobicity, emulsion type, emulsifier-aroma interactions and creaming. Xanthan led to a reduced headspace replenishment. Interfacially adsorbed OSA starch and xanthan-OSA starch interaction influenced diacetyl release over emulsions. OSA starch alone interacted with 3-pentanone. This study demonstrates the potential impact of emulsifying and thickening systems on aroma release systems and highlights that specific interactions may compromise product quality.

Authors: M. Alroaithi and S. Sajjadi
Further ref: RSC Adv., 2016, 6, 79745​

This work focuses on a two-stage polymerisation process for the production of uniform polymer beads. Highly uniform droplets were firstly produced by a stirred-vessel membrane emulsification device. Methyl methacrylate (MMA) and a specific grade of polyvinyl alcohol (PVA) were used as monomer and stabiliser, respectively. The effects of various process parameters affecting the droplet size and uniformity including feeding policy, agitation speed, stabiliser concentration, and flowrate were investigated. The evolution of droplet size and its coefficient of variation (CV) were monitored over the course of emulsification. A new start-up policy, validated by monitoring droplet formation at the membrane surface, was introduced that eliminated the non-uniformity in the size of droplets formed early during emulsification. The mechanisms contributing to droplet size distribution broadening at the membrane surface during formation were decoupled from those acting in the emulsification vessel during circulation. The high CV obtained at low PVA concentration and high agitation speed was attributed to drop breakup and coalescence occurring in the emulsification vessel, respectively, after droplets formed. The emulsification was followed by a shear-controlled suspension polymerisation to convert the discrete droplets of monomer to polymer beads. A wide range of reactor impeller speeds and PVA concentrations was studied to find the conditions under which the droplets formed via membrane emulsification would not undergo further break-up or coalesce during polymerisations and a one-to-one copy of the initial droplets with the same CV can be achieved

Authors: K. N. Loponova, B. J. Deadman, J. Zhu, C. Rielly, R. G. Holdich, K. K. Hii, K. Hellgardt
Further ref: Chemical Engineering Journal, Volume 329, 1 December 2017, Pages 220-230​

The feasibility of an integrated continuous biphasic oxidation process was studied, incorporating (i) electrochemical generation of an oxidant, (ii) membrane emulsification and an Oscillatory Flow Reactor (OFR) to facilitate mass-transfer in a biphasic reaction system and (iii) product extraction to enable regeneration of the oxidant. The biphasic, organic solvent-free dihydroxylation of styrene by ammonium peroxodisulfate solutions (including electrochemically generated peroxodisulfate) was investigated as a model reaction, both in batch and in an OFR. Heating of peroxodisulfate in a strongly acidic solution was demonstrated to be essential to generate the active oxidant (Caro’s acid). Membrane emulsification allowed mass-transfer limitations to be overcome, reducing the time scale of styrene oxidation from several hours in a conventional stirred tank reactor to less than 50 min in a dispersion cell. The influence of droplet size on overall reaction rate in emulsions was studied in detail using fast image capturing technology. Generation of unstable emulsions was also demonstrated during the oxidation in OFR and product yields >70% were obtained. However, the high-frequency/high-displacement oscillations necessary for generation of fine droplets violated the plug flow regime. Membrane emulsification was successfully integrated with the OFR to perform biphasic oxidations. It was possible to operate the OFR/cross-flow membrane assembly in plug flow regime at some oscillatory conditions with comparable overall oxidation rates. No mass-transfer limitations were observed for droplets <60 μm. Finally, the continuous post-reaction separation was demonstrated in a single OFR extraction unit to enable continuous regeneration of the oxidant

Authors: M. S. Manga and D. W. York
Further ref: Langmuir, 2017, 33, 36, 9050-9056​​

Stirred cell membrane emulsification (SCME) has been employed to prepare concentrated Pickering oil in water emulsions solely stabilized by fumed silica nanoparticles. The optimal conditions under which highly stable and low polydispersity concentrated emulsions using the SCME approach are highlighted. Optimization of the oil flux rates and the paddle stirrer speeds are critical to achieving control over the droplet size and size distribution. Investigating the influence of oil volume fraction highlights the criticality of the initial particle loading in the continuous phase on the final droplet size and polydispersity. At a particle loading of 4 wt%, both the droplet size and polydispersity increase with increasing of the oil volume fraction above 50%. As more interfacial area is produced the number of particles available in the continuous phase diminish and coincidently a reduction in the kinetics of particle adsorption to the interface resulting in larger polydisperse droplets. Increasing the particle loading to 10 wt%, leads to significant improvements in both size and polydispersity with oil volume fractions as high as 70% produced with coefficient of variation values as low as ~30% compared to ~75% using conventional homogenization techniques.

Authors: P. S. Silva, V. M. Starov, R. G. Holdich
Further ref: Colloids Surf. A., Volume 532, 5 November 2017, Pages 297-304 ​

It is shown that formation of water based droplets in an immiscible (i.e. oil) continuous phase can be achieved using a hydrophilic porous metal membrane without prior hydrophobic treatment of the membrane surface. This avoids the need for “health and safety approval” of typical hydrophobic treatments for the membrane, which often use chemicals incompatible with pharma or food applications. To investigate this, wetting experiments were carried out: sessile droplets were used to determine static contact angles and a rotating drum system was used to determine contact angles under dynamic conditions. In the latter case the three-phase contact line was observed between the rotating drum, water and the continuous phase used in the emulsification process; a surfactant was present in the continuous phase which, in this process, has a double function: to assist the wetting of the membrane by the continuous phase, and not the disperse phase, and to stabilize the droplets formed at the surface of the porous membrane during membrane emulsification.

Authors: P. S. Silva, V. M. Starov, R. G. Holdich
Further ref: Colloids Surf. A., Volume 532, 5 November 2017, Pages 297-304 ​

t is shown that formation of water based droplets in an immiscible (i.e. oil) continuous phase can be achieved using a hydrophilic porous metal membrane without prior hydrophobic treatment of the membrane surface. This avoids the need for “health and safety approval” of typical hydrophobic treatments for the membrane, which often use chemicals incompatible with pharma or food applications. To investigate this, wetting experiments were carried out: sessile droplets were used to determine static contact angles and a rotating drum system was used to determine contact angles under dynamic conditions. In the latter case the three-phase contact line was observed between the rotating drum, water and the continuous phase used in the emulsification process; a surfactant was present in the continuous phase which, in this process, has a double function: to assist the wetting of the membrane by the continuous phase, and not the disperse phase, and to stabilize the droplets formed at the surface of the porous membrane during membrane emulsification.