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Paper Highlights

Distribution nucleation: Quantifying liquid distribution on the particle surface using the dimensionless particle coating number 

Control of nucleation in wet granulation often determines the size and structure of the final granules. After a decade of research, our knowledge of “immersion nucleation”, where a large droplet engulfs fine particles, is relatively well established. However, far less is known about the second mechanism called “distribution nucleation”, where the powder particles are gradually coated by a layer of small droplets. In this paper, the similarities between particle coating and granulation were used to define the five steps of distribution nucleation. A Bernoulli model was developed to describe the fractional surface coating F, and a new dimensionless parameter, the particle coating number Φp, was defined as the ratio of the theoretical area coated by the drops, assuming no overlap, to the total surface area of the particle.

The particle coating number was experimentally validated by adding drops randomly over the surface of a particle and measuring the fractional surface coating using image analysis. The particle coating number can also be used to predict the effect of changing particle size, surface area, liquid level, or drop size on the coating fraction, which is in turn known to be linked to granulation kinetics. The particle coating number opens up new options for granulation process control, and is expected to be valuable in a variety of particle wetting and coating applications where small drops are distributed over larger particles.

Waithira I.J. Kariuki, Ben Freireich, Rachel M. Smith, Martin Rhodes, Karen P. Hapgood, Chemical Engineering Science, Volume 92, 5 April 2013, Pages 134-145


Precipitating smooth amorphous or pollen structured lactose microparticles


Lactose microparticles with pollen-like or smooth amorphous morphology were produced using the convective antisolvent technique via single droplet drying.  The pollen-like particles was either composed of straight needle-like or short entwined dendrites. Observation of a smooth network like structure suggested that a ‘pinched off’ mechanism might be one possible route in the formation of the precipitated smooth microspheres.  Further experiments revealed that the smooth precipitated particles can be produced using fine atomized droplet typically used in a spray dryer.


Pollen lactose particles

Mansouri, S., Woo, M.W., Chen, X.D.  Making uniform whey, lactose and composite lactose-whey particles from the dehydration of single droplets with antisolvent vapour.  2013 (accepted - Drying Technology).

Yue, S., Mansouri, S., Woo, M.W., Chen, X.D.  Antisolvent vapour precipitation of droplets with multi-components:  non-soluble encapsulation and simultaneous precipitation of soluble materials. 2013 (accepted – Chemical Engineering Research and Design)

Mansouri, S., Chin, G.Q., Ching, T.W., Woo, M.W., Fu, N., Chen, X.D.  Precipitating smooth amorphous or pollen structured lactose microparticles by manipulating the growth and self-assembly mechanism.  2013 (accepted– Chemical Engineering Journal).

Mansouri, S., Fu, N., Woo, M.W., Chen, X.D.  Uniform amorphous lactose microspheres form convective –dehydration antisolvent precipitation under normal atmospheric pressure.  Langmuir, 2012 (doi: 10.1021/la302301h).


Superparamagnetic Iron Oxide Nanoparticles (SPIONs) to improve the delivery of malaria DNA vaccine

SPIONs can be used as therapeutic and diagnostic agents due to their unique magnetic characteristics, provided that they are stable in physiological conditions. They are also biodegradable and biocompatible for in vivo uses and can be functionalised to target antigen-presenting cells (i.e. dendritic cells. Here the use of SPIONs to enhance the delivery of DNA vaccine for malaria is investigated through a series of in vitro and also in vivo studies.

Ho, J., Al-Deen, F., Aboodi, A., Selomulya, C., Xiang, S., Plebanski, M., Forde, G., 2011, N,N’-Carbonyldiimidazole-mediated functionalization of superparamagnetic nanoparticles as vaccine carrier, Colloids and Surfaces B: Biointerfaces, 83, 83-90.

Al-Deen, F. N., Selomulya, C., Williams, T., 2013, On designing stable magnetic vectors as carriers for malaria DNA vaccine, Colloids and Surfaces B: Biointerfaces, 102, 492– 503.

Al-Deen, F., Ho, J., Selomulya, C., Ma, C., Coppel, R., 2011, Superparamagnetic Nanoparticles for Effective Delivery of Malaria DNA Vaccine, Langmuir, 27 (7), pp 3703–3712.

Al-Deen, F., Selomulya, C., Ma, C. Xiang, S., Plebanski, M., Coppel, R.,  2013, On the efficacy of malaria DNA vaccination with magnetic gene vectors, Journal of Controlled Release, Volume 168, Issue 1,10–17





Foam granulation: Binder dispersion and nucleation in mixer-granulators

 A new alternative method of wet granulation has been developed where foam delivery of binder is used to granulate the powder particles. This study investigated binder distribution in wet granulation and focused on the nucleation stage, The interactions of foam quality and the powder flow pattern are discussed and two distinct wetting and nucleation mechanisms are proposed: (1) under bumping flow, a low-quality foam tends to induce localised wetting and nucleation. The wetting and nucleation is "foam drainage" controlled. (2) Under roping flow, foam will be dispersed by the motion of the agitated powder. The wetting and nucleation is "mechanical dispersion" controlled.

Tan, M.X.L. and K.P. Hapgood, Foam granulation: Binder dispersion and nucleation in mixer-granulators. Chemical Engineering Research and Design, 2011. 89: p. 526–536.





Facile spray-drying assembly of uniform microencapsulates with tunable core-shell structures and controlled release properties

Microencapsulates with defined core-shell structures are of interest for applications such as controlled release and encapsulation, due to the feasibility of fine-tuning individual functionalities of different parts. Here we report a new approach for efficient and scalable production of such particles. Eudragit® RS (a copolymer of ethyl acrylate, methyl methacrylate and a low content of methacrylic acid ester with quaternary ammonium groups) was used as the main shell component, with silica as the core component, formed upon a single-step spray drying assembly. The method is capable of forming uniform core-shell particles from homogeneous precursors without the use of any organic solvents.

Liu, W., Wu, W., Selomulya, C., Chen, X. D. 2011, Facile spray-drying assembly of uniform microencapsulates with tunable core-shell structures and controlled release properties, Langmuir, 2011, 27 (21), pp 12910–12915.

Liu, W., Wu, W., Selomulya, C., Chen, X. D., 2013, On designing particulate carriers for encapsulation and controlled release applications, Powder Technology, in press, doi: 10.1016/j.powtec.2012.02.012.

Liu, W., Wu, W., Selomulya, C., Chen, X. D., 2012, Spray drying of monodispersed microencapsulates: implications of process parameters on microstructural properties and controlled release functionality, Journal of Microencapsulation 29: 7, 677-684




Fabrication of uniform microencapsulates for controlled release applications

Microparticles with homogeneous properties are crucial for pharmaceutical applications where the prior knowledge of exact drug loading and release behaviour is essential to achieve targeted therapeutic goals. Various methods such as membrane microemulsion or templating to assemble uniform particles often involve multiple steps, including post-processing for purification and recovery, with additional chemical reactivity is often required to form solid particles, rendering less flexibility in the procedure. Spray drying is a common method to produce pharmaceutical particles, although control over the particle properties poses a challenge. Here we used a specially designed dryer utilising a micro-fluidic-aerosol-nozzle to atomize monodisperse droplets from a range of precursors, to generate uniform microencapsulates for controlled release applications. The versatility of the device enabled microparticles with easily tunable drug release kinetics to be assembled by adjusting the drying conditions or the composition of the precursors, including the use of dopants or different solvents. Significant adjustment of the release profiles could be realized by manipulating the microstructure of the microparticles. Due to the homogeneity of the particles, a direct correlation between the microstructural properties and release mechanisms could be obtained, the knowledge of which is crucial for the design of spray-dried polymeric-based pharmaceutical particles.

Wu, W., Liu, W., Selomulya, C., Chen X. C., 2011, On Spray Drying of Uniform Silica-Based Microencapsulates for Controlled Release, Soft Matter, 7, 11416-11424.

Liu, W., Wu, W., Selomulya, C., Chen, X. D., 2011, A single step assembly of uniform microparticles for controlled release applications, Soft Matter, 7, 3323 - 3330.


Assembly of magnetic microcomposites via microfluidic spray drying

A microfluidic jet spray drier producing single trajectory droplets with identical thermal history was used to obtain monodisperse particles with precise morphology. The method employed a moderate temperature range (≤ 300 oC), and was able to handle multi-component precursors to form solid particles in a single step. Spray drying of a stable colloidal suspension containing iron chloride, lactose, and silica nanoparticles produced microcomposites with platelet-like morphology due to the nanoparticles in the precursor. Subsequent calcination caused the formation of iron oxide crystals of 10 nm to 1 μm on the surface of the particles. Both calcination period and post-drying conditions affected the magnetic properties of the composites, with the increase in magnetization correlating well with the proportion of magnetite phase in the iron oxide crystals.

Amelia, R., Wu, W., Chen, X., and Selomulya, C., 2012, Assembly of magnetic microcomposites from low pH precursors using a novel micro-fluidic-jet-spray-dryer, Chemical Engineering Research and Design, 90, 150-157.

Amelia, R., Wu, W., Cashion, J., Bao, P., Zheng, R., Chen, X. D., Selomulya, C., 2011, Microfluidic spray drying as a versatile assembly route of functional particles, Chemical Engineering Science, 66, 5531-5540.


Formation of hollow granules from liquid marbles: Small scale experiments

The formation of hollow granules from hydrophobic powders in a high-shear mixer granulator has been investigated by changing the binder/powder mass ratio and studying its effects on granule size and structure. The final granule shape and size distribution are dependent on the liquid to solid ratio if the liquid marble nucleation process starts with a preformed droplet template.

Eshtiaghi, N., B. Arhatari, and K.P. Hapgood, Producing hollow granules from hydrophobic powders in high-shear mixer granulators. Advanced Powder Technology, 2009. 20(6): p. 558-566.