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Spray drying with a three channel nozzle

20th May 2013


Micheal Whelehan, Philipp John and Nurhan T Dunford examine the production of core-shell microcapsules by spray drying using a 3-Fluid nozzle in a single step process.

For more than 50 years spray drying has been successfully employed in a vast number of scientific and/or industrial applications as a simple, efficient, reliable and scalable technique to convert aqueous or organic solutions, emulsions, dispersions and suspensions (for convenience all will be referred to as liquid/spray solutions for the rest of this article) into a dry powder.

For the process different nozzle systems can be employed and the one selected will depend on the requirements of the user. For example, at an industrial level a rotary disc nozzle is mainly employed, while for laboratory scale research and pilot scale production a 2-Fluid nozzle is commonly used1.

The latter nozzle system consists of an inner and outer channel (Fig. 1a) and during operation a liquid solution is pumped through the inner channel to the nozzle tip where it is atomised by compressed air/nitrogen flowing through the outer channel. This procedure results in the formation of fine droplets, which are subsequently dried using hot gas to form a powder.

While spray drying is mainly considered as a 'dehydration process', it has been demonstrated that it can also be employed as a viable encapsulation technique. Spray drying is the oldest microencapsulation technique employed within the food industry1-3. In this operation the 'active material(s)' is dissolved/suspended in the spray solution and becomes entrapped within the powder matrix during the drying process (Fig. 1b); the produced particles are commonly referred to as 'matrix microcapsules or microbeads'3.

This approach has been very successful and enabled the encapsulation of thousands of different products; from pharmaceuticals, bioactives, essential oils, aroma compounds and food additives, providing the encapsulated material with a myriad of benefits4.

Nevertheless spray drying as an encapsulation process is not without its disadvantages, and can result in relatively low loading of the encapsulated material, as well as insufficient protection of labile and sensitive products1,5 (due to emulsion preparation and/or surface exposure on the dry microbead). These drawbacks have prevented the technology from being used to encapsulate numerous sensitive and high value products for biotechnology, medical, cosmetic and food industries.

To overcome the above problems, BÜCHI Labortechnik AG has developed a 3-Fluid nozzle system for their spray drying technology1,5,6, which allows encapsulation of a product within core-shell microcapsules (Fig. 2, displays the structural differences between a matrix and core-shell microcapsule) in a single step process.

For this 3-Fluid nozzle system three separate channels are available, one each for core liquid, shell (usually a polymer) liquid and atomising gas (Figure 1c).

The system is set up in such a manner that both the shell and core liquids meet at the tip of the nozzle to form a concentric liquid, which is atomized and dried to form the core-shell microcapsules.

Use of this innovative system has already enabled scientists to successfully encapsulate fish oil (Fig. 3a.5), a fluorescent marker (Fig.3b7), a monoclonal antibody (Fig. 3c), and a solution of diclofenac1, within core-shell microcapsules. This method not only enabled appropriate amounts of the solutions to be encapsulated, while potentially offering greater control over the release of the encapsulated material, but it also provided additional protection to the encapsulated material by enabling elimination of the emulsion preparation step.

The recent work performed with the 3-Fluid nozzle has demonstrated how spray drying could be employed in the future as a standard methodology to produce core-shell microcapsules at a lab and pilot scale.

The incorporation of the 3-Fluid nozzle into the BÜCHI spray dryer does not reduce the reliable and simple nature of the entire (spray drying) operation, and only requires one additional feed pump to be added to the setup. It is anticipated that this system has the ability to significantly increase the number of products that can be microencapsulated by spray drying, and in the future may be employed at an industrial setting.

Indeed the lack of reliable, efficient and simple production techniques has hindered the commercial application of core-shell microcapsule4. This gap could now be possibly filled by the 3-Fluid nozzle system.

For more information at www.scientistlive.com/eurolab

Micheal Whelehan is Product Specialist Encapsulation & Spray Drying, and Philipp John is Group Project Manager Encapsulation & Spray Drying, BUCHI Labortechnik AG, Flawil, Switzerland. www.buchi.com. Nurhan T Dunford is Professor at Oklahoma State University, Stillwater, OK, USA.

References:

1. Ramtoola et al., Expert Opinion in Drug Delivery, 9, 1463-1474 (2012).

2. Mahdi et al., Drying Technology, 26, 816-835 (2008).

3. Rè, Drying Technology, 24, 433-446 (2006).

4. Whelehan et al., Journal of Microencapsulation, 28, 669-688 (2011).

5. Dunford & Legako, Journal of Food Science 75, 394-400 (2010)

6. http://www.buchi.com/Mini_Spray_Dryer_B-290_Accesso.182.0.html <

7. http://www.rcsi.ie/technologiesforlicense.





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