Morphology and Properties of Spray-Dried Particles

Spray drying is, by definition, the transformation of a feed of liquid (solution or dispersion) or paste material into a dried particulate powder. The feed liquid is atomized into small droplets of several dozens to a few hundreds pm, which are dried to the powder by contacting with a hot drying medium (Masters, 1991). The volume mean particle size of the powder is typically in the range 10 pm dyso 1 mm, with mean particle sizes of 50 pm dyso 300 pm being more frequent in practice. 

Modem Diyir Technology Volume 3 Product Quality and Formulation, First Edition. 

Oils and fats Fish oils (DHA. EPA). sea budcdiom oil, lycopene 

Other Enzymes, leavening agents, psyllium, yeast 

Chapter 5 of Volume 1 described in detail how the flow patterns of hot air and the trajectories of the drying droplets can be analyzed by computational fluid dynamics 

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Chapter 5 Understanding and preventing structural changes during drying of gels Chapter 6 Morphology and properties of spray-dried particles Chapter 7 Particle formulation in spray fluidized beds... 

Walzel, P., Furuta, T. (2011). Morphology and properties of spray-dried particles. In E. Tsotsas A. S. Mujumdar (Eds.), Modern drying technology. Product quality and formulation (Vol. 3, pp. 231-294). London Wiley. 

The surface structure of spray-dried particles can be regarded as a key for fine particle adhesion in customer appUcations. This effect is needed for example, for inhalation therapies when fine active particles with d < 5 im are added to spray-dried carrier particles within the size range 60-100 im in order to obtain a dose unit with reasonable fiowabihty and with proper detachment properties of the fines. Experiments with mannitol (Maas et ol., 2009) gave rise to quite different surface morphologies when sprayed into air at different temperatures. In the case of low air exhaust temperatures, T= 80 °C, the carrier particles exhibit a fairly smooth surface. At an exhaust air temperature of T= 130 °C, the particles show rough surfaces formed by crystals covering the particle surface, see Fig. 6.5. In this case, the air temperature is a vehicle to adjust the desired adhesion properties. 

Powders intended for nasal administration have to be optimized in terms of particle size and morphology as these properties are related to potential irritation in the nasal cavity [23], Certain procedures (e.g., spray drying process) can modify the particle size of the drug powder raw material, but in order to optimize the morphology and flowability properties of some pure drug powders, excipients need to be used. Sacchetti et al. [28] reported that the use of mannitol as a filler and hydroxy-propylmethyl cellulose (HPMC) as a shaper of spray-dried caffeine microparticles modified the typical needle shape of spray-dried caffeine to a more convenient roundish shape. Further addition of polyethylene glycol (PEG) resulted in increased... 

Some empirical observations can help to understand how the feedstock physical state (i.e., suspension, emulsion, solution) and the physicochemical properties of the formulation components relate to the morphology and surface characteristics of the spray dried particles. As mentioned above shell formation will occur when one of the formulation components reaches its solubility and precipitates leading to the formation of a solid shell that may be either amorphous or crystalline. Low aqueous solubility components tend to precipitate early in the drying process and lend to form corrugated... 

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