High-pressure homogenisation

Four methods may be applied to prepare nanoemulsions (covering the droplet radius size range of 50 to 200 nm) high-pressure homogenisation (aided by an appropriate choice of surfactants and cosurfactants) application of the PIC method appHcation of the PIT concept and the dilution of a microemulsion. 

The production of small (submicron) droplets requires the application of large amounts of energy, as the process of emulsification is generally very inefficient (as illustrated below). 

The intensity of the process or the effectiveness in making small droplets is often governed by the net power density (c(t))  

Notably, it may be useful to emulsify in steps of increasing intensity, particularly with emulsions having a highly viscous disperse phase. 

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Based on shear forces high pressure homogeniser... 

A widely used technique for cell disruption is high-pressure homogenisation. Shear forces generated in this treatment are sufficient to completely disrupt many types of cell. A common... 

In all of the above equations, is assumed to be constant and uniform throughout the flow field. In most items of bioprocess equipment, however, there is a spatial distribution of energy dissipation. The definition of an average or a maximum energy dissipation rate is notoriously difficult in the case of bioprocess equipment such as high pressure homogenisers, centrifuges, pumps and microfiltration units which all have complex flow fields. 

The ability to derive the intrinsic mechanical properties of yeast cells should now allow the mechanisms of high-pressure homogenisation to be determined unambiguously, and a priori predictions of the extent of cell disruption to be made for given homogeniser conditions. This should allow better process optimisation. 

Keck, C. M., and Muller, R. H. (2006), Drug nanocrystals of poorly soluble drugs produced by high pressure homogenisation, Ear. J. Pharm. Biopharm., 62, 3-16. 

Krause, K.P. Muller, R.H. Production and characterisation of highly concentrated nanosuspensions by high pressure homogenisation. Int. J. Pharm. 2001, 214 (1-2), 21-24. 

Floury, J., Desrumaux, A., Axelos, M. A. V., and Legrand, J. (2002). Degradation of methyl-cellulose during ultra-high pressure homogenisation. Food Hydrocolloids 16, 47-53. 

Thiebaud, M., Dumay, E., Picart, L., Guiraud, J. P., and Cheftel, J. C. (2003). High-pressure homogenisation of raw bovine milk—Effects on fat globule size distribution and microbial inactivation. Int. Dairy J. 13, 427—439. 

Large liposomes are formed when phospholipids are hydrated at temperature above their phase transition temperature (T). Although MLVs are normally formed when lipid fihns are hydrated below T, these can be transformed into small vesicles by using high pressure homogenisation. 

Reducing the emulsion droplet size by using high-pressure homogenisation. The smaller droplets are less deformable and coalescence is prevented. In addition, the accumulation of suspension particles at the O/W interface is prevented. 

Their preparation often requires special application techniques, such as the use of high-pressure homogenisation as well as ultrasound. Such equipment (e.g., the Microfluidizer) has become available only during recent years. 

In spite of the above difficulties, several companies have introduced nanoemulsions onto the market, and their benefits will be evaluated within the next few years. Nanoemulsions have been used in the pharmaceutical industry as drug-delivery systems [5], although the acceptance by customers of nanoemulsions as a new type of formulation depends on how they are perceived and their efficacy. With the advent of new instruments for high-pressure homogenisation, and the competition between various manufacturers, the cost of nanoemulsion production wiU surely and may even approach that of classic macroemulsions. Fundamental investigations into the role of surfactants in the process [6,7] will lead to optimised emulsifier systems such that a more economic use of surfactants will doubtless emerge. 

In all cases, there was an increase in nanoemulsion radius with increase in the R(0/S). However, when using the high-pressure homogeniser the droplet size could be maintained at values below 100 nm at high R(0/S) values. With the PIT method, there was a rapid increase in r with increase in R 0/S) when the latter... 

As expected, the nanoemulsions prepared using high-pressure homogenisation showed a lower Ostwald ripening rate when compared to systems prepared using the PIT method. This is illustrated in Figure 14.18, which shows plots of versus... 

Ease of manufacture and scale up The spontaneity of formation of micro emulsions makes their manufacturing and scale up very easy as compared to other colloidal carriers such as emulsions or liposomes which require specialised instruments such as high pressure homogenisers for their manufacturing. 

Ehsan S and Marshall WD (2001) High-pressure homogenisation prior to slurry introduction electrothermal atomic absorption spectrometry for metal determination in wood pulps. J Anal Atom Spec-trom 16 1180-1184. 

Liedtke, S. Wissing, S. Muller, R. H. Mader, K., Influence of high pressure homogenisation equipment on nanodispersions characteristics. International Journal of Pharmaceutics (2000) 196,183-185. 

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