Formulation of colloidal dispersions from preformed polymers

2 Formulation of colloidal dispersions from preformed polymers 

The technologies involving the formation of particles from preformed polymers are widely used in the field of in vivo delivery of drugs, proteins or DNA. Obviously, none of these methods is based on emulsion polymerization but in vivo applications are important for colloids, in terms of scientific and technical challenges, added value and improvement of life for humans. 

Polyelectrolytes have been used in the formation of particles and the most promising structures are from the natural polymers such as chitosans (Sinha et al, 2004) and alginates 

The simplest method to obtain particles is the solvent displacement developed by Fessi et al. (1987). The polymer, dissolved in a water-miscible organic solvent, is slowly added to an aqueous solution containing a surfactant or a non-ionic stabilizer such as poly(vinyl alcohol) or PEO-PPO-PEO triblock copolymers. On reaching the dispersing phase, the solvent drops diffuse in water but the water-insoluble polymer precipitates in the form of colloidal particles, on condition that the polymer concentration be low enough to prevent the formation of aggregates. 

Supercritical fluid technology is a very attractive method for producing particles in high yield exempt of traces of solvent. The supercritical fluid of choice is CO2 because of its low critical temperature (31°C), natural abundance and relative environment friendliness. This technology has recently been reviewed by Richard and Deschamps (2003). 

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Many manufacturing methods are available for the synthesis of latex particles exhibiting appropriate functionalities and three main approaches can be followed (a) polymerization in heterogeneous media (b) modification of preformed particles (see Arshady, 1999) (c) formulation of colloidal dispersions from preformed polymers. 

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