Preparation of Biomaterials and Pharmaceutical Formulations

The reduction of polymer viscosity also facilitates the mixing of the polymer with an active component [156], The ability of CO2 to foam polymers provides a convenient method to prepare scaffolds for the application of tissue engineering, providing an environment able to promote the differentiation and growth of tissue. Particle formation [157] provides a route to prepare formulations with controlled release characteristics via encapsulation. The use of CO2 also provides a convenient method to deliver coatings to pharmaceutical formulations [158], A detailed discussion of polymer processing for various pharmaceutical apphca-tions has recently been published [159], 

One of the interesting apphcations where scC02-processing of polymeric materials is beneficial is the method of PGSS (Particles from Gas Saturated Solution). PGSS is a technique able to form polymer/active compound foams, solid particles, or droplets [160]. The principle of the technique is for CO2 to form a gas-saturated solution/suspension which may then be foamed or passed through a nozzle to produce sohd particles or droplets. The technique is suited to thermally labile components, since the process is undertaken at near ambient temperature. Control of particle size has been achieved by the introduction of N2 back-pressure in the collection chamber, as demonstrated by Hao et al. [161] with poly(DL-lactic acid). The PGSS method has been shown to enhance the dissolution characteristics of nifedipine from PEG 400 [162, 163]. 

The formation of a sohd dispersion may be achieved by the impregnation of an active component from a supercritical solution. The benefit of this approach is that it often results in the active component being molecularly dispersed within the host matrix [5], which is advantageous compared to the reduced bio-availabiUty in the crystallized form which may be formed in the case of traditional methods. Furthermore, this study [5] proved that the impregnation of a drug from a supercritical solution reduces the water uptake into the formulation as a result of the interaction between the polymer and the drug, which helps to 

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