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Erosion front

When a hydrophobic polymer with a physically dispersed acidic excipient is placed into an aqueous environment, water will diffuse into the polymer, dissolving the acidic excipient, and consequently the lowered pH will accelerate hydrolysis of the ortho ester bonds. The process is shown schematically in Fig. 6 (18). It is clear that the erosional behavior of the device will be determined by the relative movements of the hydration front Vj and that of the erosion front V2- If Vj > V2, the thickness of the reaction zone will gradually increase and at some point the matrix will be completely permeated with water, thus leading to an eventual bulk erosion process. On the other hand, if V2 = Vj, a surface erosion process wiU take place, and the rate of polymer erosion will be completely determined by the rate at which water intrudes into the matrix. [Pg.132]

The erosion front between the dissolution medium and the erosion (or dissolving) surface... [Pg.148]

Harland et al.12 developed a model for drug release based on mass balances of the drug and the solvent at the swelling front and the erosion front. The release profile was found to be a combination of Fickian and zero order, as shown by Eq. (5.16) ... [Pg.148]

Computer simulation of eroding matrices (Fig. 8.36) can give an accurate representation of the process and can predict the position of the erosion front and the weight of the matrix. [Pg.322]

A co-operative diffusion of water molecules in and oligomers out gives rise to sharp reaction-erosion fronts close to the surface in a mechanism similar to that for the creation of the surface layer as proposed by Li et al. [Pg.106]

Zvgourakis, IG (1990) Development and temporal evolution of erosion fronts in bioerodible controlled release derices. Chem. Eng. Sci, 45, 2359-2366. [Pg.473]


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See also in sourсe #XX -- [ Pg.227 ]




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