Abstract
A number of new polymeric materials are being explored for possible utilization as carriers for the controlled release of biologically active agents. The morphological structure of most polymers is heterogeneous, consisting of two phases, namely crystalline and amorphous. These two phases are present in varying amounts depending on the composition and the thermal and processing history of the polymer, and are dispersed throughout the body of the polymer. Transport of active agents in such materials is influenced therefore by their molecular structure since the permeabilities of the two phases are different. Crystalline domains in a semi-crystalline polymer are virtually impermeable relative to the amorphous phase; consequently, the diffusing molecule has to follow a tortuous path through the permeable amorphous phase. This permeable phase is interspersed between the impermeable domains serving as boundaries or walls. It is evident that the characteristics of transport in the permeable-impermeable domains of a heterogeneous polymer are similar to those in a porous medium. Thus the release of an active agent from either the heterogeneous polymer or the porous matrix carrier can be analyzed analogously (see, e.g., Peterlin, 1979, Harland and Peppas, 1986).
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Fan, Lt., Singh, S.K. (1989). Stochastic Model for Diffusion in Porous or Heterogeneous Polymer Matrix. In: Controlled Release. Polymers, vol 13. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-74507-2_6
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DOI: https://doi.org/10.1007/978-3-642-74507-2_6
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