| Research Abstract |
We have studied novel application works in the field of drug engineering using plasma-irradiated organic polymers including pharmaceutical aids. The study of the plasma-induced surface radicals of organic polymers is very important for understanding of the nature of plasma treatment. Plasma-induced surface radicals of monocarbohydrates (α-and β-glucose), dicarbohydrates (maltose and cellobiose), and polycarbohydrates (cellulose and its derivatives) were studied in detail by electron spin resonance (ESR) coupled with the systematic computer simulations. The ESR study on plasma-irradiated cellulose derivatives revealed that the plasma-induced radicals formed vary with the nature of substituents in a sensitive manner. These findings provide a basis for further application works in the preparation of new pharma-ceutically useful materials.
We also studied on the mechanically induced free radical (mechanoradical) formation of glucose-based polycarbohydrates such as cellulose and amylose base
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d on ESR on its comparison with plasma-induced radicals. One of the most intriguing facts is that the component radicals are all glucose-derived mid-chain alkyl radicals as in the case of plasma irradiation, although it is known that mechanoradicals are produced by the polymer main-chain scission. It can be reasonably assumed, therefore, that the mechanoradicals primarily formed by 1, 4-glucosidic bond cleavage of polycarbohydrates at room temperature underwent a hydrogen abstraction from the glucose units to give rise to the glucose-derived mid-chain alkyl radicals.
Since each parameter to specify the plasma eventually affects the intensity of plasma, "plasma power", to generate the surface radicals, we have examined to develop the method to estimate the plasma power useful for experimental and practical designs of plasma treatment. It was shown that the formation of myo-inositol radical could be able to use as an index of the effective plasma power. Even if the parameters of plasma operational conditions such as actual discharge wattage, system pressure, the geometry of plasma apparatus or the location of materials are changed, the plasma power will be deduced by measuring the quantity of myo-inositol radicals.
On the basis of findings from a series of studies on the nature of plasma-induced radicals formation on a variety of polymers, we were able to develop several novel drug delivery systems (DDS) preparation, which include (1) preparation of multilayered tablets applicable for reservoir-type DDS of sustained- and delayed- release, and (2) fabrication of functionalized composite powders applicable for matrix-type DDS by mechanical applications of plasma-irradiated powder polymers. The advantages of the present approach for preparation of DDS are (1) totally dry process, (2) facile control of drug release rates, (3) avoidance of direct plasma-exposure to drugs, and (4) polymer modification without affecting the bulk properties. Thus, it is hoped that more practical applications will be developed in the course of attempt now in progress. Less
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