Research Abstract |
Novel materials, particulate designs and preparations and characterization of materials and particulate devices were investigated to develop drug delivery systems under international cooperation. 1)Search of novel materials Chitosan fine powder was prepared to utilize as microparticulate drug carriers by co-grinding with hydrophobic additives : especially, stearic acid was effective for down-sizing the chitosan particles, leading to production of 1.8μm microparticles. Similarly, co-grinding with hydrophobic DTPA stearylamide(DTPA-SA)produced 2.0μm microparticles, probably making it possible to apply as gadolinium carriers for neutron capture therapy of cancers. In addition, as a membrane material, mixtures of lecithin with additives were developed for bioerodible microcapsules. The composite latices with N-isopropylacrylamide shells were also synthesized for thermosensitively drug-releasing microcapsules. 2)Particulate designs and preparations Ethylcellulose microcapsules were prepared by
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a novel dry-blendingf method. Thermosensitively drug-releasing microcapsules, exhibiting an exceptionally sharp response, diclofenac ready-made suspensions with a strong release-suppression during storage and a prolonged release property after administration, bioerodible lecithin microcapsules for intraarterial injections in tumor tissues were designed and successfully prepared by a spouted bed process. For neutron capture therapy, Gs-DTPA-SA-containing nanoemulsions and chitosan nanoparticles, strongly binding the highly water-soluble Gd-DTPA, were newly prepared. 3)Characterization of dosage forms It was emphasized that the very thin membrane of the microcapsules developed for the ready-made suspensions could strongly suppress the release of diclofenac incorporated in the cores of ion-exchange resin, probably leading to practical use of this type of dosage forms. The nanoemulsions made it possible to accumulate gadolinium to tumor tissues at 189 ppm after intraperitoneal and intravenous injections with tumor-bearing hamsters. The chitosan nanoparticles induced an excellent in vivo suppression of tumor growth after intratumoral injections in the trials of neutron capture therapy through adhesion to cell surface due to their positive surface-charge and incorporation into the cells by endocytosis due to their optimal particle size. Less
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