Endogenously Triggered Polymer-based Drug Delivery Systems

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The final polymer was used to produce redox-sensitive polymeric nanoparticles by a simple emulsion method. The efficiency of the redox system was tested in reductive environment, using paclitaxel as a model drug. The results indicate that in the first 48h 20% of paclitaxel was released in a non-reductive environment. In contrast, when sodium dithionite (reductive agent) was applied, the system released about 52% of the drug in the first 3hours and about 80% within 36h. Even though this study provided evidences for possible new redox-sensitive polymeric drug delivery systems, additional investigations must be executed with DT-diaphorase, NADPH and GSH to simulate tumor microenvironments and better assess the system [8,54].
Glucose sensitive polymer based drug delivery systems are specially used to control glucose levels in diabetes mellitus, by releasing insulin when glucose concentration increases. These systems are usually design using three distinct approaches: oxidation of glucose by glucose oxidase (GOx), binding of glucose to boronic acids and coupling of glucose to concanavalin-A (con-A) [3]. The first approach, based on GOx, uses glucose as substrate and produces gluconic acid and H2O2. It is not the direct influence of glucose that triggers a response in the system, but the presence of the products of the enzymatic reaction. Usually, pH-sensitive polymers are used in order to obtain glucose sensitive drug delivery systems which will disassembly or solubilize in acidic conditions, causing the release of the drug.
Glucose-sensitive porous membranes with grafted PAAc gates and GOx were prepared by grafting PAAc and immobilizing GOx onto porous poly(vinylidene fluoride) (PVDF) membranes [55]. The grafted PAAc provides pH-sen...

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