However, there still exist numerous and barriers for polymer-based vehicles to achieve ideal transfection efficiency. For transfection, polymeric nanoparticles have no structure as magic as viruses to enter cells and just depend on the unpredictable endocytosis. Thus on one hand more detailed information about the endocytosis mechanism obtained by varying technical methods is needed to increase the entrance into the cells. On the other hand, the size, surface potential and N/P ratio (ratio of nitrogen of polymer to phosphate of DNA) were deeply investigated and some targeting groups like nuclear localization signal were integrated to the nanoparticles. Morover, the escape of nanoparticles from the organelle and DNA from the complexes is one of the key elements influencing the transfection efficiency. For example, particular interest was garnered by PEI mainly for its organelle-escape units. Another big problem for polymeric nanoparticles is the cytotoxicity, which results from poor biodegradability. So the degradable moieties have been incorporated into polymer, such as coating with human serum albumin, dextran, PEG and so forth. Out of these, the specific hurdle for transfection is that polymeric nanoparticles are foreign materials whose invasion will lead to the immune response by the body. The most effective solution is PEGylation, which help avoid the clearance of the reticuloendothelial system. Many researchers are dedicated to devising polymer-based vehicles for exogenous gene transfection and great efforts have been made for gene transfection .
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This review describes the synthesis, properties, and, in particular, biomedical and pharmaceutical applications of an upcoming class of polymeric networks and assemblies based on cyclodextrins (CDs). CDs are cyclic oligosaccharides composed of α-1,4-coupled -glucose units, which contain a hydrophobic internal cavity that can act as a host for various, generally lipophilic, guest molecules. Because of this unique physicochemical property, commonly referred to as inclusion complex formation, CDs have often been used to design polymeric materials, such as hydrogels and nanoparticles. Polymeric systems based on CDs exhibit unique characteristics in terms of mechanical properties, stimuli-responsiveness, and drug release characteristics. In this contribution, first, an outline is given of covalently cross-linked polymeric networks in which CD moieties were structurally incorporated to modulate the network strength as well as the complexation and release of low molecular weight drugs. Second, physically assembled polymeric systems are discussed, of which the formation is accomplished by inclusion complexes between polymer-conjugated CDs and various guest molecule-derivatized polymers. Due to their physical nature, these polymeric systems are sensitive to external stimuli, such as temperature changes, shear forces and the presence of competing CD-binding molecules, which can be exploited to use these systems as injectable, in situ gelling devices. In recent years, many interesting CD-containing polymeric systems have been described in literature. These systems have to be optimized and extensively evaluated in preclinical studies concerning their safety and efficacy, making future clinical applications of these materials in the biomedical and pharmaceutical field feasible.
Cyclodextrin-Based Polymeric Materials: ..
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