Thermoresponsive polymers as gene and drug delivery vectors: architecture and mechanism of action.

INTRODUCTION: This topic is important as it allows for improved specificity in drug delivery, providing possibilities for reduced side effects, and thereby improved pharmacotherapy. As a wealth of different polymers and mechanisms of action has been suggested, a systematic overview of the field is of current importance. AREAS COVERED: This article presents an overview over a selection of thermoresponsive polymers suitable as excipients in systems for gene and drug delivery with particular emphasis on the influence of polymer structure, composition, molecular weight (MW) and architecture on the responsive mechanisms. Due to the immense number of reports on these increasingly popular materials, focus has been restricted to the use of micelle-forming polymers with a lower critical solution temperature, temperature-responsive hydrogels for drug delivery applications and temperature-sensitive polymers as non-viral vectors for polynucleotide delivery. Specific examples covered are poly-(N-isopropylacrylamide) (PNIPAAM), Pluronics and their derivatives. It is concluded that the studies constitute an excellent platform for development of thermoresponsive systems with improved gene and drug delivery properties. EXPERT OPINION: A thorough knowledge of factors important for loading efficiency and drug release is necessary to be able to develop optimal nano-carriers for the future. Other issues that are not fully understood is how small the carriers need to be, and which manufacturing procedures should be used.