Smart polymeric carriers for drug delivery temperature-responsive nanocarriers

5 Smart polymeric carriers for drug delivery temperature-responsive nanocarriers 

Among the most commonly used thermosensitive polymers are poly(iV-isopropylacrylamide) (pNIPAAm) and pluronics (polyethylene glycol-b-polypropylene oxide-b-polyethylene glycol, PEG-h-PPO-h-PEG). The most extensively studied thermosensitive polymer is pNIPAAm with an LCST of 32°C. This has been used as a hydrophobic block of polymeric micelles with a PEG corona, as well as a hydrophilic shell combined with several other hydrophobic blocks. Work on the synthesis and applications of NIPAAm polymers as components for DDS (in most cases micelles) has been extensively described in several reviews over the years (Aoshima and Kanaoka, 2008 Schmaljohann, 2006 TaleUi and Hennink, 2011 Wei c/ /.,2009). 

Another well-known thermosensitive polymer often used as a micellar component for drug delivery is pluronics (Kabanov et al, 2002 Batrakova and Kabanov, 2008). These triblock copolymers consist of a poly(propylene oxide) middle block flanked by two PEG blocks. They self-assemble into micelles with a PPO block above the LCST of this block. Pluronic micelles loaded with DOX (SP1049C) have reached phase II-III clinical trials, where they have demonstrated slower clearance than the free drug, as well as antitumour activity in advanced MDR adenocarcinoma patients, with acceptable toxicity profile and antitumour activity (Valle et a/., 2011). 

In summary, thennosensitive polymers can prove very valuable as components of drug delivery systems. This is mainly attributable to the easy preparation of nanoparticles by only changing the solution temperature, which in most cases results in spontaneous self-assembly. However, to confer controlled release properties on these systems, either local hypo- or hyperthermia has to be applied or they need to be combined with another stimulus, such as pH or enzyme sensitivity for taUorable and controlled drug release properties. 

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