Thermosensitive Poly(N‐isopropylacrylamide)‐g ‐Polyamidoamine Dendrimer Derivatives: Preparation and the Drug Release Behaviors

Abstract Summary: A series of thermally responsive dendritic core‐shell polymers were prepared based upon dendritic polyamidoamine (PAMAM), modified with carboxyl end‐capped linear poly(N‐isopropylacrylamide) (PNIPAAm‐COOH) in different ratios via an esterification process to obtain PNIPAAm‐g‐PAMAM. The graft ratio of PNIPAAm could be adjusted by changing the feed ratio of PAMAM‐OH to PNIPAAm‐COOH and was verified by 1H NMR and gel penetration chromatography (GPC). The lower critical solution temperature (LCST) of PNIPAAm‐g‐PAMAM evaluated by UV‐vis spectrophotometer was about 32 °C. Indomethacin (IMC) as a model drug was loaded in the thermosensitive polymer‐grafted dendrimer derivative and its release behavior was studied below and above its LCST (27 °C vs 37 °C). Results showed that the LCST of PNIPAAm‐g‐PAMAM was around 32 °C compared with that of the pure PNIPAAm. The release behavior of the indomethacin entrapped in the internal cavities of the PNIPAAm‐g‐PAMAM showed that almost 77% of the drug was cumulatively released at 27 °C after 10 hours, whereas only 20% was released at 37 °C. The release rate of IMC from the IMC/PNIPAAm‐g‐PAMAM complex at 37 °C is significantly slower than that at 27 °C, which indicates that the PNIPAAm chains grafted on the surface of PAMAM dendrimer could act as a channel switching on‐off button through expending or contracting in response to the temperature variation and could control the drug release by varying the surrounding temperature.