Synthesis of thermosensitive PVA-g-NIPAAm nanohydrogels by radiation polymerization

Thermosensitive nanohydrogels that are triggered by changes in environmental temperature thus resulting in in situ hydrogel formation have recently attracted the attention of many investigators for biomedical applications. In addition, Nanohydrogel are considered suitable drug delivery systems for their unique features, such as a large surface to volume ratio, and for the possibility to tune their size and properties. In the present work, nanohydrogels of poly (vinyl alcohol) -g-N-isopropyl acrylamide (PVA-g-NIPAAm) are synthesized with too lower X-ray radiation dose between 1-20 Gy of PVA and NIPAAm dilute aqueous solution at ambient temperature in the presence of tetrakis(hydroxymethyl)phosphonium chloride (THPC) due to its rapid oxygen scavenging abilities and hydrogen peroxide as a source of hydroxyl radical. The dynamic light scattering (DLS) measurement showed nano size dimension with narrow size distribution for the synthesized nanohydrogels. The nanohydrogels were characterized by FT-IR, swelling studies, thermal analysis and rheological analysis. FT-IR spectrum confirms incorporation of NIPAAm during the grafting process on PVA. The phase transition temperature of the nanohydrogels were examined using differential scanning(DSC).A clear endothermic point was observed in the DSC thermograms of PNIPAAm and PVA-g-NIPAAm nanohydrogels around 28 °C and 33°C, respectively. Swelling investigations of nanohydrogels indicated high equilibrium swelling ratio and fast response rates as well as temperature and pH dependence of equilibrium swelling ratio. The mechanical properties of hydrogels are of great importance particularly if they are to be used in controlled drug delivery applications. The viscoelastic properties of synthesized nanohydrogels, as investigated rheologically, indicate that the gel had good mechanical strength

Keywords:

Nanohydrogels , thermosensitive , radiation , swelling , N-isopropylacrylamide