Thermosensitive Fluorescence of an UCST-type Hybrid Functional Hydrogel
Nikola Majstorović, Seema Agarwal
Abstract
Mechanically strong, functional hybrid hydrogel networks with upper critical solution temperature (UCST)-type thermosensitivity for volume change and temperature-controlled fluorescence are presented. Thermosensitive poly(N-acryloyl glycinamide)/poly(glycidyl methacrylate) (PNAGA/PGMA) interpenetrating network (IPN) functional hydrogels were prepared sequentially by photoinitiated radical polymerization. Amine moieties were introduced by a ring-opening reaction of GMA, followed by subsequent coupling of fluorescein isocyanate (FITC). Fourier transform infrared and differential scanning calorimetry were deployed to prove the successful incorporation of the PGMA network and the introduction of amino groups. Equilibrium swelling at different temperatures in pure water and phosphate-buffered saline (PBS) was conducted to study the thermosensitive properties of the IPN hydrogels. The IPN hydrogels retained their thermophilic swelling properties after the introduction of PGMA and showed increased mechanical strength. The fluorescence properties of the IPN hydrogels were studied by fluorescence spectroscopy at temperatures from 10 to 40 °C in water and PBS and under acidic and alkaline conditions. Fluorescence activity of FITC-coupled IPN hydrogels with a weight ratio (PGMA/PNAGA) of around 0.5 showed an increased temperature dependence in aqueous medium compared to dissolved FITC. Thermosensitive fluorescent PNAGA IPN hydrogels may function as thermometers or thermosensitive devices.