Synthesis of a Stimulus-Sensitive Copolymer with Response to Temperature and pH in Silicone Catheters

This work aimed to synthesize a graft copolymer with temperature- and pH-responsive properties. The synthesis of SR-cat-g-(NVCL/NVIM) was carried out using the direct irradiation method with a ⁶⁰Co gamma-ray source (Gammabeam 651 PT). The temperature- and pH-responsive monomers, N-vinylcaprolactam (NVCL) and N-vinylimidazole (NVIM), respectively, were grafted onto silicone catheters. The effects of irradiation dose and monomer concentration on grafting efficiency were studied. A direct relationship was found between grafting efficiency and both irradiation dose and monomer concentration. As these parameters increased, the grafting percentage also increased. The biomaterial was characterized by using Fourier-Transform Infrared Spectroscopy (FT-IR), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), swelling, and a water contact angle measurement. The swelling behavior was also investigated by varying temperature and pH. The Lower Critical Solution Temperature (LCST) was observed around 34 °C, and pH sensitivity was detected between pH 8 and 8.5. Mechanical tests were performed to conduct a systematic analysis relating to the grafting percentage and the ratio between grafted polymers and Young's modulus. Finally, the loading and release capacity of norfloxacin in the modified catheters was evaluated.