The biological stimuli for governing the phase transition temperature of the “smart” polymer PNIPAM in water

A lack of sufficient knowledge regarding the behaviour of stimuli-responsive polymers to biological stimuli hinders the potential use of responsive polymers as biomaterials and medical devices. Hence, in this study, we demonstrate the impact of various globular proteins on the phase transition temperature of poly(N-isopropylacrylamide) (PNIPAM) in an aqueous solution through the use of fluorescence spectroscopy, dynamic light scattering (DLS), Fourier transform infrared (FTIR) spectroscopy and field-emission scanning electron microscopy (FESEM). Furthermore, we describe the molecular interaction of PNIPAM with proteins by the MolDock method. Our experimental and docking studies revealed that such proteins as α-chymotrypsin (CT), insulin (In) and haemoglobin (Hb) decreased the lower critical solution temperature (LCST) of the polymer, whereas succinyl-concanavalin A (SCA) increased the LCST of PNIPAM. The LCST changed upon increasing the concentration of protein from 0.5 mg/mL to 1 mg/mL. The thermoresponsive behaviour of PNIPAM can be significantly altered by the functional groups present in the protein. The findings of the present study can be used in the engineering of bioresponsive smart PNIPAM-based devices.