Comprehensive Insight into the Protein–Surface Biomolecular Interactions on a Smart Material: Complex Formation between Poly(<i>N</i>-vinyl Caprolactam) and Heme Protein

Proteins are naturally occurring biopolymers that exhibit a wide range of functional applications. Meticulous knowledge about biomolecular interactions between polymeric biomaterials and body fluids or proteins is essential for designing biospecific surfaces and understanding protein–polymer interactions beyond existing limitations. In this regard, we studied the comparative effect of heme proteins such as cytochrome c, myoglobin, and hemoglobin on the phase behavior of poly(N-vinyl caprolactam) (PVCL) aqueous solution and demonstrated various biomolecular interactions in the polymer–protein complex with the aid of various biophysical techniques. Absorption spectroscopy, steady-state fluorescence spectroscopy, Fourier transform infrared spectroscopy, dynamic light scattering studies, laser Raman spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy were carried out at room temperature to examine the changes in absorbance, fluorescence intensity, molecular interactions, particle size, agglomeration behavior, and surface morphologies. Furthermore, differential scanning calorimetry studies were also performed to analyze conformational changes, coil to globule transition, and phase behavior in the presence of proteins. With the addition of heme proteins, the lower critical solution temperature of PVCL increases toward higher temperature. The present study may help in designing smart biomaterials and stimulate more novel concepts in polymer–protein interactions. It also helps in the development of a biomimetic polymer for "smart" applications such as pulsatile drug release systems and controlled bioadhesion by temperature-mediated hydrophilic/hydrophobic switching.