Raman, IR and thermal study of a new highly biocompatible phosphorylcholine-based contact lens

In this study, vibrational Raman and IR spectroscopy coupled to thermogravimetry (TG) and differential scanning calorimetry (DSC) have been used to characterize the Proclear™ lens, a biomimetic soft contact lens composed of Omafilcon A, a phosphorylcholine (PC)-modified poly(2-hydroxyethyl-methacrylate) (PHEMA), whose main monomer is 2-methacryloyloxy-ethylphosphorylcholine. Raman and IR spectra showed that the PC component is actually incorporated into the polymer. The νOH Raman stretching region demonstrated that the Proclear™ lens contains a higher amount of water (59% by TG analysis) than commercial PHEMA lenses, confirming that the PC incorporation has noticeably altered the material properties. DSC comparative analysis was carried out on Proclear™ and PHEMA lenses as well as Acuvue™ (Etafilcon A), a commonly used soft contact lens with a water content comparable to that of Proclear™. The latter revealed to be characterized by a significantly higher free water fraction than PHEMA; this result explains why the former lens absorbs few tear components than the latter. Conversely, free water fraction was found to be nearly the same for Proclear™ and Acuvue™ lenses; the noticeably lower protein adsorption reported for the former was explained, partially at least, in relation to the different organization of water molecules in the two lenses.