Physicochemical stability of contact lenses materials for biomedical applications

Purpose: The physicochemical stability, thermal and water plasticizing effect on transport properties of contact lenses (CL) were analyzed to verify its capacity to maintain the original properties after being dehydrated and rehydrated.Methods Two daily disposable (nesofilcon A and delefilcon A) and two monthly CL (comfilcon A and lotrafilcon B) were used. Measurements of refractive index (RI), water content (WC), chemical structure and thermal properties were taken: new (N), after dehydration (D) and rehydrated (R). RI and WC were accessed using a digital automated refractometer (CLR-12-70). Chemical structure was evaluated by a Fourier Transformed Infrared Spectroscopy (FTIR-ATR) and Differential Scanning Calorimetry (DSC) with a calorimeter (Mettler Toledo DSC-821).Results The FTIR spectrum of N, D and R was quite similar for all CL, with higher differences observed in the transmission between 35003000 cm(-1) due to the hydroxyl group (OH). After dehydration and rehydration, there were no significant changes in the chemical structure. RI and WC of the CL rehydrated did not vary significantly from the initial CL (p > 0.05) and thermal properties also confirm that the behavior did not change. It was observed that the glass-transition temperature decrease with increased WC.Conclusion No significant alterations were observed in the physicochemical structure of the materials after dehydration and rehydration showing a good stability of their components. The strong water plasticizing effect in the silicone hydrogel lens materials improves flexibility and chain mobility and may should be considered for other biomedical applications. (C) 2019 Spanish General Council of Optometry. Published by Elsevier Espana, S.L.U.The authors acknowledge support from the Portuguese Foundation for Science and Technology in the framework of the Strategic Funding through the Chemistry Research Centre (UID/QUI/0686/2016) and the Physics Research Centre (UID/FIS/04650/2019) of University of Minho