Dynamic wettability of pHEMA-based hydrogel contact lenses

Standard methods of contact angle analysis include sessile drop, captive bubble and Wilhelmy plate techniques; however, these methodologies are not particularly well suited for assessing the wettability of the surfaces of formed hydrogel contact lenses. This paper describes two methodologies that are adaptations of previously described techniques. The maximum adherent force method is an adaptation of the dynamic Wilhelmy plate technique that allows the assessment of whole, finished contact lenses. The dynamic photographic method allows the simultaneous assessment of the front and back surfaces of strip samples for the assessment of advancing and receding contact angles. Lenses investigated were made from polyhydroxyethyl methacrylate, hydroxyethyl methacrylate/methacrylic acid and hydroxyethyl methacrylate/glycerol methacrylate. The lenses were manufactured by lathing, spin-casting or cast-moulding techniques. Overall, both techniques demonstrated few differences between the wettability of different lens materials and no differences between materials of the 'same' lens type but manufactured by different methods. These findings are consistent with the results of clinical studies, which have shown little difference between contact lens surface wettability in vivo, which may be due to the apparent natural surface wettability-enhancing properties of the pre-lens tear film.