Impact of manufacturing technology and material composition on the mechanical properties of hydrogel contact lenses.

Hydrogel materials are not only different as a result of different co-monomer compositions but also as a result of the manufacturing method used to produce them. Hydrogel contact lenses fabricated by different methods are subjected to markedly different processing steps, which are likely to affect the resultant material network structure of a lens. The mechanical performance of five soft contact lens types was investigated using one conventional technique (tensile test) and three novel techniques (probe, tear and ball milling tests). The five lens groups consisted of three polyhydroxyethyl methacrylate (pHEMA) lenses which were each manufactured by a different technique: lathing, spin-casting and cast-moulding, a HEMA/methacrylic acid (HEMA/MAA) cast-moulded lens and a HEMA/glycerol methacrylate (HEMA/GMA) cast-moulded lens. Overall, the results show that the best mechanical performance is obtained for the pHEMA lenses, with some differences occurring between the lenses. The HEMA/GMA lens showed the worst performance.