XPS and surface-MALDI-MS characterisation of worn HEMA-based contact lenses

XPS and MALDI-MS were used to analyse initial adsorption events in the fouling of HEMA-based contact lenses. All of the lenses tested accumulated tear film deposits within 10 min of wear. XPS indicated the presence of mainly proteinaceous deposits, with indications of some contributions by mucins or lipids on some lenses and the nature of the deposit being influenced by the lens chemistry. MALDI-MS detected the presence of surface-adsorbed species with molecular weights <15 kDa. While lysozyme could be identified by comparison of MALDI-MS signals with known protein mass and assignments are suggested for some other signals, several other species, with MWs less than that of lysozyme, could not be identified as no ocular proteins with corresponding MWs had been reported in previous biochemical tear film analyses. These species, and others, were also detected in MALDI-MS analysis of reflex tear film, suggesting that the adsorbed unidentified species were not simply products of surface-induced dissociation of adsorbing higher-MW proteins. This short-term wear study detected rapid interface conversion and demonstrated the utility and surface sensitivity of XPS and MALDI-MS in characterising contact lens deposits at the initial stages when sub-monolayer adsorbed amounts are present on lenses.