Paper AS-TuP19
Mapping of a Natural Lubricant Network on the Surface of Silicone Hydrogel Materials Using Surface and Bulk Chemistry Techniques

Tuesday, October 30, 2012, 6:00 pm, Room Central Hall

Commercial silicone hydrogel contact lenses (SiHy) are ophthalmic devices designed to correct vision as well as function as an ocular bandage for therapeutic purposes. Surface wettability, modulus, surface topography as well as bulk water content are some of the factors that influence lens comfort and performance. Contact lens surface wettability is believed to be an important factor in comfort as well as overall patient satisfaction. Tear confluence across a lens surface may be improved by the presence of well-chosen biomolecules, capable of retaining moisture. Very recently the application of a natural lubricant hyaluronate (HA), to a daily use multi purpose solution (MPS), Biotrue™ has been reported.

In these studies HA was used in conjunction with a surfactant system present in Biotrue^TM MPS. The exclusive formulation of Biotrue^TM was designed to improve hydration and wettability of various SiHy contact lens materials. Improvements in moisture retention are attributed to the use of high molecular weight HA present in Biotrue™ capable of high water retention. Presence of HA on a lens surface acts as a wetting agent and improves the properties of SiHy contact lens materials. To our knowledge there is no published literature reporting on a visualization method of HA on SiHy contact lenses surfaces.

The purpose of this research was to develop a direct method to demonstrate the presence of a HA network on the surface of SiHy contact lenses using surface chemistry techniques. Senofilcon A^® and balafilcon A^® were chosen to investigate the interaction of HA with SiHy materials. Atomic Force Microscopy (AFM) was applied to examine the topography of both materials in the hydrated and dehydrated state. The visualization of HA chains was done using Confocal Laser Scanning Microscopy (CLSM) and Differential Interference Contrast (DIC) microscopy using a dye selective for HA (Safranin).

Senofilcon A^® and balafilcon A^® were soaked in Biotrue^TM for 4 hours. Lenses were then soaked in 3 mL of Safranin solution. After 3 min the samples were rinsed with DI water for 3 min to remove any unbound dye. Samples were imaged using an Olympus CLSM equipped with a DIC attachment. Individual confocal images were captured using an air objective sequentially across the sample. A large mosaic was generated using fiducial marks stitched together from the individual images. SiHy lenses incubated with Safranin solution but not exposed to Biotrue^TM were characterized as control. Additionally applicability of X-ray Photoelectron Spectroscopy (XPS) for HA mapping on the lenses surface was examined. AFM was used in parallel to study modification of the lens surfaces with HA biopolymer.