ToF-SIMS Analysis of Commercial Contact Lenses
ToF-SIMS was used to investigate the surface composition of two commercial contact lenses. Lens material I is composed of 2-hydroxy-ethyl methacrylate (HEMA) and glycerol methacrylate.1 This lens material composition was developed to mitigate discomfort due to “dryness.” Lens material II is composed of 2-hydroxy-ethyl methacrylate (HEMA) and 2-methacryloxyethyl phosphorylcholine cross-linked with ethyleneglycol dimethacrylate.1 The addition of the phosphorylcholine improves biocompatibility by mimicking the polar lipids found in cell membranes; this helps maintain hydration and decrease protein deposition. 
Figure 1 shows the positive secondary ion ToF-SIMS spectra acquired from Lens I (top spectrum) and Lens II (bottom spectrum). Lens I is characterized by a series of O-containing hydrocarbons including CH3O+, C2H5O+, C3H7O+, and C9H11O4+, which are characteristic of the HEMA material. Lens II is characterized by peaks from the 2-methacryloxyethyl phosphorylcholine component: C2H6PO4+, C5H13NPO3+, and C5H15NPO4+. The data demonstrate the sensitivity of ToF-SIMS to detect differences in the molecular composition of contact lens materials.

 
  

 Figure 1. Positive secondary ion ToF-SIMS spectra acquired from Lens I (top) and Lens II (bottom). 

 

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1 R. Watanabe, Contact Lens Spectrum, 27, 21 (2012).