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Tannin A Schmidt, Heather Sheardown, Michael Lee Samsom; Human Ocular Surface Boundary Lubrication of Model Conventional and Silicone Hydrogels by Proteoglycan 4. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4651.
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© ARVO (1962-2015); The Authors (2016-present)
Recent data indicates that high friction may contribute to contact lens (CL) discomfort. Studies indicate that proteoglycan 4 (PRG4), a mucin-like glycoprotein found in the eye, reduces friction between the cornea-eyelid interfaces by acting as a natural boundary lubricant. It has been shown that PRG4 can reduce friction at a polydimethylsiloxane-cornea interface, indicating that it could be effective for CL materials. The objective of this study was to determine the ocular surface (human cornea or eyelid) boundary lubricating ability of PRG4 on model conventional hydrogel (CH) and silicone hydrogel (SH) CL materials.
Fresh human corneas and eyelids were obtained from the Alberta Lions Eye Bank and the UCalgary body donation program, respectively. A CH (poly(2-hydroxyethyl methacrylate) [pHEMA]) and 2 model SH (pHEMA,Methacryloxypropyltris(trimethylsiloxy)silane [pHEMA TRIS] and N,N-Dimethylcrylamide, TRIS [DMAA TRIS]) lens materials were prepared. PRG4 was obtained from bovine cartilage culture and suspended in saline at 300µg/mL. Tissues and CL materials were mounted on a BOSE ELF3200 biomechanical tester, forming eyelid-lens and cornea-lens interfaces. These surfaces were articulated at effective sliding speeds of 0.3-30 mm/s, and pressures of 18-23 kPa. CH and SH (n=6) were tested in saline and PRG4 baths at the cornea-lens interface, and SH (n=5) were tested at the eyelid-lens interface. Static and kinetic friction coefficients were calculated.
PRG4 reduced friction on model SH but not CH lenses. Kinetic friction coefficients (averaged over speeds) for pHEMA were similar in both saline and PRG4: cornea (saline=0.13±0.02, PRG4=0.14±0.02), mean±SEM. PRG4 reduced friction on pHEMA TRIS: cornea (saline=0.21±0.03, PRG4=0.18±0.03; p<0.01), eyelid (saline=0.19±0.03, PRG4=0.13±0.03; p<0.05). PRG4 reduced friction on DMAA TRIS (p<0.05): cornea (saline=0.17±0.03, PRG4=0.13±0.03, p<0.05), eyelid (saline=0.13±0.04, PRG4=0.09±0.03; p<0.05).
PRG4 functioned as an effective boundary lubricant of model SH lenses. To effectively reduce friction of lenses, PRG4 must be able to adsorb/interact with, and modify the surface. PRG4 may require a hydrophobic moiety (e.g. TRIS) to adsorb to. Future studies will examine incorporation of PRG4 on/in model SH lenses, and contribute towards the development of low friction, and potentially more comfortable, CL materials.
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