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Chunzi Liu, Charles W Scales, Gerald G. Fuller; Crosslink density influences the adhesive strength of silicone hydrogel surfaces against corneal epithelial cells. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1761.
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© ARVO (1962-2015); The Authors (2016-present)
The crosslink density in soft hydrogel materials can significantly affect their adhesion to different surfaces, i.e. the greater the degree of cross-linking, the lower the adhesion. In contact lens (CL) applications, lens/cornea or lens/eyelid adhesion should be minimized to facilitate removal, allow for sufficient lens movement, and prevent discomfort. Yet, the effect of crosslinking on the adhesion of CLs to the human cornea remains unknown. Here we used a customized rheometer to examine the adhesive strength between corneal epithelial cells and silicone hydrogel formulations with systematically varied crosslink densities.
To quantify the strength of adhesion (SoA) between corneal epithelial cells and silicone hydrogel materials, step strain deformations were applied onto mucin-expressing telomerase immortalized human corneal epithelial cell monolayers in contact with a silicone hydrogel lens. The resulting stress relaxations of a series of silicone hydrogel materials derived from senofilcon A with increasing crosslink densities (i.e. L1, L2, L3, L4 and L5 containing crosslinker levels of 1.2, 1.35, 1.5, 1.65, and 1.8 %, respectively) and delefilcon A were tested accordingly. The measured stress relaxations were directly influenced by the tenacity of adherence of the cells against the displaced lens surface. These stresses were converted to an effective modulus and the residual unrelaxed modulus provided a direct indication of SoA.
Within the senofilcon-derived series, L1 (containing the lowest crosslink density) showed the highest SoA (39.1 ± 32.67 Pa) compared to L2 (1.6 ± 10.77), L3 (11.3 ± 4.00 Pa), L4 (5.4 ± 9.01 Pa), and L5 (5.6 ± 8.63 Pa). The delefilcon A lens (38. 8± 26.61 Pa) exhibited a comparable SoA to L1 (p=0.495), suggesting the surface of delefilcon A has a lower crosslink density and a higher SoA to corneal epithelia than lenses with greater degrees of crosslinking, i.e. L2 (p=0.037), L3 (p=0.072), L4 (p=0.048), and L5 (p=0.048).
These results demonstrate that increasing crosslink density diminishes the adherence of lenses to mucin-expressing corneal epithelial cells. Consequently, the adhesiveness of CLs to ocular tissues may impact the comfort level for lens wearers and affect ease of removal. This result provides guidance on development of silicone hydrogel formulations to further improve CL comfort and handling.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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