Cheng Lily, Muller Susan J, Radke Clayton J
Department of Chemical Engineering, University of California, Berkeley, CA, USA.
Curr Eye Res. 2004 Feb;28(2):93-108. doi: 10.1076/ceyr.28.2.93.26231.
Modern application of soft contact lenses demands safe and comfortable wear over extended time periods up to one month. Lenses that exhibit and sustain complete water wetting allow thick tear-film deposition, minimize film rupture, and permit smooth tear recovery upon lid closure. Water contact angles determined using an air bubble captive on a lens best gauge the in-vivo wetting state. To achieve highly water wetting lenses demands that contact-angle hysteresis be eliminated and that the advancing and receding angles both approach zero. Since lens wear exposes the anterior surface to tear proteins, lens wettability should be measured in the presence of tear-film components.
A captive-bubble technique is applied to measure the advancing and receding contact angles of two commercial silicone-hydrogel lenses: PureVision (PV) and Focus Night & Day (CF) and a standard HEMA (hydroxethyl-methacrylate) hydrogel lens: Acuvue (AV). In the captive-bubble method, an air bubble immersed in aqueous solution is brought into contact with the contact lens. The contact angle through water during bubble expansion yields the receding angle. Bubble contraction gives the water advancing angle. Contact-angle hysteresis is the difference between the advancing and receding angles.
In isotonic solution, all three lenses display considerable contact-angle hysteresis with advancing angles of almost 90 degrees. When lysozyme and/or mucin were added to the aqueous solution, hysteresis was eliminated, and equivalent and high water wetting was achieved for the three lenses. Only the advancing angle in isotonic solution provided discriminating evidence for differences in surface chemistry. Covalent attachment of polyethyleneglygol (PEG) to the PV lens surface achieved complete water wetting independent of the presence of tear protein in the solution.
The captive-bubble technique provides contact angles that are relevant to on-eye lens wear. Both advancing and receding contact angles are important to lens wettability performance. When lysozyme and/or mucin are present in the solution, PV, CF, and AV lenses display low advancing and receding contact angles indicative of equivalent wettability performance. This result is due to molecular adsorption of the proteins onto the lens external surface. Covalently attached PEG on the PV lens not only provides complete water wetting but also minimizes or even eliminates protein adsorption.
现代软性隐形眼镜的应用要求在长达一个月的长时间佩戴过程中安全舒适。能够展现并维持完全水润的镜片可使泪膜厚沉积，减少泪膜破裂，并在眼睑闭合后实现泪液的顺利恢复。使用捕获在镜片上的气泡测定的水接触角最能衡量体内的湿润状态。要实现高度水润的镜片，需要消除接触角滞后现象，使前进角和后退角都接近零。由于佩戴镜片会使前表面暴露于泪液蛋白质中，因此应在泪膜成分存在的情况下测量镜片的润湿性。
采用捕获气泡技术测量两种商用硅水凝胶镜片：PureVision（PV）和Focus Night & Day（CF）以及一种标准的羟乙基甲基丙烯酸酯（HEMA）水凝胶镜片：Acuvue（AV）的前进角和后退角。在捕获气泡法中，将浸入水溶液中的气泡与隐形眼镜接触。气泡膨胀过程中透过水的接触角产生后退角。气泡收缩产生水前进角。接触角滞后是前进角和后退角之间的差值。
在等渗溶液中，所有三种镜片都表现出相当大的接触角滞后，前进角接近90度。当将溶菌酶和/或粘蛋白添加到水溶液中时，滞后现象消除，三种镜片实现了等效的高水润性。只有等渗溶液中的前进角为表面化学差异提供了区分性证据。将聚乙二醇（PEG）共价连接到PV镜片表面可实现完全水润，而与溶液中泪液蛋白质的存在无关。
捕获气泡技术提供了与眼上镜片佩戴相关的接触角。前进角和后退角对镜片的润湿性都很重要。当溶液中存在溶菌酶和/或粘蛋白时，PV、CF和AV镜片显示出低前进角和后退角，表明具有等效的润湿性。这一结果是由于蛋白质分子吸附到镜片外表面。PV镜片上共价连接的PEG不仅提供完全水润，还能使蛋白质吸附最小化甚至消除。
