隐形眼镜中润湿性研究检测方案(表面张力仪)

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Wettability of contact lensOverview Overview Wettability can be defined as an ability of the liquidto spread on the solid surface. When a liquid spreadswettability is termed to be good， but if the liquidbeads up the wettability is poor. Contact angle valueof 90° is typically considered as a threshold value(Figure 1). Figure 1Good wettability (left)， poor wettability (right) 4 [Progress Together] Wettability is especially important to contact lenses as the lenssurface should support a continuous tear film. Poor wettabilityof the contact lens is related to reduced visual performance，an increase in surface deposition and discomfort. A recentlydiscovered material for contact lens manufacturing is the siliconehydrogel， which is suitable for long-term use as it has improvedoxygen delivery on the ocular surface. However， this material hasbeen reported to have reduced wettability compared to othermaterials used in hydrogel contact lenses. This reduced wettabil-ity has been addressed with different types of surface treatmentsand coatings while trying to maintain a good oxygen permea-bility. Plasma treatment has been a popular choice to increasethe hydrophilicity of the lens. Different coatings have also beencommon1. To study the effectiveness of surface treatments， thewettability of the contact lens needs to be evaluated. Wettability can be evaluated through contactangle measurements Contact angle is a measure of wettability and is also a widelyaccepted method for wettability evaluation of the contact lens. Thecontact angle is measured at the three-phase contact point wheresolid (contact lens surface)， liquid (tear film) and gas (air) meet. Figure 2 Contact angle is determined by the three-phase contact point wheresolid， liquid and gas meet. Contact angles are often said to be either static or dynamicdepending on whether this three-phase contact point is in motionor not. The dynamic contact angle is further divided into advancingand receding contact angles. Advancing contact angle is measuredwhen the liquid front is moving across the air-exposed lens surfaceand receding when the contact line is withdrawn back. The differ-ence between the two contact angles is contact angle hysteresis. Receding and advancing contact angles are both importantmeasures of contact lens wettability. The advancing contactangle develops when the eyelid closes and the tear film on thelens starts to recover. A receding angle forms when the eyelidis opened and the tear film starts rupturing on the lens. Captive bubble method to mimic a real-lifesituation There are three commonly used methods to measure contactangles； sessile drop， captive bubble， and Wilhelmy plateWilhelmy plate offers an automated method for dynamic contactangle measurements but it is not well suited for contact lensesdue to shape requirements for the sample. A sessile drop is themost commonly used static contact angle measurement techniqueand can be used for dynamic measurements as well. The mainproblem with the sessile drop method in the case of contact lensesis that the measurements are done in air and the surface of thelens needs to be dried prior the measurements which can alterthe surface. Captive bubble method offers the best technique to mimic thereal-life situation. The contact lens surface is immersed in a liquidthroughout the measurement process and thus does not undergcdehydration.An air bubble is used to measure the contact anglesFigure 3 shows an air bubble on contact lens surface immersedin water. Figure 3Captive bubble measurement on a contact lens. Conclusions Wettability is one of the most important factors when consideringthe surface properties of the contact lens. Wettability can be linkedto biocompatibility and comfort. Contact angle measurements， andespecially captive bubble measurements， provide a simple methodfor wettability evaluation of the contact lens. [1] Wagner， H.， "Polish up your practice： Today's contact lens surfaces"，Review of Optometry Aug 15 (2018) 36. Contact us at info@biolinscientific.com 润湿性可以用来描述液体在固体表面铺展的性能。当液体铺展很好时润湿效果被认为是好的，而当液体倾向于变成液滴时，润湿效果则是比较差的。接触角的值为90°被认为是典型的分界值。对于隐形眼镜来说润湿性非常重要，因为隐形眼镜表面需要形成连续的泪液膜。不好的润湿性会降低视觉功能，并增加表面沉积物和不适感。最近发现用于隐形眼镜生产的材料是硅树脂水凝胶材料，它适合于长时间使用，因为改善了视角面的透氧率。但是，据报道这种材料相对于其他的水凝胶隐形眼镜材料来说降低了润湿性。这种降低的润湿性在不同类型的表面处理和涂层中被提出，因为还需要保持良好的透氧率。等离子处理是一种增加眼镜亲水性的常用选择。不同的涂层也很通用。为了研究表面处理的有效性，需要来评估隐形眼镜的润湿性能。