Objectives:Cosmetic contact lenses are increasingly popular because of their eye enhancing cosmetic benefits. The pigment particles used in these lenses can impact lens surface characteristics. This article examines the surface characteristics and the differences between the clear and the pigmented regions among five limbal ring design lenses.Methods:Scanning electron microscopy was used to determine the location and depth of the pigment particles from the lens surface. The coefficient of friction (CoF) was determined with a Basalt-MUST microtribometer at clear and pigmented regions on either the front or the back surface. Atomic force microscopy was used to determine the surface roughness of each lens in root-mean-square (RMS) units at clear and pigmented regions. A linear mixed model for repeated measures was used for the analysis of the CoF and RMS roughness to compare all lenses.Results:Four lens types had pigments exposed on the surface and one lens type had pigment fully enclosed. The CoF difference between clear and pigmented regions were similar and not statistically significant (P=0.0124) for the lens type with pigments enclosed, whereas the CoF difference for the other four lens types showed statistically significant difference (P<0.0001).Conclusions:Of the lenses tested here, cosmetic contact lenses with pigments enclosed in the lens matrix provided a more consistent surface between clear and pigmented regions compared with lenses that had exposed pigments.
Nowadays, ultrasonic motors (USMs) are used widely in a large variety of applications such as camera auto-focus mechanisms, devices in automobiles, industrial servo control in precision positioning, intelligent robotics, ultra-precision measuring, and medical equipment. USM is driven by traction force at high-frequency oscillations (>40 kHz) and the characteristics and life of the motor are strongly related to the friction material used in the tribological contact. In this study, two purposely built test rigs, including a USM and a high-frequency (up to 4000 r/min) reciprocating machine (HFRM), were developed. The reciprocating machine ran with a small amplitude and a high-frequency motion was used to examine the wear behaviour of the friction pairs. Different materials such as advanced surface coating (chromium titanium aluminium nitride, and diamond-like coating) on stainless steel substrates were used to investigate their combined tribological performance with the aim to be used in the USM context. A matrix screening test for material selection purpose were also carried out using the HFRM and the tribological performance of the chosen material pairs were subsequently investigated using the USM. The ranking results of the material pairs from the USM tests agreed with those from the HFRM tests. HFRM results could correlate well with the USM results by considering energy input into the wear system. Thus, HFRM can be used as a screening tool for selecting materials using in USMs.
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