Surface AFM microscopy of unworn and worn samples of silicone hydrogel contact lenses

Abstract

Purpose. To evaluate the qualitative and quantitative topographic changes in the surface of worn contact lenses (CLs) of different materials using atomic force microscopy (AFM). Methods. The topography of five different CL materials was evaluated with AFM over a surface of 25 lm 2 according to previously published experimental setup. Average roughness (R a ) and root mean square (Rms) values were obtained for unworn and worn samples. Results. The R a value increased for balafilcon A (11.62-13.68 nm for unworn and worn samples, respectively), lotrafilcon A (3.67-15.01 nm for unworn and worn samples, respectively), lotrafilcon B (4.08-8.42 nm for unworn and worn samples, respectively), galyfilcon A (2.81-14.6 nm for unworn and worn samples, respectively), and comfilcon A (2.87-4.63 nm for unworn and worn samples, respectively). Differences were statistically significant for all lenses except Rms and R a for comfilcon A, and R a parameter for balafilcon A (p > 0.05). The least relative increase was observed for some balafilcon A samples and for some of these samples the roughness decreased after the lenses had been worn. Conclusion. The changes in surface roughness between unworn and worn lenses are different for different silicone-hydrogel materials. Overall all CLs increased the degree of surface roughness after being worn, even for very short periods of time. However, for samples of balafilcon A, roughness increases at a lower extent or even can decrease as compared to unworn samples of the same material due to filling of the macropores.

Advanced morphological analysis of siloxane‐hydrogel contact lenses

“…The lowest values of height parameters (Sq and Sa) was found in the CLs samples of CL rins , whereas the others CLs samples have different values of the height parameters (Sq and Sa), all higher than the corresponding values of CL rins . It could be emphasized that the obtained results are in close agreement with the statistical and fractal analysis of the siloxane‐hydrogel CLs mentioned in Bettuelli et al (2013), Tavazzi et al (2015), Lira et al (2008), and González‐Méijome et al (2009). On the other hand, both in theory and in experimental results, it is observed that the density of peaks and curves are dependent on the sampling interval, while the interaction effects of neighboring asperities are directly correlated with the distribution and radius of asperities and the depth of indentation by specific mechanisms.…”

Advanced morphological analysis of siloxane‐hydrogel contact lenses

“…The lowest values of height parameters (Sq and Sa) was found in the CLs samples of CL rins , whereas the others CLs samples have different values of the height parameters (Sq and Sa), all higher than the corresponding values of CL rins . It could be emphasized that the obtained results are in close agreement with the statistical and fractal analysis of the siloxane‐hydrogel CLs mentioned in Bettuelli et al (2013), Tavazzi et al (2015), Lira et al (2008), and González‐Méijome et al (2009). On the other hand, both in theory and in experimental results, it is observed that the density of peaks and curves are dependent on the sampling interval, while the interaction effects of neighboring asperities are directly correlated with the distribution and radius of asperities and the depth of indentation by specific mechanisms.…”

AFM in peak force mode applied to worn siloxane-hydrogel contact lenses

“…This fact has permitted the preservation of the last surface layer formed on the CL and for that the Ra and Rq values reported here are higher. Our observation that the Lotrafilcon B material (corresponding to the AO CL) presents, on average, fewer changes in topography after wear coincides with previous reported observations [6,7]. No more values for the other parameters have been found in the literature for the AO CL, it being impossible to make more direct comparisons.…”

“…Also, the value of Rq (44.7±27.6 nm) obtained here is higher than those reported by Lira et al [7] (7.3±5.5 nm) and by González-Meijome et al [6] (11.59±4.91 nm). In our study the CLs were not washed at the end of the wearing period, only removed from the eye and stored in a preservative saline solution, in contrast to the other works commented.…”

“…In this sense, it seems that this argument is corroborated in our study since the worn AO CLs present values of adhesion higher than those of the P CLs, due to the formation of a more uniform surface layer on the Our results for the AO CL can be compared with others reported in the literature. The value of Ra (32.4±17.7 nm) obtained by us is higher than those reported by Lira et al [7] (4.96±4.1 nm) and by González-Meijome et al [6] (8.42±4.14 nm).…”

Hydrogel Contact Lenses Surface Roughness and Bacterial Adhesion

“…Thus, senofilcon A incorporates an internal wetting agent (polyvinyl pyrrolidone) that apparently leaches to the lens surface, and the Aquaform TM technology used in comfilcon A minimizes lens dehydration by forming hydrogen bonds with water molecules, creating a naturally hydrophilic contact lens that retains water inside the lens (Szczotka-Flynn L, 2007;Whittaker G, 2008). The roughness parameters obtained for these lenses were similar to those observed previously in silicone-hydrogel contact lenses lacking surface treatment, such as galyfilcon A and comfilcon A Gonzalez-Meijome et al, 2009), but lower than those reported for surface-treated designs (Gonzalez-Meijome et al, 2006a;Guryca et al, 2007). Despite the similar surface appearance of silicone hydrogels included here and those examined by others, (Teichroeb et al, 2008; Gonzalez-Meijome et al, 2009) Teichroeb et al observed higher roughness parameters for senofilcon A than Comfilcon A when measuring a 25 μm 2 area.…”

Advanced morphological analysis of siloxane‐hydrogel contact lenses

“…The lowest values of height parameters (Sq and Sa) was found in the CLs samples of CL rins , whereas the others CLs samples have different values of the height parameters (Sq and Sa), all higher than the corresponding values of CL rins . It could be emphasized that the obtained results are in close agreement with the statistical and fractal analysis of the siloxane‐hydrogel CLs mentioned in Bettuelli et al (2013), Tavazzi et al (2015), Lira et al (2008), and González‐Méijome et al (2009). On the other hand, both in theory and in experimental results, it is observed that the density of peaks and curves are dependent on the sampling interval, while the interaction effects of neighboring asperities are directly correlated with the distribution and radius of asperities and the depth of indentation by specific mechanisms.…”

AFM in peak force mode applied to worn siloxane-hydrogel contact lenses

“…This fact has permitted the preservation of the last surface layer formed on the CL and for that the Ra and Rq values reported here are higher. Our observation that the Lotrafilcon B material (corresponding to the AO CL) presents, on average, fewer changes in topography after wear coincides with previous reported observations [6,7]. No more values for the other parameters have been found in the literature for the AO CL, it being impossible to make more direct comparisons.…”

“…Also, the value of Rq (44.7±27.6 nm) obtained here is higher than those reported by Lira et al [7] (7.3±5.5 nm) and by González-Meijome et al [6] (11.59±4.91 nm). In our study the CLs were not washed at the end of the wearing period, only removed from the eye and stored in a preservative saline solution, in contrast to the other works commented.…”

“…In this sense, it seems that this argument is corroborated in our study since the worn AO CLs present values of adhesion higher than those of the P CLs, due to the formation of a more uniform surface layer on the Our results for the AO CL can be compared with others reported in the literature. The value of Ra (32.4±17.7 nm) obtained by us is higher than those reported by Lira et al [7] (4.96±4.1 nm) and by González-Meijome et al [6] (8.42±4.14 nm).…”

Hydrogel Contact Lenses Surface Roughness and Bacterial Adhesion

“…Thus, senofilcon A incorporates an internal wetting agent (polyvinyl pyrrolidone) that apparently leaches to the lens surface, and the Aquaform TM technology used in comfilcon A minimizes lens dehydration by forming hydrogen bonds with water molecules, creating a naturally hydrophilic contact lens that retains water inside the lens (Szczotka-Flynn L, 2007;Whittaker G, 2008). The roughness parameters obtained for these lenses were similar to those observed previously in silicone-hydrogel contact lenses lacking surface treatment, such as galyfilcon A and comfilcon A Gonzalez-Meijome et al, 2009), but lower than those reported for surface-treated designs (Gonzalez-Meijome et al, 2006a;Guryca et al, 2007). Despite the similar surface appearance of silicone hydrogels included here and those examined by others, (Teichroeb et al, 2008; Gonzalez-Meijome et al, 2009) Teichroeb et al observed higher roughness parameters for senofilcon A than Comfilcon A when measuring a 25 μm 2 area.…”

Advanced morphological analysis of siloxane‐hydrogel contact lenses

“…The lowest values of height parameters (Sq and Sa) was found in the CLs samples of CL rins , whereas the others CLs samples have different values of the height parameters (Sq and Sa), all higher than the corresponding values of CL rins . It could be emphasized that the obtained results are in close agreement with the statistical and fractal analysis of the siloxane‐hydrogel CLs mentioned in Bettuelli et al (2013), Tavazzi et al (2015), Lira et al (2008), and González‐Méijome et al (2009). On the other hand, both in theory and in experimental results, it is observed that the density of peaks and curves are dependent on the sampling interval, while the interaction effects of neighboring asperities are directly correlated with the distribution and radius of asperities and the depth of indentation by specific mechanisms.…”

AFM in peak force mode applied to worn siloxane-hydrogel contact lenses

“…This fact has permitted the preservation of the last surface layer formed on the CL and for that the Ra and Rq values reported here are higher. Our observation that the Lotrafilcon B material (corresponding to the AO CL) presents, on average, fewer changes in topography after wear coincides with previous reported observations [6,7]. No more values for the other parameters have been found in the literature for the AO CL, it being impossible to make more direct comparisons.…”

“…Also, the value of Rq (44.7±27.6 nm) obtained here is higher than those reported by Lira et al [7] (7.3±5.5 nm) and by González-Meijome et al [6] (11.59±4.91 nm). In our study the CLs were not washed at the end of the wearing period, only removed from the eye and stored in a preservative saline solution, in contrast to the other works commented.…”

“…In this sense, it seems that this argument is corroborated in our study since the worn AO CLs present values of adhesion higher than those of the P CLs, due to the formation of a more uniform surface layer on the Our results for the AO CL can be compared with others reported in the literature. The value of Ra (32.4±17.7 nm) obtained by us is higher than those reported by Lira et al [7] (4.96±4.1 nm) and by González-Meijome et al [6] (8.42±4.14 nm).…”

Hydrogel Contact Lenses Surface Roughness and Bacterial Adhesion

“…Thus, senofilcon A incorporates an internal wetting agent (polyvinyl pyrrolidone) that apparently leaches to the lens surface, and the Aquaform TM technology used in comfilcon A minimizes lens dehydration by forming hydrogen bonds with water molecules, creating a naturally hydrophilic contact lens that retains water inside the lens (Szczotka-Flynn L, 2007;Whittaker G, 2008). The roughness parameters obtained for these lenses were similar to those observed previously in silicone-hydrogel contact lenses lacking surface treatment, such as galyfilcon A and comfilcon A Gonzalez-Meijome et al, 2009), but lower than those reported for surface-treated designs (Gonzalez-Meijome et al, 2006a;Guryca et al, 2007). Despite the similar surface appearance of silicone hydrogels included here and those examined by others, (Teichroeb et al, 2008; Gonzalez-Meijome et al, 2009) Teichroeb et al observed higher roughness parameters for senofilcon A than Comfilcon A when measuring a 25 μm 2 area.…”