Microscopic investigations of surface texture of siloxane‐hydrogel contact lenses

Abstract

Purpose: The objective of this article was to investigate experimentally the 3‐D surface of unworn/worn contact lenses (CLs) using stereometric analysis applied to atomic force microscopy (AFM) micrographs. Materials and methods: Fractal and stereometric analyses were applied in micromorphology investigations of siloxane‐hydrogel CLs made of Filcon V. Qualitative and quantitative study of surface texture was made using statistical parameters of 3‐D surface roughness, according with ISO 25178‐2: 2012 for: CLrins (unworn CLs taken from the blister and rinsed with deionized water); CLworn‐smooth (worn for 8 h and presenting a smooth‐type morphology), and CLworn‐sharp (worn for 8 h and presenting a sharp‐type morphology). Results: Fractal analysis reveals fractal nature at nanometer scale of all surface samples. The fractal dimensions determined by enclosing boxes method of the studied samples are: Df = 2.25 ± 0.01 for CLrins, Df = 2.29 ± 0.01 for CLworn‐smooth and Df = 2.40 ± 0.01 for CLworn‐sharp. Conclusions: Surface statistical parameters can be deduced by analyses of micromorphology and fractal structure of the 3‐D surface of CLs. The variation of these parameters provides quantitative information on the effects of wear, such as in the cases of the two morphologies which can be found after 8 h wear of Filcon V CLs. POLYM. ENG. SCI., 59:E442–E451, 2019. © 2019 Society of Plastics Engineers

Fractal dimension analysis: A link between porous polystyrene films patterns and cancer cell patterns

“…The surface roughness is present in many physical phenomena, including friction, adhesion, and tribology; these phenomena present hierarchical structures at micro and nano scales of great importance in biomaterials engineering with biomedical applications. [ 25–27 ] Research on roughness has used a statistical and descriptive tool known as power spectral density (PSD), which is based on 2D topographic analysis using a discrete Fourier transform. [ 28 ] The power spectrum in the 2D for a randomly rough surface where the statistical properties are invariant and isotropic is defined by: [ 23,24 ] Where is the surface roughness power spectrum, is the wavevector, is the surface height profile, is the height profile taken from the surface plane reference point, ( x,y ) is the position vector in the x‐y ‐plane, <> is the substrate height measured from the average surface plane, is an exponential term that depends on the wavevector and the position vector, and i is a complex number.…”

“…The surface roughness is present in many physical phenomena, including friction, adhesion, and tribology; these phenomena present hierarchical structures at micro and nano scales of great importance in biomaterials engineering with biomedical applications. [25][26][27] Research on roughness has used a statistical and descriptive tool known as power spectral density (PSD), which is based on 2D topographic analysis using a discrete Fourier transform. [28] The power spectrum in the 2D for a randomly rough surface where the statistical properties are invariant and isotropic is defined by: [23,24] C q ð Þ ¼…”

Advanced morphological analysis of siloxane‐hydrogel contact lenses

“…Commercial CLs made of Filcon V (Safilens, Italy) containing dimethyl‐acrylamide, tris‐trimethylsilys, poly‐(dimethyl‐siloxane)‐dimethacrylate, ethyleneglycol‐dimethacrylate, and phthalocyanine copper were studied (Stach et al, 2017, 2019). The characteristics of analyzed CLs (power ranging from −1.00 D to −4.00 D) are the following: FDA group, I; content of water, 49%; O 2 Dk/t, 5.3 × 10 −14 m s −1 Pa −1 ; Young's modulus, 7.06 × 10 5 Pa; and tensile strength, 2.14 × 10 6 Pa.…”

“…Several studies have examined the surface properties and local topography of CLs before and after wear (Abadías, Serés, & Torrent‐Burgués, 2015; González‐Méijome, López‐Alemany, Almeida, & Parafita, 2009; Lira, Santos, Azeredo, Yebra‐Pimentel, & Oliveira, 2008) using different advanced imaging techniques (Stach et al, 2017, 2019).…”