Direct Laser Interference Patterning of Diffraction Gratings in Safrofilcon-A Hydrogel: Fabrication and Hydration Assessment.

Daniel Sola,Stephan Milles,Andrés F Lasagni

doi:10.3390/polym13050679

Abstract

Refractive index modification by laser micro-structuration of diffractive optical devices in ophthalmic polymers has recently been applied for refractive correction in the fields of optics and ophthalmology. In this work, Safrofilcon-A hydrogel, used as soft contact lenses, was processed by direct laser interference patterning (DLIP) to fabricate linear periodic patterns on the surface of the samples. Periodic modulation of the surface was attained under two-beam interference by using a Q-switched laser source with emission at 263 nm and 4 ns pulse duration. Features of processed areas were studied as a function of both the interference spatial period and the laser fluence. Optical confocal microscopy used to evaluate the topography of the processed samples showed that both structured height and surface roughness increased with laser fluence. Static water contact angle (WCA) measurements were carried out with deionized water droplets on the structured areas to evaluate the hydration properties of DLIP structures. It was observed that the laser structured areas induced a delay in the hydration process. Finally, microstructural changes induced in the structured areas were assessed by confocal micro-Raman spectroscopy showing that at low laser fluences the polymer structure remained almost unaltered. In addition, Raman spectra of hydrated samples recovered the original shape of areas structured at low laser fluence.

Highlights

We have recently proposed direct laser interference patterning (DLIP) as a novel approach to fabricate diffraction gratings on the surface of ophthalmic polymers to be used for refractive correction [35,36,37]
The polymer samples were structured with periodic line-like patterns adjusting the experimental setup according to equation 1 to induce spatial periods of 3 μm and 6 μm on the surface of the sample
Safrofilcon-A hydrogel polymers employed as soft contact lenses were structured on the surface with linear periodic patterns using DLIP with UV pulsed laser radiation in the nanosecond range

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The processing rates reported to date to structure areas of large dimensions, such as the cornea, are low, which hinders their application on a real scale This limitation can be overcome if the whole pattern, instead of line by line, is transferred to the sample at once. Accounting for the fact that the final sample is softened by hydration, it is important to assess to what extent the laser structuring modifies the capability of the hydrogel to be hydrated This evaluation will provide the limiting laser processing parameters to modify the refractive index. We investigate how wettability and the hydration process of the polymer sample may be affected by the laser-induced surface patterning For this purpose, periodic patterns are fabricated by means of DLIP under two-beam configuration with a pulsed laser emitting at 263 nm, and pulsewidth in the nanosecond range. Static water contact angle (WCA) measurements are carried out with deionized water droplets on the structured areas to evaluate the hydration properties of DLIP structures

Laser Setup

Materials

DLIP Structuring

Microstructural Characterization

Conclusions