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

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.

New Approach toward Laser-Assisted Modification of Biocompatible Polymers Relevant to Neural Interfacing Technologies

“…Concerning our experimental results, two main disadvantages of the ns-laser ablation of medical grade PDMS can be underlined: (i) the re-deposition of the ablated material (debris) in the zone adjacent to the ablated areas and (ii) the formation of very rough microstructures. However, our experimental findings, especially regarding UV ns-laser ablation, confirmed the results reported by other authors [ 26 , 39 , 40 ] that the ns-laser treatment of PDMS induced more prominent chemical transformations in the local area of impact rather than the fs-laser irradiation [ 21 , 22 ]. The significant chemical activation of the surface is the reason to prefer ns-laser treatment of PDMS elastomer.…”

“…It is also worth noting our findings that the time interval between both processes—the laser treatment and the metallization—is not a critical parameter as it is proposed by Laude et al [ 33 ] and Dupas-Bruzek et al [ 34 ] in their experimental works on UV ns-laser surface modification of medical grade PDMS in air for miniaturization of nerve electrodes and tracks metalized by electroless plating of Pt. Numbers of references reporting on nanosecond or femtosecond laser processing by wavelengths in UV, ViS or NIR spectrum of different polymers (e.g., poly-methyl methacrylate (PMMA), polyethylene terephthalate (PET), polyimide (PI), polystyrene (PS), polycarbonate (PC), polydimethylsiloxane (PDMS)) are available in the literature [ 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. Producing tracks (channels) and holes on polymer’s surface for the development the of micro/nanostructured based devices is of great interest for various applications in microfluidics, micromechanics, photonics, medicine, and biology.…”

“…Producing tracks (channels) and holes on polymer’s surface for the development the of micro/nanostructured based devices is of great interest for various applications in microfluidics, micromechanics, photonics, medicine, and biology. The high-quality of the polymers modifications has been evaluated in terms not only of their application purposes, but also in terms of laser control of their optical, wettability and/or structural properties as proposed D. Sola et al [ 21 , 22 , 35 ] and other authors N.C.Y. Tham et al [ 36 ], Bahador Farshchian et al [ 37 ], and Carmela De Marco et al [ 38 ].…”

“…Medical grade PDMS elastomers and other biocompatible polymers have been very successfully processed by nanosecond and femtosecond lasers, as the first step of fabrication of multielectrode arrays (MEAs) implantable neural devices and microfluidic systems [5,[13][14][15][16][17][18][19][20][21][22][23]. Laser-induced local micro-structuring and chemical transformations lead to the formation of a highly active catalytic surface by increasing the surface energy and wettability of the polymers.…”

Femtosecond Laser Densification of Hydrogels to Generate Customized Volume Diffractive Gratings

“…However, fabrication of subsurface or volumetric gratings within hydrogels remains challenging. Other than fs laser densification, subsurface patterning can be also achieved by Multibeam interference lithography (MBIL) and bottom-up self-assembly-based methods; however, these methods have key limitations. , For instance, MBIL can only fabricate periodic structures with geometries that are allowed by the incident angles, wavelengths, and intensities of the interfering beams. On the other hand, bottom-up strategies, although faster and scalable, rely on self-assembly processes optimized for specific materials and process conditions, limiting their use to fabricate custom-designed defect-free subsurface structures with precise orientation and/or alignment.…”