Nano-Second Laser Interference Photoembossed Microstructures for Enhanced Cell Alignment

Alba Martínez,Jesús M De La Fuente,Dirk J Broer,Sandra González-Lana,Cees W M Bastiaansen,Laura Asín,Carlos Sánchez-Somolinos

doi:10.3390/polym13172958

Abstract

Photoembossing is a powerful photolithographic technique to prepare surface relief structures relying on polymerization-induced diffusion in a solventless development step. Conveniently, surface patterns are formed by two or more interfering laser beams without the need for a lithographic mask. The use of nanosecond pulsed light-based interference lithography strengthens the pattern resolution through the absence of vibrational line pattern distortions. Typically, a conventional photoembossing protocol consists of an exposure step at room temperature that is followed by a thermal development step at high temperature. In this work, we explore the possibility to perform the pulsed holographic exposure directly at the development temperature. The surface relief structures generated using this modified photoembossing protocol are compared with those generated using the conventional one. Importantly, the enhancement of surface relief height has been observed by exposing the samples directly at the development temperature, reaching approximately double relief heights when compared to samples obtained using the conventional protocol. Advantageously, the light dose needed to reach the optimum height and the amount of photoinitiator can be substantially reduced in this modified protocol, demonstrating it to be a more efficient process for surface relief generation in photopolymers. Kidney epithelial cell alignment studies on substrates with relief-height optimized structures generated using the two described protocols demonstrate improved cell alignment in samples generated with exposure directly at the development temperature, highlighting the relevance of the height enhancement reached by this method. Although cell alignment is well-known to be enhanced by increasing the relief height of the polymeric grating, our work demonstrates nano-second laser interference photoembossing as a powerful tool to easily prepare polymeric gratings with tunable topography in the range of interest for fundamental cell alignment studies.

Highlights

This article is an open access articleSurface polymeric microstructures are key elements for the development of different scientific and technological areas [1]
It was shown that photoembossed structures obtained through a pulsed holographic exposure directly carried out at the surface relief development temperature present enhanced relief with respect to those prepared by performing a conventional room temperature (RT)
Optimum relief heights reached using the high-temperature exposure-modified photoembossing protocol are more than double than those obtained carrying out exposure at RT

Summary

Introduction

This article is an open access articleSurface polymeric microstructures are key elements for the development of different scientific and technological areas [1]. In the area of biomedicine, it is well recognized that surface topographic microstructures play a major role in regulating important aspects of cell behavior (migration, cell adhesion, proliferation, differentiation) and morphology, which are key to achieve functional tissue constructs for tissue regeneration and transplants, as well as the successful preparation of artificial in vitro biomimetic biological systems [5,6,7,8,9,10,11] Given their relevance, a large effort has been done over the last decades to advance towards surface relief polymeric structures with a wide variety of patterns, increasing resolution and complexity, and produced in a wide range of materials. The use of an appropriate solvent selectively removes certain areas of the film and generates a surface relief structure with the same features as the employed mask [3,12,13,14]

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Conclusion