Micrometric Wrinkled Patterns Spontaneously Formed on Hydrogel Thin Films via Argon Plasma Exposure.

Carmen M González-Henríquez,Mauricio A Sarabia-Vallejos,Juan Rodríguez-Hernández,Adolfo Del Campo-García,Diego F Veliz-Silva

doi:10.3390/molecules24040751

Abstract

The generation of microstructured patterns on the surface of a specific polymeric material could radically improve their performance in a particular application. Most of the interactions with the environment occur at the material interface; therefore, increasing the exposed active surface considerably improves their range of application. In this article, a simple and reliable protocol to form spontaneous wrinkled patterns using a hydrogel layer is reported. For this purpose, we took advantage of the doctor blade technique in order to generate homogenous films over solid substrates with controlled thickness and large coverage. The hydrogel wrinkle formation involves a prepolymerization step which produces oligomers leading to a solution with increased viscosity, enough for doctor blade deposition. Subsequently, the material was exposed to vacuum and plasma to trigger wrinkled pattern formation. Finally, a UV-polymerization treatment was applied to fix the undulations on top. Interestingly, the experimental parameters allowed us to finely tune the wrinkle characteristics (period, amplitude, and orientation). For this study, two main aspects were explored. The first one is related to the role of the substrate functionalization on the wrinkle formation. The second study correlates the deswelling time and its relationship with the dimensions and distribution of the wrinkle pattern. In the first batch, four different 3-(trimethoxysilyl)propyl methacrylate (TSM) concentrations were used to functionalize the substrate in order to enhance the adhesion between hydrogel film and the substrate. The wrinkles formed were characterized in terms of wrinkle amplitude, wavelength, pattern roughness, and surface Young modulus, by using AFM in imaging and force spectroscopy modes. Moreover, the chemical composition of the hydrogel film cross-section and the effect of the plasma treatment were analyzed with confocal Raman spectroscopy. These results demonstrated that an oxidized layer was formed on top of the hydrogel films due to the exposure to an argon plasma.

Highlights

Over the last few years, material surface micro-modification—both physically and chemically—has become an important topic for researchers in the area of material science due to its interesting characteristics which may be useful in various application fields such as optoelectronic devices [1,2], smart fabrics [3], biocompatible surfaces for cell growth [4], cell contact screening platforms [5], mechanical sensors, energy storage, and chemical detectors [6], among others.Surface modifications can be generated at different length scales on the material surface by varying the experimental conditions for their fabrication
These results demonstrated that an oxidized layer was formed on top of the hydrogel films due to the exposure to an argon plasma
The hypothesis is that based on the fact that TSM molecules are gradually chemisorbed on the silicon substrate, the chemical composition of the self-assembled monolayer (SAM) can be varied

Summary

Introduction

Over the last few years, material surface micro-modification—both physically and chemically—has become an important topic for researchers in the area of material science due to its interesting characteristics which may be useful in various application fields such as optoelectronic devices [1,2], smart fabrics [3], biocompatible surfaces for cell growth [4], cell contact screening platforms [5], mechanical sensors, energy storage, and chemical detectors [6], among others.Surface modifications (chemical or topographical) can be generated at different length scales on the material surface by varying the experimental conditions for their fabrication. Chemistry and surface microstructure play a fundamental role in the surface properties of the material and, for instance in bio-related applications, these two characteristics significantly alter the way biological media react [7] In this context, surface properties have been reported to be critical in the development of novel biomaterials. Different methodologies for surface micro-modification have been carried out in the past years, such as laser/electron-beam, micro- [9,10] or nano-lithography [11], magnetron sputtering [12], photolithography [13], or chemical etching [14] These methods have the advantage of allowing high resolutions and control in surface patterning shapes and dimensions, but at the expense of long fabrication times and expensive manufacturing processes. The research group of Chung et al [16]

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Conclusion