Tensile strength of oxygen plasma-created surface layer of PDMS

Abstract

Polydimethylsiloxane (PDMS) is a commonly used silicone elastomer with broad applications. Particularly for bioengineering use, PDMS is treated with oxygen plasma with which its surface is oxidized to allow positive interaction with water and live cells. In exchange for the acquisition of hydrophilicity, the oxidized PDMS becomes mechanically brittle so that resulting formation of cracks affects the system in various ways. However, tensile strength (TS), which is an inherent capacity of a material to withstand tensile loads before breaking and is thus a key parameter limiting the use of the material, remains unclear regarding oxidized PDMS. Here we determine the TS of oxide layers created on the surface of PDMS based on micro-stretch experiments using a custom-made device. We show that the surface layer displays cracks upon tensile loading of small strains of within 10% to have a TS of ~10–100 kPa, which is approximately two orders of magnitude lower than that of unmodified PDMS. We further show that the TS sharply decreases with oxidation duration to become highly brittle, while the thickness of the resulting oxide layer finally reaches a plateau even with prolonged plasma treatment. Consequently, we suggest that gradual surface modification of PDMS takes place only within a finite region even with prolonged plasma treatment, as distinct from previously held assumptions. These quantitative data provide critical design information for the oxide layer of plasma-hydrophilized PDMS.

Deformable 96-well cell culture plate compatible with high-throughput screening platforms

“…In PDMS-based bioreactors, the initially hydrophobic PDMS is often functionalized with oxygen plasma to enhance cell adhesion [ 40 ]. Yet, we found in preliminary studies that such plasma treatment is not suitable for the present case because highly brittle glass-like layers are produced, and cracks are inevitably created on the fragile layer even with subtle stretching to consequently degrade the image quality of automated image analyses necessary for high-throughput screening [ 41 ]. With the APTMS-treated substrate, we did not detect in phase-contrast microscopy cracks after cyclic stretching, thus suggesting that APTMS-treated wells function as a cell culture substrate that is mechanically endurable even with the challenge of cyclic stretch.…”

Microcontact Peeling: A Cell Micropatterning Technique for Circumventing Direct Adsorption of Proteins to Hydrophobic PDMS

“…With this treatment, an oxide layer with a thickness of ß50 nm is created on the PDMS surface (Ohishi et al, 2016). 7. Gently drop a copper electron microscopy grid on the plasma-treated PDMS surface with a vacuum tweezer.…”

“…However, treatments for hydrophilizing silicone materials often make the surface mechanically brittle so that resulting formation of cracks in the fine features reduces the accuracy and applicability of the micropatterning. For example, the PDMS surface hydrophilized by the current protocol yields a crack even with a small tensile strain of ∼9% (Ohishi et al., ).…”

“…Some proteins other than ECM have, however, been reported to be denatured upon adsorption to the hydrophobic surface of the bare PDMS (Anderson & Robertson, ; Biasco et al., ; Zelisko & Brook, ). If a microfeatured PDMS stamp is hydrophilized in advance in order to keep the intactness of the proteins to be transferred, a highly brittle, glass‐like oxide layer is created on the surface, which would be cracked upon physical contact with the substrate (Ohishi, Noda, Matsui, Jile, & Deguchi, ).…”

Multifunctional Hyperelastic Structured Surface for Tunable and Switchable Transparency

“…The optical properties of the PDMS such as transparency can also be impaired by this operation. The silica-like layer is brittle and no longer shows the hyperelastic behavior of the original PDMS film which in turn results in the formation of micro cracks [38,39]. In order to avoid the adverse effects of the surface activation, we try the plasma treatment using an oxygen plasma gun to restrict the activation process to the selected spots on the PDMS film, where resonators will be positioned (see Figure 5c).…”