The controlled formation of ordered, sinusoidal structures by plasma oxidation of an elastomeric polymer

Abstract

This letter describes a technique for generating waves on polydimethylsiloxane ͑PDMS͒ patterned in bas-relief. The PDMS is heated, and its surface oxidized in an oxygen plasma; this oxidation forms a thin, stiff silicate layer on the surface. When the PDMS cools, it contracts and places the silicate layer under compressive stress. This stress is relieved by buckling to form patterns of waves with wavelengths from 0.5 to 10 m. The waves are locally ordered near a step or edge in the PDMS. The wavelength, amplitude, and pattern of the waves can be controlled by controlling the temperature of the PDMS and the duration of the oxidation. The mechanism for the formation and order of the waves is described.

Reversible on-demand cell alignment using reconfigurable microtopography

“…For a given strain, the ability to generate waves is determined primarily by oxidation time (hence modulus and SiO 2 film thickness on the substrate surface) and the bulk polymer modulus [13,20,22]. Wave feature size was analyzed for dry and cell culture media-wetted plasma oxidized PDMS substrates subjected to 9 intervals of compression (∼11% strain) and uncompression over a period of 9 d (24 h between each compression and uncompression).…”

“…Wavelength, λ, can be approximated from the oxidized layer thickness,t, and Young's modulus of the oxidized surface, E s , and the bulk polymer, E p [13,22]: (1) As noted by Bowden et al, this equation may not describe the waves exactly because the oxidized PDMS surface layer is not fully characterized and the boundaries between the oxidized surface and bulk polymer may not be discrete, but it does convey the general relation of wavelength to oxidation time [13]. Amplitude, A, can be described by the following approximation, (2) where Δ/W is the compressive strain (Δ = imposed compressive transverse displacement, W = original width of the substrate) [23].…”

“…Here, we describe a reconfigurable microtopographical system customized for cell culture and imaging that consists of reversible wavy microfeatures on poly (dimethylsiloxane) (PDMS). The wavy features are created by compression-induced buckling of a brittle thin film on the surface of a PDMS substrate [13]. We observed that by uncompressing such a substrate, the microfeatures would also reversibly disperse, so that by applying or releasing compressive strain, waves could be obtained or removed, respectively.…”

“…The Epo-Tek was cured under UV light for 2 h. The PDMS pre-mold was then removed leaving the final Epo-Tek mold consisting of blocks of epoxy sized 1.5 cm × 1.5 cm × 0.3 cm. 15:1 prepolymer to curing agent PDMS was poured into the Epo-Tek molds and substrate wells were cut out once the PDMS was room temperature cured overnight then oven cured at 60°C for 2−3 h. Wavy micropatterns were generated on elastomeric polymer surfaces by oxidizing the substrate to create a brittle thin film, then compressing it [13]. Upon release of the compressive strain the microfeatures dissipated, thus creating a reversible surface topography.…”

Surface instability of an elastic half space with material properties varying with depth

“…Generally, surface wrinkling has been considered as an undesirable phenomenon to be avoided. However, in emerging areas such as micro/nano-fabrication and bio-engineering, wrinkling can be used to produce controlled nanoscale features (Bowden et al (1999), Moon et al (2007), Efimenko et al (2005)). It has been proposed that these may be useful for applications such as diffraction gratings, patterned platforms for cell adhesion or nano-fluidic channels.…”