A Self‐Assembly Approach to Chemical Micropatterning of Poly(dimethylsiloxane)

Abstract

Dedicated to Professor David N. Reinhoudt on the occasion of his 65th birthday Polydimethylsiloxane (PDMS) elastomers are widely used in biomedical devices, such as medical implants, catheters, and contact lenses, because of their biocompatibility and physical properties. [1][2][3] PDMS elastomers can be easily molded into (sub)micrometer features and are optically transparent and relatively chemically inert, which are ideal properties for applications in soft-lithographic techniques. In many softlithographic applications, the low-energy surface of PDMS can be used advantageously, for example, in microcontact printing of nonpolar species [4] and the transfer-printing technique pioneered by Rogers and co-workers. [5,6] However, the unmodified PDMS surface is hydrophobic, and surface modification is required to print polar inks or proteins, [7][8][9] to facilitate cell growth, [10] to improve compatibility, [11,12] and for use in microfluidics.[13] A range of methods have been developed to alter the surface chemistry of PDMS; most involve UV/ozone treatment [14] or an oxygen plasma, [15] and subsequent functionalization by forming alkylsilane monolayers. Yet, there is to date no single-step procedure that allows the introduction of a wide range of functional groups on the PDMS surface in a spatially controlled way. Herein, we demonstrate a novel way to selectively modify the surface of a silicone elastomer through minimization of interfacial free energy and the self-assembly of functional molecules at the surface by mirroring the distribution of surface energies on a template. Chaudhury and co-workers [16] have exploited surface energy to drive allyl-functionalized perfluorinated polyethers to the surface of PDMS. Our approach generalizes the principle of surface free energy minimization to drive both hydrophilic and hydrophobic molecules to a surface, thus replicating the pattern on the template surface.This surface-induced self-assembly-based method of chemically micropatterning of PDMS is shown schematically in Figure 1. A micropatterned alkylthiolate self-assembled monolayer (SAM) on gold is used as a topographically flat, chemical master. Subsequently, a mixture of Sylgard 184 PDMS and a small amount (< 5 wt %) of vinyl-terminated small molecules with different head groups is cured against this master. The small molecules preferentially accumulate near the surface areas with complementary surface energy to minimize the unfavorable interactions of the PDMS polymers with the SAMs. During the hydrosilylation (curing) reaction, the silicon hydride groups present in the cross-linking agent of the Sylgard 184 react with the vinyl groups of both the crosslinking dimethylsiloxane oligomers as well as the added functional molecules, thereby "freezing" the chemical pattern into the PDMS elastomer (Figure 1 e). After careful removal of the PDMS, facilitated by water to weaken the interfacial bonds on the hydrophilic areas, flat PMDS surfaces patterned with sub-micrometer features of different chemical functionalities are...

Amorphous silicon balanced photodiode for microfluidic applications

“…This elastomer presents excellent features for use in microfluidic devices such as biocompatibility, optical transparency, relatively high chemical inertia, and low manufacturing costs. 15,16 These properties are coupled with an easy fabrication process (soft lithography) and the possibility to achieve multilayer PDMS structures 17 as well as an easy bonding with the glass 18 . The PDMS used in this work to make the microfluidic structures is the Sylgard 184 from Dow Chemicals with a 1:10 ratio between the curing agent and the base elastomer.…”

Gut-on-a-chip: Current progress and future opportunities

“…PDMS is the dominant material used for OoC systems because of its cell-and researcher-friendly properties [72]. For cells, PDMS provides a biologically inert, gaspermeable, non-toxic surface with low adhesion [73,74]. This generally leads to more cellcell interactions in the devices compared to cell-substrate interactions in traditional 2D culture models.…”

Relevance of organ(s)-on-a-chip systems to the investigation of food-gut microbiota-host interactions

“…Although some materials, such as polymethyl methacrylate (PMMA) (Zhang et al 2017;Sriram et al 2018) and glass (Kulthong et al 2018), are used on occasion for the microfluidic devices employed for OoC, the material most typically used for the support structure is polydimethylsiloxane (PDMS). PDMS is an inexpensive biologically inert, gas permeable, non-toxic polymer that displays low adhesion, allowing more cell-cell interactions than cell-substrate interactions (Mata et al 2005;van Poll et al 2007). Because of its transparency, it is suitable for the microscopy requirements that accompany the OoC platform.…”