One-step in-mould modification of PDMS surfaces and its application in the fabrication of self-driven microfluidic channels

Abstract

Poly(dimethylsiloxane) (PDMS) has become the material of choice for fabricating microfluidic channels for lab-on-a-chip applications. Key challenges that limit the use of PDMS in microfluidic applications are its hydrophobic nature, and the difficulty in obtaining stable surface modifications. Although a number of approaches exist to render PDMS hydrophilic, they suffer from reversion to hydrophobicity and, frequently, surface cracking or roughening. In this study, we describe a one-step in-mould method for the chemical modification of PDMS surfaces, and its use to assess the ability of different surfactants to render PDMS surfaces hydrophilic. Thin films of ionic and non-ionic surfactants were patterned into an array format, transferred onto silicone pre-polymer, and subsequently immobilized onto the PDMS surface during vulcanization. The hydrophilicity of the resulting surfaces was assessed by contact angle measurements. The wettability was observed to be dependent on the chemical structure of the surfactants, their concentration and interactions with PDMS. The morphology of modified PDMS surfaces and their change after wetting and drying cycles were visualized using atomic force microscopy. Our results show that while all surfactants tested can render PDMS surfaces hydrophilic through the in-mould modification, only those modified with PEG-PDMS-PEG copolymer surfactants were stable over wetting/dying cycles and heat treatments. Finally, the in-mould functionalization approach was used to fabricate self-driven microfluidic devices that exhibited steady flow rates, which could be tuned by the device geometry. It is anticipated that the in-mould method can be applied to a range of surface modifications for applications in analytical separations, biosensing, cell isolation and small molecule discovery.

A polydopamine peptide coating enables adipose‐derived stem cell growth on the silicone surface of cochlear implant electrode arrays

“…Since silicone can be made more hydrophilic by surface functionalization, various complex chemical activation techniques have been devised to achieve a more hydrophilic surface. [13][14][15] Another method represents cold plasma-assisted modification of silicone surfaces, which enables improved cell adherence and hydrophilicity. 16 Recently, Lee et al 17 described bioinspired polydopamine (PD)-based coating as a simple method for surface Correspondence to: P. Schendzielorz; e-mail: Schendziel_P@ukw.de functionalization.…”

Bonding and in‐channel microfluidic functionalization using the huisgen cyclization

“…Many traditional processes for PDMS bonding initially result in silanol‐rich surfaces. While under special conditions it is possible to render such surfaces wettable, it is much more difficult to convert them to organofunctional surfaces . The azide/alkyne surfaces described above, once in a microchannel, remain chemically reactive: three walls containing one functional group and the fourth wall containing another functional group, a situation analogous to that described by Lee and Cheung .…”

“…Bioanalytical applications typically require the presence of biorecognition elements within the microfluidic channel, and benefit from tethering hydrophilic entities within the channel to improve wettability and reduce resistance to flow . While a variety of key strategies have been developed to immobilize proteins and other biological entities before the device is assembled, it is much more challenging to introduce them on the channel surface post‐assembly.…”

Effects of the morphology of sulfobetaine zwitterionic layers grafted onto a silicone surface on improving the hydrophilic stability, anti‐bacterial adhesion properties, and biocompatibility

“…Functional materials with hydrophilic groups are the best options for modification materials. Polyhydroxy compounds, such as poly(ethylene glycol) (PEG), and poly(vinyl alcohol)(PVA), cell adhesive species and other biologically active components have typically been immobilized on the activated silicone surface. Chemically covalent attachments, such as those introduced through the “grafting‐to” approach based on hydrosilylation or click chemistry and the “grafting‐from” approach based on surface‐initiated atom transfer radical polymerization (SI‐ATRP) are the most frequently used methods for providing satisfactory stability and durability of the constructed hydrophilic surfaces.…”