Peg Surface Modification to Control Biofouling in Microfluidic High Content Screening Devices
Authors: Goh Sharon C.-M. , Hsu HuanHsuan , Fang Qiyin , Selvaganapathy Ravi , Chen Hong , Brash John , Andrews David 
Published: February 2020

High content screening (HCS) is a valuable research technique for biological assays and to identify drug candidates1. Miniaturization of the HCS platform has significantly reduced processing time and improved the productivity of early drug discovery1. Recently, our group developed a prototype micro optofluidic cell sensing device with localized dosing control for pathogen sensing2. The device is composed of glass wells for cell growth and PDMS microchannels with polycarbonate (PC) membrane valves which are electrically stimulated for controlled drug release2. However, experiment failure caused by cells adhering to and blocking the PDMS channels and PC membrane is of concern. Loss of any amount of sample is critical as it compromises the long term reliability of the device.

Protein adsorption on materials is an essential prerequisite for cell adhesion, providing nutrients and anchorage for adherent cell lines3. This process, called biofouling, is mediated by surface hydrophobicity4. Implementation of surface modification strategies to further reduce the hydrophobicity of PDMS and PC membrane may be applied to decrease cell adhesion. Plasma treatment, UV treatment, metal coating, dynamic surface modification and polyethylene glycol (PEG) grafting are all commonly practiced antifouling techniques. Among these, PEG grafting is considered one of the most efficient and well documented technique for modifying PDMS surfaces5. Hence, PEG grafting procedures will be applied to modify antifouling PDMS and PC surfaces.

The procedure for PEG grafting is presented in Fig. 1. A (3-Aminopropyl) triethoxysilane (APTES) layer is formed on PDMS and PC surfaces to tether the PEG-DA chains. Utilizing APTES and PEG-DA to modify both materials is advantageous in this field as most grafting procedures are specific to the material it was designed for. This method may also be applied to related silicon materials. Conversely, the hydrophilic nature of glass may reduce cell adhesion. Thus, APTES alone is used to increase glass biofouling and localize cell growth within the wells.

Fig. 2 shows a 66% reduction in albumin adsorption on PDMS-PEG compared to unmodified PDMS. These preliminary results proves that the antifouling modification strategy for PDMS was successful. Quantification of protein adsorption on modified PC membrane and glass as well as cell adhesion experiments will be conducted in the near future. These modifications will then be applied to a new prototype device and tested for long term stability.

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