Cieza-Hernandez, Ruben J.

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    Targeting PDMS hydrophobicity for study of small hydrophobic molecule-driven cell responses in vitro
    (2018) Cieza-Hernandez, Ruben J.; Domenech, Maribella; College of Engineering; Torres, Madeline; Almodovar, Jorge; Rivera, Nilka; Department of Chemical Engineering; Morales-Vélez, Alesandra C.
    Poly(-dimethyl siloxane) (PDMS) has been the main polymer employed in micro and nano scale devices. Its chemical and physical properties are ideal for molding and soft patterning of microfluidic devices. Despite the great advances achieved with PDMS-based microfluidic devices, its hydrophobic properties have been a main limitation for its routine implementation in standard cell biology studies and drug assays. Chemical and physical modifications of PDMS have been shown to reduce the hydrophobicity of PDMS but display incompatibility with cell culture applications due to recovery of hydrophobicity. Therefore, to overcome some of the challenges associated with PDMS hydrophobicity, we evaluated a novel method for reducing the hydrophobicity of the bulk PDMS for cell culture and cell-based assays. In our method, a biocompatible oligomer, polyethylene oxide silane amphiphile (PEO-SA) was incorporated into the bulk PDMS to different concentrations: 2wt%, 9wt% and 14wt%. PEO-SA is one of the most used polymer additives for enhancing the hydrophilicity of polymers and decrease adsorption in hydrophobic stable substrates such as silicones. The incorporation of PEO-SA at different concentrations into the PDMS was analyzed by spectroscopy FTIR, and measurements of the surface contact angle on each substrate. Optical transparency, drug absorption and impact on viability assays, and biocompatibility were done to select those PDMS modifications that best reduced hydrophobic absorption without negatively impacting cell behavior. Results obtained showed that PEO-SA was incorporated into the PDMS reducing it hydrophobicity and surface properties over 3 months. The optical transparency of the PDMS was not altered when modified with PEO-SA. Small molecule absorption was qualitatively and indirectly evaluated by fluorescent microscopy and cell viability analysis, showing that there was a reduction in absorption of hydrophobic molecule proportional to the concentration of PEO-SA. Biocompatibility was analyzed by viability and proliferation assays, which corroborate a no toxicity of the modified PDMS, though a reduction in the cell proliferation was modulated by addition of PEO-SA above 9wt%. PDMS+PEO-SA 2wt% is a potential option for replacing the pristine PDMS for cellular assays in which small hydrophobic molecules are involved.