(33c) Engineering Surface Hydrophobicity of Zein Films Via Self-Assembly

Zein, a corn prolamin, has been widely studied as a biopolymer due to its film-forming abilities. Zein protein has almost equal amount of hydrophobic and hydrophilic amino acids, which allows for self-assembly. In this research, we utilized this property to modify the surface properties of films obtained via soft-lithography method. Zein films were prepared by casting on polydimethylsilohexane (PDMS) substrate, which was either exposed (PDMS O+) or non-exposed to oxygen plasma (PDMS O-). Oxygen plasma is known to make PDMS hydrophilic by inducing –OH groups on the surface. Zein solution was prepared by dissolving in aqueous ethanol and mixing with a plasticizer, oleic acid, and emulsifier. After zein films were formed in desiccator, they were peeled off of PDMS with ease. It was found that zein’s surface that was in contact had different water contact angle (WCA) values depending on the plasticizer content and whether PDMS was exposed to oxygen plasma. WCA of zein films were decreased when it was cast on oxygen plasma exposed PDMS compared to regular PDMS. In addition, increase in oleic acid content resulted in a larger change in the difference between the cases of PDMS O- and PDMS O+. The change in the hydrophilicity, which was measured by WCA method, were further investigated by Atomic Force Microscopy experiments.  Both topography and force measurements were conducted on zein films with varying oleic acid and PDMS substrates. We also demonstrated that by using a mask with a pattern, it is possible to obtain zein films with varying hydrophilicity. This enables us to develop microfluidic, sensor, tissue engineering platforms based on the need at hand. We believe that zein’s ability to self-assemble can be exploited by using this facile technique to obtain free-standing films with different water affinities.