Fabrication and evaluation of physical properties and cytotoxicity of zein-based polyurethanes

Polyurethane prepolymer (PUP) was first synthesized from polycaprolactone diol and isophorone diisocyanate; and then a series of zein-based polyurethane (ZEPU) sheets was fabricated from PUP and zein (ZE) using a hot press and moulding process without addition of other additives. Effects of ZE content (WZE) on the structure and properties of the resultant ZEPU sheets were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, dynamic mechanical analysis, tensile testing, and dissolubility testing in alcohol. The results indicated that cross-linking and grafting reactions occurred between ZE and PUP to form new polyurethane showing a higher thermal stability, flexibility, and alcohol-resistance than the neat ZE sheets. For example, the elongation at break of ZEPU with 50 % WZE was 211.2 %, which was 47 times higher than that of neat ZE sheet. ZE molecules acted as both cross-linkers and polymer fillers in ZEPU sheets. The cytotoxicity and cytocompatibility of ZEPU sheets were evaluated by cell culture in vitro. The ZEPU sheets showed non- or low-cytotoxicity, and L929 cells grew and expanded well on the surfaces of the sheets with WZE over 50 %. Undoubtedly, the fabrication of ZE-based polyurethanes without toxic additives such as catalysts, cross-linkers and chain extenders improved the physical properties and cytocompatibility of zein, thus widening the possible range of applications for zein-based biomaterials.