Analysis of the differences in self-assembly behaviour, molecular structure and drug delivery performance between α and β-Zein

The past decade has witnessed rapid development in zein-based drug delivery systems. However, the lack of a deep understanding of self-assembly and co-self-assembly between drug and zein has limited its application. In this work, α and β-zein, the main ingredients of zein, were separated and the different self-assembly behaviour was investigated, respectively. In ethanol solution, α-zein shows uncontrollable self-assembly and explosive nucleation. The nano-mechanical properties investigated by AFM show that α-zein nanoparticles self-assembled in the ethanol possessed a higher adhesion force (99.45 ± 6.90 nN), which explains its uncontrollable self-assembly. After loading with paclitaxel (PTX), Young's modulus of α-zein had significantly reduced from 525.57 ± 53.82–95.35 ± 20.98 MPa, which implies that the PTX-α-zein nanoparticle has a loose structure. The interaction between drug and carrier was studied using a fluorescence quenching experiment, and the mathematical model was established. The result shows that the main driving force for interaction between PTX and α-zein is the hydrophobic force, while interaction between PTX and β-zein is hydrogen bonding and Van der Waals forces. The negative ΔG value indicates that the binging between PTX and α-zein or β-zein is a spontaneous process although the nature of the interaction is somewhat different. An in vitro cytotoxicity study shows that the different self-assembly behaviour resulted in different cell viability. Finally, a possible self-assembly mechanism of α and β-zein was proposed. It is anticipated that a fundamental understanding of self-assembly between drug and α or β-zein will provide an important foundation for its application in biological and material fields.