Hydrogel Composite Membranes Incorporating Iron Oxide Nanoparticles as Topographical Designers for Controlled Heteronucleation of Proteins

In this study, we exploited the possibility of tuning physical-chemical properties of hydrogel composite membranes (HCMs) surfaces, by using iron oxide nanoparticles (NPs) as topographical designers, with the aim of examining the effect of surface topography and wettability on the heterogeneous nucleation of protein crystals. On the basis of roughness and contact angle measurements, it was found that surface structural characteristics, in addition to chemical interactions between the surface and protein molecules, have influence on the heterogeneous nucleation of lysozyme and thermolysin crystals to different extents. We demonstrated that increasing the amount of NPs incorporated in the hydrogel matrix promotes protein nucleation to a higher extent, potentially due to the increase of local solute concentration, arising from the enhanced wetting tendency in the Wenzel regime, and physical confinement at rougher hydrophilic surfaces. An extensive crystallographic analysis suggested the tendency of the growing crystals to incorporate hydrogel materials, which allows inducement of protein conformational states slightly different from those covered by standard crystallization methods. Protein flexibility can be thus sampled by changing the amount of NPs in the HCMs, with negligible influence on the quantity and quality of X-ray diffraction data.