Sol–Gel Synthesis of Phosphorylcholine Zwitterion-Decorated Silica Gels

Zwitterion-functionalized silica particles are desirable as antifouling, highly hydrated, biocompatible materials. Existing methods to covalently attach zwitterionic groups to the silica particle surface generally require significant synthesis and purification procedures, and these have largely tended to focus on sulfobetaine-type zwitterionic moieties. This work describes a simple, one-pot, acid-catalyzed sol-gel synthesis approach to create phosphorylcholine (PC)-type zwitterionic silica gels via the condensation of hydroxyl groups on L-α-glycerophosphorylcholine (GPC) with silanol groups generated during the sol-gel reaction. The approach was successfully employed to create both PC-modified xerogels and ionogels (ionic liquid electrolyte-rich silica-supported gels). Silica gel particle morphologies and surfaces were characterized using scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS). EDS data revealed the presence of approximately 2-3 wt % phosphorus (from GPC) on all silica surfaces after thoroughly washing them postreaction. PC-functionalized ionogels displayed shear-thinning behavior and an approximately 2 to 4-fold increase in shear viscosity versus the control ionogel synthesized without GPC, while thermal analysis indicated that all ionogels yielded similar total silica content (5-7 wt %). This study indicates the promise of a simple, one-pot method for generating PC-decorated silica gels and presents future design possibilities for other novel materials leveraging zwitterionic molecules that possess hydroxyl groups.