Prevention of Oxygen Inhibition of PolyHIPE Radical Polymerization Using a Thiol-Based Cross-Linker

Polymerized high internal phase emulsions (polyHIPEs) are highly porous constructs currently under investigation as tissue engineered scaffolds. We previously reported on the potential of redox-initiated polyHIPEs as injectable bone grafts that space fill irregular defects with improved integration and rapid cure. Upon subsequent investigation, the radical-initiated cure of these systems rendered them susceptible to oxygen inhibition with an associated increase in uncured macromer in the clinical setting. In the current study, polyHIPEs with increased resistance to oxygen inhibition were fabricated utilizing a tetrafunctional thiol, pentaerythritol tetrakis(3-mercaptoproprionate), and the biodegradable macromer, propylene fumarate dimethacrylate. Increased concentrations of the tetrathiol additive provided improved oxygen resistance as confirmed by polyHIPE gel fraction while retaining the requisite rapid cure rate, compressive properties, and pore architecture for use as an injectable bone graft. Additionally, thiol-methacrylate polyHIPEs exhibited increased degradation under accelerated conditions and supported critical markers of human mesenchymal stem cell activity. In summary, we have improved upon current methods of fabricating injectable polyHIPE grafts to meet translational design goals of improved polymerization kinetics under clinically relevant conditions without sacrificing key scaffold properties.