Optimized peptide functionalization of thiol-acrylate emulsion-templated porous polymers leads to expansion of human pluripotent stem cells in 3D culture

Highly porous polymers produced by polymerization of the continuous phase of a high internal phase emulsion have been developed as scaffolds for 3D culture of human pluripotent stem cells. These emulsion-templated polymerized high internal phase emulsion (polyHIPE) materials have an interconnected network of pores that provide support for the cells, while also allowing both cell ingress and nutrient diffusion. Thiol-acrylate polyHIPE materials were prepared by photopolymerization, which, due to a competing acrylate homopolymerization process, leads to a material with residual surface thiols. These thiols were then used as a handle to allow postpolymerization functionalization with both maleimide and a maleimide-derivatized cyclo-RGDfK peptide, via Michael addition under benign conditions. Functionalization was evaluated using an Ellman's colorimetric assay, to monitor the residual thiol concentration, and X-ray photoelectron spectroscopy. Maleimide was used as a model molecule to optimize conditions prior to peptide-functionalization. The use of triethylamine as a catalyst and a mixed ethanol-aqueous solvent system led to optimized reaction between surface-bound thiols and maleimide. Peptide-functionalized materials showed improved attachment and infiltration of human pluripotent stem cells over 7 days, demonstrating their promise as a scaffold for 3D stem cell culture and expansion.