Polypeptide-Grafted Macroporous PolyHIPE by Surface-Initiated <i>N</i>-Carboxyanhydride (NCA) Polymerization as a Platform for Bioconjugation

Abstract

A new class of functional macroporous monoliths from polymerized high internal phase emulsion (polyHIPE) with tunable surface functional groups was developed by direct polypeptide surface grafting. In the first step, amino-functional polyHIPEs were obtained by the addition of 4-vinylbenzyl or 4-vinylbenzylphthalimide to the styrenic emulsion and thermal radical polymerization. The obtained monoliths present the expected open-cell morphology and a high surface area. The incorporated amino group was successfully utilized to initiate the ring-opening polymerization of benzyl-l-glutamate <i>N</i>-carboxyanhydride (BLG NCA) and benzyloxycarbonyl-l-lysine (Lys­(Z)) NCA, which resulted in a dense homogeneous coating of polypeptides throughout the internal polyHIPE surfaces as confirmed by SEM and FTIR analysis. The amount of polypeptide grafted to the polyHIPE surfaces could be modulated by varying the initial ratio of amino acid NCA to amino-functional polyHIPE. Subsequent removal of the polypeptide protecting groups yielded highly functional polyHIPE-<i>g</i>-poly­(glutamic acid) and polyHIPE-<i>g</i>-poly­(lysine). Both types of polypeptide-grafted monoliths responded to pH by changes in their hydrohilicity. The possibility to use the high density of function (−COOH or −NH₂) for secondary reaction was demonstrated by the successful bioconjugation of enhanced green fluorescent protein (eGFP) and fluorescein isocyanate (FITC) on the polymer 3D-scaffold surface. The amount of eGFP and FITC conjugated to the polypeptide-grafted polyHIPE was significantly higher than to the amino-functional polyHIPE, signifying the advantage of polypeptide grafting to achieve highly functional polyHIPEs