A supramolecular two-photon-active hydrogel platform for direct bioconjugation under near-infrared radiation

A supramolecular hydrogel assembled from partially methacrylated polyethyleneimine (PEI) and with direct photopatterning capabilities at near-infrared (NIR) wavelengths is presented. The chemically-modified branched PEI macromolecules were characterized by FTIR and NMR spectroscopy to quantify the degree of methacrylation. A highly hydrophilic polymer network with water content up to 95% was prepared. The hydrogel microstructure in aqueous solution was characterized using confocal laser scanning microscopy (CLSM), which revealed a porous network with large interconnected cavities. The photo-sensitive PEIMA hydrogel was activated by two-photon laser irradiation and micropatterns formed at its interface when probes with free carboxylic acid or hydroxyl groups were present in solution. Direct patterning of the hydrogel matrix with different biomolecules, and without additional photo-initiators, is demonstrated in two-photon microscopy experiments.