Mosiewicz, K.A. et al. Nat. Mater. 12, 1072–1078 (2013).

Hydrogels mimicking the natural environment of a cell are useful scaffolds for three-dimensional cell culture. Control over the spatial patterning of extracellular matrix proteins and growth factors within a hydrogel is important for replicating a physiological microenvironment. Although photopatterning is a promising technique for this purpose, photopatterning of delicate full-length proteins has not yet been broadly achieved owing to the lack of accessible approaches. Mosiewicz et al. harnessed photocaging to expose reactive lysine residues at defined positions within a hydrogel. This allows the covalent anchoring of peptide substrates attached to a protein of interest via a reaction catalyzed by the enzyme transglutaminase factor XIII. With this method, the authors were successful at directing mesenchymal stem cell migration, showing that the cells preferentially moved into the protein-patterned regions of the hydrogel.