Synthetic three-dimensional scaffolds for cell and tissue engineering routinely utilize peptide ligands to provide sites for cell adhesion and to promote cellular activity. Given the fact that recent studies have dedicated great attention to the mechanisms by which cell behavior is influenced by various ligands and scaffold material properties, it is surprising that little work to date has been carried out to investigate the influence of covalently bound ligands on hydrogel material properties. Herein we report the influence of three common ligands utilized in tissue engineering, namely RGD, YIGSR and IKVAV, on the mechanical properties of cross-linked poly(ethylene glycol) (PEG) hydrogels. The effect of the ligands on hydrogel storage modulus, swelling ratio, mesh size and also on the diffusivity of bovine serum albumin through the hydrogel were investigated in detail. We identified conditions under which these ligands strikingly influence the properties of the material. The extent of influence and whether the ligand increases or decreases a specific property is linked to ligand type and concentration. Further, we pinpoint mechanisms by which the ligands interact with the PEG network. This work thus provides specific evidence for interactions between peptide ligands and cross-linked PEG hydrogels that have a significant impact on hydrogel material and transport properties. As a result, this work may have important implications for interpreting cell experiments carried out with ligand-modified hydrogels, because the addition of ligand may affect not only the scaffold's biological properties, but also key physical properties of the system.
2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.