Phototunable Mechanical Properties of Azobenzene-Containing Hydrogels

Abstract

The mechanical properties of the extracellular matrix are dynamic and change during biological processes such as disease progression and wound healing. Most synthetic (or man-made) tissue scaffolds have static properties. Therefore it is necessary to replate cells in order to determine the effects that different matrix mechanical properties have on cells, and virtually impossible to study the effects of a dynamically changing modulus on cell growth. There have been several scaffolds recently developed with tunable mechanical properties, but few exhibit any reversibility which is important for simulating repeated wounding and healing cycles. In this work, we develop a gelatin based hydrogel with azodianiline (ADA) as a secondary crosslinking unit. Upon irradiation with 365 nm light the gel softens as the ADA undergoes a photoisomerization. These changes can be reversed upon exposure to visible light. With applications in mechanobiology in mind, contraction at the cellular scale was measured, as well as the macroscopic changes in the shear elastic modulus and compressive modulus in response to exposure to UV and visible light.