Modulation of hydrogel stiffness by external stimuli: soft materials for mechanotransduction studies

Mechanotransduction is an important process in determining cell survival, proliferation, migration and differentiation. The extracellular matrix (ECM) is the component of natural tissue that provides structural support and biochemical signals to adhering cells. The ECM is dynamic and undergoes physical and biochemical changes in response to various stimuli and there is an interest in understanding the effect of dynamic changes in stiffness on cell behaviour and fate. Therefore, stimuli-responsive hydrogels have been developed to mimic the cells' microenvironment in a controlled fashion. Herein, we review strategies for dynamic modulation of stiffness using various stimuli, such as light, temperature and pH. Special emphasis is placed on conducting polymer (CP) hydrogels and their fabrication procedures. We believe that the redox properties of CPs and hydrogels' biological properties make CPs hydrogels a promising substrate to investigate the effect of dynamic stiffness changes and mechanical actuation on cell fate in future studies.