The ability to modify on demand the viscoelastic properties of hydrogels through the use of an externally applied stimulus such as light remains a challenge.
MIT MRSEC researchers have developed stimuli-responsive hydrogel materials that can change their mechanical properties upon exposure to light. This light induced effect can change the stiffness of the network by up to 100,000 times. Insights generated from these studies will aid in the development of programmable hydrogels with specific stress-relaxing or energy-dissipating properties.
Figure 1. The viscoelastic mechanical properties of a hydrogel network can be programmed using bioinspired metal-coordinate crosslinks sensitive to UV light. Depending on the metal ion used to crosslink the hydrogel, the stiffness can be increased by 1000x, decreased by 100x, or remain unchanged by UV-irradiation.
The demonstrated ability to switch on demand, pre-programmed viscoelastic properties of hydrogel materials could have broad impact on biomedical materials engineering. For example, this technology will allow for the development of 3D printable hydrogels with programmable viscoelastic properties needed in synthetic tissue engineering.
Figure 2. By mixing different metal-coordinate crosslinks, the viscoelastic properties of hydrogel materials can be programmed and reversibly switched with external stimuli. For example, shown above are similar looking hydrogels with very different, but switchable, properties: a gel with fluid-like properties (left) and a gel with solid-like properties (right). The gels contain metal-coordinate crosslinks with different UV-controllable oxidation states.