Disclosed are methods, compositions, reagents, systems, and kits to prepare materials with viscoelastic properties that respond to irradiation with light. Various embodiments show that bio-inspired histidine:transition metal ion complexes allow precise and tunable control over the viscoelastic properties of polymer networks containing these types of crosslinks pre and post-irradiation. These materials have the potential to aid biomedical materials scientists in the development of materials with specific stress-relaxing or energy-dissipating properties.