2. Made with both covalently and ionically crosslinked materials, the resulting hydrogel is both extremely resilient and tough. Ionic crosslinking of sodium alginate with Ca2+ ions dissipates mechanical loads, as proven in previous hydrogel experiments. Dissipating energy, or converting mechanical energy into heat, is important so that mechanical energy will not break crosslinks and propagate cracks through the material. Crosslinking with PEG chains is critical because they increase the hydrogel’s stretchability, as the long covalent crosslinks allow the material to be pulled.
Alone, these materials are limited. PEG hydrogels have low fracture energy and, therefore, can’t be stretched too far. Sodium alginate bolsters the PEG with Ca2+ crosslinks to dissipate loads, increasing the material’s fracture energy. Meanwhile, sodium-alginate hydrogels with Ca2+ crosslinks alone can’t be stretched and don’t exhibit resiliency.
The team tested several molecular weights of the PEG, each with and without crosslinked alginate. Through experiments, the scientists were able to determine the prime PEG molecular weight (length) and Ca2+ concentration for the toughest, most resilient result. They also added a “nanoclay” in different quantities between network spaces, in order to vary the material’s viscosity for feeding through a 3D printer.
The hydrogel is expected to find homes in many biomedical applications, as well as robotics. The scientists hope to improve the resolution of the 3D printers to enhance the qualities of the interdependent matrix and produce highly accurate structures.
