Processing tough supramolecular hydrogels with tunable strength of polyion complex

- Polyion complex precipitates are plasticized by saline water for processing.
- The viscoelastic materials can be processed by compression moulding and extruding.
- The processing window depends on relatively amount and concentration of saline water.
- The equilibrated gels possess high toughness, self-recovery and healing abilities.

The rapid developments of tough hydrogels have promoted the applications of this kind of soft materials in loading bearing systems. However, tough gels usually have poor processibility, which is crucial for the construction of complex structures with gels. In this paper, we demonstrate the processing of tough polyion complex (PIC) hydrogels by simple compression moulding or extruding, which relies on the distinct strength of ionic bonds during and after the processing. The PIC precipitates formed by mixing the solutions of polycation and polyanion, poly(3-(methacryloylamino)propyl-trimethylammonium chloride) and poly(sodium p-styrenesulfonate), are plasticized by saline solution with selected concentration. These raw materials, initially weak and viscoelastic, are easily processed into different shapes. After swelling the as-prepared gels in water to dialyze out the salt and counterions of PIC, tough equilibrated gels are obtained with the imposed shapes during processing. These gels with 50-70 wt% water show good mechanical properties, with tensile fracture stress, fracture strain and tearing fracture energy being 3.7 MPa, 700% and 8 × 103 J/m2, respectively. These mechanical properties can be effectively tailored by tuning the charge ratio of PIC. However, the concentration of saline water has negligible influence on the mechanical properties of final equilibrated gels. The resultant PIC gels also exhibit stimuli-triggered healing properties owing to the dynamic and reversible nature of the ionic bonds. This study should promote the applications of tough PIC gels in structural elements of soft actuators and synthetic tissues.