An inorganic cross-linked quadruple shape memory hydrogel with high mechanical performance

Shape memory hydrogels (SMHs) have been the subject of great interest in recent years. However, there were few reports on the simultaneous multiple shape memory and high mechanical performance. Therefore, a novel nanocomposite (NC) hydrogel poly (acrylic acid)/Chitosan/ Laponite (PAA/CS/Laponite) was developed by using Laponite as physical cross-linker. In order to achieve three temporary shapes, the PAA/CS/Laponite was soaked in iron chloride hexahydrate (FeCl₃), sodium hydroxide (NaCl) and sodium hydroxide (NaOH) respectively to (a) form metal coordination; (b) gain the chains entanglement of chitosan; (c) get the microcrystalline structure of chitosan. The maximum shape fixity ratio of PAA/CS/Laponite can reach 100% in 1 minute and it can be restored its original shape within 5 minutes. Moreover, PAA/CS/Laponite showed excellent mechanical performance. The maximum tensile and compressive strengths were 0.73 MPa and 13.1 MPa. By comparison with PAA/CS obtained from our previous work, the tensile strength, elongation at break and compressive strength increased by 2.21 times, 1.46 times, and 3.26 times respectively. Scanning electron microscopy (SEM) showed that the obtained sample has uniform honeycomb network structures which can effectively explain why the gel has strong mechanical performance. These characteristics make PAA/CS/Laponite have huge application potential in reality.