Thermal actuation of hydrogels from PNIPAm, alginate, and carbon nanofibres

Abstract

Composite ionic-covalent entanglement (ICE) hydrogel networks were prepared from poly(N-isopropylacrylamide), alginate, and carbon nanofibres. An optimised triple network hydrogel with 86% water content exhibited a compressive strength of 3.0 6 0.1 MPa and 66 6 13 mS/cm electrical conductivity. Thermal actuation was shown to have a shorter response time for gels containing nanofibres, compared to those which did not and hydrogel samples more than halved in volume within 1 minute when placed in a 60 8C water bath. Controlled dye release was demonstrated as a potential application and used to further quantify thermal actuation over short times. Joule heating techniques were used to electronically actuate the hydrogel samples, removing the traditional requirements for immersion in a temperature controlled liquid. It is expected that devices based on these materials will find potential applications in soft robotics and micro fluidics.

Trends in polymeric shape memory hydrogels and hydrogel actuators

“…[94][95][96][97][98][99] PNIPAM hydrogels can swell at temperatures below LCST and shrink upon heating to a temperature above LCST. [100][101][102] In contrast, hydrogels derived from polymers featuring a UCST show their phase transition at an upper critical solution temperature, which means they can shrink when cooled below their UCST. Examples for such hydrogels are: poly(vinyl methyl ether) (PVME) and poly(ethylene oxide) (PEO).…”

Development of Thermoinks for 4D Direct Printing of Temperature‐Induced Self‐Rolling Hydrogel Actuators

“…Pores control water in‐pore diffusion and absorption/desorption, thereby affecting hydrogel swelling rate and degree (Figure S1d, Supporting Information). [ 46 ] The transport of water molecules depends also on their physical interactions (hydrogen bonds, hydrophilic/hydrophobic phenomena) with the network backbone. Swelling ratios at 12 and 42 °C are presented in Figure S2a–c in the Supporting Information.…”

Shape changing hydrogels and their applications as soft actuators

“…Thermo‐responsive hydrogels are always prepared by utilizing polymers with LCST or upper critical solution temperature behaviors. PNIPAM is the most commonly and extensively studied thermo‐responsive polymer, since its sharp volume change can be actuated at a mild LCST around 33 C . Various thermo‐responsive hydrogels based on PNIPAM have been reported.…”