Hydrogel core flexible matrix composite (H-FMC) actuators

The hydrogel core, flexible matrix composite (H-FMC) actuator is a muscle-like device that employs soft, pH-responsive hydrogels to directly convert chemical energy into mechanical work. Preliminary modelling of the H-FMC concept has revealed that the use of composites in this way can improve the useful work output of a hydrogel by over 1500%. However, this analysis assumed the use of a solid hydrogel core within the H-FMC actuator. In order to improve the speed, and thus power output of the H-FMC actuator, this core must be composed of micro or even nano-dimensioned elements. The work presented shows that actuation performance benefits can be realised by switching from commonly investigated fast actuating systems composed of fibres or beads, to a solid core containing coiled channels. Although unconventional, such a configuration has been manufactured, proving its feasibility. This work also shows, via finite element analysis (FEA), that for actuation speed and blocking stress performance an increased number of channels is preferential. Furthermore, moderate coiling of the channels has a positive effect on actuation free strain. Increasing the tightness of the coil to its extremes has a beneficial effect on actuation speed, but leads to a reduction in free strain potential. It is anticipated that this work will guide the design of H-FMC actuators into the future, with such devices having great potential in a range of applications including robotics and morphing structures.