a (Slowly produced by hexamethylenetetramine and glucono-δ-lactone)
3. Fuel-driven temporary materials
3.1. Fuel-driven temporary gels
Temporary gels are the earliest and most frequently reported fuel-driven temporary materials. Thus far, more than one type of temporary gel has been presented. The majority of temporary gels are formed upon the addition of the chemical fuel and gradually collapse with fuel exhaustion. While some other temporary gels, on the contrary, carry out a “gel-sol-gel” cycle by the drive of the chemical fuel. They dissolve with the fuel feeding and slowly regelation as the consumption of the chemical fuel. Additionally, there are still a few gels that can temporarily swell or deswell as the reaction network proceeds. They will be potential candidates for developing a fuel-driven gel actuator. In this section, we will demonstrate fuel-driven temporary gels systemically and try to summarize some principles of fabricating such a kind of material.