Fig. 3: Selection of fuel by toxicity and propulsion ability.

a Comparison of various edible fuel candidates according to their minimal surface tension \({\sigma }_{\min }\) when mixed with water and toxicity index value \({I}_{{{\rm{toxic}}}}\). Circular or square symbols denote volatile small molecules with high or low solubility, respectively, while triangular symbols represent larger amphiphilic molecules or polymers. Filled symbol indicates solids at room temperature (297 K) and 1 atm, whereas empty symbols denote liquid. b Experimental setup for comparing the motion capabilities of liquid fuels. c Comparison of speed and traveled distance with lecithin, propylene glycol, and ethanol.