Fig. 2: Manufacture and testing of boat-shaped body samples.
a Manufacturing process of boat-shaped body samples. (i) Commercial feed pellets (approximate density 0.7 g/m3) were first ground into powder for reshaping. (ii) The powder was then mixed with the selected binder and, optionally, hydrophobic additives in water. (iii) The mixture was heated to 90 °C and stirred to disperse the components evenly. (iv) The mixture was then poured into silicone molds to shape hulls and rectangular bars for bending tests. (v) The samples were frozen, removed from the mold, and subjected to freeze-drying to remove all the water and produce the final porous structure. b Water absorption results of recipes based with three different binders (starch, flour, and gelatin); legend indicates material mass ratios in each recipe. c Comparison of water absorption ratio (blue bars) and flexure modulus (yellow bars) of seven recipes with different types and quantity of hydrophobic additives: shellac, fish oil, and beeswax. A higher water absorption ratio corresponds to less water resistance, which is not desirable for the aquatic robot. The flexure modulus reflects the material’s strength against bending load, which is used as an indicator of the material’s structural integrity. Error bars show the standard deviation of tests on three separate samples.
