Figure 3: How we compared the effectiveness of duplicated spinules with natural examples.

(A) Annotated SEM image depicting the distances between all of the main spinule surfaces, interfaces and separate spinules. These measurements were used to compare the efficiency and accuracy; (a) spinule height; (b) spinule width, midway; (c) spinule base width; (d) nanotip thickness; and (e) radius of curvature. A reference scale bar (bottom left of LHS image) = 1.5 μm. (B) A diagram comparing the shape and dimensions of an individual as well as a representative spinule constructed from culture plastic and biological materials that are typically used in experimental biomedicine and biotechnology, specifically chitosan, alginate, and silk fibroin. The width and height scales are not to true scale, but are comparative. It was assumed that spinule height is important for function, and ecologically, that assumption is correct regarding clearing dirt particles. However, wettability and bactericidal functions are nearly identical between all of the spinule compositions and the natural spinule. This diagram shows that the different material properties all replicate the shape of the spinules almost perfectly. However, the main differences relate to the spinule dimensions, particularly length, which does vary significantly between the spinule compositions. Another variance was the spinule tip curvature. (I) The natural spinule had a strongly inflected tip and thin base; (II) the polystyrene replica of the spinule had a large base and was less curved; (III) alginate and chitosan spinules were slightly thinner than the natural spinules and had a more pronounced tip curvature; (IV) chitosan-based spinules possessed a tip curvature identical to the natural spinules and almost the same height. (V) Similar properties were observed for silk. (VI) Spinules composed of chitosan and keratin were almost identical in height, with a bent tip and slightly less curvature than the natural spinule. In this diagram we have measured the tall spinules only. The short spinules in the packing arrangement are identical in shape, tip dimension and separation distance, but smaller in size by 3–5x.