> the distance between nanopillars matters far more than their height, with tightly packed pillars about 60 nanometres apart working best

I'd be concerned about ruling-out asbestos-like risks.

If the pillar diameters are similar the spacing (as implied by the picture) then ~60nm is in the ballpark of ~250nm asbestos fibers, which appear to be carcinogenic. [0]

[0] https://www.sciencedirect.com/science/article/abs/pii/S14384...