Laser-processed antiadhesive bionic combs for handling of nanofibers inspired by nanostructures on the legs of cribellate spiders

Nanofibers are drawing the attention of engineers and scientists because their large surface-to-volume ratio is favorable for applications in medicine, filter technology, textile industry, use in lithium-air batteries and in optical sensors. However, when transferring nanofibers to a technical product in the form of a random network of fibers, referred to as non-woven fabric, the stickiness of the freshly produced and thus fragile nanofiber non-woven remains a problem. This is mainly because nanofibers strongly adhere to any surface because of van der Waals forces. In nature, there are animals that are actually able to efficiently produce, process, and handle nanofibers: cribellate spiders. For that, the spiders use the calamistrum, a comb-like structure of modified setae on the metatarsus of the hindmost (fourth) legs, to which the 10 – 30 nm thick silk nanofibers do not stick due to a special fingerprint-like surface nanostructure. In this work, we present a theoretical model of the interaction of linear nanofibers with a sinusoidal corrugated surface. This model allows a prediction of the adhesive interaction and, thus, the design of a suitable surface structure to prevent sticking of an artificially non-woven of nanofibers. According to the theoretical prediction, a technical analogon of the nanoripples was produced by ultrashort pulse laser processing on different technically relevant metal surfaces in the form of so-called laser-induced periodic surface structures (LIPSS). Subsequently, by means of a newly established peel-off test, the adhesion of an electrospun polyamide fiber-based non-woven was quantified on such LIPSS-covered titanium-alloy and steel samples, as well as on polished (flat) control samples as reference. The latter revealed that the adhesion of electrospun nanofiber non-woven is significantly lowered on the nanostructured surfaces than on the polished surfaces.