The Texas Horned lizard has the ability to harvest moisture from ambience with its skin and to transport water directionally to its snout; at the same time water is hindered to flow in opposite direction. We present a passive microfluidic device for directional liquid transport which is inspired by this natural role model. To this end, we deduce a subnatural capillary network from the measurement data of the Texas Horned lizard's skin. We adapt the network to various liquid-polymer combinations with the help of a mathematical model. Applying a CO₂ laser we engrave the structures into poly(methyl methacrylate) (PMMA). By distance measurements we verify that our devices transport liquids of different contact angles in a preferential direction, while stopping it in opposite direction. The applied network of interconnected capillary channels is advantageous, when it comes to defects during production or when particles block part of the capillary channels. The proposed concept is thought to be useful for micro-analysis devices and lubrication.

Bacterial adhesion and biofilm formation on surfaces are associated with persistent microbial contamination, biofouling, and the emergence of resistance, thus, calling for new strategies to impede bacterial surface colonization. Using ns-UV laser treatment (wavelength 248 nm and a pulse duration of 20 ns), laser-induced periodic surface structures (LIPSS) featuring different sub-micrometric periods ranging from ~210 to ~610 nm were processed on commercial poly(ethylene terephthalate) (PET) foils. Bacterial adhesion tests revealed that these nanorippled surfaces exhibit a repellence for E. coli that decisively depends on the spatial periods of the LIPSS with the strongest reduction (~91%) in cell adhesion observed for LIPSS periods of 214 nm. Although chemical and structural analyses indicated a moderate laser-induced surface oxidation, a significant influence on the bacterial adhesion was ruled out. Scanning electron microscopy and additional biofilm studies using a pili-deficient E. coli TG1 strain revealed the role of extracellular appendages in the bacterial repellence observed here.

We present a device for passive unidirectional liquid transport. The capillary channels used are bioinspired by the shape of the spermathecae (receptaculum seminis) of rabbit fleas (Spilopsyllus cuniculi) and rat fleas (Xenopsylla cheopis). The spermatheca is an organ of female fleas that stores sperm until suitable conditions to lay eggs are found. We translated and multiplied the natural form and function of a spermatheca to create a continuous capillary system from which we designed our microfluidic device based directly on the model from nature. Applying the Young-Laplace equation, we derived a theoretical description of local liquid transport, which enables model-guided design. We arranged the bioinspired capillaries in parallel and engraved them in poly(methyl methacrylate) (PMMA) plates by CO₂ laser ablation. The fabricated structures transport soapy water passively (i.e., without external energy input) in the forward direction at velocities of about 1 mm·s⁻¹ while halting the liquid fronts completely in the backward direction. The bioinspired capillary channels are capable of unidirectional liquid transport against gravity. Distance and velocity measurements prove the feasibility of the concept. Unidirectional passive liquid transport might be advantageous in technical surfaces for liquid management, for instance, in biomedical microfluidics, lab-on-chip, lubrication, electronics cooling and in micro-analysis devices.

Laser structuring enables modification of sample topography, surface chemistry, and/or physical properties of materials. Examples of these processes are ripple, nap or wall formation, surface oxidation, induction of polymerization reactions, or changes in crystallinity or contact angle. These – most of the time – interrelated modifications are exploited widely for biomedical applications. They range from cell-repellent surfaces for easy-to-replace cardiac pacemakers, control of cell proliferation required in regenerative medicine, to increased cell adhesion for cell arrays. Furthermore, ns-laser-induced nanoripples were used for formation of gold nanowires for future surface plasmon resonance sensors directly integrated into biotechnological devices. Additive nano- and microscale manufacturing by two-photon polymerization allows for considerable progress in cell scaffold formation, paving the path for in vitro–grown organs, bones, and cartilages. The very same fs-laser-based technique was also used for biomimetic microneedles with enhanced liquid spreading on their surface. Microneedles are promising candidates for low-cost, high-throughput drug delivery and vaccination applicable even by nonmedically trained personnel. Microfluidic systems fabricated by fs-lasers have enabled progress in 3D microscopy of single cells and in studies on thrombocyte activation with the help of nanoanchors. Explicating the abovementioned and further biomedical applications, the authors put special focus on the achieved limits pointing out what scientists have accomplished so far in their pursuit of extreme scales.

Due to their uniquely high surface-to-volume ratio, nanofibers are a desired material for various technical applications. However, this surface-to-volume ratio also makes processing difficult as van der Waals forces cause nanofibers to adhere to virtually any surface. The cribellate spider Uloborus plumipes represents a biomimetic paragon for this problem: these spiders integrate thousands of nanofibers into their adhesive capture threads. A comb on their hindmost legs, termed calamistrum, enables the spiders to process the nanofibers without adhering to them. This anti-adhesion is due to a rippled nanotopography on the calamistrum. Via laser-induced periodic surface structures (LIPSS), these nanostructures can be recreated on artificial surfaces, mimicking the non-stickiness of the calamistrum. In order to advance the technical implementation of these biomimetic structured foils, we investigated how climatic conditions influence the anti-adhesive performance of our surfaces. Although anti-adhesion worked well at low and high humidity, technical implementations should nevertheless be air-conditioned to regulate temperature: we observed no pronounced anti-adhesive effect at temperatures above 30 °C. This alteration between anti-adhesion and adhesion could be deployed as a temperature-sensitive switch, allowing to swap between sticking and not sticking to nanofibers. This would make handling even easier.

Since nanofibers have a high surface-to-volume ratio, van der Waals forces render them attracted to virtually any surface. The high ratio provides significant advantages for applications in drug delivery, wound healing, tissue regeneration, and filtration. Cribellate spiders integrate thousands of nanofibers into their capture threads as an adhesive to immobilize their prey. These spiders have antiadhesive nanoripples on the calamistrum, a comb-like structure on their hindmost legs, and are thus an ideal model for investigating how nanofiber adhesion can be reduced. We found that these nanoripples had similar spacing in the cribellate species Uloborus plumipes, Amaurobius similis, and Menneus superciliosus, independent of phylogenetic relation and size. Ripple spacing on other body parts (i.e., cuticle, claws, and spinnerets), however, was less homogeneous. To investigate whether a specific distance between the ripples determines antiadhesion, we fabricated nanorippled foils by nanosecond UV laser processing. We varied the spatial periods of the nanoripples in the range ~ 203–613 nm. Using two different pulse numbers resulted in ripples of different heights. The antiadhesion was measured for all surfaces, showing that the effect is robust against alterations across the whole range of spatial periods tested. Motivated by these results, we fabricated irregular surface nanoripples with spacing in the range ~ 130–480 nm, which showed the same antiadhesive behavior. The tested surfaces may be useful in tools for handling nanofibers such as spoolers for single nanofibers, conveyor belts for producing endless nanofiber nonwoven, and cylindrical tools for fabricating tubular nanofiber nonwoven. Engineered fibers such as carbon nanotubes represent a further candidate application area.