The surgical connection of blood vessels, anastomosis, is a critical procedure in many reparative, transplantation, and reconstructive surgical procedures. However, effective restoration of circulation is complicated by pathological clotting (thrombosis) or progressive occlusion due to excess cell proliferation that often leads to additional surgeries and increases morbidity and mortality risk for patients. Pharmaceutical agents have been tested to prevent these complications, but many have unacceptable systemic side effects. Therefore, an alternative approach to deliver these drugs at the site of injury in a controlled manner is necessary. The objective of this study was to develop electrospun nanofibers composed of polyester poly(lactide- co-glycolide) (PLGA), poly(ethylene oxide) (PEO), and positively charged copolymer, poly(lactide- co-glycolide)- graft-polyethylenimine (PgP) for electrostatic binding and release of heparin for application as an antithrombotic microvascular suture. PgP was synthesized with different coupling ratios between PLGA and branched polyethylenimine (bPEI) to obtain PgP (∼1 PLGA grafted to 1 bPEI) and PgP (∼3.7 PLGA grafted to 1 bPEI). Nanofiber yarns (PLGA/PEO/PgP and PLGA/PEO/PgP) were fabricated by electrospinning. Heparin immobilization on the positively charged nanofiber yarns was visualized using fluorescein-conjugated heparin (F-Hep), and the amount of immobilized F-Hep was higher on both PLGA/PEO/PgP and PLGA/PEO/PgP than yarns without PgP (PLGA/PEO). We also found that F-Hep was released from both PgP-containing yarns in a sustained manner over 20 days, while over 60% of F-Hep was released within 4 h from PLGA/PEO. Finally, we observed that heparin-eluting nanofiber yarns with both PgP and PgP showed significantly longer clotting times than nanofiber yarns without PgP. The clotting time of PLGA/PEO/PgP was not significantly different than that of free heparin (0.5 μg/mL). These results show that heparin-eluting electrospun nanofiber yarns may offer a basis for the development of microvascular sutures with anticoagulant activity.

Proboscises of butterflies are modelled as elliptical hollow fibres that can be bent into coils. The behaviour of coating films on such complex fibres is investigated to explain the remarkable ability of these insects to control liquid collection after dipping the proboscis into a flower or pressing and mopping it over a food source. By using a thin-film approximation with the air–liquid interface positioned almost parallel to the fibre surface, capillary pressure was estimated from the profile of the fibre surfaces supporting the films. The film is always unstable and the proboscis shape and movements have adaptive value in collecting fluid: coiling and bending of proboscises of butterflies and moths facilitate fluid collection. Some practical applications of this effect are discussed with regard to fibre engineering.

The proboscis of butterflies and moths consists of two C-shaped fibres, the galeae, which are united after the insect emerges from the pupa. We observed that proboscis self-assembly is facilitated by discharge of saliva. In contrast with vertebrate saliva, butterfly saliva is not slimy and is an almost inviscid, water-like fluid. Butterfly saliva, therefore, cannot offer any viscoelastic adhesiveness. We hypothesized that capillary forces are responsible for helping butterflies and moths pull and hold their galeae together while uniting them mechanically. Theoretical analysis supported by X-ray micro-computed tomography on columnar liquid bridges suggests that both concave and convex liquid bridges are able to pull the galeae together. Theoretical and experimental analyses of capillary forces acting on natural and artificial proboscises show that these forces are sufficiently high to hold the galeae together.

Insect feeding devices with unobstructed channels offer a wetting–dewetting dichotomy that allows fluid to be self‐contained but the channels to be self‐cleaning. An explanation of this unprecedented robustness is previously lacking. C‐faced channels are fabricated with different openings and their surfaces are modified to study the effects of different contact angles on channel wettability. X‐ray microcomputed tomography (micro‐CT) reveals hidden features of wetting–dewetting transitions of droplets in these channels. A wetting–dewetting phase diagram is theoretically constructed and experimentally validated to reveal the conditions for which a liquid will spread to form a column that is self‐contained in these channels. This study significantly relaxes the requirements for materials to be wettable and self‐contain fluids. This work offers promising new applications for microfluidics that can keep the empty channels clean but allow efficient transport of probing liquids.

The classification of equilibrium shapes of liquid bodies on ribbons has been done in a limiting case when the deposited drops are larger than the ribbon width yet small enough not to deform the surface by its own weight. In contrast to cylindrical fibers, the ribbons were not able to accommodate the barrel-like drops: only the one-sided liquid columns and the clam-shell drops were observed in this series of experiments. The two-sided columns and clam-shells were formed by coating the ribbons with thin films and letting the film break due to its inherent capillary instability. A simple mechanical reasoning for the column/clam-shell transition is offered.