Water and Blood Repellent Flexible Tubes

Abstract

A top-down scalable method to produce flexible water and blood repellent tubes is introduced. The method is based on replication of overhanging nanostructures from an aluminum tube template to polydimethylsiloxane (PDMS) via atomic layer deposition (ALD) assisted sacrificial etching. The nanostructured PDMS/titania tubes are superhydrophobic with water contact angles 163 ± 1° (advancing) and 157 ± 1° (receding) without any further coating. Droplets are able to slide through a 4 mm (inner diameter) tube with low sliding angles of less than 10° for a 35 µL droplet. The superhydrophobic tube shows up to 5,000 times increase in acceleration of a sliding droplet compared to a control tube depending on the inclination angle. Compared to a free falling droplet, the superhydrophobic tube reduced the acceleration by only 38.55%, as compared to a 99.99% reduction for a control tube. The superhydrophobic tubes are blood repellent. Blood droplets (35 µL) roll through the tubes at 15° sliding angles without leaving a bloodstain. The tube surface is resistant to adhesion of activated platelets unlike planar control titania and smooth PDMS surfaces.

Figure 1

Fabrication process of flexible water and blood repellent tubes. (a) Schematic of the fabrication process with corresponding images of templates (a_i) and replica (a_ii) tubes. PDMS is cured between two coaxially aligned tubes. Outside of the inner tube was nanostructured by HCl etching and the structures were covered with 20 nm of titania film using ALD. Sacrificial etching of the template was used to release the PDMS/titania tube. SEM micrographs of, (b) Template aluminum tubes with scale bar of 100 µm and higher magnification inside the tube with scale bar of 5 µm, (c) Finished superhydrophobic PDMS/titania replicas with scale bar of 5 µm, (d) Side view of the same sample with scale bar of 20 µm.

Figure 2

Characterization of water and blood repellency. (a) Advancing and receding water contact angle on planar superhydrophobic PDMS/titania sample, (b) Snapshots of a 2 µL water droplet rolling off from the surface tilted at 7°. Images of a 35 µL human blood droplet on the, (c) superhydrophobic sample, (d) on the smooth PDMS/titania control sample, (e) Blood droplet sliding off the superhydrophobic PDMS/titania sample without a trace showing the surface is blood repellent, (f) Blood droplet sliding off a smooth PDMS/titania control surface leaving a clear trace.

Figure 3

Droplets in flexible superhydrophobic and control tubes. (a) Acceleration of a 35 µL sliding water droplet inside superhydrophobic PDMS/titania and (b) inside smooth PDMS/titania control tubes with 4 mm inner diameter (the error bars represent s.d. of three measurements), (c,d) Images for comparison the transfer of 200 µL human blood in inclination angle Φ = 45° from point A to B in (c) superhydrophobic PDMS/titania tube without any visual trace of blood inside the tube and (d) smooth PDMS/titania control tube with a clear trace of the blood. (e) Flexibility demonstration of the tubes showing they were not broken after several bending and twisting.

Figure 4

Platelet adhesion test. SEM micrographs of samples after 20-min incubation in platelet rich plasma on (a) smooth titania and (b) smooth PDMS (c) superhydrophobic PDMS/titania before incubation (d) superhydrophobic PDMS/titania after incubation. Scale bars are 20 µm in (a–d). Images of surfaces after incubation in platelet rich plasma on (e) superhydrophobic PDMS/titania surface, (f) smooth titania, (g) smooth PDMS. Scale bars are 5 mm in (e–g).