Water and Blood Repellent Flexible Tubes

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 degrees (advancing) and 157 +/- 1 degrees (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 degrees for a 35 mu L 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 mu L) roll through the tubes at 15 degrees sliding angles without leaving a bloodstain. The tube surface is resistant to adhesion of activated platelets unlike planar control titania and smooth PDMS surfaces.Peer reviewe

Robust and Programmable Superhydrophobic Surfaces

This thesis deals with design, fabrication and characterization of robust and programmable superhydrophobic surfaces. The content is divided into two main categories. The first part is dedicated to fabrication of durable superhydrophobic surfaces and their performance characterization, including blood compatibility. The second part focuses on programmable superhydrophobic/superhydrophilic surfaces. A new fabrication process was introduced to produce durable superhydrophobic silicon surfaces, based on geometrical modification of the surface without any hydrophobic coating. The fabrication process is based on a combination of inductively coupled plasma-reactive ion etching (ICP-DRIE) and metal-assisted chemical etching (MaCE). Elimination of hydrophobic coating made the surface chemically and thermally robust, but due to use of silicon, the mechanical fragility issue remained. A biomimetic approach inspired by the exoskeleton of insects such as Armadillidium, was introduced to tackle the mechanical robustness. The new hybrid material consists of elastomeric overhang nanostructures covered by a thin layer of metal oxide. The elastomer part can bend and deform without breaking, while the hard metal oxide layer protects the surface from mechanical damage. We used atomic layer deposition (ALD) and replica moulding to produce such hybrid PDMS/titania surfaces. Our new fabrication process is based on sacrificial etching of the aluminum template and the transfer of titania film from the template to the PDMS. Subjecting the surfaces to a battery of mechanical, thermal, chemical and radiation tests demonstrated extremely durable superhydrophobicity. As an extension to replica moulding/sacrificial template process, we introduce a new way to make hydrophobic and hemophobic elastomeric tubes. The tubes showed a dramatic drag reduction for water and blood droplets compared to control tubes. A programmable superhydrophobic surface was introduced using hierarchical silicon micro and nanostructures covered by photo-switchable materials. Combination of ICP-DRIE and RIE were used to produce silicon T-shaped microstructures. Colloidal deposition was done to introduce nanoscale roughness. These structures were then conformally coated with photoactive titania using ALD. Fast and reversible transition of superhydrophobic to hydrophobic, hydrophilic and superhydrophilic state was demonstrated using UV-exposure and thermal annealing

Superhydrophobic Blood-Repellent Surfaces

Superhydrophobic surfaces repel water and, in some cases, other liquids as well. The repellency is caused by topographical features at the nano-/microscale and low surface energy. Blood is a challenging liquid to repel due to its high propensity for activation of intrinsic hemostatic mechanisms, induction of coagulation, and platelet activation upon contact with foreign surfaces. Imbalanced activation of coagulation drives thrombogenesis or formation of blood clots that can occlude the blood flow either on-site or further downstream as emboli, exposing tissues to ischemia and infarction. Blood-repellent superhydrophobic surfaces aim toward reducing the thrombogenicity of surfaces of blood-contacting devices and implants. Several mechanisms that lead to blood repellency are proposed, focusing mainly on platelet antiadhesion. Structured surfaces can: (i) reduce the effective area exposed to platelets, (ii) reduce the adhesion area available to individual platelets, (iii) cause hydrodynamic effects that reduce platelet adhesion, and (iv) reduce or alter protein adsorption in a way that is not conducive to thrombus formation. These mechanisms benefit from the superhydrophobic Cassie state, in which a thin layer of air is trapped between the solid surface and the liquid. The connections between water-and blood repellency are discussed and several recent examples of blood-repellent superhydrophobic surfaces are highlighted.Peer reviewe

Robust hybrid elastomer/metal-oxide superhydrophobic surfaces

We introduce a new type of hybrid material: a nanostructured elastomer covered by a hard photoactive metal-oxide thin film resembling the exoskeleton of insects. It has extreme water repellency and fast self-recovery after damage. A new fabrication method for replicating high aspect ratio, hierarchical re-entrant aluminum structures into polydimethylsiloxane (PDMS) is presented. The method is based on a protective titania layer deposited by atomic layer deposition (ALD) on the aluminum template. The ALD titania transfers to the elastomeric scaffold via sacrificial release etching. The sacrificial release method allows for high aspect ratio, even 100 μm deep and successful release of overhanging structures, unlike conventional peeling. The ALD titania conformally covers the 3D multihierarchical structures of the template and protects the polymer during the release etch. Afterwards it prevents the high aspect ratio nanostructures from elasticity based collapse. The resulting nanostructured hybrid PDMS/titania replicas display robust superhydrophobicity without any further fluoro-coating or modification. Their mechanical and thermal robustness results from a thick nanostructured elastomeric layer which is conformally covered by ceramic titania instead of a monolayer hydrophobic coating. We have demonstrated the durability of these replicas against mechanical abrasion, knife scratches, rubbing, bending, peel tape test, high temperature annealing, UV exposure, water jet impingement and long term underwater storage. Though the material loses its superhydrophobicity in oxygen plasma exposure, a fast recovery from superhydrophilic to superhydrophobic can be achieved after 20 min UV irradiation. UV-assisted recovery is correlated with the high photoactivity of ALD titania film. This novel hybrid material will be applicable to the large area superhydrophobic surfaces in practical outdoor applications.Peer reviewe

Fabrication of elastic, conductive, wear-resistant superhydrophobic composite material

Funding Information: This research was supported by Academy of Finland project “Silicon mushrooms: microengineered liquid repellency (# 297360). This work utilized the OtaNano research infrastructure and the cleanroom facilities of Micronova. Publisher Copyright: © 2021, The Author(s).A polydimethylsiloxane (PDMS)/Cu superhydrophobic composite material is fabricated by wet etching, electroless plating, and polymer casting. The surface topography of the material emerges from hierarchical micro/nanoscale structures of etched aluminum, which are rigorously copied by plated copper. The resulting material is superhydrophobic (contact angle > 170°, sliding angle < 7° with 7 µL droplets), electrically conductive, elastic and wear resistant. The mechanical durability of both the superhydrophobicity and the metallic conductivity are the key advantages of this material. The material is robust against mechanical abrasion (1000 cycles): the contact angles were only marginally lowered, the sliding angles remained below 10°, and the material retained its superhydrophobicity. The resistivity varied from 0.7 × 10–5 Ωm (virgin) to 5 × 10–5 Ωm (1000 abrasion cycles) and 30 × 10–5 Ωm (3000 abrasion cycles). The material also underwent 10,000 cycles of stretching and bending, which led to only minor changes in superhydrophobicity and the resistivity remained below 90 × 10–5 Ωm.Peer reviewe

Robust Superhydrophobic Silicon Without a Low Surface-Energy Hydrophobic Coating

Peer reviewe

Non-stick properties of thin-film coatings on dental-restorative instruments

Molemmat tiedostot Word-muodossa. Pitää muuttaa pdf:ksi tai eivät siirry Aaltodociin.The non-stick properties of thin-film coatings on dental-restorative instruments were investigated by static contact-angle measurement using dental filler resin as well as by scanning electron microscopy of the amount of sticking dental restorative material. Furthermore, using a customized dipping measurement set-up, non-stick properties were evaluated by measuring force-by-time when the instrument was pulled out of restorative material. Minor improvements in non-stick properties were obtained with commercial diamond-like carbon and commercial polytetrafluoroethylene-based coatings. Major improvements were obtained with an in-house fabricated superhydrophobic coating prepared by a multistep process consisting of surface microstructuring by etching in hydrogen fluoride (HF): hydrogen peroxide (H2O2)(1:1; vol/vol), atomic layer deposition of a 7 nm coating of aluminium oxide and titanium oxide, and a self-assembled monolayer of fluorinated organosilicon. Superhydrophobic coatings provide a possible future solution to prevent unwanted adherence of composite restorative material to dental instrumentsPeer reviewe