3D Microprinting of Super‐Repellent Microstructures: Recent Developments, Challenges, and Opportunities

Liquid super-repellent surfaces, characterized by a low liquid–solid contact fraction, allow various liquids to bead up and freely roll off. Apart from liquid repellency, these surfaces feature several unique properties, including inter alia, self-cleaning, low-friction, anti-icing, and anti-biofouling, making them valuable for a vast array of applications involving liquids. Essential to achieve such super-repellency is the bio-inspired reentrant or doubly reentrant micro-topography. However, despite their unique interfacial properties, the fabrication of these delicate 3D topographies by conventional microfabrication methods is extremely challenging. Recently, emerging 3D microprinting technologies, particularly two-photon lithography, have brought new scope to this field. With unparalleled design freedom and flexibility, 3D microprinting greatly facilitates the design, testing, and studying of complex 3D microstructures. Here, applications of 3D microprinting in the design and fabrication of super-repellent microstructures are summarized, with a focus on their remarkable properties, and new functionalities offered by these intricate 3D topographies. Current challenges and new opportunities of emerging 3D microprinting techniques to further advance liquid super-repellent materials are also discussed

Regeneration of β-Cyclodextrin Based Membrane by Photodynamic Disulfide Exchange — Steroid Hormone Removal from Water

The occurrence of steroid hormones in water and their serious impact on human and ecosystem demand high performance materials for efficient removal of such micropollutants. Here, an affinity membrane is developed for hormone removal with regenerable binding sites. By using photodynamic disulfides as a linker, UV induced detachment of β‐CD ligands from the membrane surface is demonstrated. The macroporous base membrane is first fabricated via a polymerization induced phase separation method using 2‐hydroxyethyl methacrylate (HEMA) and ethylene dimethylacrylate (EDMA) monomers. Then the affinity membranes are prepared by immobilizing β‐CD ligands to the poly(HEMA‐co‐EDMA) base membrane through the 2‐carboxyethyl disulfide linker. The β‐CD functionalized affinity membrane shows a 30% increase of E2 hormone uptake compared with the base membrane, attributed to the formation of CD‐hormone host–guest inclusion complexes. The photodynamic disulfide linkers enable UV‐induced detachment of blocked β‐CD ligands from and reattachment of fresh β‐CD ligands to the membrane surface after each adsorption cycle, thus conferring the affinity membrane with excellent regenerative properties. It is anticipated that the use of dynamic covalent bonds for binding ligands will be of interest for developing smart affinity membranes with regenerable and readjustable surface properties

Material‐Independent 3D Patterning Via Two‐Photon Lithography and Discontinuous Wetting

The fabrication of complex 3D structures composed of micrometer-sized features made of different functional materials is an immensely important and yet highly challenging task. Here, a method is developed to fabricate multimaterial 3D structures with micrometer precision by combining macroscopic 3D printing (digital light processing), with two-photon lithography (2PL) and material-independent discontinuous dewetting. Specifically, 3D inherently superhydrophobic objects are first printed by DLP, followed by creating hydrophilic micropatterns on their surface using 2PL. By exploiting the effect of discontinuous wetting, the selective deposition of solutions of functional materials into microscopic hydrophilic regions on the surface of 3D structures, with high resolution and great design flexibility is demonstrated. Importantly, the method is material-independent and enables the micropatterning of a variety of functional materials dispersed in aqueous solutions including polydopamine, silica, or Ag nanoparticles. As an exemplary application, it is shown that conductive Ag electrodes can be created on the curved surface of 3D-printed objects to construct structural electronics. The flexibility, high resolution, and material diversity in designing multimaterial 3D structures open exciting new functionalities and possibilities in a variety of applications including advanced electronics, soft robotics, and chemical or bioengineering

3D Printing of Superhydrophobic Objects with Bulk Nanostructure

The rapid development of 3D printing (or additive manufacturing) technologies demands new materials with novel properties and functionalities. Superhydrophobic materials, owing to their ultralow water adhesion, self-cleaning, anti-biofouling, or superoleophilic properties are useful for myriad applications involving liquids. However, the majority of the methods for making superhydrophobic surfaces have been based on surface functionalization and coatings, which are challenging to apply to 3D objects. Additionally, these coatings are vulnerable to abrasion due to low mechanical stability and limited thickness. Here, a new materials concept and methodology for 3D printing of superhydrophobic macroscopic objects with bulk nanostructure and almost unlimited geometrical freedom is presented. The method is based on a specific ink composed of hydrophobic (meth)acrylate monomers and porogen solvents, which undergoes phase separation upon photopolymerization to generate inherently nanoporous and superhydrophobic structures. Using a desktop Digital Light Processing printer, superhydrophobic 3D objects with complex shapes are demonstrated, with ultralow and uniform water adhesion measured with scanning droplet adhesion microscopy. It is shown that the 3D-printed objects, owing to their nanoporous structure throughout the entire volume, preserve their superhydrophobicity upon wear damage. Finally, a superhydrophobic 3D-printed gas-permeable and water-repellent microfluidic device and a hierarchically structured 3D-printed super-oil-absorbent are demonstrated

Substrate-Independent and Re-Writable Surface Patterning by Combining Polydopamine Coatings, Silanization, and Thiol-Ene Reaction

Polydopamine coating is a unique, simple, and substrate-independent surface functionalization strategy. Techniques for secondary functionalization, patterning, and re-functionalization of polydopamine modified materials are important to broaden the scope of applications of such materials in a variety of fields. Here, a facile and substrate-independent strategy for surface functionalization and patterning is presented. This approach combines the advantages of three important methods: facile and substrate-independent polydopamine coating, versatile gas phase silanization, and rapid thiol-ene photoclick reaction for patterning. They demonstrate equally efficient functionalization and patterning of diverse materials, such as glass, polytetrafluoroethylene, aluminum, polypropylene, or polyethylene. They also show the possibility of controlled chemical removal of the patterns or surface functionalization by treatment with tetrabutylammonium fluoride, which allows re-modification or re-patterning of the substrate. Thus, this universal and powerful approach for substrate independent surface modification and patterning can significantly facilitate the development of novel functional materials and devices useful for various applications

3D printing of inherently nanoporous polymers via polymerization-induced phase separation

3D printing offers enormous flexibility in fabrication of polymer objects with complex geometries. However, it is not suitable for fabricating large polymer structures with geometrical features at the sub-micrometer scale. Porous structure at the sub-micrometer scale can render macroscopic objects with unique properties, including similarities with biological interfaces, permeability and extremely large surface area, imperative inter alia for adsorption, separation, sensing or biomedical applications. Here, we introduce a method combining advantages of 3D printing via digital light processing and polymerization-induced phase separation, which enables formation of 3D polymer structures of digitally defined macroscopic geometry with controllable inherent porosity at the sub-micrometer scale. We demonstrate the possibility to create 3D polymer structures of highly complex geometries and spatially controlled pore sizes from 10 nm to 1000 µm. Produced hierarchical polymers combining nanoporosity with micrometer-sized pores demonstrate improved adsorption performance due to better pore accessibility and favored cell adhesion and growth for 3D cell culture due to surface porosity. This method extends the scope of applications of 3D printing to hierarchical inherently porous 3D objects combining structural features ranging from 10 nm up to cm, making them available for a wide variety of applications

Electrical Conductivity and Photodetection in 3D‐Printed Nanoporous Structures via Solution‐Processed Functional Materials

3D-printed conductive structures are highly attractive due to their great potential for customizable electronic devices. While the traditional 3D printing of metal requires high temperatures to sinter metal powders or polymer/metal composites, low or room temperature processes will be advantageous to enable multi-material deposition and integration of optoelectronic applications. Herein, digital light processing technology and inkjet printing are combined as an effective strategy to fabricate customized 3D conductive structures. In this approach, a 3D-printed nanoporous (NPo) polymeric material is used as a substrate onto which a nanoparticle-based Ag ink is printed. SEM and X-ray nano computed tomography (nanoCT) measurements show that the porous morphology of the pristine NPo is retained after deposition and annealing of the Ag ink. By optimizing the deposition conditions, conductive structures with sheet resistance <2 Ω sq−1 are achieved when annealing at temperatures as low as 100 °C. Finally, the integration of an inkjet-printed photodetector is investigated based on an organic semiconductor active layer onto the NPo substrate. Thus, the potential of this approach is demonstrated for the additive manufacturing of functional 3D-printed optoelectronic devices

3D printing of inherently nanoporous polymers via polymerization-induced phase separation

3D printing offers flexibility in fabrication of polymer objects but fabrication of large polymer structures with micrometer-sized geometrical features are challenging. Here, the authors introduce a method combining advantages of 3D printing and polymerization-induced phase separation, which enables formation of 3D polymer structures with controllable inherent porosity

Superoleophobic Slippery Lubricant-Infused Surfaces

| openaire: EC/H2020/725513/EU//SuperRepel | openaire: EC/H2020/337077/EU//DROPCELLARRAYThe ability to create superoleophobic surfaces repellent toward low-surface-tension liquids is important for various applications, and has been recently demonstrated using re-entrant or doubly re-entrant microtopography. Liquid droplets on such surfaces feature composite liquid–solid–air interfaces, whereas composite liquid–lubricant–air interfaces would have potential for additional repellency. Here, the development of a novel slippery superoleophobic surface with low adhesion is demonstrated via combining doubly re-entrant microtopography with slippery lubricant-infused porous surfaces. This is realized by using 3D direct laser writing to fabricate doubly re-entrant micropillars with dedicated nanostructures on top of each pillar. The top nanostructures stabilize the impregnated slippery lubricant, while the re-entrant geometry of the micropillars prevents lubricant from spreading. The slippery layer reduces the adhesion of liquid to the pillars, as proved using scanning droplet adhesion microscopy (SDAM), while the doubly re-entrant micropillars make the surface superoleophobic. This novel interface combining two extremes, superoleophobicity and slippery lubricant-infused surface, is of importance for designing superoleophobic and superhydrophobic surfaces with advanced liquid repellent, anti-icing, or anti-fouling properties.Peer reviewe