Microfluidics Assisted Fabrication of Three-Tier Hierarchical Microparticles for Constructing Bioinspired Surfaces

Abstract

Construction of textured bioinspired surfaces with refined structures that exhibit superior wetting properties is of great importance for many applications ranging from self-cleaning, antibiofouling, anti-icing, oil/water separation, smart membrane, and microfluidic devices. Previously, the preparation of artificial surfaces generally relies on the combination of different approaches together, which is a lack of flexibility to control over the individual architecture unit, the surface topology, as well as the complex procedure needed. In this work, we report a method for rapid fabrication of three-tier hierarchical microunits (structures consisting of multiple levels) using a facile droplet microfluidics approach. These units include the first-tier microspheres consisting of the second-tier close-packed polystyrene (PS) nanoparticles decorated with the third-tier elegant polymer nanowrinkles. These nanowrinkles on the PS nanoparticles are formed according to the interfacial instability induced by gradient photopolymerization of N-isopropylacrylamide (NIPAM) monomers. The formation process and topologies of nanowrinkles can be regulated by the photopolymerization process and the fraction of carboxylic groups on the PS nanoparticle surface. Such a hierarchical microsphere mimics individual units of bioinspired surfaces. Therefore, the surfaces from self-assembly of these fabricated two-tier and three-tier hierarchical microunits collectively exhibit "gecko" and "rose petal" wetting states, with the micro-and nanoscale structures amplifying the initial hydrophobicity but still being highly adhesive to water. This approach offers promising advantages of high-yield fabrication, precise control over the size and component of the microspheres, and integration of microfluidic droplet generation, colloidal nanoparticle self-assembly, and interfacial polymerization-induced nanowrinkles in a straightforward manner.

Microfluidic formation of crystal-like structures

“…Similar approaches have been also explored for the formation of colloidosomes, 131 celloidosomes, 132 photonic materials 116 and three-tier hierarchical assemblies. 133 However, with the exception of the work by Yi et al, 130 these approaches required a step external to the microfluidic device in order to facilitate the droplet evaporation with consequent self-assembly of the compartmentalised particles. Controlled self-assembly of several structures containing chemically functionalised particles has instead been introduced by Xu et al 114 In their work, the authors were able to fabricate droplet crystals having different structures based on the combination of chemical particle properties and self-assembly internal to the droplets.…”

Plasmonic Nanocrystal Arrays on Photonic Crystals with Tailored Optical Resonances

“…PMs consisted of well-ordered SiO 2 NPs were fabricated using a droplet-based microfluidic platform ( Figure 1 a). 40 The SiO 2 NPs with different diameters (200 ± 10, 250 ± 10, and 280 ± 10 nm) were purchased from the Nanjing Rainbow company (Nanjing, China). These PMs ( Figure 1 b) were then used as templates for manufacturing PPMs via the Au thin film deposition ( Figure 1 c) and thermal annealing ( Figure 1 d).…”

Injectable Microfluidic Hydrogel Microspheres for Cell and Drug Delivery

“…These layered microspheres with multiple structures can be used as constructable units to construct bioinspired surfaces by self‐assembly on various substrates. [ 29 ] For example, Gao et al. [ 30 ] developed a microfluidic assembly method to efficiently produce hydrogel microspheres with reactive multidomains.…”