Fast and Simple Fabrication of Multimaterial Hierarchical Surfaces Using Acoustic Assembly Photopolymerization (AAP)

Abstract

contributing to many potential uses such as spatial control of fluid, drug delivery, droplet manipulation, water-harvesting, and lab-on-a-chip devices. [3][4][5][6][7][8] Additionally, these surfaces were also found to be beneficial for biomedical applications such as drug screening and tissue engineering, owing to their shorter reaction times and less usage of rare biological samples or reagents.A variety of approaches have been developed for the fabrication of multimaterial and/or hierarchically structured surfaces with wettability contrast, including CNC machining, [5] spray coating, [9,10] wire electrical discharge machining, [11] vapor deposition, [12] lithography, [13] and laser microfabrication. [14,15] Although these techniques have enabled the direct fabrication of surfaces with tunable wetting properties, significant challenges still exist in producing complex 3D surface structures in an eco-friendly fashion. For example, hierarchical surfaces developed by the spray coating method undergo chemical instability after exposure to organic solvents. Machining and laser-based manufacturing processes are limited to single materials such as elastomers or metals. Moreover, the surface structure topology fabricated using a conventional direct fabrication approach is usually limited to one or two levels only.Combining two or more direct fabrication techniques is a common approach to address the aforementioned challenges and achieve higher structural complexities. For instance, Lee et al. [16] prepared microscale groove surface patterns using machining and compression molding, resulting in a superhydrophobic anisotropic surface (CA:150°). Additional dip-coating created nanoscale patterns to induce low sliding angles, enabling liquid transportation. Peng et al. [17] utilized templating and diffusion-controlled bucking to generate a dual-structured hierarchical surface with microsized wrinkles. To enhance the biocompatibility, the surface was chemically modified using dopamine-glycopolymer. Other indirect micro-fabrication methods, including surface wrinkling by thermal annealing, [18] electrochemical etching followed by deposition, [19] and colloidal crystal templating, [20] have been investigated for developing hierarchical surfaces with a high wettability contrast. Nevertheless, it is difficult to precisely control the dimensions of the Multimaterial surfaces with hierarchical features have many potential applications in self-cleaning, droplet manipulation, microfluidics, and biomedicine, owing to their wide range of functionalities induced by structural and material contrasts. Here, a fast and sustainable manufacturing method, acoustic assembly photopolymerization (AAP), is presented for productions of such surfaces. In the novel AAP process, an external acoustic field is used to assemble microparticles to microsized patterns, while the photocuring is combined with the acoustic assembly to produce multilevel hierarchical features, such as cones and wrinkles ranging from nanometer to micrometer. The mechanism unde...