Acousto-fluidic system assisting in-liquid self-assembly of microcomponents

Abstract

In this paper, we present the theoretical background, design, fabrication and characterization of a micromachined chamber assisting the fluidic self-assembly of micro-electro-mechanical systems in a bulk liquid. Exploiting bubble-induced acoustic microstreaming, several structurally-robust driving modes are excited inside the chamber. The modes promote the controlled aggregation and disaggregation of microcomponents relying on strong and reproducible fluid mixing effects achieved even at low Reynolds numbers. The functionality of the microfluidic chamber is demonstrated through the fast and repeatable geometrical pairing and subsequent unpairing of polymeric microcylinders. Relying only on drag and radiation forces and on the natural hydrophobicity of SU-8 in aqueous solutions, assembly yields of approximately 50% are achieved in no longer than ten seconds of agitation. The system can stochastically control the assembly process and significantly reduce the time-to-assembly of building blocks.

Three-dimensional polymeric microtiles for optically-tracked fluidic self-assembly

“…Finally, fluidic SA experiments performed in the dedicated acousto-fluidic platform [17] (Fig. 9) evidence that neither the uncomplete SU-8 derivatization through the vapor-deposited SAM nor the slight asymmetry in layer thickness of some of the microtiles appear to significantly affect the SA dynamics of the microtiles.…”

“…7b) show a slight difference in thickness between the superposed SU-8 layers. The difference Figure 9: Frames from a high-speed recording of the SU-8 microtiles in bulk water [17] self-assembling into crystalline clusters of varying topology. Scale bar is 200 µm.…”

“…We aimed at adopting an analog geometry for our microscopic vehicles. However, in the corresponding microfluidic platform [17] the microtiles are completely immersed in a single liquid phase and cannot be constrained to preserve their initial vertical orientation indefinitely. As a consequence, even assuming an initial population of identically oriented microtiles, two subpopulations with opposite orientations, i.e.…”

“…They can by design coordinate laterally in water through hydrophobic interactions and shape matching independently of their vertical orientation to form close-packed, square lattice clusters. The microtiles feature a central marker aiding the real-time optical tracking and automated closed-loop control of their fluidic SA [16] performed by a dedicated platform [17]. The fabrication process makes use of copper as thick sacrificial layer and allows the wafer-level production of tens of thousands of microtiles in a single batch-in line with the massively parallel and scalable nature of SA.…”

Magnetic interactions in 2D and 3D arrays

“…In this chapter, we study the three-dimensional self-assembly of anisotropic silicon particles as a fabrication technique for 3D silicon micromachining. Self-assembly of microfabricated objects in two dimensions has received wide attention with promising results [Goldowsky et al, 2013;Tkachenko and Lu, 2015] and very complex shapes [Mastrangeli et al, 2014]. The transition to three dimensions is of technological importance for complex structures such as photonic band gap materials [Vlasov et al, 2001;Woldering et al, 2011], metamaterials fabricated from cubic building blocks [Belov et al, 2013], three-dimensional electrical networks [Gracias et al, 2000] and 3D cross-point architectures for computer memories .…”