Acoustic streaming vortices enable contactless, digital control of droplets

Abstract

Advances in lab-on-a-chip technologies are driven by the pursuit of programmable microscale bioreactors or fluidic processors that mimic electronic functionality, scalability, and convenience. However, few fluidic mechanisms allow for basic logic operations on rewritable fluidic paths due to cross-contamination, which leads to random interference between “fluidic bits” or droplets. Here, we introduce a mechanism that allows for contact-free gating of individual droplets based on the scalable features of acoustic streaming vortices (ASVs). By shifting the hydrodynamic equilibrium positions inside interconnected ASVs with multitonal electrical signals, different functions such as controlling the routing and gating of droplets on rewritable fluidic paths are demonstrated with minimal biochemical cross-contamination. Electrical control of this ASV-based mechanism allows for unidirectional routing and active gating behaviors, which can potentially be scaled to functional fluidic processors that can regulate the flow of droplets in a manner similar to the current in transistor arrays.

Mechanowetting drives droplet and fluid transport on traveling surface waves generated by light-responsive liquid crystal polymers

“…Fluid propulsion driven by capillary forces is ubiquitous in nature, 1 and it has inspired many fluid manipulation strategies in the industry, such as functional textiles for self-cleaning fabrics, 2 antiviral surface design, 3 and inkjet printing. 4 Capillary forces are also utilized in microfluidics, 5 enabling the transport of fluids by using, e.g., surface acoustic waves, [6][7][8][9][10] molecular motors, 11 or static wetting gradients. [12][13][14][15][16][17][18][19] Wetting gradients can also be actively controlled by applying an electric potential between the droplet and the (conducting or dielectric) substrate, as in electrowetting, [20][21][22][23] and by using materials that exhibit a chemically induced modification of the contact angle when exposed to light.…”

Arrested Coalescence of Ionic Liquid Droplets: A Facile Strategy for Spatially Organized Multicompartment Assemblies

“…It should be noted that the IL droplets in 3D architectures might not be connected to all the neighbor droplets, but still could form free-standing 3D multicompartment assemblies via the arrested coalescence and ultraviolent polymerization (Figure 6g,h) as long as a certain amount of IL droplets were connected together. Although only column 3D structures are presented in this work, we believe more abundant structures and more automatic procedures would be realized by the combination with some cutting edge technologies such as 3D droplet printing, [41] acoustofluidics, [42] and digital microfluidics. [43]…”

Acoustofluidic Droplet Sorter Based on Single Phase Focused Transducers

“…Acoustofluidics, the fusion of acoustics and microfluidics, can effectively manipulate and sort picolitre droplets via noninvasive, mild, and highly biocompatible acoustic forces. [ 35–53 ] Therefore, acoustofluidic sorters often have advantages in biocompatibility. [ 54–56 ] However, current acoustofluidic droplet sorters have deficiencies in their energy conversion rate, which hinders their further development.…”