Towards combinatorial mixing devices without any pumps by open-capillary channels: fundamentals and applications

Abstract

In chemistry, biology, medical sciences and pharmaceutical industries, many reactions have to be checked by transporting and mixing expensive liquids. For such purposes, microfluidics systems consisting of closed channels with external pumps have been useful. However, the usage has been limited because of high fabrication cost and need for a fixed setup. Here, we show that open-capillary channels, which can be fabricated outside a clean room on durable substrates and are washable and reusable, are considerably promising for micro-devices that function without pumps, as a result of detailed studies on the imbibition of open micro-channels. We find that the statics and dynamics of the imbibition follow simple scaling laws in a wide and practical range; although a precursor film obeying a universal dynamics appears in the vertical imbibition, it disappears in the horizontal mode to make the design of complex micro-channel geometry feasible. We fabricate micro open-channel devices without any pumps to express the green florescent protein (GFP) by transporting highly viscous solutions and to accomplish simultaneous chemical reactions for the Bromothymol blue (BTB) solution. We envision that open-capillary devices will become a simple and low-cost option to achieve microfluidic devices that are usable in small clinics and field studies.

Geometry-induced capillary emptying

“…he interaction of liquids with solids has been a fertile topic for physicists, chemists, mathematicians, and engineers, providing fundamental insights into the properties of matter, for example, the necessity of attractive molecular forces (1)(2)(3), explaining the rich phenomenology of wetting (4-7) and superhydrophobicity (8)(9)(10)(11), and leading to the development of modern microfluidic devices (12)(13)(14)(15). One of the prototypical examples of this is the capillary rise of a liquid in a vertical tube, where the shape and location of the meniscus (the interface separating the liquid from the gas) are determined by the surface tensions, the geometry of the capillary, and the strength of the gravitational force, as firmly established by comprehensive studies spanning several centuries (16).…”

Pattern Formation by Staphylococcus epidermidis via Droplet Evaporation on Micropillars Arrays at a Surface

“…A UVL-56 Handheld UV lamp was used (6 Watt and wavelength of 365 nm) for 30 min followed by incubation at 30 o C for 30 s. The experiments were performed in triplicates. Contact angle measurements of water and S. epidermidis droplets on epoxy surfaces were carried out by placing a water droplet with bacteria suspension of 6.3x10 6 CFU/mL, 8.0x10 7 CFU/mL and 5.0x10 9 CFU/mL on the epoxy substrates. After deposition, the droplets evaporated at room temperature.…”

Scaling crossover in thin-film drag dynamics of fluid drops in the Hele-Shaw cell

“…In this respect, the present problem is closely related to the dynamics governed by thin film dissipation such as the imbibition of textured surfaces. [33][34][35][36][37][38] In this sense, our problem is quasi two-dimensional, although the geometry of the Hele-Shaw cell is often associated with a purely two-dimensional problem. ρ in depends on its kinematic viscosity ν in only slightly (see the details for Methods).…”