Rapid manufacturing of micro-drilling devices using FFF-type 3D printing technology

Micro-drilling devices with different blade shapes were fabricated with a rapid and facile manufacturing process using three-dimensional (3D) printing technology. The 3D-printed casting mold was utilized to customize the continuous shape of the blades without the need for expensive manufacturing tools. A computational fluid dynamics simulation was performed to estimate the pressure differences (fluidic resistance) around each rotating device in a flowing stream. Three types of blades (i.e., 45°, 0°, and helical type) were manufactured and compared to a device without blades (i.e., plain type). As a result, the device with the 45° blades exhibited the best drilling performance. At a rotational speed of 1000 rpm, the average drilling depth of the device with the 45° blades to penetrate artificial thrombus for 90 s was 3.64 mm, which was ~ 2.4 times longer than that of helical blades (1.51 mm). This study demonstrates the feasibility of using 3D printing to fabricate microscale drilling devices with sharp blades for various applications, such as in vivo microsurgery and clogged water supply tube maintenance.

Early turbulence and pulsatile flows enhance diodicity of Tesla’s macrofluidic valve

Microfluidics has enabled a revolution in the manipulation of small volumes of fluids. Controlling flows at larger scales and faster rates, or macrofluidics, has broad applications but involves the unique complexities of inertial flow physics. We show how such effects are exploited in a device proposed by Nikola Tesla that acts as a diode or valve whose asymmetric internal geometry leads to direction-dependent fluidic resistance. Systematic tests for steady forcing conditions reveal that diodicity turns on abruptly at Reynolds number $${\rm{Re}}\approx 200$$ Re ≈ 200 and is accompanied by nonlinear pressure-flux scaling and flow instabilities, suggesting a laminar-to-turbulent transition that is triggered at unusually low $${\rm{Re}}$$ Re . To assess performance for unsteady forcing, we devise a circuit that functions as an AC-to-DC converter, rectifier, or pump in which diodes transform imposed oscillations into directed flow. Our results confirm Tesla’s conjecture that diodic performance is boosted for pulsatile flows. The connections between diodicity, early turbulence and pulsatility uncovered here can inform applications in fluidic mixing and pumping.

Cross-Sectional Dimension Dependence of Electroosmotic Flow in Fractal Treelike Rectangular Microchannel Network

The present work theoretically and numerically studies the electroosmotic flow (EOF) within a fractal treelike rectangular microchannel network with uniform channel height. To obtain minimum EOF fluidic resistance, the microchannel cross-sectional dimensions of the fractal network are optimized. It is found that the cross-sectional dimension dependence of EOF fluidic resistance within a symmetric fractal network is only dependent on the channel width when the total channel volume is constant, and the optimal microchannel widths to reach the minimum EOF fluidic resistance satisfy the scaling law of κ = N−1 (where κ is the width ratio of the rectangular channels at two successive branching levels, N is the branching number); however, for the symmetric fractal network with constant total surface area, the optimal cross-sectional dimensions should simultaneously satisfy κ = N−1 and H = S 4 l 0 1 − γ N 1 − ( γ N ) m + 1 (where H is the channel height, S is the total channel surface area, l0 is the channel length at the original branching level, γ is the channel length ratio at two successive branching levels and m is the total branching level) to obtain the minimum EOF fluidic resistance. The optimal scaling laws established in present work can be used for the optimization design of the fractal rectangular microchannel network for EOF to reach maximum transport efficiency.

Description of a Hydrogel-Based Micro-Valve As a Library Element for Matlab Simulink

We propose a planar hydrogel-based micro-valve design which is modeled as a library element for Matlab Simulink. For this test case, a pressure pump (voltage source) in series with a micro-valve model (variable fluidic resistance) is built up. The micro-valve subsystem is separated in four main parts. Based on the applied temperature stimulus, the equilibrium length is determined according to an experimentally verified fit function. Furthermore, the equilibrium length considers a static hysteresis effect which is modeled in analogy to the saturation of magnetization in electric transformers. In a second step, the transient behavior follows a first order differential equation, but the cooperate diffusion coefficient is size dependent affecting the rise time of the system. This causes a faster swelling than deswelling of the hydrogel. In the third section, the stiffness property is implemented to calculate the maximum sealing pressure and the resulting gap between the hydrogel and the wall. The fluidic resistance of the micro-valve considers a three-dimensional geometry and is calculated based on a look-up table, extracted from a fluid-structure-interaction (FSI) model generated from a finite element structure. The proposed model allows a full description of the fluidic hydrogel-based micro-valve and is part of an upcoming microfluidic toolbox for Matlab Simulink containing passive elements and optional chemical reactions like mixing fluids and enzyme reactions for future applications.

ELECTROOSMOTIC FLOW IN TREE-LIKE BRANCHING MICROCHANNEL NETWORK

As a kind of microchannel layout with good transport performance, tree-like branching microchannel network has been widely used for microfluidic systems, however, the optimal analysis of the tree-like branching microchannel network for electroosmotic flow (EOF) to reach a minimized fluidic resistance still needs a deep study. In this work, the EOF in tree-like branching microchannel network is theoretically and numerically studied. It is found that there is an optimal structure of the tree-like branching network for the EOF to achieve a minimum fluidic resistance under the size constraint of constant total channel volume. This work found that the optimal channel radii of the tree-like network for EOF to reach a minimum fluidic resistance satisfy the relationship of [Formula: see text], where [Formula: see text] is the radius of the parent channel, [Formula: see text] is the radius of the child channels and [Formula: see text] is the total number of child channels. This formula can be regarded as an extended Murray’s law for EOF and is helpful for the optimization design of tree-like branching microchannel network for EOF to reach maximum transport efficiency under the constant applied driven voltage.

An integrated inertial microfluidic vortex sorter for tunable sorting and purification of cells

Sorting of target cells from complex cellular samples into a high-purity product is challenging yet essential for downstream cell biology research and clinical diagnostics. Inertial microfluidics is an emerging technology attracting a lot of interest for passive and label-free sorting of cells with high throughput. Here, we introduce an inertial microfluidic device based on our vortex sorting platform for continuous size-based double sorting and purification of the larger target cells from the smaller background cells. Our device uses a microscale chamber with three outlets as a sorting unit, and integrates it into a specific topology to enable double sorting and purification functionalities. With properly designed fluidic resistance network and optimized flow conditions, we demonstrated continuous sorting of spiked human cancer stem-like cells from human blood with >90% efficiency and >1,500× enhanced purity, as well as removal of red blood cells with ~99.97% efficiency. We envision this integrated vortex-aided sorter can serve as a viable tool for size-based sorting of large target cells from complex cellular samples. Furthermore, this vortex-aided sorting platform can be integrated into more sophisticated topology with versatile functions for other cell sorting applications.