The methodology for manufacturing array of microdevices that features a varying cross-section is introduced towards the development of complex devices that are more prone to be adapted in-field. In this paper stereolithography or digital light, processing is assessed for developing asymmetric split-and-recombine micromixers that can be tested under a machine vision system. To test the proposed manufacturing methodology an array of 6 microdevices with a varying depth from 100 to 1000 micrometers were characterized using an Infinite Focus Measurement to verify the feasibility of the proposed methodology for a large range of length-to-depth ratios. Surface metrology showed that molds were produced within 4 to 10 mm of absolute deviational error.

Split and Recombine (SAR) micromixers devices were manufactured employing microfabrication methods derived from the semiconductor industry to engrave polydimethylsiloxane (PDMS) such as photolithography, or to a lesser extent micromachining or laser ablation of other materials. However, these methodologies have several limitations; they are often expensive, require special infrastructure such as clean rooms and may have long production cycles for new designs. Moreover, devices are manufactured using a soft lithography technology that is limited to a singular cross-section depth. An Envisiontec Perfactory P3 Mini Multilens additive manufacturing equipment that uses a 60 mm lens system and with a work tray of 84 x 63 x 230 mm and with a pixel resolution of up to 50 μm for the used material. The equipment was loaded with a white Flex Series ABS resin characterized by a yield stress of 65MPa and a Young's modulus of 1772 MPa. An Otoflash pulse curing chamber from the same supplier with a wavelength between 300 and 700 nanometers, with a lamp of 11 watts of power and 10 pulses per second.

An array of six assymetric asymmetric SAR micromixers (ASAR) were developed with a width of 1000 µm and a varying depth of 100, 250, 500, 750, 900 and 1000 µm for depth-to-width ratio of 1:10, 1:4, 1:2, 3:4, 9:10 and 1:1 respectively.

For characterization of the molds, an Alicona Infinite Focus Measurement Machine has been employed for surface characterization. This device allows the acquisition of datasets at a high depth of focus similar to a Scanning Electronic Microscope. Infinite Focus Microscopy (IFM) has shown to be capable of capturing images with a lateral resolution down to 400 nm providing 3D datasets with very accurate results. For this work, each mold depth array element was measured twice for a total number of 36 samples.

The molds were used to pour polydimethylsiloxane (PDMS) to produce the micromixing structures.

A syringe pump and two plastic syringes were used to individually supply fluorescent particles and a solution of blue dye and distilled water through the micromixer inlets at same flow rate. A flow rate of 1 ml/min was applied to the microdevice to test the device sealing. Two machine vision setups were employed: an inverted microscope with a ultra high-speed camera and an inverted microfluidic microscope were implemented to evaluate used to assess the performance of a micromixer using the concentration field including parameters such as mean concentration (C_m), standard deviation (σ), coefficient of variation (CoV) or mixing index (M).

Methodology for the production of an array of micromixers with a variable cross-section in a single step was successfully implemented.