The MBA was fabricated through standard soft lithography processes (23). The layout of this device can be seen in fig. S1 (A and B). Briefly, silicon wafers (Micro Materials and Research Consumables) were cleaned in an oxygen plasma in a custom reactive ion etcher (ANFF-Q) for 10 min at a pressure of 200 mtorr and 200 W. SU-8 2100 (MicroChem) was then spin-coated to a thickness of 100 μm and patterned as per the manufacturer’s recommendations. All bake steps were ramped up and down to minimize stress and SU-8 thickness variation. This process formed the master for the soft lithographic process.

The master was then treated with chlorotrimethylsilane (CTMS, Sigma-Aldrich) each time before molding. This was accomplished by placing a few drops of CTMS on the master and allowing it to evaporate. Concurrently, polydimethylsiloxane (PDMS) base and curing agents (Sylgard 184, Dow Corning) were mixed and degassed. The PDMS mixture was then poured over the master, degassed to remove and residual bubbles, and then baked at 85°C for 20 min. A 100 mm by 75 mm glass slide (ProSciTech) was also spin-coated with a thin layer of PDMS and baked for 20 min at 85°C. Each layer of the device was cut to size, and holes were punched for inlets, outlets, and through holes with a 0.75-mm biopsy punch (ProSciTech).

All PDMS parts were cleaned with Scotch Magic tape (Scotch), before assembly. The device was then assembled by plasma-bonding the three pieces of the devices sequentially. That is, the bottom part of the device was bonded to the glass slide, followed by the bonding of the devices’ top piece. All plasma bonding was performed in a plasma cleaner (Harrick) with an oxygen pressure of 400 to 500 mtorr for 30 s. All alignment was performed manually, and devices were allowed to bake at 65°C overnight to facilitate bonding. A final, filled device can be seen in fig. S1D. Devices were then autoclaved, dried, and stored before use.

Plugs and connective tubing were also custom-fabricated. Plugs consisted of a 22-g blunt needle (BRICO Medical Supplies) tubes separated from their top plastic bases and inserted into a 5-mm PDMS cylinder and autoclaved. All inlets and outlets were blocked with plugs while not in operation. Connective tubing consists of a 500-mm length of polyethylene tubing (PE50, BD Biosciences). Blunt needle tubes were inserted into one end of the tubing, while full blunt 22-g blunt needles were inserted to the other. Tubing was sterilized with 70% (v/v) ethanol and dried before use.

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