Automated routing for fluidic and pneumatic channels in standardized microfluidic platforms using CAD software

We present a generalizable and accessible method to automatically route fluidic and pneumatic channels using Fusion software's printed circuit board (PCB) designer. This method significantly reduces the time-consuming and extensive manual labor in designing and realizing complex microfluidic networks. Furthermore, this approach promotes standardization practices using custom Fluidic Circuit Boards (FCBs).

INTRODUCTION
Increasing the complexity of microfluidic networks typically results in channel routing problems, especially when connecting and parallelizing various microfluidic units. Routing inside chips, such as FCBs, is generally performed manually or with custom-designed tools from the design automation field [1]. While routing algorithms have been successful in routing control layers in valve-based designs or fluidic channels in continuous flow devices and digital droplet microfluidics [1], they are still not widely adopted or are not always applicable to the design of FCBs. Significant improvements in user-friendly and open-source tools for automated routing have been made recently [2, 3], but these tools are typically limited to single-layer designs and do not apply to complex and dense microfluidic networks. Therefore, we demonstrate an approach that uses the built-in PCB designer of Fusion to route a complex microfluidic network. Next, we demonstrate the fabricability of this network using micromilling.

PROOF-OF-CONCEPT: MULTI-OOC ROUTING
To illustrate the proposed workflow, we show the routing process for a multi-OoC platform aimed at studying mechanobiology in the knee joint, combining both fluidic communication and pneumatic stimulation inside a well-plate format platform [4]. We modified our previously developed OoC-units [4, 5] to comply with the ISO standard [6, 7] for chip dimensions (15x30 mm2) and port locations (Fig.1). Then, we created a component library with port locations, physical dimensions, and exclusion zones to enable the routing of all components. We designed a flow path and physical layout based on considerations of the Translational Organ-on-chip Platform and the envisioned mechanobiology studies [4, 6, 7] (Fig.2A). Next, an electronics schematic with all components and interconnections was designed in Fusion. Components were placed on the PCB according to the physical layout, and areas for multilayer routing and exclusion zones were defined (Fig.2B). Then, the connections were automatically routed based on design rules for wire (channel) width and spacing. Minor final adjustments were made manually to refine via placement and eliminate sharp corners. Finally, the resulting routing (Fig.2C) was linked to a Fusion 3D design to create all microfluidic channels in the routing block and FCB, which were then fabricated from polymethylmethacrylate (PMMA) sheets by micromilling. The FCB, OoCs, and routing block were successfully assembled leak-free and with functional pneumatics (Fig.2D-E).

CONCLUSION & OUTLOOK
Overall, we propose a straightforward method to automatically route complex microfluidic and pneumatic networks with minor manual adjustments. Specifically, a standardized component library can be generated, allowing researchers to design networks and automatically generate the routing. This enables the design of custom FCBs and thereby supports the adoption of such platforms, which is key in current standardization efforts [6, 7].