Traditional microfluidic systems for cell culture, while offering high throughput, suffer from the "tyranny of numbers," requiring extensive external equipment and complex designs. Highly integrated monolithic chips, while achieving high parallelization (e.g., up to 1500 independently addressable chambers), lack design flexibility and require a complex design cycle and specialized software. This necessitates a more versatile and adaptable approach. The authors propose a modular microfluidic platform composed of standardized components, building upon their previously reported modular platform. This approach leverages a fluidic circuit board (FCB) analogous to printed circuit boards, connecting predefined microfluidic building blocks (MFBBs) for customized applications. Other modular systems exist, but often rely on direct MFBB connections or passive chip selection on a breadboard. In contrast, the proposed system uses an FCB as a single baseplate to control and connect multiple MFBBs, benefiting from ISO WA standardization for interoperability and scalability. The innovation here is the inclusion of an active function within the FCB – an MFBB enabler – facilitating plug-and-play functionality and selective parallel operation of mLSI chips. This represents the first modular plug-and-play system for mLSI chips and is demonstrated using an mLSI MFBB and a dosing MFBB with distinct architectures. The system’s state-saving capability further enhances its versatility.

The literature review highlights the limitations of existing microfluidic cell culture systems. Highly integrated monolithic chips offer high parallelization but suffer from inflexibility and complexity. The “tyranny of numbers” describes the increased complexity and equipment needs associated with scaling up microfluidic systems. The introduction of microvalves significantly improved system control, enabling chips with numerous independently addressable chambers. However, developing and operating these complex chips remains challenging. The authors cite existing modular microfluidic systems that rely on direct MFBB connections or passive chip selection on breadboards, contrasting these with their FCB-based approach that offers greater control and standardization.

The study focuses on the design and implementation of a modular microfluidic system for parallel cell culture. Two key MFBBs are developed: a 64-chamber mLSI MFBB for parallel cell culture and a liquid dosing MFBB with a high dynamic range. The 64-chamber mLSI MFBB utilizes a combinatorial multiplexer with 8 control channels to independently address each chamber. The valves operate in a "push-up" configuration, where pressurizing the control channels blocks flow. The design incorporates a bypass channel to purge the system without contaminating the chambers. Two variations of the mLSI MFBB were fabricated with minor adjustments to optimize cell culture. The dosing MFBB uses pulse width modulation (PWM) metering to achieve a high dynamic range of mixing ratios. It comprises two fluid inlets, a purge inlet, three outlets, and ten valves. Different hydraulic resistances allow for varied flow rates, while PWM control generates various concentration profiles. The FCB acts as a central controller, connecting multiple MFBBs via an external interconnection block (EIB). Latching valves on the FCB allow for independent and parallel operation of multiple MFBBs. The FCB itself has 13 MFBB control channels, each branching to three MFBB ports, and is controlled by FCB valves. The system's operation is demonstrated through the parallel and selective control of the mLSI and dosing MFBBs, and the successful culture of HUVECs in the mLSI MFBB is shown as a proof of principle. All components adhere to ISO WA standards, ensuring compatibility and ease of expansion.

The authors successfully developed and demonstrated a modular plug-and-play system for mLSI chips. This system uses an FCB to control multiple MFBBs, including a 64-chamber mLSI MFBB and a dosing MFBB, independently and in parallel. The FCB's ability to "save" valve states enables the simultaneous operation of both MFBBs using a shared set of control lines. The study demonstrated the successful culture of HUVECs in the chambers of an unmounted mLSI MFBB, validating the system's functionality for cell culture applications. The use of standardized components and the modular design allows for flexibility and scalability. The 64-chamber mLSI MFBB uses a combinatorial multiplexer to independently address each chamber, enabling high-throughput screening of up to 64 different conditions. The dosing MFBB utilizes PWM to achieve a wide dynamic range in concentration profiles, providing precise control over the delivered fluids. The system’s design adheres to ISO WA standards, facilitating future expansion and compatibility with other standardized components. The number of independently addressable chambers (k) is calculated based on the number of control channels (N) using provided equations, where N=8 yields 64 chambers. The bypass channel ensures efficient purging of the system without chamber contamination. Brightfield micrographs illustrate the design and operation of both MFBBs and the FCB. The high dynamic range of the dosing MFBB is achieved by varying hydraulic resistances and using pulse width modulation. The successful HUVEC culture demonstrates the system’s suitability for cell culture applications.

The developed modular plug-and-play system significantly advances microfluidic cell culture technology by addressing the limitations of monolithic chip designs. The system’s flexibility allows for easy adaptation to different experimental questions, while the modularity enables scalability and cost-effectiveness. The ability to operate multiple MFBBs in parallel and independently drastically increases throughput and experimental control. The successful culture of HUVECs validates the system's suitability for biological applications. The adoption of ISO WA standards further enhances the system's compatibility and potential for widespread adoption within the field. Future research could focus on expanding the library of standardized MFBBs to include a wider range of functionalities, and integrating advanced detection and analysis techniques to further enhance the system’s capabilities.

This research presents a novel modular plug-and-play system for highly parallel microfluidic cell culture. The system successfully addresses the limitations of current approaches by offering flexibility, scalability, and ease of use. The successful demonstration of HUVEC culture validates its potential for biological applications. The use of standardized components ensures compatibility and facilitates future expansion.

While the system demonstrates significant advantages, potential limitations exist. The current system is limited to 64 independently addressable chambers in the mLSI MFBB. Future work may explore scaling this to a larger number of chambers. The current MFBB library is relatively small, and expanding it to include other functionalities is a direction for future research. The complexity of the system might present challenges for users unfamiliar with microfluidic technology. A comprehensive user manual and robust software support may be needed to improve accessibility.