Welcome and Introduction by Conference Co-Chairpersons -- Scope of the Conference and Topics Covered
Albert Folch, Professor of Bioengineering, University of Washington
Sunitha Nagrath, Professor of Chemical Engineering and Biomedical Engineering, University of Michigan-Ann Arbor, United States of America

High Resolution Negative Space 3D Printing for Microfluidics
Gregory Nordin, Professor, Brigham Young University, United States of America

While there is great interest in 3D printing for microfluidic device fabrication, a main challenge has been to achieve feature sizes that are in the truly microfluidic regime (<100 µm). A key issue is that microfluidic devices are comprised primarily of negative space features, which therefore dominate 3D printing resolution requirements, as compared to positive space features that are typical for many other 3D printing applications. Consequently, we have developed our own stereolithographic 3D printers and materials that are specifically tailored to meet these needs. We have shown 3D printed channels as small as 18 µm x 20 µm, and have recently reduced this to 2 µm x 2 µm. We have also developed active elements such as valves and pumps with the smallest valves having an active area of only 15 µm x 15 µm. In this presentation we discuss how such results are achieved and demonstrate miniaturized components including small (<1mm^3) fast (~1 ms) mixers and isoporous membranes with 7 µm pores. We also demonstrate integrated 3D printed devices such as for controllable cell chemotaxis. Advances in negative space 3D printing open the door to replacing expensive cleanroom fabrication processes with 3D printing, with the additional advantage of fast (~5-15 minute), parallel fabrication of many devices in a single print run due to their small size.

Modular Design Workflows for 3D Printed Microfluidics
Noah Malmstadt, Professor, Mork Family Dept. of Chemical Engineering & Materials Science, University of Southern California, United States of America

3D printing brings with it a plethora of advantages for microfluidic applications. Principle among these are rapid prototyping, iterative design, and the ability to avoid the cost and overhead of cleanrooms. However, there is also an inherent advantage in being able to design and build devices in a truly three-dimensional, rather than layer-by-layer, geometry. One simple domain in which the advantages of true 3D routing are clear is in mixing. Control over a 3D geometry allows for multiple complex mixing configurations--herringbones, relamination mixers, chaotic advection--to be trivially constructed and recombined.

We have used these principles of 3D design to construct devices and systems for bioanalytical assays, for manufacturing biomaterials, and for industrial-scale manufacturing of novel materials. This talk will examine all of these applications and the manner in which 3d-centric microfluidic design can enable them.

Additive Manufacturing for Microfluidic and Wearable Sensor Systems
Bonnie Gray, Professor of Engineering Science, Simon Fraser University, Canada

We are surrounded by sensors in our daily lives. These (usually) small, inobtrusive devices constantly capture data about our environment, and what we see, hear, and do. Sensors form the foundation for analysis systems and are an integral part of every closed-form system. Many sensors seek to provide more continuity for health and well-being via constant monitoring of important health parameters. Similarly, other sensors seek to address the health of other systems, such as preventing failures in the power grid. Sensors as discrete components may be difficult to integrate into low-profile systems, such as textile-based systems, for development of smart clothing. These and other sensors systems could benefit from 3D printing or other additive manufacturing methods, via the integration of conventional printing materials with new functional (e.g., sensing or actuating) printed materials. Sensors could thus be easily tailored and printed to individual needs and more easily integrated with other printed components. This presentation focuses on development of wearable and other printed sensors that are designed directly on textiles, or fabricated using 3D printing methods for easier integration with fluidic housings. We discuss the current state-of-the-art, and present examples of integrated textile-based and printing-based sensors. We investigate how advances in flexible devices and systems (electronics, sensors, actuators, microfluidics) and additive manufacturing (e.g., printing) can be adapted to low-profile, non-obtrusive, and personalized sensor systems.

Integration and DFM for Microfluidics
Leanna Levine, Founder & CEO, ALine, Inc., United States of America

Most microfluidic cartridges require integration of mixed materials and components to create the complete functional product architecture. This talk will address the key considerations for DFX while leveraging a range of prototyping techniques including 3D printing, CNC machining, Injection molding and Laminate Fluid Circuit Technology, to position a product for transfer to scale up with high volume manufacturing techniques.

Rapid Micromolding of Sub-100 Micron Microfluidic Devices Using an 8K Resin 3D Printer
Amar Basu, Professor, Electrical and Computer Engineering, Wayne State University, United States of America

Microfluidics relies on the ability to manufacture sub-100 micrometer fluidic channels. Conventional lithographic methods provide high resolution but have turnaround time of several days, while rapid prototyping methods (e.g., laser cutters, craft cutters, fused deposition modeling) have feature sizes of several hundred microns or more.  This talk describes a single-day process for fabricating sub-100 µm channels, leveraging a low-cost 8K digital light projection (DLP) 3D resin printer.  The process can create microchannels with 44 µm lateral resolution and 25 µm height, posts as small as 400 µm, aspect ratio up to 7, structures with varying z-height, integrated reservoirs for fluidic connections, and a built-in tray for casting.  This talk will cover the key process steps (mold printing, post-treatment, and casting polydimethylsiloxane (PDMS) elastomer)  and discusses strategies to obtain robust structures, prevent mold warpage, facilitate curing and removal of PDMS during molding, and recycle the solvents used in the process.  This process provides a balance between resolution, turnaround time, and cost (~USD 5 for a 2 × 5 × 0.5 cm3 chip) that may be useful for many microfluidics labs.

3D-Printed Microfluidic Circuitry via Alternative Additive Manufacturing Strategies
Ryan Sochol, Associate Professor, University of Maryland, College Park, United States of America

Over the past decade, researchers have demonstrated that additive manufacturing—or “three-dimensional (3D) printing”—approaches provide powerful means for achieving integrated microfluidic circuits and systems.  Although the majority of developments in the area of 3D-printed microfluidic circuitry have relied on mesoscale “vat photopolymerization” techniques, such as “stereolithography”, there are a wide range of additive manufacturing approaches that offer utility for microfluidic circuit design, fabrication, and integration.  In this talk, Prof. Ryan D. Sochol will discuss how his Bioinspired Advanced Manufacturing (BAM) Laboratory is leveraging the capabilities of alternative additive manufacturing technologies—namely “PolyJet 3D Printing” and “Two-Photon Direct Laser Writing”—to realize 3D-printed microfluidic circuits for soft robotic applications… including a soft robotic “hand” that plays Nintendo.

Biochemical Assays in Variable Height Microfluidic Devices
Mark Burns, T. C. Chang Professor of Engineering, University of Michigan, United States of America

Processing of solid particles in 3D-printed fluidic channels has the potential to expand the application space of microfluidic systems. As an example, selective binding of proteins, DNA, and other biological substances is used in assays to detect pathogens, diagnose disease, and guide patient treatment. The capture of these substances can take place in a bulk liquid phase, which is generally simpler, or on a solid surface, which provides the benefit of straightforward two-dimensional result interpretation. We combine these two techniques to achieve the best of both worlds. We use an antibody sandwich assay with the capture antibody immobilized on the solid surface of microbeads, each of which has a specific diameter corresponding to one protein in a multiplexed adsorption assay. The beads are then introduced into a microfluidic channel with varying heights, allowing each bead size to become trapped at a distinct location. This method effectively transforms a three-dimensional suspension into a two-dimensional layout, simplifying the reading of binding results. The channel is currently constructed using a variable etch of a glass substrate in hydrofluoric acid but we hope to use other techniques such as 3D printing to produce these chips. One printing technique we have developed, dual-wavelength stereolithography, could eventually fulfill this goal but the current resolution is too low.

High-Throughput Lung Microphysiological Systems
Shuichi Takayama, Professor, Georgia Research Alliance Eminent Scholar, and Price Gilbert, Jr. Chair in Regenerative Engineering and Medicine Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology & Emory University School of Medicine, United States of America

There is a need to better understand lung disease, accelerate drug discovery, and better predict human clinical trial outcomes and individualized drug responses. This presentation will describe efforts to develop microphysiological systems (MPSs) to accomplish this goal. Specific topics include the first microfluidic lung-on-a-chip developed at Michigan. A Transwell-96 based air-blood barriers that can be coupled with automated flow cytometry. And a 384 well format assay using lung Organoids with Reversed Biopolarity (lung-ORBs). Specific applications include single-ORB based high-throughput assays of SARS-CoV-2 infection and therapeutics, neutrophilic inflammation studies, and analyzing the injurious effects of fluid mechanical effects associated with lung stethoscope sounds.

Micro Innovations Defining the New Frontiers of Liquid Biopsy
Sunitha Nagrath, Professor of Chemical Engineering and Biomedical Engineering, University of Michigan-Ann Arbor, United States of America

Microfluidic technologies were always at the forefront of innovations in liquid biopsies. There were several corner stone microfluidic technologies that enabled sensitive and yet specific identification of blood-based biomarkers. The confluence of technology advancement and rapid developments in molecular characterization techniques pushed the boundaries of liquid biopsies thus enhancing the clinical utility of blood biopsies. Several such key enabling technologies will be presented. How isolation of circulating tumor cells using novel microfluidic technologies can enable precision diagnostics will be demonstrated with the example clinical case studies.

Custom and Mass Manufacturing of High Resolution Microfluidics by Low Cost SLA 3D Printing
David Juncker, Professor and Chair, McGill University, Canada

I will present our work on stereolithography DLP and LCD 3D printing for microfluidics and notably how it elevated and transformed capillaric circuits (CC); CCs are structurally-encoded pre-programmed capillary microfluidics operating without moving part, peripherals nor computer, and powered by the free surface energy of paper. Capillaric circuits are hierarchically built from basic elements such as microchannels, resistances, pumps, valves (incl. stop-, trigger-, retention-, retention burst-, and domino-valves) and more complex sub-systems such as microfluidic chain reactions for scalable, algorithmic liquid handling operations. The progression from replica molding to digital manufacturing – i.e. from a digital file to functional device thanks to new hydrophilic inks – will be illustrated with various designs, notably the ELISA chip for point-of-care diagnostics. The potential of ultra-low cost LCD 3D printers and custom inks for microfluidics will be illustrated via microfluidic mixers, active valves, ELISA chips, and by mass manufacturing thousands of organ-on-chip devices in a single run. SLA 3D printing together with tailored inks pave the way for high-resolution distributed manufacturing of ready-to-use microfluidic systems (e.g. CCs with structurally encoded algorithms ) anywhere, by anyone who can spare US$300 to buy an LCD 3D printer.

Bioengineered Human Embryo and Organ Models
Jianping Fu, Professor, Mechanical Engineering, Biomedical Engineering, Cell & Developmental Biology, University of Michigan-Ann Arbor, United States of America

Early human development remains mysterious and difficult to study.  Recent advances in developmental biology, stem cell biology, and bioengineering have contributed to a significant interest in constructing controllable, stem cell-based models of human embryo and organs (embryoids / organoids).  The controllability and reproducibility of these human development models, coupled with the ease of genetically modifying stem cell lines, the ability to manipulate culture conditions and the simplicity of live imaging, make them robust and attractive systems to disentangle cellular behaviors and signaling interactions that drive human development.  In this talk, I will describe our effort in using human pluripotent stem cells (hPSCs) and bioengineering tools to develop controllable models of the peri-implantation embryonic development and early neural development.  The peri-implantation human embryoids recapitulate early post-implantation developmental landmarks successively, including amniotic cavity formation, amniotic ectoderm-epiblast patterning, primordial germ cell specification, development of the primitive streak, and yolk sac formation.  I will further discuss an hPSC-based, microfluidic neural tube-like structure (or µNTLS), whose development recapitulates some critical aspects of neural patterning in both brain and spinal cord regions and along both rostral-caudal and dorsal-ventral axes.  The µNTLS is further utilized for studying development of different neuronal lineages, revealing pre-patterning of axial identities of neural crest progenitors and functional roles of neuromesodermal progenitors and caudal gene CDX2 in spinal cord and trunk neural crest development.  We have further developed dorsal-ventral patterned, microfluidic forebrain-like structures (µFBLS) with spatially segregated dorsal and ventral regions and layered apicobasal cellular organizations that mimic human embryonic brain development in pallium and subpallium areas, respectively.  Together, both µNTLS and µFBLS offer 3D lumenal tissue architectures with an in vivo-like spatiotemporal cell differentiation and organization, useful for studying human neurodevelopment and disease.

Taking a Liquid Biopsy from Lab to Clinic: What It Takes to Get Ready for Prime Time
Daniel Hayes, Stuart B. Padnos Professor of Breast Cancer Research, University of Michigan Rogel Cancer Center, United States of America

A tumor biomarker liquid biopsy test, is not just an assay for circulating proteins, tumor cells, or cell free DNA. Rather, it is a precisely developed assay that has high analytical validity and clinical utility for a specific use context. Clinical utility requires consideration of several factors and the generation of high levels of evidence that use of the assay, compared to not having the results at all, improves patient outcomes – preferably either quality or quantity of life. These issues will be discussed in the presentation.

Whole Blood Microfluidics
Ian Papautsky, Richard and Loan Hill Professor of Bioengineering, Co-Director, NSF Center for Advanced Design & Manufacturing of Integrated Microfluidics, University of Illinois at Chicago, United States of America

Microfluidic devices based on inertial microfluidics have attracted considerable attention for applications in blood fractionation and liquid biopsy due to their label-free nature. However, these devices can be complex, deliver limited throughput, and rely on sample dilution, making them challenging to deploy as routinely used tools. We are developing platforms capable of label-free separation from unmodified whole blood to rapidly fractionate blood cells or screen rare cell populations, for downstream analysis or drug screening.