Education: A modular approach to microfluidics in the teaching laboratory

Abstract

This article seeks to educate the reader about the role played by the microfluidics teaching lab in the education of science, technology, engineering and mathematics for students of all ages. The discussion is intended to serve as a general guide to educators about the lab philosophy, goals, lab experiments and required equipment and reagents necessary for a successful microfluidics teaching laboratory. We hope that this article will stimulate other groups and companies to describe what they are doing to encourage education in this sector. At LabSmith we have developed a modular approach for teaching and demonstrating microfluidics that allows the end user to tailor the laboratory to course goals without an impact on the package of experimental equipment required and available to them. Thus, it is possible to educate students either in the art of microfluidics or use microfluidics to educate students about fundamental physical, chemical, or biological principles. The laboratory experiments discussed here are for students with educational experience at high school, undergraduate, graduate, and post-graduate levels.

Introduction

Globally, much attention is being paid to Science, Technology, Engineering, and Maths (STEM) education for students in K-12, undergraduate, graduate, and post-graduate education levels.¹ The emphasis varies widely depending on location. Countries with success in economic growth due to investments in STEM education such as China, Korea, India and Singapore have to support and fund the pipeline of skilled scientists and engineers to maintain the flow of these experts, fuelling even greater investment in STEM training.^2–5 In regions attempting to increase their economic growth using science and technology it is clear that a successful economic future depends on regional investments in training and retaining a critical mass of highly skilled personnel in science and engineering.^6,7 In the so-called first world Western countries where the recent economic crisis has underscored the need for knowledge-based economies there are two divergent situations. (1) European self-assessments point to a need to improve the attraction of K-12 STEM education, as well as a need to invest in training people at post-graduate level in order to maintain a vibrant, skilled and innovative workforce and thus be knowledge-based economy leaders.^8,9 (2) The fact that the US is losing its lead in the development of science and technology has been attributed, in large part, to a lack of investment in STEM at the K-12 level of education (pre-university level) by the National Academies of Sciences.^10,11

What, then, is the role of the laboratory in training students in STEM education? The many studies performed give mixed results which can be pulled out of context.^12,13 The truth is more complex than a single study can encompass.¹² What is clear is that the impact of the teaching laboratory depends heavily on course objectives, the link to the classroom curriculum and course philosophy. Much of the value of the laboratory is as a controlled “real world scenario” to help students build the following:¹⁴

1. Comprehension skills. Students must read and understand the in-laboratory objectives and interpret them to practice.

2. Planning skills. The time limitation of most teaching labs means students must develop a lab strategy in order to succeed.

3. Critical thinking skills. During the laboratory session, troubleshooting “on the fly” is required. In order for students to think on their feet, they must employ deductive reasoning, practical thinking, and know enough about what is happening in the lab to develop and execute responses according to what is happening in real time.

4. Research skills. The ability to interpret their data relies partially on pulling it into the context of existing scientific literature and properly controlling the experiment to vary critical parameters for testing a hypothesis.

5. Knowledge of statistics. The students can only understand the significance of their results if they conduct a statistically significant number of tests.

6. Technical writing. The students must distil their results into a lab report that can be read and understood by another.

7. Wonder and curiosity. Abstract concepts appeal to a small percentage of people as a source of awe and inspiration. Seeing abstract concepts reduced to practice can help students connect to the power of scientific inquiry and technical achievement. This can attract students to fields in science and engineering in a way concepts and textbooks cannot.

Microfluidics in the teaching laboratory

A general definition of microfluidics, from Effenhauser, is “the controlled transport and manipulation of liquid solutions, suspensions, or microscopic objects in a volume regime of about 1 femtolitre to microlitres with the dimension of the channels containing the liquid in the one micrometre to hundred micrometre range”.¹⁵ The practical incarnation of microfluidics is often on a so-called microfluidic chip—an analogue to the integrated circuit with fluid path connections rather than electrical connections in planar structure fabricated in a variety of materials.^15,16 The integration of multiple functions related to fluid manipulation, transport and analysis is often called “lab-on-a-chip”.^15,16 The world of microfluidics technology development and application is completely interdisciplinary and varied including physics, engineering, chemistry, biochemistry, and biology.¹⁶

Given the goals set forth above, what is the role of the microfluidics teaching lab in STEM education? One can simplify course philosophies into “teach microfluidics” or “use microfluidics to teach”. “Teach microfluidics” courses focus on the practical training of students about the principles and practice of microfluidics. Typical curricula with microfluidics as the focus include chip design, chip application, or both at the advanced undergraduate, graduate, or post-graduate continuing education level. The “Use microfluidics” course focuses on foundational concepts for the education of students entering the fields of engineering, physics, chemistry, and biology, using microfluidics as a platform to teach foundational concepts or principles for these varied fields. As a result, the “Use microfluidics” philosophy may be suited for students with less STEM course work under their belt, such as high school students or lower level undergraduate courses. Table 1 lists the types of microfluidics experiments one can use for either the “Teach” or “Use” microfluidics philosophies, linking them to the underlying disciplines and principles that could be illustrated in a “Use” lab, and listing the type of equipment that are required.

Table 1 Microfluidics education lab objectives and requirements grid

One observes that tools required for “Teach” and “Use” courses can be the same, but depending on the type of course, they may be used very differently by the laboratory organizer, falling somewhere in the spectrum between a do-it-yourself (DIY) boundary where the student is responsible for everything from modelling, chip design, chip fabrication, system set-up, and final chip testing and demonstration to a black box boundary where the chip is pre-made, the test system is complete for the students (built by the instructor or complete as purchased), and the focus is on varying the conditions controlled by the black box to test a hypothesis or observe the effects of these instrument parameters on a microfluidic phenomenon. In truth, most experiments will fall somewhere in between, although there is value in what can be learned at the extremes of either boundary. Fig. 1 shows a decision making grid for educators on where they should place their curriculum in the DIY/black box spectrum, highlighting the relationship between the level of the student and the pre-work for the instructor. With increasing experience on the side of the student, more of the laboratory session can take on the DIY flavour, particularly in the case of the “Teach microfluidics” course. However, experienced students, such as those on chemistry, biochemistry, or molecular biology courses, can also derive a strong benefit from a course that is primarily a “Use microfluidics” course on the black box end of the spectrum. Such a course can use instruments as sophisticated as chip-based mass spectrometry to teach students applied techniques in proteomics and genomics. This can be used to understand a more fundamental biological question or as a practical lab to train outgoing upperclassmen or graduate students on equipment that they may use in R&D laboratories.

Fig. 1 Diagram of relationship between student level, instructor preparation of laboratory, and level of student involvement in constructing the microfluidic experiment.

One should keep in mind the trade-offs between the DIY and black box model. Students working in the DIY model may gain a deeper understanding that comes from building their own system but lose the benefit of hands on experience with the commercial instruments commonly found in academic and industry research labs.¹⁷

“Teach” and “Use” microfluidics courses—curricula and tools for both types of teaching labs

A number of microfluidics experiments can be used for either the “Teach” or “Use” microfluidics course tracks. One of the simplest experiments uses electric or flow fields to make a microfluidic injection of a sample plug in a microfluidic channel cross. In this experiment, students observe the difference between a time-dependent injection and so-called “pinched” injection.¹⁸ This can be used to teach everything from how to make a microfluidic injection (Teach) to calculating voltage or electrical resistance or flow resistance in a fluid circuit (Use—for engineering, physics), to the impact of the injection plug size and reproducibility on dispersion in separations (Use—for analytical chemistry). By adjusting the channel geometry and using a Y as the entry point, one can illustrate mixing simply by imaging a dye introduced at one port (Teach and Use—for transport) or illustrate mixing, pH, and precipitation by using solutions with a pH indicator and differing pH, or a super saturated solution and a precipitating agent (Use—for chemistry, chemical engineering, materials science).¹⁹

Tools for microfluidics teaching laboratories

Curricula

There are a number of examples in the literature of pure research papers or scientific education papers that can be used as the basis for curricula.^15–26 While the education of undergraduate and graduate students is usually the sole focus of papers describing laboratory experiments using microfluidics, at least one author described microfluidics labs for elementary, middle school, and high school.²⁰ Harvard has recently gained publicity for employing a DIY chip fabrication technique refined by a local high school physics teacher for their extension and undergraduate microfluidics courses.²¹ Many laboratories are a mix of the Teach and Use regardless of where they fall in the DIY spectrum. They often fall mid-range in the DIY to black box spectrum (Fig. 1), into the modular category, with students often making chips of predetermined design for a selected application in chemistry, biochemistry/biology, or engineering, then testing it on standard or preset equipment. The equipment can also be set up by the student for a full DIY experience. Students are asked to create straightforward geometries using simple chip fabrication with materials from Jell-O,²⁰ Shrinky Dinks,²² paper,²³ and transparencies²¹ to polyurethane^24–26 and polydimethylsiloxane.¹⁹ Pressure driven flow from syringe pumps is the most common driver, with one article found that boasts the ability to do free zone electrophoresis of food dyes on a student-made chip.²⁴ Woolley et al. have also published a detailed teaching lab experiment through the Analytical Digital Sciences Library (http://www.adsl.org), describing a capillary electrophoresis experiment on a microfluidic chip including the experiment description, write-up, list of equipment and reagents, and the LabView data acquisition visuals.²⁷ While a number of teaching lab experiments are reported in the literature and on the Internet, there is no place yet for one-stop microfluidics curriculum shopping.

Materials and equipment

A chemistry department may find that they have all the chemicals and chemical experience on hand to pull together the materials for chip fabrication and testing, but they may find themselves stumped as to the best and most cost effective instrumentation they should use for student labs. Jury-rigged solutions can be cheap, but often cause delays and impede the performance of the laboratory, and therefore the student. Similarly, engineering departments may find that they have a strong understanding and resources for sensor development and testing, but may stumble when it comes to controlling pH to generate electroosmotic flow in a substrate. Some basic guidelines to the full requirements—instrument and material—of some core microfluidics experiments are helpful. The grid in Table 1 shows what principles may be illustrated, into what discipline(s) it falls, and what equipment is required. Table 2 shows a list of vendors of the instrumentation required or desired for the microfluidics experiments in Table 1.

Table 2 Vendors and products for the microfluidics teaching lab

In a real world anecdotal example, the upper level engineering course, MEMS Processing-ME/ECE 141B at University of California—Santa Barbara, was viewed to be a success by teaching assistant Mr Sustarich and Professor Sumita Pennathur.²⁸ However, there is room for improvement. Mr Sustarich explains, “Taking an experiment that is usually done in a controlled environment to a classroom has its challenges. Something that would allow for precise application of electrodes to fluid ports—or pressure, on an easy to control automated CCD/objective stage with a coherent light source would be optimum.”²⁸

The modular approach to span the DIY/black box spectrum

Mr Sustarich's classroom experience with live microfluidics demonstrations and laboratories is consistent with what LabSmith has observed for everything from classroom demos to lab courses to lab experiments for R&D. The approach used by LabSmith is to provide a modular breadboard platform that has both flexibility (for experimentation, teaching, learning, creating) AND stability (for demonstrations, reproducibility, and proof-of-concept) (Fig. 2). The company also offers microfluidics equipment that includes instruments for controlling high voltage in up to eight ports, pressure driven flow, visualization and an optically addressable breadboard with bread-boardable fluid connectors including valves. In addition, LabSmith is building a collection of short application notes that can be used as the basis of lab curricula, on-the-job training, and instrument testing and operational instruction. This modular approach is flexible and can accommodate the full spectrum of student involvement from DIY to the black box approach. The equipment required for a modular approach to controlling electrokinetic and pressure driven microfluidics experiments is listed in Table 2, showing a variety of vendors for each module. The solution to Mr Sustarich's problem offered by LabSmith is shown in Fig. 2, and described in detail below.

Fig. 2 LabSmith Education LabPackage set-up for controlling both pressure and electrokinetic flows generated in a microfluidic chip. Shown in this photograph: the HVS448 8-channel high voltage (3000 V) sequencer, the SVM340 synchronized video microscope, the integrated breadboard (iBB) with SPS01 syringe pumps and AV201-360 automated valves connected to a microfluidic ChipShop PMMA microfluidic chip (injection cross configuration for separations). The chip is connected to the syringes or high voltage power supply by LabSmith CapTite™ microfluidic connectors (bonded port connectors, one-piece fittings, and reservoirs shown here). LabSmith CapTite reservoirs shown filled with pH 7, 10 mM phosphate buffer (Thermo Fisher Scientific) or Oregon Green fluorescent dye (Life Technologies, Inc.). All hardware shown in this image is supplied by LabSmith, Inc.

The microscope as lab bench

A modular, inverted, fluorescence synchronized video microscope (SVM340) has been developed by LabSmith for imaging microfluidic prototypes. This unique system combines bottom-up viewing and illumination with a motionless sample stage, enabling the visualization of microsystems without perturbing the fluid flow. The motionless stage also acts an optically accessible “lab bench,” with unhindered access for external electrical and fluid connections. Traditional microscopes, in which optics are housed in a stationary head above a moving stage, have several drawbacks for these experiments:

-The moving stage can easily perturb the microfluidic system

-The microscope's objective impedes access to the microfluidic chips, fluid circuits or cell plates and other hardware

-Standard illumination can quench the fluorescent dyes used to view the particles or microorganisms.

The inverted fluorescence synchronized video microscope (Fig. 2) was designed to provide high-quality imaging and video for micro- and nano-systems. The microscope's small size allows the unit to be used on a desk or bench top. Microscope images are displayed on a computer, so there is no need for overhead viewing optics. The stage is immobile and the camera module moves to image the sample, so the microfluidic breadboard is unperturbed.

Fig. 3 shows an exploded view of the microscope's major components. A camera module contains the optics. An LED ring illuminator module can be used to provide external illumination at a variety of wavelengths for fluorescent and dark field microscopy. Stroboscopic illumination prevents quenching of fluorescent dyes. The camera and illumination modules both attach to an X/Y stage that moves beneath a stationary stage top. This design lets students construct microsystems directly on the microscope and allows unimpeded connection to other equipment. The microscope's small size allows the unit to be used on a desk or bench top. Stroboscopic illumination prevents quenching of fluorescent dyes.

Fig. 3 Exploded view of the LabSmith SVM340 microscope's major components.

High voltage power supply

The LabSmith HVS448 (Fig. 2) delivers high voltage control (up to 6000 V), current control and monitoring for eight channels. Each channel can be programmed and sequenced using the same LabSmith Sequence software. LabView drivers are also available for total experimental control. High voltage cables, electrode clips and platinum electrodes are also provided and the HVS448 is also compatible with Micronit's electroosmosis interfaces.

The modular pumps, valves, interconnects and the optically addressable breadboard

The LabSmith LabPackage for microfluidics also includes zero dead volume valves, SPS01 syringe pumps, CapTite™ interconnects for tubing-to-tubing connections and tubing-to-chip connections that are often required to ensure control and connection of complex fluid circuits including chips. LabSmith's uProcess™ software allows students or the course instructor to program the valve and syringe operation sequences that are computer-controlled. All these components can be constructed on an optically addressable breadboard, the integrated breadboard (iBB) shown with pumps, valve, and chip in Fig. 2, and mounted directly onto the SVM340 synchronized video microscope, replacing a conventional microscope stage. One can see from Fig. 2 that the chip can be easily connected to both the high voltage power supply viaelectrodes and CapTite™ reservoirs and/or the SPSO1 syringe pumps.

Application notes/curriculum

Simplification of the elements of lab course/training curricula into training modules is valuable to train bench scientists at any level using either the Teach or Use microfluidics approaches. An example of this versatility is the LabSmith “Making a Microfluidic Injection” application note.²⁹ This instructional module lists equipment and reagents required to perform this experiment. It is derived from the procedure for one of the “Teach”-type laboratories for the undergraduate upper level MEMs course at University of California-Santa Barbara. This microfluidic injection module can also be used as the core for hands-on training or demonstrations for professional scientists as part of demonstrations and microfluidics workshops at scientific conferences.

Conclusion

Educators developing the content and structure of courses that can include student laboratories have limited time and resources. Microfluidics laboratories offer the opportunity to engage students in the microscopic world at a reasonable cost in time and money. One of the strengths of the microfluidics laboratory is that the technique allows students to induce and observe phenomena that are difficult to create in the macroscopic scale. This can capture their imagination, attracting more students to the fields of science, technology, and mathematics; these human resources are sorely needed for the economic health and stability of every region of the world.

The primary challenge for the instructor is to commit to the objective(s) of the laboratory course. Will it teach microfluidics or use microfluidics to teach an underlying physical principle, or both? Most laboratory procedures found in the literature are a hybrid of these, teaching some basic microfluidic lab techniques and principles whilst also teaching basic principles in the natural sciences or engineering.

Having selected the objectives of the microfluidics teaching course, instructors are further challenged to determine how to best use the laboratory time. Traditional fabrication of microfluidic chips may be outside the scope of even an upper level undergraduate course. As described above, a number of solutions exist that use less expensive and less time-consuming fabrication methods than traditional methods. Cheap materials ranging from non-traditional materials such as Jell-O or Shrinky Dinks to more typical materials such as PDMS can be cheaply fabricated using simplified techniques that do not require a clean room. Standard, prefabricated chips are also available in a wide variety of materials including polymers and glass, from a number of manufacturers, with standardization driving costs down. Much of the equipment including syringe pumps, high voltage power supplies, microscopes, connectors and other tools for microfluidics are available from multiple sources, several are given in this paper.

One bright spot for the educator is that curriculum developed for one level of student can usually be simplified for a less experienced student, or tailored to a higher level student, simply by increasing or decreasing the student's involvement in creating the laboratory platform. On the spectrum of DIY to black box, many students can derive a great benefit from being responsible for the completion of only part of what is required for a microfluidics experiment to be successful, with the instructor preparing the rest. This can be applied to simplify a complex experiment for a less experienced student, or simplify one element of an experiment so that a more advanced student can focus entirely on an in-depth study on one component of the experiment. This modularised approach to the curriculum is fully supported by the modular nature of what is available commercially; allowing instructors to provide the full range of microfluidics laboratory procedures from DIY to black box for their student, often using the same equipment.

Resources for microfluidics teaching laboratory procedures are not as easily accessible as the equipment. This is because microfluidics spans so many disciplines; there is currently no venue for “one stop” curriculum shopping. An exciting opportunity exists to knit this multi-disciplinary field into a curriculum platform that is similarly modular and exploitable by the multiple educational applications it can underpin.

All opinions are those of the authors and do not reflect the views of Lab on a Chip or the Royal Society of Chemistry.

Acknowledgements

I gratefully acknowledge Professor Sumita Pennathur and Mr Jess Sustarich from UCSB for material from their laboratory and several helpful discussions. I also wish to thank Professor Patrick Holt of Bellarmine College and Professor Lisa Holland of West Virginia University for their helpful comments.

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