June 15, 2016 (Vol. 36, No. 12)

Miniscule Volumes, Under Exquisite Control, Mean Big Gains in Medical Research and Patient Care

Since its inception in the early 1980s, microfluidics has consolidated influences from multiple disciplines—engineering, physics, chemistry, biochemistry, nanotechnology, and biotechnology—while expanding its range of biomedical platforms and associated downstream applications. For example, there are numerous biomedical and research applications in which low volumes of fluids are processed to achieve multiplexing, automation, and high-throughput screening.

Microfluidic behavior relies on precise control and manipulation of fluids that are geometrically constrained within some type of small-scale device. The devices known as microfluidic chips consist of microchannels that are etched or molded into materials such as silicon, glass, or plastic. Among the many advantages of these systems over macro-scale assay systems (such as plate- or tube-based systems) are dramatically reduced reaction sizes, assay times, and reagent usage rates—as well as lower costs.

Typically, microfluidic chips handle liquids on the order of nanoliter to picoliter. Both capillary-based (passive) as well as micropump- and valve-based (active) fluid-control techniques have been developed. The utility of microfluidics has expanded greatly in keeping with the research and development pace in cellular biology, molecular diagnostics, proteomics, and DNA sequencing. Some of the more well-known examples of microfluidic technologies are inkjet printheads, lab-on-a-chip systems, and biosensors for monitoring of toxins or pathogens.

State-of-the-art developments in microfluidics development and applications will be presented at Microfluidics Congress: USA, which will take place July 11–12 in Philadelphia. This meeting will incorporate presentations on microfluidics strategy and technology along with case studies and applications in medical research. Both corporate and academic scientists and researchers will be attending and sharing their knowledge. GEN interviewed several of the presenting scientists in advance of this meeting to highlight some of the unique advances in microfluidics that they will be presenting.

Microscale Acoustofluidics

A technical innovation called acoustofluidics is slated for presentation by Tony Jun Huang, Ph.D., professor of bioengineering science and mechanics at Pennsylvania State University. He will highlight numerous biomedical systems that fuse acoustics and fluidics. These systems have not only passed the proof-of-concept stage, they have also demonstrated biological relevance.

In microscale acoustofluidic systems, power intensities and frequencies stay within biocompatible bounds. Essentially, the acoustic manipulation process do not alter cellular properties. “The energy intensity used in acoustofluidics,” says Dr. Huang, “is very similar to that used in ultrasonic imaging for pregnancy testing, which has shown to be inherently safe.”

In fact, this technology is so biologically gentle it can be used to transfer proteins, high molecular weight DNA, and live cells without damage or loss of viability. That makes it suitable for a wide variety of applications including proteomics and cell-based assays. Acoustofluidics is capable of delivering high-precision, high-throughput, and high-efficiency cell/particle/fluid manipulation in a small, inexpensive device about the size of a cell phone.

One of the important downstream application Dr. Huang plans to highlight is the detection and isolation of circulating tumor cells for cancer diagnostics. “This technology excels with rare cells,” notes Dr. Huang. “It both isolates and preserves intact cells for subsequent genotypic and potentially therapeutic analyses.”

Scientists in the Penn State University laboratory of Tony Jun Huang, Ph.D., provided this image, which shows acoustic tweezers separating circulating tumor cells from blood cells.

Capillary Microfluidics

David Juncker, Ph.D., an associate professor of biomedical engineering at McGill University, will present a session on capillary microfluidic systems, which are capable of rapid prototyping for immunoassays and bacterial detection. In particular, Dr. Juncker will describe capillary flow driven systems that use hydrophilic materials (primarily silicon chips) with etched microchannels designed to control flow. Such systems, asserts Dr. Juncker, lead to “more complicated circuits capable of complex fluidic functions.”

Dr. Juncker leads a team of scientists at McGill’s Micro & Nano Bioengineering Lab. The lab’s work on capillary microfluidics in one dimension ranges from continuous flow on thread to digital capillary fluidics on strings. “We use the thread and string as mixers and are using the same ideas for tissue engineering,” explains Dr. Juncker.

Some of the lab’s downstream applications include immunoassays for cardiac disease and bacterial testing for urinary tract infections (UTIs). “Our E. coli bacterial test for UTI has an assay time of approximately seven minutes compared with classical culturing methods on the order of hours to days,” mentions Dr. Juncker. A broad range of input samples can be tested including urine, serum, and plasma. “Using immunoassay antibody detection,” continues Dr. Juncker, “we are able to essentially count bacteria with this methodology.”

He called their 3D printing for rapid bacterial testing process “transformative for students” because the half to one hour time to design and synthesize prototypes allows for fast and immediate redesign when needed. “This allows them to use this reiterative process to quickly overcome hurdles they encounter and quickly build more complex circuits,” asserts Dr. Juncker. His team has combined expertise in biomaterials, energy, and fluid flow, along with the biological aspects of immunology and microbiology.

Dr. Juncker and his colleagues have been very prolific authors, with over 21 published papers since 2013 alone in numerous journals. “We’re also planning to move forward with DNA testing as another application of our research,” he notes.

Paper-Based Microfluidics

Charles Henry, Ph.D., professor of chemistry and leader of the Henry Group at Colorado State University (CSU), will describe recent developments in paper-based microfluidics for human clinical and environmental diagnostics. Advantages of paper-based devices include potential ease of use, low cost, and ease of disposability.

“We’ve tested and used everything from ordinary Whatman filter paper to copy paper,” he says. In human diagnostics applications, the Henry group has collaborated with the veterinary, microbiology, psychology and other departments at CSU to develop singleplex and multiplex assays for bacterial and viral targets including West Nile Virus, Middle East respiratory syndrome, tuberculosis, human papillomavirus, and Zika virus.

For clinical diagnostics, notes Dr. Henry, “recent efforts have centered on adapting peptide nucleic acid with colorimetric detection assays using paper-based matrices for rapid bacteria and virus detection.”

In environmental monitoring and detection using paper-based microfluidics, Dr. Henry has a team of international collaborators and several publications on the topic. Their research focus is on detection of metals and reactive organic compounds in the context of personal exposure assessment where porous microfluidics provides unique capabilities in terms of rapid response and sensitive analysis in an affordable package. Their lab-on-paper publications utilize the combination of electrochemical and colorimetric detection for rapid screening of gold and iron in industrial applications.

“One adaptation of paper-based sensing is a wearable device to measure PM2.5 exposure in environmental diagnostics for mortality/morbidity screening,” explains Dr. Henry. Another recent project utilized electrochemical detection with paper-based microfluidic devices where photolithography was used to make microfluidic channels on filter paper. Screen-printing technology was used to fabricate electrodes on the paper-based microfluidic devices. Utility was demonstrated with the determination of glucose, lactate, and uric acid in biological samples using oxidase enzyme reactions.

Droplet Microfluidics

Droplet microfluidics, an enabling technology for high-throughput screening analysis, will be covered at Microfluidics Congress: USA by Carolyn Ren, Ph.D., professor, Canada Research Chair in Droplet Microfluidics and Lab-on-a-Chip Technology, Department of Mechanical and Mechatronics Engineering, University of Waterloo. She will describe several high-throughput applications that make use of nanoliter-sized drops. Dr. Ren’s laboratory has evaluated gas-liquid systems as well as systems that rely on two immiscible liquids.

“This talk will primarily focus on liquid-liquid droplet microfluidics,” informs Dr. Ren. “This entails fundamental transport phenomena of droplet generation, trapping and sorting, physical modeling of droplet generation in different geometries, and droplet sorting in T-junctions.”

The nanoliter-scale volumes of liquid reagents tested in her research are roughly a 1,000-fold reduction compared with plate-based assays. “This is a platform-enabling technology that can be applied to drug screening, DNA sensing, and protein crystallization along with other applications,” she asserts. “Samples are encapsulated into droplets (such as water into an oil stream microchannel) to produce uniform drops where each droplet is analogous to a reactor.” Dr. Ren’s lab-on-a-chip research also incorporates electrical sensing mechanisms such as capacitance and microwave sensing.

Biomedical Outlook

All manner of microfluidics advances—from materials, design, to downstream applications—will be discussed at Microfluidics Congress: USA. In particular, new technologies, strategies, and approaches will be presented in microfluidics materials, design, control, and bioresearch/biomedical uses. Incremental progress continues apace from developments in new materials to improvements in volume precision and liquid-handling control. Moreover droplet, digital, centrifugal, and acoustic technologies continue to be refined.

Functional microfluidic applications demonstrated by biomedical scientists and clinicians are expanding and wide-ranging. They include many varieties of assays—cellular, protein, immunological, and nucleic acid along with biological pathogens (bacterial and viral) and chemical and environmental monitoring. For many future biomedical questions, ranging from macromolecular diagnostics to synthetic biology, part of the research and applied pathway toward logical solutions will include some specialized version of microfluidics.

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