As early as the 6th century BC, key strategies for winning a war were laid out by Sun Tzu in one of the oldest military books ever written. Among his most important lessons were: to know your enemies, and to be fast. When it comes to modern medicine, things are no different: an early diagnosis will drastically increase your chances of defeating a disease.
Microfluidic systems have proven their worth for many biological applications and promise to deliver as much if not more for the field of diagnostics. Could they become a companion tool to help doctors improve diagnosis, or even replace them for faster and more accessible point-of-care diagnostics?
The current bottleneck in diagnosticsImproved screening has been shown to lead to a significant decrease in mortality associated with many diseases, such as breast and cervical cancer1. Indeed, formerly incurable diseases can now be weakened, if not eliminated altogether; for example, 92% of patients whose invasive cervical cancer is detected at an early stage survive within 5 years, compared to 17% if the cancer is detected once it has already metastasized to a distant tissue2. Now that such life-saving treatments exist, a greater effort needs to be concentrated towards the development and implementation of diagnostic tools, which are still lagging behind rapid therapy development.
Only 46% of women with cervical cancer are diagnosed at an early stage2. In fact, diagnosis can be a difficult task for doctors, traditionally solely facilitated by costly detection tools, often based on nonspecific, and potentially harmful, imaging techniques.
Moreover, these tools require access to refined medical facilities, which are often overloaded. This can result in excessive waiting times that can make patients miss the time frame during which the disease is still treatable. Consequently, there is an urgent need for a shift to cheap, fast, accurate and high throughput diagnostic tools.
Fortunately, microfluidic technology should soon live up to these high standards.
Micro-tools for detecting micro-culpritsMicrofluidic tools can be envisioned as miniaturized laboratories. They contain channels with dimensions ranging from tens to hundreds of microns that facilitate the handling of small volumes of fluid3, such as blood. The gains from such downscaling are immense. Benefits include:
• Shortened time reactions
• Minuscule volumes of reagents and samples
• Higher sensitivity
• Less human intervention and thus fewer errors
• A massive throughput
• An unbeatable low cost of mass fabrication
After all, microscopic diseases call for microscopic tools.
Such advantages are bound to democratize diagnostics by facilitating financial and physical access to assays for a wide range of diseases4. For example, Chin et al. have successfully tested a microchip in Rwanda that identifies HIV and syphilis with an impressive accuracy, requiring only pricking your finger and an LED placed on a cell phone to interpret the results5. Such tools are bound to provide much needed help with HIV diagnosis: for example, UNAIDS reports that only 38% of people in Nigeria infected with HIV were aware of the infection in 20176.
According to Prof. Paul Yager at the University of Washington:
“The big advantage would be for populations that do not have (convenient, timely or affordable) access to the diagnostics capabilities of large centralized hospitals or other commercial labs. This would include people at home in the developed world, people in low-resource settings in the developing world, and people in a variety of care settings (e.g. nursing homes) that cannot currently afford to house expensive high-end instruments.”Prof. Yager also points to cellphones as a trend that potentiates microfluidic diagnostic tools7:
“A new technological trend in clinical practice is to use cell phones as a source of information for home diagnosis, or monitoring of health, or monitoring ongoing treatment. To get chemical information there is a need for products that can collect information on biomarkers at home. Microfluidic devices can fill this need. There are many challenges to make such devices inexpensive, easy to use, but the home pregnancy test (and related lateral flow tests for malaria or HIV), demonstrate that such devices can be made and used by untrained users. The potential to change medicine is real and impending.”
In the same vein, paper-based microchips, simply fabricated with an inkjet printer and a UV lamp promise to further facilitate their large-scale usage in remote areas of developing countries8. Such simplicity could enable these tests to be done at home, thereby potentially bypassing the stigma that refrains many people from taking the HIV test.
On the other hand, microfluidic technology has also inspired new diagnostic protocols that were not previously attainable in macroscopic assays. Prof. Chwee Teck Lim at the National University of Singapore along with other groups has pioneered the development of microfluidic chips to isolate circulating tumor cells (CTCs) from blood9,10. These rare and fragile cells are responsible for spreading secondary cancers throughout the body and are nearly impossible to detect using normal bench-top procedures. Their isolation marks a crucial step, not only for detecting and monitoring cancer progression, but also for refining treatments, as Prof. Lim explains:
“Currently, cancer diagnosis involves tumor biopsy which is highly invasive, painful, and cannot be performed frequently, mainly once before chemotherapy and once after. Liquid biopsy, which refers to isolating CTCs from blood is less invasive, less painful and can be performed more frequently since blood can be easily obtained via venepuncture. This means we can sample cancer cells at various time points and this can lead to a real-time monitoring of the patient’s condition and the effectiveness of the therapy the patient is receiving. Also, there are cases where doing a tumor biopsy can be dangerous due to the way the tumor is located and getting CTCs from liquid biopsy is the only viable option.”Indeed, the isolation and characterization of the patient’s very own diseased cells paves the way for the future of diagnostic tools.
How much more personalized could it get?Microfluidic models are not being developed only for diagnostics: it is hoped they will fill an important gap in pre-clinical models for a more efficient drug discovery process11. Progress in this direction also holds great promise for the field of diagnostics. For example, Benam et al.12 reconstituted key elements of chronic obstructive pulmonary disease (COPD) in a lung-on-a-chip model.
COPD can have viral or bacterial causes; in their model, they used viral by-products to induce COPD, and identified macrophage colony-stimulating factor as a novel potential biomarker for the disease. They discovered the first potential biomarker specific to viral COPD, which could help guide therapy by preventing unnecessary antibiotic use. Now that researchers are learning to use induced pluripotent stem cells extracted from patients, such microfluidic models are bound to come one step closer to becoming personalized avatars13.
Organoids also hold great promise for creating ever more personalized microfluidic diagnostic tools. This novel concept is illustrated by a recent study where intestinal organoids derived from patient’s biopsies were introduced into a microfluidic chip that introduced flow and cyclic deformation14. Importantly, they show that the transcriptome of cells inside the chip matches better that found in vivo compared to organoids outside of the chip; this clearly demonstrates that the microfluidic platform adds significant value towards the physiological relevance of the model. Such tools could be used not only to detect pathological biomarkers and early signs of diseases, but also to track the progress of the disease and tailor the therapies to the patient’s unique needs.
We are not there yet. Many challenges exist; according to Prof. Lim, “Implementing such microfluidic diagnostics requires careful integration into the existing workflow in the clinic. This can often be difficult and requires significant changes either to the infrastructure or processes and as such, it can lead to resistance from current practitioners.”
Be that as it may, microfluidic tools are already being successfully used for the diagnosis of some diseases, as Prof. Yager points out:
“The biggest impact globally of ‘conventional’ microfluidics to date is probably the use of the Cepheid GeneXpert cartridge-and-instrument system, which allows highly-sensitive multiplexed PCR to be performed on raw samples in a simple laboratory environment. Through subsidization by the Bill & Melinda Gates Foundation, this instrument is widely used in the developing world to diagnose and monitor HIV and TB, as well as a variety of other infectious agents.”
To what extent will microfluidics take over?Hypochondriacs will be happy to know that one day, with the onset of diagnostics microfluidic tools, their very own bathrooms could be turned into personal hospitals. While we are a long way from this, it is promising to see that microfluidic tools have already influenced the field of diagnostics. This is all the more of an encouraging development, as microfluidics have yet to make similar impact on patients in other areas such as drug discovery. This is probably because microfluidic applications for drug discovery rely on workflows that require long term cell culture and exploratory protocols. In contrast, microfluidic point-of-care tools have been purposely designed to remain simple such that they can be used in remote low resource settings. Yet, behind this apparent simplicity hide decades worth of intricate and ground-breaking research.
Medical practitioners need not worry though, as their work requires many responsibilities that microfluidic tools cannot entirely take on as of today. For example, nothing could replace their intuition, a quality Sun Tzu considered essential for defeating enemies. After all, the book is called the Art, and not the Science, of War.
1. Hoerger, T. J. et al. Estimated Effects of the National Breast and Cervical Cancer Early Detection Program on Breast Cancer Mortality. Am. J. Prev. Med. 40, 397–404 (2011).
2. American Cancer Society. Cancer Facts and Figures 2018. Am. Cancer Soc. 1–71 (2018). doi:10.1182/blood-2015-12-687814
3. Whitesides, G. M. The origins and the future of microfluidics. Nature 442, 368–373 (2006).
4. Yager, P. et al. Microfluidic diagnostic technologies for global public health. Nature 442, 412–418 (2006).
5. Chin, C. D. et al. Microfluidics-based diagnostics of infectious diseases in the developing world. Nat. Med. 17, 1015–9 (2011).
6. UNAIDS. HIV: Country facts datasheet. http://www.unaids.org/en/regionscountries/countries/nigeria (2017).
7. Martinez, A. W. et al. Simple telemedicine for developing regions: camera phones and paper-based microfluidic devices for real-time, off-site diagnosis. Anal. Chem. 80, 3699–707 (2008).
8. Martinez, A. W., Phillips, S. T., Whitesides, G. M. & Carrilho, E. Diagnostics for the Developing World: Microfluidic Paper-Based Analytical Devices. Anal. Chem. 82, 3–10 (2010).
9. Nagrath, S. et al. Isolation of rare circulating tumour cells in cancer patients by microchip technology. Nature 450, 1235–9 (2007).
10. Hou, H. W. et al. Isolation and retrieval of circulating tumor cells using centrifugal forces. Sci. Rep. 3, 1259 (2013).
11. Balijepalli, A. & Sivaramakrishan, V. Organs-on-chips: research and commercial perspectives. Drug Discov. Today 22, 397–403 (2017).
12. Benam, K. H. et al. Small airway-on-a-chip enables analysis of human lung inflammation and drug responses in vitro. Nat. Methods 13, 151–7 (2016).
13. Belair, D. G. et al. Human Vascular Tissue Models Formed from Human Induced Pluripotent Stem Cell Derived Endothelial Cells. Stem Cell Rev. Reports 11, 511–525 (2015).
14. Kasendra, M. et al. Development of a primary human Small Intestine-on-a-Chip using biopsy-derived organoids. Sci. Rep. 8, 1–14 (2018).