Search

Mobile sensing based on the integration of microfluidic device and smartphone, so-called MS2 technology, has enabled many applications over recent years, and continues to stimulate growing interest in both research communities and industries. In particular, it has been envisioned that MS2 technology can be developed for various cell functional assays to enable basic research and clinical applications. Toward this direction, in this paper, we describe the development of a MS2-based cell functional assay for testing cell migration (the Mkit). The system is constructed as an integrated test kit, which includes microfluidic chips, a smartphone-based imaging platform, the phone apps for image capturing and data analysis, and a set of reagent and accessories for performing the cell migration assay. We demonstrated that the Mkit can effectively measure purified neutrophil and cancer cell chemotaxis. Furthermore, neutrophil chemotaxis can be tested from a drop of whole blood using the Mkit with red blood cell (RBC) lysis. The effects of chemoattractant dose and gradient profile on neutrophil chemotaxis were also tested using the Mkit. In addition to research applications, we demonstrated the effective use of the Mkit for on-site test at the hospital and for testing clinical samples from chronic obstructive pulmonary disease patient. Thus, this developed Mkit provides an easy and integrated experimental platform for cell migration related research and potential medical diagnostic applications.

Chemotaxis is a classic mechanism for guiding cell migration and an important topic in both fundamental cell biology and health sciences. Neutrophils are a widely used model to study eukaryotic cell migration and neutrophil chemotaxis itself can lead to protective or harmful immune actions to the body. While much has been learnt from past research about how neutrophils effectively navigate through a chemoattractant gradient, many interesting questions remain unclear. For example, while it is tempting to model neutrophil chemotaxis using the well-established biased random walk theory, the experimental proof was challenged by the cell's highly persistent migrating nature. A special experimental design is required to test the key predictions from the random walk model. Another question that has interested the cell migration community for decades concerns the existence of chemotactic memory and its underlying mechanism. Although chemotactic memory has been suggested in various studies, a clear quantitative experimental demonstration will improve our understanding of the migratory memory effect. Motivated by these questions, we developed a microfluidic cell migration assay (so-called dual-docking chip or D2-Chip) that can test both the biased random walk model and the memory effect for neutrophil chemotaxis on a single chip enabled by multi-region gradient generation and dual-region cell alignment. Our results provide experimental support for the biased random walk model and chemotactic memory for neutrophil chemotaxis. Quantitative data analyses provide new insights into neutrophil chemotaxis and memory by making connections to entropic disorder, cell morphology and oscillating migratory response.

Neutrophil migration and chemotaxis are fundamentally important biological processes and have direct relevance to various health problems. Microfluidic devices provide useful experimental tools for the quantitative analysis of neutrophil chemotaxis in controlled microenvironments. However, such experiments often require specialized research facilities and lengthy cell preparation from a large amount of blood. In this paper, we report a new, yet simple, all-on-chip method for the magnetic isolation of untouched neutrophils directly from small volumes of blood, followed by chemotaxis testing on the same microfluidic device. Furthermore, we incorporated a cell-docking structure to the microfluidic device for better control of the cells’ initial positions before the chemotaxis test and for improved data analysis. The whole experiment can be performed in less than 25 minutes. We successfully validated this method by testing neutrophil chemotaxis to both purified chemoattractant (i.e. fMLP) and clinical samples (sputum from patients with Chronic Obstructive Pulmonary Disease, COPD). Thus, the “all-on-chip” method can be a useful tool for research and clinical applications that require rapid and accurate chemotaxis testing of untouched neutrophils.

Chronic obstructive pulmonary disease (COPD) is a common lung disease characterized by narrowed airways, resulting in serious breathing difficulty. Previous studies have demonstrated that inflammatory infiltration of leukocytes in the airway is associated with the pathogenesis of COPD. In the present study, we employed a microfluidic approach to assess the effect of COPD sputum on activated human peripheral blood T cell migration and chemotaxis under well-controlled gradient conditions. Our results showed considerable basal migration of T cells derived from peripheral blood of COPD patients and healthy controls in the medium control groups. By contrast, the migration of T cells from COPD patients and healthy controls was significantly inhibited in the presence of a gradient of sputum supernatant from COPD patients. Furthermore, chemotaxis of T cells from COPD patients or healthy subjects toward an SDF-1α gradient was clearly inhibited by sputum samples from the COPD patients. The inhibition effect revealed by the microfluidic cell migration experiments provides new information about the complex involvement of T cell trafficking in COPD.

Chemotaxis is a classic mechanism for guiding cell migration and an important topic in both fundamental cell biology and health science. Neutrophil is a widely used model to study eukaryotic cell migration and neutrophil chemotaxis itself can lead to protective or harmful immune actions to the body. While much has been learnt from past research about how neutrophils effectively navigate through a chemoattractant gradient, many interesting questions remain unclear. For example, while it is tempting to model neutrophil chemotaxis using the well-established biased random walk theory, the experimental proof was challenged by the cell’s highly persistent migration nature. Special experimental design is required to test the key predictions from the random walk model. Another question that interests the cell migration community for decades concerns the existence of chemotactic memory and its underlying mechanism. Although chemotactic memory has been suggested in various studies, a clear quantitative experimental demonstration will improve our understanding of the migratory memory effect. Motivated by these questions, we developed a microfluidic cell migration assay (so-called dual-docking chip or D2-Chip) that can test both the biased random walk model and the memory effect for neutrophil chemotaxis on a single chip enabled by multi-region gradient generation and dual-region cell alignment. Our results provide experimental support for the biased random walk model and chemotactic memory for neutrophil chemotaxis. Quantitative data analyses generate new insights into neutrophil chemotaxis and memory by making connections to entropic disorder, cell morphology and oscillating migratory response.

Mobile sensing based on the integration of microfluidic device and smartphone, so-called MS2 technology, has enabled many applications over recent years, and continues to stimulate growing interest in both research communities and industries. In particular, it has been envisioned that MS2 technology can be developed for various cell functional assays to enable basic research and clinical applications. Toward this direction, in this paper, we describe the development of a MS2-based cell functional assay for testing cell migration (the Mkit). The system is constructed as an integrated test kit, which includes microfluidic chips, a smartphone-based imaging platform, the phone apps for image capturing and data analysis, and a set of reagent and accessories for performing the cell migration assay. We demonstrated that the Mkit can effectively measure purified neutrophil and cancer cell chemotaxis. Furthermore, neutrophil chemotaxis can be tested from a drop of whole blood using the Mkit with red blood cell (RBC) lysis. The effects of chemoattractant dose and gradient profile on neutrophil chemotaxis were also tested using the Mkit. In addition to research applications, we demonstrated the effective use of the Mkit for on-site test at the hospital and for testing clinical samples from chronic obstructive pulmonary disease patient. Thus, this developed Mkit provides an easy and integrated experimental platform for cell migration related research and potential medical diagnostic applications.

Netrin-1 is well-known for its chemoattractive and chemorepulsive properties for axon guidance. Early studies report that netrin-1 inhibits granulocyte migration. On the other hand, netrin-1 can promote cancer cell migration and invasion. The underlying mechanisms are not well understood, which requires more in-depth characterizations of netrin-1 mediated immune and cancer cell migration. The present study, for the first time, employs microfluidic devices that are recently developed to quantitatively investigate the effects of netrin-1 on the motility and chemotaxis of human blood neutrophils and human breast cancer cells under well-controlled gradient conditions. The results show that netrin-1 reduces chemokinetic motility of human neutrophils, which is accompanied with reduced cell polarization and spreading. In addition, netrin-1 reduces neutrophil chemotaxis to N-formyl-Met-Leu-Phe on fibronectin substrate but interestingly not on collagen substrate. By contrast, netrin-1 promotes the migration of human breast cancer cells. Furthermore, it is found that netrin-1 reduces neutrophil chemotaxis to the supernatant of human breast cancer cell culture. Collectively, this microfluidic cell migration study provides quantitative characterizations of the effects of netrin-1 on the motility and chemotaxis of neutrophils and breast cancer cells, and further suggests the potential role of netrin-1 in regulating neutrophil recruitment to breast cancer microenvironments.