Development of a microfluidic cell-based biosensor integrating a millisecond chemical pulse generator

A Microfluidic Array Device for Single Cell Capture and Intracellular Ca2+ Response Analysis Induced by Dynamic Biochemical Stimulus

A microfluidic array was constructed for trapping single cell and loading identical dynamic biochemical stimulation for gain a better understanding of Ca2+ signalling in single cells by applying extracellular dynamic biochemical stimulus. This microfluidic array consists of multiple radially aligned flow channels with equal intersection angles, which was designed by a combination of stagnation point flow and physical barrier. Numerical simulation results and trajectory analysis shown the effectiveness of this single cell trapping device. Fluorescent experiment results demonstrated the effects of flow rate and frequency of dynamic stimulus on the profiles of biochemical concentration which exposed on captured cells. In this array chip, the captured single cells in each trapping channels were able to receive identical extracellular dynamic biochemical stimuli which being transmitted from the entrance at the middle of the microfluidic array. Besides, after loading dynamic Adenosine Triphosphate (ATP) stimulation on captured cells by this device, consistent average intracellular Ca2+ dynamics phase and cellular heterogeneity were observed in captured single K562 cells. Furthermore, this device is able to be used for investigating cellular respond in single cells to temporally varying environments by modulating the stimulation signal in terms of concentration, pattern, and duration of exposure.

A review on microfluidics manipulation of the extracellular chemical microenvironment and its emerging application to cell analysis

Spatiotemporal manipulation of extracellular chemical environments with simultaneous monitoring of cellular responses plays an essential role in exploring fundamental biological processes and expands our understanding of underlying mechanisms. Despite the rapid progress and promising successes in manipulation strategies, many challenges remain due to the small size of cells and the rapid diffusion of chemical molecules. Fortunately, emerging microfluidic technology has become a powerful approach for precisely controlling the extracellular chemical microenvironment, which benefits from its integration capacity, automation, and high-throughput capability, as well as its high resolution down to submicron. Here, we summarize recent advances in microfluidics manipulation of the extracellular chemical microenvironment, including the following aspects: i) Spatial manipulation of chemical microenvironments realized by convection flow-, diffusion-, and droplet-based microfluidics, and surface chemical modification; ii) Temporal manipulation of chemical microenvironments enabled by flow switching/shifting, moving/flowing cells across laminar flows, integrated microvalves/pumps, and droplet manipulation; iii) Spatiotemporal manipulation of chemical microenvironments implemented by a coupling strategy and open-space microfluidics; and iv) High-throughput manipulation of chemical microenvironments. Finally, we briefly present typical applications of the above-mentioned technical advances in cell-based analyses including cell migration, cell signaling, cell differentiation, multicellular analysis, and drug screening. We further discuss the future improvement of microfluidics manipulation of extracellular chemical microenvironments to fulfill the needs of biological and biomedical research and applications.

A microfluidic platform with pneumatically switchable single-cell traps for selective intracellular signals probing

To investigate rapid suspension cell signaling, a microfluidic platform was urgently needed for flexibly manipulation of single cells and simultaneous generation of controllable chemical signals to stimulate single cells. In this paper, a microfluidic biosensor was developed to monitor intracellular calcium signal, integrated with single-cell trapping, chemical stimulation and releasing. Selective entrapment and discharge of individual cell were achieved by controlling the deformable membrane with pneumatic traps. The activation of intracellular calcium signal was qualitatively and quantitatively investigated by high-controllable chemical single-cell stimulation based on flexible hydrodynamic gating. And performing chemical stimulation and control assay in the same channel would improve the experimental robustness and effectiveness. Further investigation of the cellular responses to ATP pulses of varying concentrations and durations indicated that 20 μM ATP pulses with duration as short as 200 ms resulted in the same level of Ca²⁺ response induced by sustained stimulations. Washing with buffer for 30 s was sufficient for single cell to recover from receptor desensitization caused by ATP stimulation. In addition, the responses of cells to ATP stimulation were heterogeneous. The developed microfluidic method opens up a new avenue for intracellular signaling studies and drug screening.

Active droplet sorting in microfluidics: a review

The ability to manipulate and sort droplets is a fundamental issue in droplet-based microfluidics. Various lab-on-a-chip applications can only be realized if droplets are systematically categorized and sorted. These micron-sized droplets act as ideal reactors which compartmentalize different biological and chemical reagents. Array processing of these droplets hinges on the competence of the sorting and integration into the fluidic system. Recent technological advances only allow droplets to be actively sorted at the rate of kilohertz or less. In this review, we present state-of-the-art technologies which are implemented to efficiently sort droplets. We classify the concepts according to the type of energy implemented into the system. We also discuss various key issues and provide insights into various systems.

Cellular Architecture Regulates Collective Calcium Signaling and Cell Contractility

A key feature of multicellular systems is the ability of cells to function collectively in response to external stimuli. However, the mechanisms of intercellular cell signaling and their functional implications in diverse vascular structures are poorly understood. Using a combination of computational modeling and plasma lithography micropatterning, we investigate the roles of structural arrangement of endothelial cells in collective calcium signaling and cell contractility. Under histamine stimulation, endothelial cells in self-assembled and microengineered networks, but not individual cells and monolayers, exhibit calcium oscillations. Micropatterning, pharmacological inhibition, and computational modeling reveal that the calcium oscillation depends on the number of neighboring cells coupled via gap junctional intercellular communication, providing a mechanistic basis of the architecture-dependent calcium signaling. Furthermore, the calcium oscillation attenuates the histamine-induced cytoskeletal reorganization and cell contraction, resulting in differential cell responses in an architecture-dependent manner. Taken together, our results suggest that endothelial cells can sense and respond to chemical stimuli according to the vascular architecture via collective calcium signaling.

Droplet microfluidics in (bio)chemical analysis

Droplet microfluidics may soon change the paradigm of performing chemical analyses and related instrumentation.

A microfluidic digital single-cell assay for the evaluation of anticancer drugs

Digital single-cell assays hold high potentials for the analysis of cell apoptosis and the evaluation of chemotherapeutic reagents for cancer therapy. In this paper, a microfluidic hydrodynamic trapping system was developed for digital single-cell assays with the capability of monitoring cellular dynamics over time. The microfluidic chip was designed with arrays of bypass structures for trapping individual cells without the need for surface modification, external electric force, or robotic equipment. After optimization of the bypass structure by both numerical simulations and experiments, a single-cell trapping efficiency of ∼90 % was achieved. We demonstrated the method as a digital single-cell assay for the evaluation of five clinically established chemotherapeutic reagents. As a result, the half maximal inhibitory concentration (IC50) values of these compounds could be conveniently determined. We further modeled the gradual decrease of active drugs over time which was often observed in vivo after an injection to investigate cell apoptosis against chemotherapeutic reagents. The developed method provided a valuable means for cell apoptotic analysis and evaluation of anticancer drugs.

Encapsulation of single cells on a microfluidic device integrating droplet generation with fluorescence-activated droplet sorting

Encapsulation of single cells is a challenging task in droplet microfluidics due to the random compartmentalization of cells dictated by Poisson statistics. In this paper, a microfluidic device was developed to improve the single-cell encapsulation rate by integrating droplet generation with fluorescence-activated droplet sorting. After cells were loaded into aqueous droplets by hydrodynamic focusing, an on-flight fluorescence-activated sorting process was conducted to isolate droplets containing one cell. Encapsulation of fluorescent polystyrene beads was investigated to evaluate the developed method. A single-bead encapsulation rate of more than 98 % was achieved under the optimized conditions. Application to encapsulate single HeLa cells was further demonstrated with a single-cell encapsulation rate of 94.1 %, which is about 200 % higher than those obtained by random compartmentalization. We expect this new method to provide a useful platform for encapsulating single cells, facilitating the development of high-throughput cell-based assays.

Analysis of intercellular calcium signaling using microfluidic adjustable laminar flow for localized chemical stimulation

The propagation of intercellular calcium signals provides a mechanism to coordinate cell population activity, which is essential for regulating cell behavior and organ development. However, existing analytical methods are difficult to realize localized chemical stimulation of a single cell among a population of cells that are in close contact with one another for studying the propagation of calcium wave. In this work, a microfluidic method is presented for the analysis of contact-dependent propagation of intercellular calcium wave induced by extracellular ATP using multiple laminar flows. Adjacent cells were seeded ∼300 μm downstream the intersection of a Y-shaped microchannel with negative pressure pulses. Consequently, the lateral diffusion distance of the chemical at cell locations was limited to ∼26 μm with a total flow rate of 20 μL min(-1), which prevented the interference of diffusion-induced cellular responses. Localized stimulation of the target cell with ATP induced the propagation of intercellular calcium wave among the cell population. In addition, studies on the spread of intercellular calcium wave under octanol inhibition allowed us to characterize the gap junction mediated cell-cell communication. Thus, this novel device will provide a versatile platform for intercellular signal transduction studies and high throughput drug screening.