Yiwei Li

Rapid Assembly of Heterogeneous 3D Cell Microenvironments in a Microgel Array.

Heterogeneous 3D cell microenvironment arrays are rapidly assembled by combining surface-wettability-guided assembly and microdroplet-array-based operations. This approach enables precise control over individual shapes, sizes, chemical concentrations, cell density, and 3D spatial distribution of multiple components. This technique provides a cost-effective solution to meet the increasing demand of stem cell research, tissue engineering, and drug screening.

Agarose-based microfluidic device for point-of-care concentration and detection of pathogen.

Preconcentration of pathogens from patient samples represents a great challenge in point-of-care (POC) diagnostics. Here, a low-cost, rapid, and portable agarose-based microfluidic device was developed to concentrate biological fluid from micro- to picoliter volume. The microfluidic concentrator consisted of a glass slide simply covered by an agarose layer with a binary tree-shaped microchannel, in which pathogens could be concentrated at the end of the microchannel due to the capillary effect and the strong water permeability of the agarose gel. The fluorescent Escherichia coli strain OP50 was used to demonstrate the capacity of the agarose-based device. Results showed that 90% recovery efficiency could be achieved with a million-fold volume reduction from 400 μL to 400 pL. For concentration of 1 × 10(3) cells mL(-1) bacteria, approximately ten million-fold enrichment in cell density was realized with volume reduction from 100 μL to 1.6 pL. Urine and blood plasma samples were further tested to validate the developed method. In conjugation with fluorescence immunoassay, we successfully applied the method to the concentration and detection of infectious Staphylococcus aureus in clinics. The agarose-based microfluidic concentrator provided an efficient approach for POC detection of pathogens.

Microfluidic Chemical Function Generator for Probing Dynamic Cell Signaling

Cellular environments are inherently dynamic and generally involve complex, temporally varying signals. Reconstruction of these environments with high spatial and temporal fidelity and simultaneous imaging of intracellular dynamics in live cells remains a major challenge. In this paper, a microfluidic chemical function generator (μCFG) was proposed for probing cell dynamic signaling with high temporal resolution. By combining a hydrodynamic gating module with a chaotic advection mixing module, the μCFG was able to generate a variety of chemical waveforms, such as digital pulsatile chemical waveforms with a frequency higher than 10 Hz and analog chemical waveforms with a frequency higher than 0.2 Hz. The shape, frequency, amplitude, and duty cycle of the waveforms could be also conveniently modulated. To demonstrate the capability of μCFG of probing fast biological processes and elucidate signal transduction pathways in complex signaling networks, a variety of temporal responses of Ca2+ signaling to ATP-induced activation of the P2Y receptor, a prototypical G-protein coupled receptor (GPCR), were investigated in live cells by precisely and dynamically controlling their microenvironment.