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Dongqing Li

Publications and source records attributed to Dongqing Li.

At least 19 recordsLinked to original sources
PubMed2024

Spatiotemporal single-cell roadmap of human skin wound healing.

Wound healing is vital for human health, yet the details of cellular dynamics and coordination in human wound repair remain largely unexplored. To address this, we conducted single-cell multi-omics analyses on human skin wound tissues through inflammation, proliferation, and remodeling phases of wound repair from the same individuals, monitoring the cellular and molecular dynamics of human skin wound healing at an unprecedented spatiotemporal resolution. This singular roadmap reveals the cellular architecture of the wound margin and identifies FOSL1 as a critical driver of re-epithelialization. It shows that pro-inflammatory macrophages and fibroblasts sequentially support keratinocyte migration like a relay race across different healing stages. Comparison with single-cell data from venous and diabetic foot ulcers uncovers a link between failed keratinocyte migration and impaired inflammatory response in chronic wounds. Additionally, comparing human and mouse acute wound transcriptomes underscores the indispensable value of this roadmap in bridging basic research with clinical innovations.

Humans↗
PubMed2007

Three-dimensional modeling of transport of nutrients for multicellular tumor spheroid culture in a microchannel.

The growth dynamics of avascular tumors in a microchannel bioreactor is investigated. A three-dimensional flow and nutrient transport model, incorporating the multicellular tumor spheroid (MTS) growth model, has been developed to study the influence of nutrients (oxygen and glucose) supply and distribution on the MTS growth. Numerical simulations based on the EMT6/Ro tumor cells show that the continuous-flow perfusion is more efficient to deliver nutrients to the MTS than the diffusion-only static culture. It is further demonstrated that as long as there is bulk flow, the growth of a single tumor spheroid at the early stage is insensitive to the flow velocity and the channel size. For multiple tumor spheroids in the same microchannel, however, increasing the perfusion velocity can improve the nutrient environment for the disadvantageous downstream tumor spheroid. The flow shear stress exerting on the MTSs in the current microchannel bioreactor is estimated to be far below the critical value to affect the MTS growth, which means that there is still much room for increasing perfusion velocity to satisfy the higher nutrient requirement by the growing tumor spheroids.

Animals↗
PubMed2006

Modeling micropatterned antigen-antibody binding kinetics in a microfluidic chip.

The reaction kinetics of antigen-antibody binding in the electrokinetically controlled microfluidic heterogeneous immunoassays has been investigated by numerical simulations. A two-dimensional computational model was employed to include the mass transport (convection and diffusion) and binding reaction between the antigen in the bulk flow and the immobilized antibody at the channel surface. The influence of the bulk velocity, the concentrations of the antibody and antigen, and the geometry of the microchips was studied for a variation of conditions and the guidance for designing of microfluidic immunoassay was provided. The model also shows that electrokinetically driven immunoassays have better reaction kinetics than pressure-driven ones, resulting from the plug-like velocity profile. Finally, a multi-patch immunoassay chip was analyzed and the reaction kinetics was optimized by rearranging the reaction patches at the channel surfaces.

Antigen-Antibody Complex↗
PubMed2006

A microfluidic fluorous solid-phase extraction chip for purification of amino acids.

An electrokinetically-driven microfluidic chip was developed to realize beads-based solid-phase extraction (SPE) of amino acids. This chip uses a two-level (deep/shallow) poly(dimethylsiloxane) (PDMS) microchannel network to confine the fluorous reversed-phase silica beads within the SPE chamber. The mixture of fluorous tagged and non-tagged amino acids was carried into the fluorous solid-phase extraction (F-SPE) chamber by electrokinetic pumping and was successfully separated and extracted. By adding a reference material to the sample, the extraction efficiency of the eluted fluorous-tagged amino acid was calculated using the detection results from mass spectrometry (MS). The F-SPE microchips showed good reproducibility and efficiency, yielding an average extraction efficiency of 55% with a RSD of 10.6% under the typical experimental conditions.

Amino Acids↗
PubMed2006

Dielectric force and relative motion between two spherical particles in electrophoresis.

When two particles close to each other are in electrophoretic motion, each particle is under the influence of the nonuniform electric field generated by the other particle. Two particles may attract or repel each other due to the dielectric force, depending on their positions in the nonuniform electric field. In this work, the dielectric interaction and the subsequent relative motion of the two arbitrarily oriented spherical particles are analyzed. The dielectric force is obtained by integrating the Maxwell stress. The result is valid for arbitrary orientations of the particles under the thin electrical-double-layer assumption. The magnitude of the dielectric force is compared to the so-called inertia-induced force, which shows that the dielectric force is normally much greater than the inertia-induced force. The relative velocity of particles is determined by the force balance between the dielectric force and the Stokes drag. The regions of attraction and repulsion are defined. It is shown that a pair of particles eventually aligns parallel to the externally applied electric field, except in the case where the two particles are initially oriented perpendicular to the electric field. A closed-form analytical solution is obtained for the particle trajectory by using the approximate expression for the dielectric force valid for not-too-closely located particles.

Journal Article↗
PubMed2006

Continuous separation of microparticles by size with direct current-dielectrophoresis.

Direct current-dielectrophoresis (DC-DEP), the induced motion of the dielectric particles in a spatially nonuniform DC electric field, is demonstrated to be a highly efficient method to separate the microparticles by size. The locally nonuniform electric field is generated by an insulating block fabricated inside a polydimethylsiloxane microchannel. The particle experiences a negative DEP (accordingly a repulsive force) at the corners of the block, where the local electric-field strength is the strongest. Thus, the particle deviates from the streamline and the degree of deviation is dependent on the DEP force (i.e., the particle size). Combined with the electrokinetic flow, mixed polystyrene particles of a few micrometers difference in diameter can be continuously separated into distinct reservoirs. For separating target particles of a specific size, it is required to simply adjust the voltage outputs of the electrodes. A numerical model based on the Lagrangian tracking method is developed to simulate the particle motion and the results showed a reasonable agreement with the experimental data.

Electrophoresis↗
PubMed2006

Joule heating effects on separation efficiency in capillary zone electrophoresis with an initial voltage ramp.

An analytical model is developed to quantify the Joule heating effects on the separation efficiency in CZE with an initial voltage ramp. This model considers the temporal variations of nonuniform temperature and flow fields in the course of voltage ramping. The temperature dependence of electrical conductivity, dynamic viscosity, and mass density of the fluid is also taken into account. We demonstrate that the application of an initial voltage ramp delays the development of pressure-driven flows induced passively by the axial temperature gradients. The thermal dispersion is thus significantly reduced, resulting in a higher theoretical plate number in CZE. Such improvement in the separation efficiency is apparent in noncoated capillaries at high electric fields with an appropriate voltage ramp-up time. These predictions are consistent with previous observations in both aqueous and nonaqueous CZE that took place in uncoated capillaries. In coated capillaries where the EOF is suppressed, however, our model predicts a lower plate number in the presence of an initial voltage ramp.

Electricity↗
PubMed2006

Electrokinetic transport of charged solutes in micro- and nanochannels: the influence of transverse electromigration.

The accurate prediction of electrokinetic migration velocity and dispersion is crucial to separating electrophoretically charged solutes in micro- or nanochannels. In this paper, we investigate numerically the influence of transverse electromigration (TEM) on the solute electrokinetic transport in a series of micro- and nanochannels. The TEM, often ignored in previous studies, is demonstrated to significantly affect the solute migration velocity in nanochannels and the electrokinetic dispersion in microchannels. This is because the TEM can force either positively charged solutes into or negatively charged solutes out of the electrical double layer that forms adjacent to the negatively charged channel wall and contains the velocity gradients. Analytical solutions are also derived for characterizing the electrokinetic transport of charged solutes in nanochannels, which has been validated to be in good agreement with the numerical simulation. Moreover, we demonstrate that the proposed analytical formula for the solute migration velocity actually applies to channels of any size.

Electrophoresis↗
PubMed2005

DC-dielectrophoretic separation of microparticles using an oil droplet obstacle.

A new dielectrophoretic particle separation method is demonstrated and examined in the following experimental study. Current electrodeless dielectrophoretic (DEP) separation techniques utilize insulating solid obstacles in a DC or low-frequency AC field, while this novel method employs an oil droplet acting as an insulating hurdle between two electrodes. When particles move in a non-uniform DC field locally formed by the droplet, they are exposed to a negative DEP force linearly dependent on their volume, which allows the particle separation by size. Since the size of the droplet can be dynamically changed, the electric field gradient, and hence DEP force, becomes easily controllable and adjustable to various separation parameters. By adjusting the droplet size, particles of three different diameter sizes, 1 microm, 5.7 microm and 15.7 microm, were successfully separated in a PDMS microfluidic chip, under applied field strength in the range from 80 V cm-1 to 240 V cm-1. A very effective separation was realized at the low field strength, since the electric field gradient was proved to be a more significant parameter for particle discrimination than the applied voltage. By utilizing low strength fields and adaptable field gradient, this method can also be applied to the separation of biological samples that are generally very sensitive to high electric potential.

Electrophoresis, Microchip↗
PubMed2005

Dielectrophoretic force on a sphere near a planar boundary.

The small gap distance separating a spherical colloidal particle in electrophoretic motion from a planar nonconducting surface is a required parameter for calculating its electrophoretic mobility. In the presence of an externally applied electric field, this gap distance is determined by balancing the van der Waals, electrical double layer interaction, and gravitational forces with a dielectrophoretic (DEP) force. Here, the DEP force was determined analytically by integration of the Maxwell stress over the surface of the particle. The account of this force showed that its previous omission from the analysis always resulted in underpredicted gap distances. Furthermore, the DEP force dominated under conditions of low particle density or high electric field strength and led to much higher gap distances on the order of a few microns. In one particular case, a combination of low particle density and small particle size produced two possible equilibrium gap distances for the particle. However, the particle was unstable in the second equilibrium position when subjected to small perturbations. In general, larger particles had smaller gap sizes. The effects of four other parameters on gap distance were studied, and gap distances were found to increase with lower particle density, higher electric field strength, higher particle and wall zeta potentials, and lower Hamaker constants. Retardation effects on van der Waals attraction were considered.

Electrophoresis↗
PubMed2005

Miniaturized immunoassay microfluidic system with electrokinetic control.

A portable heterogeneous immunoassay system is presented in this paper. It consists of a poly(dimethylsiloxane) (PDMS) based microfluidic chip as the immunoreactor, a miniaturized programmable high voltage sequencer as the power supply and the flow controller, and a laser-optical fiber fluorescence detection module as the signal reader. The operation of this immunoassay system is automatic. The sequential reagent dispensing and washing processes are controlled by the programmable sequencer. The reagent consumption was only 12 microL and the assay time was only 26 min. The detection limit for Escherichia coli O157:H7 bacterial antigen with this miniaturized system was 0.3 ng/muL, lower than that obtained using fluorescence microscope in previous studies.

Antigens, Bacterial↗
PubMed2005

Wall effects on electrophoretic motion of spherical polystyrene particles in a rectangular poly(dimethylsiloxane) microchannel.

The wall effects on electrophoretic motion of spherical polystyrene particles in a rectangular poly(dimethylsiloxane) microchannel were studied experimentally. It is found that the particle electrophoretic velocity is insensitive to the trajectory between the channel sidewalls, consistent with the theoretical prediction. We also demonstrate that the electrophoretic motion of larger particles along the channel centerline is more viscously retarded by the sidewalls of a narrower channel. This observation is well predicted by incorporating the analytical models for the particle electrophoresis along the centerline of a slit channel and along the axis of a cylindrical pore.

Journal Article↗
PubMed2005

Near-wall electrophoretic motion of spherical particles in cylindrical capillaries.

In this paper, near-wall electrophoretic motion of spherical particles in cylindrical capillaries was experimentally investigated. It is demonstrated that same-sized particles move faster in smaller capillaries. This observation verifies the theoretical prediction of the wall enhancing effect in our recent paper (C. Ye, X. Xuan, D. Li, Microfluid. Nanofluid. 1 (2005)). Our experiments show that this wall enhancing effect becomes more significant when the size difference between particle and capillary becomes smaller and when a dilute electrolyte solution (i.e., thicker electric double layer) is used.

Journal Article↗
PubMed2005

Electroosmotic flow in microchannels with arbitrary geometry and arbitrary distribution of wall charge.

General solutions are developed for direct current (DC) and alternating current (AC) electroosmotic flows in microfluidic channels with arbitrary cross-sectional geometry and arbitrary distribution of wall charge (zeta potential). The applied AC electric field can also be of arbitrary waveform. By proposing a nondimensional time scale varpi defined as the ratio of the diffusion time of momentum across the electric double-layer thickness to the period of the applied electric field, we demonstrate analytically that the Helmholtz-Smoluchowski electroosmotic velocity is an appropriate slip condition for AC electroosmotic flows in typical microfluidic applications. With this slip condition approach, electroosmotic flows in rectangular and asymmetric trapezoidal microchannels with nonuniform wall charge, as examples, are investigated. The unknown constants in the proposed general solutions are numerically determined with a least-squares method through matching the boundary conditions. We find that the wall charge affects significantly the electroosmotic flow while the channel geometry does not. Moreover, the flow feature is characterized by another nondimensional time scale Omega defined as the ratio of the diffusion time of momentum across the channel hydraulic radius to the period of the applied electric field. The onset of phase shift between AC electroosmotic velocity and applied electric field is also examined analytically.

Journal Article↗
PubMed2005

Electrokinetic sample transport in a microchannel with spatial electrical conductivity gradients.

Studies of the sample transport in a microchannel with the electrical conductivity gradient are critical to develop techniques for on-chip sample transport control. A numerical model presented in this paper, consisting of the electrical potential equation, full Navier-Stokes equation and species conservation equation, is used to simulate sample transport in a microchannel with the consideration of the conductivity gradient. There are two situations studied here, sample pumping (where sample separation is minimized by employing a high-conductivity buffer in the sample region), and sample stacking (where sample separation is expedited by using a low-conductivity buffer as the sample carrier). The effects of applied electrical potential, sample diffusion coefficient and the ratio of conductivity of the driving buffer over the sample carrying buffer are investigated by using the developed model.

Buffers↗
PubMed2005

Electrokinetic generation of temporally and spatially stable concentration gradients in microchannels.

Generating stable microscale concentration gradients is key to numerous biological and chemical analyses. Microfluidic systems offer the ability to maintain laminar fluid diffusion interfaces ideal for the production of temporally stable concentration gradients. Previous efforts have focused on pressure driven flows and have relied on networks of branching channels to create streams of varying concentrations which can subsequently be combined to form the desired gradients. In this study, we numerically and experimentally demonstrate a novel electrokinetic technique which utilizes applied voltages and surface charge heterogeneity in simpler channel geometries to control and manipulate microscale concentration gradients without the need for parallel lamination. Flow rates ranged from 30 to 460 nl min(-1) for Peclet numbers between 70 and 1100. Spatial stability of 0.6 mm or greater was obtained for a wide range of gradient shapes and magnitudes over lateral dimensions of 400-450 microm. Sensitivity analysis determined that this technique is largely independent of channel depth and species electrophoretic mobility, however channel width and the diffusion coefficient of the analyte are critical. It was concluded that by adjusting applied voltages and/or channel width, this approach to concentration gradient generation can be adapted to a wide range of applications.

Journal Article↗
PubMed2005

Accelerated particle electrophoretic motion and separation in converging-diverging microchannels.

Accelerated particle electrophoretic motions were visualized in converging-diverging microchannels on poly(dimethylsiloxane) chips. The accelerated particle electrophoretic separation is highly desirable in on-chip flow cytometry and high-speed electrophoresis. The effects of electric field, particle size, particle trajectory, and channel structure on the particle electrophoretic motion are examined. We find that the ratio of the particle velocity in the throat to that in the straight channel is significantly lower than their cross-sectional area ratio. This discrepancy may be attributed to the locally higher electric field around the two poles of a particle, as compared to other regions inside the microchannel. We also find that the particle velocity ratio is increased for smaller particles moving through symmetric converging-diverging channels under lower electric fields. These variations may be attributed to the negative dielectrophoretic force that is generated by the nonuniform electric field in the converging-diverging section. In addition, we find that particle trajectory has insignificant influences on the maximum velocity ratio obtained in the throat.

Journal Article↗