Biomedical subjects

Guoqing Hu

Publications and source records attributed to Guoqing Hu.

8 recordsLinked to original sources

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

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↗

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

Analysis of DNA ploidy, cell cycle and Ki67 antigen in nasopharyngeal carcinoma by flow cytometry.

The expression of DNA ploidy, the cell cycle and Ki67 antigen in nasopharyngeal carcinoma (NPC) were studied and their relationship with the clinical biological behaviors and prognosis of NPC was evaluated. Biopsied specimens of NPC were made into cell suspension. By using cytometric double labeling Ki67 and DNA method, the expression of DNA ploidy, the cell cycle and Ki67 antigen were analyzed. The patients were followed-up for about 3 years and the relationship between the above-mentioned parameters and the clinical biological behavior and prognosis of NPC were evaluated. Of the 62 cases of NPC, the DNA aneuploid accounted for 29.03%. The S phase cells accounted for 0 to 54% in the cell cycle and the positive expression of Ki67 ranged from 0 to 52%. There were 40 cases of LPI (64.5%) including 15 negative cases and 22 cases of HPI (35.5%) respectively. The DNA anueploid content was positively related to the S phase cells. The patients having a low expression of Ki67 or DNA aneuploid in tumor cells were not sensitive to chemotherapy, liable to metastasis to distant organs and had a poor prognosis, while Ki67 showed no correlation with DNA ploidy and the cell cycle. It was suggested that DNA ploidy and Ki67 could be used as an independent and objective marker to evaluate the radiosensitivity and prognosis of NPC.

Adult↗

PubMed2005

An electrokinetically-controlled immunoassay for simultaneous detection of multiple microbial antigens.

An electrokinetically-controlled heterogeneous immunoassay microchip for multiple analyte detection was developed in this study. Numerical simulation was employed to study the transport process in a microfluidic network (microFN). The operation parameters obtained from numerical simulation was then applied to immunoassay experiment. The effectiveness of the automatic electrokinetic control was demonstrated in a separate experiment using fluorescein dye. The immunoassay microchip was made of poly(dimethylsiloxane)(PDMS)/PDMS-coated glass using soft lithography and replica molding. Multi-antigen immobilization was accomplished by adsorbing the antigen molecules onto a PDMS-coated glass slide and by using a microFN. Immobilized lysate antigen of Escherichia coli O157: H7 at different concentrations was assayed and the lower detect limit was 3 microg/mL. The assay also displayed very good specificity, when different microbial lysate antigens were immobilized, including Escherichia coli and Helicobacter pylori, and the primary and secondary antibodies were mixtures of different species. The time required for the immunoassay, from antigen coating to signal detection, was only one hour. While still an un-optimized prototype, this automatic-operating, high-throughput immunoassay microchip shows a great potential in detecting multiple pathogenic infections efficiently for clinical applications.

Antigens, Bacterial↗

PubMed2005

Smooth muscle-specific genes are differentially sensitive to inhibition by Elk-1.

Understanding the mechanism of smooth muscle cell (SMC) differentiation will provide the foundation for elucidating SMC-related diseases, such as atherosclerosis, restenosis, and asthma. In the current study, overexpression of Elk-1 in SMCs down-regulated expression of several endogenous smooth muscle-restricted proteins, including telokin, SM22alpha, and smooth muscle alpha-actin. In contrast, down-regulation of endogenous Elk-1 in smooth muscle cells increased the expression of only telokin and SM22alpha, suggesting that smooth muscle-specific promoters are differentially sensitive to the inhibitory effects of Elk-1. Consistent with this, overexpression of the DNA binding domain of Elk-1, which acts as a dominant-negative protein by displacing endogenous Elk-1, enhanced the expression of telokin and SM22alpha without affecting expression of smooth muscle alpha-actin. Elk-1 suppressed the activity of smooth muscle-restricted promoters, including the telokin promoter that does not contain a consensus Elk-1 binding site, through its ability to block myocardin-induced activation of the promoters. Gel mobility shift and chromatin immunoprecipitation assays revealed that Elk-1 binds to a nonconsensus binding site in the telokin promoter and Elk-1 binding is dependent on serum response factor (SRF) binding to a nearby CArG box. Although overexpression of the SRF-binding B-box domain of Elk-1 is sufficient to repress the myocardin activation of the telokin promoter, this repression is not as complete as that seen with an Elk-1 fragment that includes the DNA binding domain. In addition, reporter gene assays demonstrate that an intact Elk-1 binding site in the telokin promoter is required for Elk-1 to maximally inhibit promoter activity. Together, these data suggest that the differential sensitivity of smooth muscle-specific genes to inhibition by Elk-1 may play a role in the complex changes in smooth muscle-specific protein expression that are observed under pathological conditions.

Actins↗