Porous membranes have been fabricated based on the development of the perforated membrane mold [Y. Luo and R. N. Zare, Lab Chip, 2008, 8, 1688-1694] to create a single filter that contains multiple pore sizes ranging from 6.4 to 16.6 µm inside a monolithic three-dimensional poly(dimethylsiloxane) microfluidic structure. By overlapping two filters we are able to achieve smaller pore size openings (2.5 to 3.3 µm). This filter operates without any detectable irreversible clogging, which is achieved using a cross-flow placed in front of each filtration section. The utility of a particle-sorting device that contains this filter is demonstrated by separating polystyrene beads of different diameters with an efficiency greater than 99.9%. Additionally, we demonstrate the effectiveness of this particle-sorting device by separating whole blood samples into white blood cells and red blood cells with platelets.

In this work, we developed a microfluidic device for the imitation of drug metabolism in human liver and its cytotoxicity on cells. The integrated microfluidic device consists of three sections: (1) bioreactors containing poly(ethylene) glycol (PEG) hydrogel encapsulated human liver microsomes (HLMs); (2) cell culture chambers for cytotoxicity assay; and (3) integrated micro solid-phase extraction (SPE) columns to desalt and concentrate the products of enzymatic reaction. To verify the feasibility of the integrated microchip, we studied uridine 5'-diphosphate-glucuronosyltransferase (UGT) metabolism of acetaminophen (AP) and the cytotoxicity of products on HepG2 cells. The products of the reaction in one region of the device were injected into the cell culture chamber for cytotoxicity assay, while those in another region were directly detected online with an electrospray ionization quadrupole time-of-flight mass spectrometer (ESI-Q-TOF MS) after micro-SPE pre-treatment. Semiquantitative analysis achieved in the experiments could be related to the drug-induced HepG2 cell cytotoxicity. Total analysis time for one product was about 30 min and only less than 4 μg HLM protein was required for one reaction region. The results demonstrated that the established platform could be used to imitate drug metabolism occurring in the human liver, thereby replacing animal experiments in the near future. In addition, the integrated microchip will be a useful tool for drug metabolism studies and cytotoxicity assays, which are pivotal in drug development.

A novel method for the characterization of drug metabolites was developed by integrating chip-based solid-phase extraction (SPE) with an online electrospray ionization quadrupole time-of-fight mass spectrometer (ESI-Q-TOF-MS). The integrated microfluidic device was composed of circular chambers for cell culture and straight microchannels with shrink ends to pack the solid-phase material for sample cleanup and concentration prior to mass analysis. By connecting the two separated microchannels with polyethylene tubes, drug metabolism studies related to functional units, including cell culture, metabolism generation, sample pretreatment, and detection, were all integrated into the microfluidic device. To verify the feasibility of a drug metabolism study on the microfluidic device, the metabolism of vitamin E in human lung epithelial A549 cells was studied. The metabolites were successfully detected by online ESI-Q-TOF-MS with high sensitivity and short analysis time (8 min). By integrating several parallel channels, the desalting and concentration process could be simultaneously achieved. The total sample pretreatment time only needed about 15 min, and solvent consumption could be reduced to less than 100 microL. All this demonstrated that the developed microfluidic device could be a potential useful tool for cellular drug metabolism research.

A microfluidic device was integrated in a controlled coculture system, in which the secreted proteins were qualitatively and semiquantitatively determined by a directly coupled mass spectrometer. PC12 cells and GH3 cells were cocultured under various conditions as a model of the regulation of the organism by the nervous system. A micro-solid phase extraction (SPE) column was integrated in order to remove salts from the cells secretion prior to mass spectrometry detection. A three layer polydimethylsiloxane (PDMS) microfluidic device was fabricated to integrate valves for avoiding contamination between the cells coculture zone and the pretreatment zone. Electrospray ionization (ESI)-quadrupole (Q)-time of flight (TOF)-mass spectrometry was employed to realize highly sensitive qualitative analysis and to implement semiquantitative analysis. Furthermore, cell migrations under various coculture conditions were observed and discussed. The inhibition on growth hormone secretion from GH3 cells by dopamine released from PC12 cells was investigated and demonstrated. Thus, the developed platform provides a useful tool on cell to cell signaling studies for disease monitoring and drug delivery control.