A Microfluidic Experimental Method for Studying Cell-to-Cell Exosome Delivery-Taking Stem Cell-Tumor Cell Interaction as a Case.

Cell-to-cell communication must occur through molecular transport in the intercellular fluid space. Nanoparticles, such as exosomes, diffuse or move more slowly in fluids than small molecules. To find a microfluidic technology for real-time exosome experiments on intercellular communication between living cells, we use the microfluidic culture dish's quaternary ultra-slow microcirculation flow field to accumulate nanoparticles in a specific area. Taking stem cell-tumor cell interaction as an example, the ultra-slow microcirculatory flow field controls stem cell exosomes to interfere with tumor cells remotely. Under static coculture conditions (without microfluidics), the tumor cells near stem cells (<200 µm) show quick breaking through from its Matrigel drop to meet stem cells, but this 'breaking through' quickly disappears with increasing distance. In programmed ultra-slow microcirculation, stem cells induce tumor cells 5000 µm far at the site of exosome deposition (according to nanoparticle simulations). After 14 days of programmed coculture, the glomeration and migration of tumor cells were observed in the exosome deposition area. This example shows that the ultra-slow microcirculation of the microfluidic culture dish has good prospects in quantitative experiments to study exosome communication between living cells and drug development of cancer metastasis.

Manipulating nanoliter fluid circuits on an all-glass chip by the magnetic field.

Actively controlled nanoliter fluid circuits are an urgently needed technology in electronics, biomedicine, chemical synthesis, and biosensing. The difficulty lies in how to drive the microfluid in an isolated and airtight manner in glass wafer. We used a magnetic oscillator pump to realize the switching of the circulation direction and controlling the flow rate of the 10nL fluid. Results of two-dimensional numerical simulations shows that the flow field can reach a steady state and a stable flow can be obtained. The contribution of each vibration cycle to the flow rate is proportional to the frequency, decays exponentially with the viscosity, is proportional to the 4.2 power of the amplitude, and is proportional to the radius. Compared with the existing fluid technology, this technology realizes the steering and flow control of a fully enclosed magnetic control fluid circuit as small as 10nL in hard materials for the first time.

A One-Square-Millimeter Compact Hollow Structure for Microfluidic Pumping on an All-Glass Chip.

A micro surface tension pump is a new type of low-cost, built-in, all-glass, microfluidic pump on a glass microchip fabricated by one-step glass etching. However, geometric minimization and optimization for practical use are challenging. Here, we report a one-square-millimeter, built-in, all-glass pump controlled by two-way digital gas pressure. The pump consists simply of two joint chambers and a piston between two gas control channels. It does not require pre-perfusion for initialization, and can immediately begin to run when a liquid enters its inlet channel. It is also more reliable than conventional micro pumps for practical use due to its ability to restart after the formation of a blocking bubble, which can serve as a valuable troubleshooting procedure. Its volumetric pump output was 0.5⁻0.7 nL·s-1 under a pump head pressure of 300 Pa.

A micro surface tension pump (MISPU) in a glass microchip.

A non-membrane micro surface tension pump (MISPU) was fabricated on a glass microchip by one-step glass etching. It needs no material other than glass and is driven by digital gas pressure. The MISPU can be seen working like a piston pump inside the glass microchip under a microscope. The design of the valves (MISVA) and pistons (MISTON) was based on the surface tension theory of the micro surface tension alveolus (MISTA). The digital gas pressure controls the moving gas-liquid interface to open or close the input and output MISVAs to refill or drive the MISTON for pumping a liquid. Without any moving parts, a MISPU is a kind of long-lasting micro pump for micro chips that does not lose its water pumping efficiency over a 20-day period. The volumetric pump output varied from 0 to 10 nl s(-1) when the pump cycle time decreased from 5 min to 15 s. The pump head pressure was 1 kPa.

A micro surface tension alveolus (MISTA) in a glass microchip.

We have designed a non-membrane micro surface tension alveolus (MISTA) in a glass microchip for direct gas exchange and micro gradient control. Hemoglobin (Hb) in the liquid phase indicates the rapid gas gradient changes of O2 and CO2 shifted by the difference in pressure between the liquid and the gas.

A vast-range speed control microchip for retention of all cell types.

This Technical Note is the first description of a large-scale logarithmic flow-rate damping system designed to retain cells of different adherence, different suspensibility and different motility. The chamber, which can easily retain and cultivate many types of cells, including high-motility cells and swimming cells, via a series of "speed bumps", readily facilitates cell retention for complex heterogeneous cultures. Yeast cells, red blood cells, rabbit bone marrow aspirate and dinoflagellate swimming cells were introduced into the chip for multi-cell retention, multi-cell culture and observation. Here, we show that the chamber creates a flow field with a ratio of end/start speeds as low as 0.01. The logarithmic distribution of flow-rate within the chamber is controlled precisely by pressure, all of the cell types that we tested were retained easily within the chamber. Many cell-cell interactions were observed, predicting a high potential for the success of on-chip heterogeneous cell experiments.

Extraction of pure cellular fluorescence by cell scanning in a single-cell microchip.

A 3-dimensional liquid flow control method has been developed to manipulate and retain a single yeast cell freely in a microchip. This method allows us to carry out single-cell experiments by selecting any desired single cell from a group, retaining the cell for cellular signal detection, and delivering reagents to the cell during continual detection and observation without any negative impact from the liquid flow on the live cell. The cell was scanned back and forth across an observation window in order to extract pure cellular fluorescent signals. Different scanning methods were discussed for effective collection of the cellular fluorescent signal. The cell scanning technique results in many advantages, such as distinguishing a small part of a cell, allowing for background correction and monitoring the switch of reagents. In addition, it is possible to evaluate the photobleaching effects on both the background and cellular fluorescence, with the latter found to be less significant in a restricted cellular environment.