Making Quasi Vivo®
Traditional, static, in vitro systems do not take into consideration flux factors such as energy, momentum and mass. Quasi Vivo® has been developed to address these key issues ensuring that the experimental data is as reliable and accurate as possible.
This is one of the biggest problems while using a fluidic system. To avoid this issue, Quasi Vivo® chambers have a patented sloped roof as well as an inlet tube which is lower and more narrow than that of the outlet tube. This unique design allows any bubbles in the system to be collected and manoeuvred towards the thicker and higher outlet tube. These bubbles are then transported to the reservoir bottle where they are expelled. This simple yet effective design means that there is no need to purge or de-gas the system.
PRESSURE AND SHEAR STRESS
By working together to remove bubbles the inlet tube, outlet tube, and sloped roof also have the function of reducing the shear stress exerted on the cells. Shear stress is a force that results from layers moving against one another in opposite directions. High shear stress is the result of high pressure increasing the velocity of the media entering the chamber. In Quasi Vivo® the narrow inlet tube has a higher pressure than the chamber and therefore controls the pressure that will be applied to the cell. The increased diameter of the outlet tube results in the pressure on the cell cultures being greatly reduced and therefore minimises the rate of shear stress.
It has been found that the sloped roof can reduce fluid velocity and shear stress tenfold when compared to earlier flat roof models, reducing overall turbulence in the cells environment. This also allows for a high flow rate should the cells require a high oxygen concentration to thrive.
OPTIMISING OXYGEN LEVELS
Whether culturing hepatocytes, creating a kidney model or replicating an air-liquid interface, a sufficient exposure to oxygen is needed. The QV500 and QV600 chambers are made of porous silicon which allows them to be gas permeable. An even oxygen distribution throughout the chambers can be guaranteed due to their specific design which creates a laminar flow. An insert can be added in the QV900 should the user wish to adjust the level of their cells and therefore alter the oxygen level the cells are subjected to. Although the chambers are airtight due to their twist lock design, the reservoir bottle is equipped with a 0.2 micron air filter ensuring contamination is not possible.
The walls of the QV500 and the QV600 are made of Polydimethylsiloxane (PDMS), a silicon based compound, which allows the chamber to have a secured structure while still being able to allow gas penetration via the structures pores. Oxygen diffusion through the walls allows the viability of cells within the system to be significantly enhanced.
In comparison the QV900 is made of acrylic and is primarily suited for industrial applications; however it can still be used in academia. It utilises rigid Teflon tubing which reduces non-specific binding and therefore decreases the chance of experimental error. The chambers and tubing are all transparent. This design allows the user to easily observe the systems behaviour under a microscope during experiments. Both PDMS and acrylic are very light. This feature combined with the system being compact allows the user to easily move the whole system to and from an incubator.
PharMed tubing is often used for in vitro systems, and although better than silicon tubing, it still has a significant level of non-specific binding as shown by the graph below. This may therefore result in experimental errors due to some ligands not reaching their intended target.
In comparison Teflon tubing shows very low adherence levels, as shown by the graph below, and is therefore a promising material for future use. This feature combined with its rigidity makes it ideal for use with the QV900 chambers when a high level of control is needed.
EASY TO USE DESIGN
All chambers are designed to have Luer lock connections allowing for increased compatibility with tubing that customers may already possess. These easy to use locks can be used to connect up to 12 chambers in series, allowing multiple cell types to be tested simultaneously.
The QV500 and the QV600 chambers have also been designed to be easily cleaned meaning reuse is possible. Both chambers can be sterilised using either ethanol or by autoclaving. The base of the chambers are ridged allowing the easy removal of 2D and 3D samples and a filter is attached to the reservoir bottle to maintain sterility when the system is in use. A filter can also be attached to the QV600 should the user wish to replicate a liquid-air interface.
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