Media dispenser

A media dispenser or a culture media dispenser is a device for repeatedly delivering small fixed volumes (typically between 1 ml and 50 ml) of liquid such as a laboratory growth medium like molten agar or caustic or volatile solvents like toluene into a series of receptacles (Petri dishes, test tubes, Fernbach flasks, etc.). It is often important that such dispensers operate without biological or chemical contamination, and so must be internally sealed from the environment and designed for easy cleaning and sterilization before use. At a minimum, a media dispenser consists of some kind of pump connected to a length of discharge tubing or a spout. Dispensers used in laboratories are also frequently connected to microcontrollers to regulate the speed and volume of the medium as it leaves the pump.

Laboratory media dispensers may include the following, among others: floating piston designs, syringe pumps, peristaltic pumps, pipettes or pipettors, and pressure injection cells. Rotodynamic pumps are generally unsuitable for dispensing laboratory media.

The floating piston type includes electrically and manually operated subtypes. Both include a check valve at either end of the device to ensure the flow of fluids in only one direction.

The electrical floating piston type of media dispenser is based on the principle of an inductive pump. This design uses a floating piston housed inside of a cylinder (typically high-grade ferromagnetic stainless steel) and vibrated according to a magnetic pulse generated by a copper coil inside the cylinder and surrounding the piston. Oscillation of the piston back and forth in the cylinder causes aspiration of fluid into the cylinder at one end followed by ejection from the other end.

A bottle top media dispensers is an inexpensive alternative to the motor-driven inductive pump. This type involves a piston on a plunger which is pushed down against a spring: as the spring pushes the piston back into its original position, it draws the medium up from a reservoir underneath. When pushed down again, plunger infuses the medium out the dispenser tip. Like the electrical model mentioned above, the bottle top dispenser has no gaskets or seals. Unlike the previous model, this one requires no electricity. However, it is limited in the total amount of medium it can dispense before the source bottle requires a refill, making it convenient for small applications but less so for larger. They are also more difficult to calibrate than the pipettes.

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Wikipedia