Visking tubing, also known as dialysis tubing, is an artificial semi-permeable membrane. Composed primarily of regenerated cellulose from wood pulp or cotton fibers, it allows certain substances to pass while blocking others, making it a valuable tool in scientific research and education.
How Visking Tubing Functions
Visking tubing operates on the principle of semi-permeability, possessing microscopic pores that selectively allow molecules to pass based on size. Small molecules like water, glucose, and various ions can readily traverse these pores, while larger molecules such as proteins and starch cannot.
The movement of substances across the membrane occurs through processes like diffusion and osmosis. Diffusion involves the net movement of solute molecules from an area of higher concentration to an area of lower concentration. Osmosis is the net movement of water molecules across a semi-permeable membrane from a region of higher water concentration (dilute solution) to a lower one (concentrated solution). This movement continues until a state of equilibrium is reached, where there is no net flow of molecules across the membrane.
Key Applications in Science
Visking tubing is extensively used in laboratory settings. A primary application is dialysis, a separation technique used to purify solutions by separating small molecules from larger ones. This process aids in protein purification, removing salts or contaminants, and forms the basis for medical dialysis in kidney failure patients to remove blood waste products.
The tubing also demonstrates osmosis and diffusion principles in educational and research settings. Experiments often involve filling tubing with a sugar solution and placing it in distilled water to observe water moving in, causing swelling. Similarly, experiments show glucose diffusing out while starch remains inside. The membrane can also concentrate solutions by allowing water to exit while retaining larger solutes.
Characteristics and Handling
Visking tubing is transparent and flexible when hydrated, supplied in rolls of various diameters. Before use, dry tubing must be hydrated by soaking it in water for at least 5 minutes to make it pliable and fully open its pores. This ensures correct membrane function.
To create a sealed bag, one end of the tubing can be tied securely with a knot or sealed with a specialized clip. The other end is then filled with the desired solution before being sealed, preventing leakage. Proper storage involves keeping the tubing in a dry environment away from direct sunlight to prevent it from becoming brittle or supporting microbial growth. While reusable for short periods, prolonged storage after initial use can lead to brittleness.