Dialysis tubing

Dialysis tubing, also known as Visking tubing, is a type of semi-permeable membrane tubing used in separation techniques that facilitates the removal or exchange of small molecules from macromolecules in solution based on differential diffusion. In the context of life science research, dialysis tubing is typically used in the sample clean-up and processing of proteins and DNA samples or complex biological samples such as blood or serums. Dialysis tubing is also frequently used as a teaching aid to demonstrate the principles of diffusion, osmosis, Brownian motion and the movement of molecules across a restrictive membrane. For the principles and usage of dialysis in a research setting, see Dialysis (biochemistry).

Dialysis occurs throughout nature and the principles of dialysis have been exploited by humans for thousands of years using natural animal or plant based membranes. The term dialysis was first routinely used for scientific or medical purposes in the late 1800s and early 1900s, pioneered by the work of Thomas Graham. The first mass-produced man-made membranes suitable for dialysis were not available until the 1930s based on materials used in the food packaging industry such as Cellophane. In the 1940s, Willem Kolff constructed the first dialyzer (artificial kidney), and successfully treated patients with renal failure using dialysis across semi-permeable membranes. Today, dialysis tubing for laboratory applications comes in a variety of dimensions and molecular-weight cutoffs (MWCO). In addition to tubing, dialysis membranes are also found in a wide range of different preformatted devices, significantly improving the performance and ease of use of dialysis.

Different dialysis tubing or flat membranes are produced and characterized as differing molecular-weight cutoffs (MWCO) ranging from 1-1,000,000 kDa. The MWCO determination is the result of the number and average size of the pores created during the production of the dialysis membrane. The MWCO typically refers to the smallest average molecular mass of a standard molecule that will not effectively diffuse across the membrane upon extended dialysis. Thus, a dialysis membrane with a 10K MWCO will generally retain >90% of a protein having a molecular mass of at least 10 kDa. Pore sizes typically range from ~10-100 Angstroms for 1K to 50K MWCO membranes.

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