See also “purification fo antibodies” using filtration, “Definitions” and  graft chains and ionic functional groups attached to membranes (under “chromatography” and “graft chains”)

Companies/Products:  3 M purificaiton .  Pall Life Sciences Mini Kleenpak  

Sartoclean CA mini cartidges (available with 3.0/0.8 um and 0.8/0.65 um cellulose acetate double membranes for the retention of partciles and larger microorganisms by means of fractionated membrane filtraiton, as well as simple membrane mini cartidge with 0.2 and 0.45 um pore size. Main applicaiton is prefiltraiton in combination with subsequent Sartogran P mini cartridge. ) 

Sartogran Sartorius 0.45/0.2 um filtration unit. 

Introduction:

Filtration is a commonly used technique for separating proteins. The filters used during filtration are often classified by retained particle size. For example, membrane microfilters generally retain partciles 0.1-10 microns in diameters.

Ultrafiltration (see outline)

Ultrafiltration membranes have pore sizes between 1 and 20 nm and are designed to provide high retention of proteins and other macromolecules. They can also be used for HPTFF. Microfiltration membrane have pore size between 0.05 and 10 um and are designed to retain cells and cell debris while allowing proteins and smaller solutes to pass into the filtrate. Virus filtration membranes are sometimes (but incorrectly) referred to as nonofiltration membranes based on their 20-70 namometer pore size. Nanofiltration is properly defined as a process that spearates solvent, monovalent salts and small organics from divalent ions and larger species. Depth filters are not typically considered as membranes since they retain key components throught the porous structure. (Van Reis, “Bioprocess membrane technology, Science 297 (2007) 16-50) 

The majority of established applications are still performed on conventional ion exchangers such as Sepharose Fast Flow Q (GE Healthcare) but charged membrane filtration (Pall Corporation, Sartorius) is becoming increasingly popular (Gagnon, p. 492).

Diafiltration

Diafiltration is a method of using ultrafilters to remove and exchange salts, sugars, and non-aqueous solvents, to separate free from bound species, to remove low molecular weight material and/or to cause the rapid change of ionic and/or pH environments. Diafiltration is performed with the same membranes as ultrafiltration and is a tangential flow filtration. During diafiltration, buffer is introduced into the recycle tank while filtrate is removed from the unit operation. In processes where the product is in the retentate (for example IgG), diafiltration washes components out of the product pool into the filtrate, thereby exchanging buffers and reducing the concentration of undersiable species. Microsolutes are removed most efficiently by adding solvent to the solution being ultrafiltered at a rate of about equal to the ultrafiltration rate.

Diafiltration is thus a convenient and efficient technique for removing or exchanging salts, removing detergents, spearating free from bound molecules, removing low MW materials, or rapidly changing the ionic or pH enviornment (WO 2005/091801).

Shaban (US 14/809,211) discloses a method of purifying an antibody from a  biologic composition by diafiltering the composition with phosphate buffered saline (PBS) such as sodium phosphate and NaCL. The method is conveniiently used with anion exchange since the method removes (Bis-tris) and particularly with the mixed mode resin Capto adhere affinity chromatography which is a mixed mode of anion exchange and hydrophobic interaction since Bis-tris is a buffer used in a Capto adhere purificaiton step and is an comtaminate. 

Hemodiafiltration: combines both standard dialysis and hemofiltration into one process, whereby a dialyzer cartridge containing a high flux membrane is used to remove substances from the blood both by diffusion and by convection. The removal of substances by diffusion is accomplished by establishing a concentraiton gadient across a semipermeable membrane by flowing a dialysate solution on one side of the membrane while simultaneously flowing blood on the opposite side of the membrane. Collins (US 6,406,631) discloses a blood dialysis system which includes a hemodiafiltraiton sytem comprising a first dialyzer and second dialysate compartment.

Depth Filtration (see outline)

Membrane Chromatography

Membrane chromatography: function similarly to packed chromatography columns, but in the format of conventional filtration modules. (Liu, “Recovery and purification process development for monoclonal antibody production” mAbs,  2:5: 480-499 (2010)

Microfiltration

Microfiltration: is a pressure driven separation process that uses membranes of a given pore size to separate components in a solution or suspension on the basis of their size differences. It is not fundamentally different from ultrafiltration or nanofiltration except in terms of the size of the molecules it retains. (Yigzaw, Biotechnol. Prog. 2006, 22, 288-296).

Type of Membranes  see outline

Typical components which pass through and are retained by membranes (WO 2005/091801)

Modes of Filtration (see outline)

Methods of Extracting Proteins from starting precipitate

By Repeated Dilution of precipitate to a final dilution factor:

(Menyawi, US 17/054,018, published as US 2021/0246162) discloses a continuous extraction/separation process for maximizing the recovery of a protein of interest from a starting precipitate/material using filtration. The method also allows liquid or diluent to be re-circulated in a closed system and thus the quantity of the liquid is maintained through the process while footprints such as large tank volume can be reduced. The method recovers at least 95% of the protein of interest in the protein comprising precipitate. According to the method, the precipitate is first mixed with a liquid in a first tank to form a suspension having a first diltuion factor (DF) and the suspension is then fed into a first filtration unit to product a first retentate and a first permeate enriched with the protein of interest. The suspension can then be diluted by adding liquid or by streaming the first retentate into the first tank to a second dilution factor. These steps are repeated until either a final dilution factor has been acheived in the first tank or a protein concentraiton of the supension in the first tanke of 0.001-0.1 g?L has been acheived. 

Types of Filter Units

Ribault (US2009/0181450A1) discloses a filter body vaing a first and second filter membrane where the second membrane has a pore diameter smaller than the pore diameter of the first membrane. A method of using the filter body where a sample is passed through the first and second membranes is also disclosed.