See also filtration membranes using graft chains with functional groups (under “filtration”)

The use of ligand “tentacles” or “extenders” to improve protein binding capacity and modify resin selectiveity involves placing a ligand on polymer chains coupled to a base matrix such as by grafting, and extend away from the base matrix surface. Ligand extenders typically create greater binding capacity because th eextnders increase ligand availability where target molecule binding exceeds taht of a monolayer adsorption on the surace. (Soice, WO 2012/015379).

Processes for Attachment of Graft Chains

Hermanson (“Immobilized Affinity Ligand Techniques” discloses chemically modifying a matrix so that the product of the process will react to form a coalent bond with a ligand of chocie. Numberous activation chemistries are described. 

Two standard methodologies for grafting polymer extenders have been developed for creating surface extenders on porous substrates such as those used in chromatogrpahy for protein separation and the like: 1) grafting of monomers form a support via a surface radical (“grafting monomers from”), and 2) grafting a preformed polymer to a support via an activating group (“grafting polymers to”). (Soice, WO 2012/015379)

Covalent ligand attachment to a carrier is typically achieved by the use of reactive functionalities on the solid support matrix such as hydroxyl, carboxyl, thiol, amino groups, and the like. In order to enhance the binding capacity of the matrix, a linking arm (linker) is ofter provided between the ligand and carrier. Such linkers will physically distance the ligand from the carrier, wehreby the target compound is allowed to interact with the ligand with minimal interference form the matrix. The use of linkers in the synthesis of chromatography matrices requires the use of a functional reagent having at least one functional group capable of reacting with a functional group on the surface of the matrix to form a covalent bond therewith; and at least one functional group capable of reacting with a functional group on the ligand to form a covalent bond therewith (Axen, US 2008/0237124 A1 and WO 2007/027139).

Shinohara 13/381,129 teaches a method for purifying an antibody monomer by passing the antibody solution containing antibody aggregates through a porous membrane having a hydrophobic porous substrate, a hydrophilic molecular chain which can have a backbone that is a polymer of at least one monomer slected from glycidyl methacrylate, glycidyl acrylate, glycidyl sorbate, glycidyl itacolate and glycidyl maeate, which is immobilized on the surface of pores of the porous substrate, and a side chain off the molecular chain. In one embodiment a functional group selected from a propylamino group, an isopropylamino group, a diethylamino group, a triethylamino group and a tripropylamino group is bonded to 60-97% of the side cahins held by the molecule chain and 3-40% of the side chains held by the molecular chain have a diol group. 

Cation Exchange Groups or Linkers with Cation Exchange Groups

Sulfphonate-functionaled groups: Axen (US 2008/0237124 and WO2007/027139) discloses a method for the manufacture of a sulphonate-functionalized carrier for cation exchange by providing a polysaccharide carrier having available hydroxyl groups (OH groups) and reacting these OH groups with vinyl sulfphonate (CH2=CH-SO3) to provide a sulfphonate-functionalized cation exchanger. In an advantegeous embodiment, the carrier comprises cross-linked polysaccharides which is done by substituting a part of the OH groups on the polysaccharide, gelling the polysaccharide solution to provide a carreir and then cross-linking the polyscharride gel by reacting OH groups of the polysaccharide. Improvided rigidity is acheived by adding a bifunctional cross-linking agent such as epicholorohydrin, allylbromide and allylglycidyl ether, having one active site such as halides, epoxides, methylol groups and one inactive site and allowing OH groups of the polysaccharide to react with the active site of the cross-linking agent, and the inactive side of the cross-linking agent is activated subsequent to the gelling which activated site is then reacted with the OH groups of the polysaccharide gel to cross-link the gel. In one embodiment, the method comprises a step of providing the polysaccharide gel with extenders such as hydrophilic polymers such as polysaccharides like dextran between carrier such as agarose or dextran and ligand.

Anion Exchange Groups or Linkers with Anion Exchange Groups 

Sulfonic acid and diethylamino groups: 

Kim (J. Membrane Science 117 (1996) 33-38) teaches grafting of an epoxy group containing polymer chain (epoxy group containing vinyl monomer (glycidyl methacrylate, GMA) onto a porous polyethylene membrane of hollow fiber form by applying radiation induced graft polymerization. Some of the epoxides of the poly-GMA graft chains can therafter be converted into a functional group  such a diol group (e.g., diethylamine (DEA)), ion-exchange group, and chelate forming group for specific adsorpition of a target protein.  

Kiyohara teaches grafting two different types of monomers, acrylic acid (AAc) and glycidyl methacrylate (GMA) onto a porous polyethylene hollow fibre by radiation indicued graft polymerization. The carboxyl group fo the AAc grafted hollow fibre was then reaction with N-hydroxysuccinimide to produce a succinimide group as an activated group. Phenylalamine (Phe) as a pseudobiospecific affinity ligand was reaction with the GMA fibre. 

Lee (WO 02/085519) discloses engrafting polymeric brushes such as glycidyl methacrylate to base materials and immobilzing functional groups to the brushes. Ogasawara (JP 012300A, published 2/19/99) also discusses an anion exchange porous holow fiber membrane for removing impurities from a mixture of a desired protein having a graft chang/branch polymer which is polymerized in the substrate.

 Koguma (Biotechnol. Prog. 2000, 16, 456-461, 2000) also teaches a porous hollow fiber membrane for protein recovery having graft chains extended form the pore surface and anion exchange groups introduced into the polymer chains.

Okamura (J. Chromatography A, 953 101-109 (20020 also teaches frafting of an epoxy-group containing polymer chain onto a hollow fiber form of a prorous polyethylene membrane by the immerision of the electron beam irradiated trunk/base polymer in glycidyl methacrylate. Subsequently, the epoxy groups produced were converted into sulfonic acid and diethylamino groups.  

Okamura (J Chromatogr A 2002 Apr 12, 953(1-2), 101-9) discloses grafting of an epoxy group containing polymer chain onto a hollow fiber form of a porous polyethylene membrane by the immersion of an electron beam-irradiated trunk polymer in glycidyl methacrylate diluted with methanol and 1-butanol. Subsequently the eopxy groups produced were converted into sulfonic acid (-SOI) and diethylamino groups (-N(C2H5).

Shirataki (US8,653,246 and US13/572983) also disclose a porous hollow fiber membrane such as polyethylene or polyvinylidene fluoride having a graft chain which are polyers of glycidyl methacrylate on a pore surace and an anion exchange group fixed to the graft chains. The graft chain has a graft rate of from 10-90% and the graft chain has 70% or more of epoxy groups replaced with the anion exchange group. Shirataki also teaches methods of purifying a protein by performing filtration using the membranes.