Conditions, such as solution pH, ionic strenght, solvent compoisition, termpature, light and electric field. These polymers are referred to as stimuli response, enivornmentally sensitive, “intelligent” or “smart” polymers. a large number of biologically active molecuels may be combined with intelligent polymer systems. The biomolecules may be conjugated to pendant groups along a polymer backbone or to one or both terminal ends of the polymer. In etiehr case, the samrt polymer may be a soluble polymer a graft or block copolymer, aphysically adsorbed polymer on a solid substrate, or a polymer change segment within a hydrogel. Hoffman, A.S., “Intelligent Polymers in Medicine and Biotechnology”, Macromol. Symp., 98, 645-664 (1995).

pH-sensitive affinity macroligands (AML): 

Eudragit S-100: is a commercially available high molar mass copolymer of methcrylic acid and methyl metharylate which precipitates sharply below pH 4.5 and has been used for the purfication of monoclonal antibodies. A drawback is that the pH of precipitation is outside the stability range of many proteins (Hilbrig, J. Chromatography B, 790 (2003), pp. 79-90).  

N-acryloyl-p-aminobenzoic acid: This AML is water soluble above a pH of 4. Below a pH of 4 the acidic residues on the polymer backbone become neutralized (protonation) and hydrophobic interactions between the uncharged polymer backbones enforce aggregation which causes the AMl to precipitate reversibly when the pH is reduced below this value.

For a polyelectrolytes see outline. 

Hoffman (US 5,998,588) discloses stimuli responsive polymers coupled to recognition biomolecules such that once a ligand is bound, it may also be ejected form the binding site by stimulating one or more conjugated polymers to cause ejection of the ligand. In one embodiment, a first stimulus precipitates the polymer while a second stimulus is ued to release the ligand. Hoffman further teaches that stimuli include pH.

Thermosensitive affinity macroligands:

Thermosenstivie polymers in aqueous solutions become soluble (hydrophoilic) at low temperatures but are insoluble (hydrophobic) at high temperatures. This hydrophilic/hydrophobic transition is reversible and occurs at a transition temperature, which is determiend by a primary structure of polymer.

Temperature sensitive smart polymers have been studied extensively. Many polymers exhibit a cloud point (CP) or lower critical solution temperature (LCST) in aqueous solutions. Examples of thermally sensitive polymers howing LCST bheavrio in aqueous solutions that have alchol groups are hydroxpropyl acrylate, hydroxpropyl methlcellulose, hydroxpropyl cellulose, hydroxyethyl cellulose, methycellulose and poly(vinyl alcohol) derivatives. Examples of thermally sensitive polyers showing LCST behavior in aqueous solutions that have N-substituted amide groups include poly(N-substiuted acrylamides), ply(N-acryloyl pyrrolidine), poly(N-acryloyl piperidein), poly(acryl-L-amino acid amides), and poly(ethyl oxazoline). Hoffman, A.S., “Intelligent Polymers in Medicine and Biotechnology”, Macromol. Symp., 98, 645-664 (1995).

poly-N-alkylacrylamides: such as poly-N-isopropylacrylamide (NIPAM) precipitate if a certain critical solution temperature (CST) is reached. The polymer exhibits thermally reversilbe soluble-insoluble changes in response to teemperature changes across lower critical solution temperature (LCST), typically at 32 C in an aqueous solution. It is present as a clear homogeneous solution at 4C and changes to compact form rapidly above the LCST and precipitates within a few seconds. The precipitate can be easily separated and collected by centrifugation.  

Conjugation of Protein A to Theremosensitive Polymers

–poly(NIPAAm)-protein A conjugates:

Chen (“polymer-protein conjugates” 6055 Biomaterials 11 (1990)) discloses a conjugate of protein A with poly(N-isopropylacrylamide) (polyNIPAAm) and used in the separation of human immunogammaglobulin. In the separation prcocess, the poly(N-isopropylacrylamide) protein A conjugates binds to the immunoglobulin and the complex can tehn be separated by precipitation upon heating aove the lower critical solution temperature of the complex. 

Hoffman, A.S., “Intelligent Polymers in Medicine and Biotechnology”, Macromol. Symp., 98, 645-664 (1995) discloses a thermally induced affinity precipitation process to recvoer IgG form oslution by using a poly(NIPAAm)-protein A conjugate.

–NIPAM

Kamihira (Biotech. & Bioengin. 75(5), 2001) pp. 570-580) dicslose immobilzing antibodies as ligands to NIPAM.