A.Kumar et al.Prog.Polym.Sci.32 (2007)1205-1237 1209 c the properties of a separation systen great fracti urthe nd d are 、solub and some low molecular weights ces hecause biomolecules.They with of its gentleness for hiological materials and easy charged groups and affinity ligands for specific scale-up features [50.51].ATPS provides aqueous binding to target biomolecule.Application of SP as environment for the partitioning of biomolecules on stimuli-responsive soluble-insoluble polymers for the basis of solubility or affinity.An example of the ligand carriers in ATPS has shown promising in Fig.2.Polymer potential [52-54].The polymer-ligand complex is are sp y part top ph and and tran or ally mes 20 sily by changing th con ditio But the o solution above LCST and can e used in the neck in this techniaue has been the separation of separated aqueous two-phase system.The thermo target biomolecule from phase-forming polymer. responsive polymers used for ATPS include This is where SP have provided an appropriate PNiPAAm,polyvinylcaprolactam (PVCL),cellu- solution.With the help of SP it is possible to lose ethers such as ethyl(hvdroxvethyl)cellulose After phase PEG 8000 。0 Ab-poly(NIPAM) oly(NIPAM Cells 0.I M NaCl 。 Centrifugation Top phas lec Centrifugation top phase PEG centrifuge PEGappropriate concentrations. ATPS has attracted a great deal of attention for the fractionation of various biological substances such as proteins, cells and some low molecular weight substances because of its gentleness for biological materials and easy scale-up features [50,51]. ATPS provides aqueous environment for the partitioning of biomolecules on the basis of solubility or affinity. An example of the ATPS system is illustrated in Fig. 2. Polymers mainly used in ATPS are poly(ethylene glycol) (PEG) and dextran or hydrophobically modified starch, e.g. hydroxypropyl starch (Reppal PES 200) as a cost-effective alternative. But the major bottle￾neck in this technique has been the separation of target biomolecule from phase-forming polymer. This is where SP have provided an appropriate solution. With the help of SP it is possible to affect the properties of a separation system. Furthermore, these polymers are water soluble, inert and do not have denaturing effects towards biomolecules. They can be derivatized, e.g. with charged groups and affinity ligands for specific binding to target biomolecule. Application of SP as stimuli-responsive soluble–insoluble polymers for ligand carriers in ATPS has shown promising potential [52–54]. The polymer–ligand complex is specifically partitioned to the top phase and can be easily recovered by changing the medium condition. Thermoresponsive polymer separates from water solution above LCST and can be used in thermo￾separated aqueous two-phase system. The thermo￾responsive polymers used for ATPS include PNiPAAm, polyvinylcaprolactam (PVCL), cellu￾lose ethers such as ethyl(hydroxyethyl)cellulose ARTICLE IN PRESS Fig. 2. Type-specific separation of animal cells in aqueous two-phase systems using antibody conjugates with temperature-sensitive polymers, PNiPAAm (poly(NIPAM)). Adopted from [53] with permission. A. Kumar et al. / Prog. Polym. Sci. 32 (2007) 1205–1237 1209