PROTEIN SORPTION AND RECOVERY BY HYDROGELS USING PRINCIPLES OF AQUEOUS 2-PHASE EXTRACTION

Use of the thermodynamic principles of aqueous two-phase extraction (A TPE) to drive protein into a crosslinked gel is developed as a protein isolation and separation technique, and as a protein loading techniqu e for drug delivery applications. A PEG/dextran gel system was chosen as a model system because PEG/dextran systems are widely used in aqueo us two-phase extraction and dextran gels (Sephadex(R)) are common chro matographic media. The effects of polymer concentrations and molecular weights, salts, and pH on the partitioning of ovalbumin matched ATPE heuristics and data trends. Gel partition coefficients (C-gel/C-soluti on) increased with increasing PEG molecular weight and concentration a nd decreasing dextran concentration (increased gel swelling). The addi tion of PEG to the buffer solution yielded partition coefficients more than an order of magnitude greater than those obtained in systems wit h buffer alone, or added salt. A combined salt/PEG system yielded an a dditional order of magnitude increase. For example, when ovalbumin sol ution (2.3 mg/mL) was equilibrated with Sephadex(R) G-50 at pH 6.75, t he partition coefficients were 0.13 in buffer, 0.11 in buffer with 0.2 2M KI, 2.3 in 12 wt% PEG-10,000 and 32.0 in 12 wt% PEG-10,000 with 0.2 2M KI. The effect of anions and cations as well as ionic strength and pH on the partitioning of ovalbumin also matched ATPE heuristics. Usin g the heuristics established above, partition coefficients as high as 80 for bovine serum albumin and protein recoveries over 90% were achie ved. In addition, the wide range of partition coefficients that were o btained for different proteins suggests the potential of the technique for separating proteins. Also, ovalbumin sorption capacities in dextr an were as high as 450 mg/g dry polymer, and the sorption isotherms we re linear over a broad protein concentration range. (C) 1998 John Wile y & Sons, Inc.