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A single-stage annular fiber coating method with co-current dry-air drying at 30 degrees C has been developed for multilayer coating of 128 &mgr;m diameter polyester thread (yarn) with latex films as a model for enzyme immobilization and development of a filament biocatalytic filter. Acrylic vinyl acetate polymer coatings were sequentially metered onto the fibers by the combination of a flexible squeegee and a red rubber annulus. The thread coater can operate over a range of 0.07-1.37 m/min thread velocities while delivering a nearly constant and reproducible polymer loading of 30. 8 +/- 1.3 mg/m. A 100% polyester, 278.9 denier thread was precoated with latex to generate an approximately 369 denier sealed filament. The filament was then coated with a latex + sulfanilamide-azocasein mixture and sealed with a polymer top coat. The permeability of the polymer sealant top coat was characterized using entrapped azocasein as a tracer molecule and monitoring the azocasein release upon rehydration of the coated threads. Azocasein release rate decreased with curing time at 30 degrees C until 2 days and was invariant after 2-3 days of curing. A 282 mOsm rehydrating solution was sufficient to suppress increased azocasein release due to top coat blistering. No enhancement in the permeability of the top coat was observed when high molecular weight water soluble polymers (WSPs) were used as fillers. This probably results from the low WSP to latex ratio used (0.05-0.1) and the slow rate of WSP leaching compared to the release of azocasein. A method using 60-120 mesh silica was also developed to study the effect of mechanical abrasion of the coated threads as measured by azocasein release kinetics.

The adsorption of proteins from high cell density yeast suspensions on mixed-mode fluoride-modified zirconia (FmZr) particles (38 to 75 microm, surface area of 29 m(2)/g and density of 2.8 g/cm(3)) was investigated using human serum albumin (HSA) added to Saccharomyces cerevesiae as the model expression host. Because of the high density of the porous zirconia particles, HSA (4 mg/mL) can be adsorbed from a 100 g dry cell weight (DCW)/L yeast suspension in a threefold-expanded bed of FmZr. The expanded bed adsorption of any protein from a suspension containing >50 g DCW/L cells has not been previously reported. The FmZr bed expansion characteristics were well represented by the Richardson-Zaki correlation with a particle terminal velocity of 3.1 mm/s and a bed expansion index of 5.4. Expanded bed hydrodynamics were investigated as a function of bed expansion using residence time distribution studies with sodium nitrite as the tracer. The adsorption of HSA on FmZr exhibited features of multicomponent adsorption due to the presence of dimers. The protein binding capacity at 5% breakthrough decreased from 22 mg HSA/mL settled bed void volume for 20 g DCW/L yeast to 15 mg HSA/mL settled bed void volume for 40 g DCW/L yeast and remained unchanged for the higher yeast concentrations (60 to 100 g DCW/L). However, the batch (or equilibrium) binding capacity decreased monotonically as a function of yeast concentration (20 to 100 g DCW/L) and the binding capacity at 100 g DCW/L yeast was fivefold lower compared with that at 20 g DCW/L yeast. The lower batch binding capacity at high cell concentrations resulted from the adsorption of cells at the surface of the particles restricting access of HSA to the intraparticle surface area. Batch (or equilibrium) and column HSA adsorption results indicated that the adsorption of HSA on FmZr occurred at a time scale that may be much faster than that of yeast cells. The zirconia particles were cleaned of adsorbed HSA and yeast with a total of 1500 to 2000 column volumes (over many cycles) of 0. 25 M NaOH, without any significant effect on the chromatographic performance.

The expanded bed characteristics of 75–103μm fluoride‐modified zirconia (FmZr) particles synthesized by a fed batch oil emulsion process were investigated. These particles are distinguished from commercially available expanded‐bed adsorbents by virtue of their high density (2.8 g/cc) and the mixed mode protein retention mechanism which allows for the retention of both cationic and anionic proteins. The linear velocity versus bed porosity data agree with the Richardson–Zaki relationship with the terminal velocity in infinite medium of 2858.4 cm/h and a bed expansion index of 5.1. Residence time distribution (RTD) studies and bovine serum albumin (BSA) adsorption studies were performed as a function of the height of the settled bed to the column diameter (H:D) ratio and degree of bed expansion with superficial velocities of 440 to 870 cm/h. The settled bed, a 2× expanded bed, and a 3× expanded bed were studied for the H:D ratios of 1:1, 2:1, and 3:1. The dynamic binding capacity (DBC) at 5% breakthrough was low (2–8 mg BSA/mL settled bed) and was independent of the H:D ratio or the degree of bed expansion. The saturation DBC was 32.3 ± 7.0 mg BSA/mL settled bed. The adsorption–desorption kinetics and intraparticle diffusion for protein adsorption on FmZr (38–75 μm) were investigated by studying the packed bed RTD and BSA adsorption as a function of temperature and flow rate. The data show that the adsorption–desorption kinetics along with intraparticle diffusion significantly influence protein adsorption on FmZr. Low residence times (∼0.8 min) of BSA result in a DBC at 5% breakthrough which is 3.5‐fold lower compared to that at 6‐fold higher protein residence time. At low linear velocity (45 cm/h) the breakthrough curve is nearly symmetrical and becomes asymmetrical and more dispersed at higher linear velocity (270 cm/h) due to the influence of slow adsorption–desorption kinetics and intraparticle diffusion.© 1998 John Wiley & Sons, Inc. Bioeng 60: 333–340, 1998.

The utility of 50 microns fluoride modified zirconia particles as an easily cleaned and steam sterilizable low pressure preparative scale stationary phase for immunoglobulin purification was investigated and its performance was compared with 40 microns ceramic hydroxyapatite type II (cHAp II) particles. The equilibrium batch binding capacity of both supports for bovine serum albumin decreases monotonically with increase in the adsorption pH, while that for bovine IgG is independent of pH, in the pH ranges studied. The dynamic binding capacity, as determined by breakthrough analysis, was 29 mg BSA/g zirconia for fluoride modified zirconia and 8.6 mg BSA/g cHAp II for cHAp II. Linear gradient conditions were developed for the separation of BSA and IgG on fluoride modified zirconia. The same separation could be accomplished in a shorter time and with better resolution on cHAp II.