Two dense pellicular agarose-glass matrices of different sizes and densities, i.e., AG-S and AG-L, have been characterized for their bed expansion behavior, flow hydrodynamics and particle classifications in an expanded bed system. A 26 mm ID column with side ports was used for sampling the liquid-solid suspension during expanded bed operations. Measurements of the collected solid phase at different column positions yielded the particle size and density distribution data. It was found that the composite matrices showed particle size as well as density classifications along the column axis, i.e., both the size and density of each matrix decreased with increasing the axial bed height. Their axial classifications were expressed by a correlation related to both the particle size and density as a function of the dimensionless axial bed height. The correlation was found to fairly describe the solid phase classifications in the expanded bed system. Moreover, it can also be applied to other two commercial solid matrices designed for expanded bed applications.
The present investigation describes a novel method for preparing spherical chitosan particles based on crosslinking with epichlorohydrin. Certain amount of pre-crosslinking agent was added to form chitosan gels by traditional inverse phase suspension polymerization. Then the gels were crosslinked by epichlorohydrin at basic condition to obtain chitosan beads. The effects of reaction conditions, such as crosslinking time, the amount of crosslinking agent and the NaOH concentration, on the physical properties of the chitosan beads were investigated. The beads were found to have more amino groups in the polymer chains than the beads crosslinked by glutaraldehyde. The capacity for copper ions is as high as 40mg/g. The beads have good mechanical strength and can be reused.
Expanded bed adsorption (EBA) is an integrative downstream processing technique for the purification of biological substances directly from unclarified feedstock. In this study, molecular chaperone GroEL, an important protein folding helper both in vivo and in vitro, was purified by the single-step EBA technique from the unclarified homogenate of recombinant E. coli cells. Compared with packed bed adsorption, the EBA technique provided a single-step approach to yield an electrophoretic purity of GroEL. After the homogenate loading and column washing in the expanded bed mode, the GroEL protein was recovered by stepwise salt-gradient elution in packed-bed or expanded-bed modes, respectively. The expanded-bed elution mode was found as efficient as the packed-bed mode in the purification of GroEL from cell disruptate.
In this article, a spherical chitosan gel crosslinked by epichlorohydrin was prepared. It was then loaded with copper ions to produce a metal chelate affinity adsorbent for protein. The uptake of bovine serum albumin (BSA) by the affinity adsorbent was investigated, and the adsorption capacity for BSA as high as 40 mg/g-wet beads was observed. The adsorption equilibrium data was well correlated by the Langmuir equation. The adsorption was considerably affected by pH. In addition, the amount of BSA adsorbed onto the beads decreased with the increasing of aqueous phase ionic strength, so adsorbed BSA can be desorbed by adjusting pH or ionic strength of the solution.
Triton X-114, an non-ionic surfactant, was modified with the affinity ligand of trypsin,p-aminobenzamidine (PAB) and the affinity surfactant (PAB-TX) was synthesized.Then, the affinity surfactant was used to prepare affinity-based colloidal gas aphrons (CGA).The stability of the affinity CGA was investigated at different temperatures and compared with that of the CGA prepared from Triton X-114.Compared with the CGA from Triton X-114, the affinity CGA showed high selective adsorption property for trypsin.In the separation of a protein mixture,recovery yield higher than 74% were achieved for trypsin and the separation factor reached over 1.5.The results showed that the affinity CGA possessed promising selectivity for separating trypsin from a protein mixture.
Upon the application of 3%yeast suspension as a feedstock to an expanded bed of Streamline AC equilibrated with 0.02 mol·L -1 phosphate buffer (pH 7.0), the transient variations of local bed voidage and particle size distribution were investigated. The experiments were carried out in a customized glass column (26 mm I.D.) modified by side ports. It was exhibited that the introduction of unclarified feedstock with a high viscosity and density induced the upward movement of particle and consequently a change in local bed voidage and particle size distribution. At a given bed height, voidage firstly decreased to a minimum and then increased to a high equilibrated value in voidage. The transient process not only included a fluctuation in particle size distribution but also involved the change in particle concentration at a certain bed height, particularly at the middle and top of the column.
