Hydrogel beads adsorbent

The use of small affinity adsorbent particles immobilized in hydrogel beads has been investigated for whole broth processing (1). The adsorbent particles can contain biospecific ligands covalently attached to a porous solid support. A mathematical model was developed to study bioproduct adsorption using immobilized affinity adsorbent beads in batch operation. 

The performance of immobilized and freely suspended affinity adsorbents was compared by calculating adsorption rates and selectivities for four different bead geometries. Simulation results indicate that the performance of finely ground adsorbent particles immobilized in hydrogel beads is superior compared to freely suspended adsorbents. The mathematical model was further used for simulation studies to investigate the effect of bead design parameters on product adsorption. 

Several assumptions are made to mathematically model the immobilized adsorbent. The small adsorbent particles are assumed to be distributed uniformly inside the hydrogel bead. The external mass transfer resistance due to the boundary layer is assumed to be negligible if the bulk solution is well stirred. This assumption is supported by the experimental observations of Tanaka et al. who studied diffusion of several substrates from well stirred batch solutions into Ca-alginate gel beads (4), However, the boundary conditions can be easily modified to incorporate external diffusion effects if needed. Furthermore product diffusion in both the hydrogel and the porous adsorbent is considered to follow Fickian laws and its diffusivity in each region is assumed to be constant. 

Single component diffusion and binding. Figure 4 shows four cases which were simulated to observe the effects of immobilization in hydrogel and reduction of adsorbent particle size. Case (a) represents a freely suspended adsorbent particle of radius 1.1 mm. Case (b) represents the same size particle immobilized in a hydrogel bead of 2.8 mm. In case (c), the same adsorbent particle as in cases (a) and (b) was assumed to be crushed to 80 smaller particles which were immobilized within a hydrogel bead of radius 2.8 mm. Case (d) represents the extreme situation in which the adsorbent particle was crushed to fine powder such that the total number of particles within the immobilized bead may be regarded as infinite. This is also... 

Figure 1 shows a schematic diagram of an immobilized affinity adsorbent bead. Hydrogel, by virtue of its extremely high water content (>90%), offers limited diffusional resistance to the desired product. It is therefore used as an inert matrix to support... 

Figures 6a,b. Effect of bioproduct diffusivity in hydrogel (D) and in adsorbent matrix (D ) on ligand consumption using immobilized adsorbent beads.

Biocatalytic reactions performed using immobilized enzyme microreactors under continuous flow mode have been found effective for hydrolysis reactions [121,158-161], with the enzyme either trapped in the matrix [159], covalently linked to modified surface wall [160,121], enzymes entrapped in hydrogels [162], or enzymes immobilized on monolith [179]. The experimental setup consists of either chip-type microreactors with activated chaimel walls where enzymes bind, enzymes that bind to beads, enzymes entrapped in the matrix, enzymes adsorbed in nanoporous materials, and most recently, nanosprings as supports for immobilized enzymes in chip-based reactors, or enzyme immobilized monolith reactors, where support is packed inside a capillary tube (Table 10.4). 

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