Hydrogel beads immobilization

Fig. 15 Optical images of DNA-based materials for environmental purpose, a DNA-alginic acid hybrid matrix coagulated by Ca2+, in fiber, film, and gel form, b DNA-immobilized porous glass beads prepared by UV-irradiation. c DNA-polyacrylamide hydrogel beads synthesized by inverse suspension polymerization...

In another approach, insulin was modified to introduce hydroxyl groups so that the hydroxylated insulin can be immobilized by forming a complex with phenylboronic acid groups on the support (Fig. 16.11). The support can be hydrogel beads made of polymers containing phenylboronic acid, e.g. poly(m-methacrylamidophenylboronic acid). The hydroxylated insulin can be displaced by the added glucose and the displaced insulin can be released. 

Tungstophosphoric acid immobilized in polyvinyl alcohol hydrogel beads as heterogeneous catalyst... 

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... 

L.C. Dong and A.S. Hoffman, Thermally reversible hydrogels III. Immobilization of enzymes for feedback reaction control, J. Control. Release, 1986, 4, 223 M. Bayhan and A. Tuncel, Uniform poly(A-isopropylacrylamide) gel beads for immobilization of a-chymotrypsin, J. Appl. Polym. Sci., 1998, 67, 1127. 

Carrageenan Extrusion, w/or w/o TPP Composite with nanotubes Nanoparticles microparticles hydrogel beads fibers Drug delivery Enzyme immobilization... 

Xanthan gum Extrusion cryogelation Hydrogel beads tablets cryog Drug delivery Enzyme immobilization Tissue engineering... 

Park TG, Hoffman AS. Immobilization and characterization of b-galactosidase in thermally reversible hydrogel beads. J. Biomed. Mater. Res. 1990 24 21-38. 

Dumitriu and coworkers finished their study with a structural analysis of the hydrogels by preparing hydrogel beads that were investigated by SEM. The beads exhibit fibrillar porons sfructures with pore sizes of 100-250 mn and fiber diameters of 1-10 pm. In previous publications, Dumitriu and Chomet observed the diffusion of immobilized enzymes out of similar chitosan-xanthan hydrogel beads [138]. This observation can be explained by the porous external and internal structure of the beads, as illustrated in Fig. 15a, b. 

Figure 9. Immobilization of antibodies, a) directly on functional beads, or b) via crosslinkers (e.g. biotin-streptavidin chemistry). Arraying onto the slide in c) print buffer or d) entrapped in hydrogel.

In protein microarrays, capture molecules need to be immobilized in a functional state on a solid support. In principle, the format of the assay system does not limit the choice of appropriate surface chemistry. The same immobilization procedure can be applied for both planar and bead-based systems. Proteins can be immobilized on various surfaces (Fig. 1) (12). Two-dimensional polystyrene, polylysine, aminosilane, or aldehyde, epoxy- or thiol group-coated surfaces can be used to immobilize proteins via noncovalent or covalent attachment (13,14). Three-dimensional supports like nitrocellulose or hydrogel-coated surfaces enable the immobilization of the proteins in a network structure. Larger quantities of proteins can be immobilized and kept in a functional state. Affinity binding reagents such as protein A, G, and L can be used to immobilize antibodies (15), streptavidin is used for biotinylated proteins (16), chelate for His-tagged proteins (17, 18), anti-GST antibodies for GST fusion proteins (19), and oligonucleotides for cDNA or mRNA-protein hybrids (20). 

Another enzyme that was studied extensively in microreactors to determine kinetic parameters is the model enzyme alkaline phosphatase. Many reports have appeared that differ mainly on the types of enzyme immobilization, such as on glass [413], PDMS [393], beads [414] and in hydrogels [415]. Kerby et al. [414], for example, evaluated the difference between mass-transfer effects and reduced effidendes of the immobilized enzyme in a packed bead glass microreactor. In the absence of mass-transfer resistance, the Michaelis-Menten kinetic parameters were shown to be flow-independent and could be appropriately predicted using low substrate conversion data. 

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.

Other examples are enzymes immobilized on beads which are trapped in a microreactor by etched weirs [88], enzymes encapsulated in hydrogel patches or sol-gel silica [89] and enzymes attached on the surface of (porous) microstructures (for example, on porous silicon manufactured by anodization of single-crystalline silicon see Figure 1.10 [91]), of mesoporous silica or polymer monoliths or directly... 

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