Biomedical Engineering Reference
In-Depth Information
and can easily be immobilized, especially on matrices bearing hydroxyl groups. Dye-ligands
are able to bind most types of proteins, especially enzymes, in a remarkably specific manner.
The interaction between the dye-ligand and proteins can be by a complex combination of
electrostatic, hydrophobic, and hydrogen bonding. Selection of the supporting matrix is
the first important consideration in dye-affinity systems. Chitosan's structure possesses a
large number of reactive groups (hydroxyl and amino) that can be readily modified using
different ligands to meet various needs.
Chitosan beads (Ch-beads) and cibacron blue F3GA(CB)-attached chitosan beads (CB-Ch-
beads) were prepared by Çetinus et al. CAT was immobilized onto these beads. The CAT
adsorption capacity of Ch-beads is higher than that of CB-Ch-beads, but CB-Ch-CAT
showed better activity according to the Ch-CAT. Because CB molecules on the CB-Ch-
beads are negatively charged, the dominant force contributing to dye and protein
interactions is electrostatic rather than hydrophobic [51].
Wei et al. reported a film-forming solution for the efficient immobilization of enzymes
on solid substrates. The solution consisted of a biopolymer, chitosan (CHIT), which was
chemically modified with a permeability-controlling agent, Acetyl Yellow 9 (AY9), using
GA as a molecular tether. A model enzyme, glucose oxidase (GOx), was mixed with the
CHIT-GDI-AY9 solution and cast on the surface of platinum electrodes to form robust
CHIT-GDI-AY9-GOx films for glucose biosensing. Chitosan chains were modified with
anionic AY9 dye in order to introduce a perm-selectivity against anions. A relatively low
sensing potential, in conjunction with the film's permeability controlling agent, allowed
for interference-free determination of the enzyme's substrate, such as ascorbate and urate,
which are commonly present in physiological samples [52].
8.3.5 Freezing-Thawing Treatment
When gelification is performed by freezing-thawing repeated cycles, the resultant gel-
like polymer systems are called cryogels, which is a process of noncovalently physically
cross-linking different from chemical hydrogels formed by covalent bonds. The porous
structure of cryogels, in combination with their chemical and mechanical stability,
makes them attractive matrices for immobilization of cells and enzymes. These materi-
als were often used in porous scaffold production to immobilize cell cultures or as tissue
regeneration templates. Scarce studies have reported the use of them as catalytic
supports.
Knowledge of thermal and surface properties of the membrane is of importance for
chitosan-based enzyme support systems. It was demonstrated by Orrego et al. that the
above properties of dried cryogel chitosan membranes can be controlled by six freezing
and thawing (F/T) treatments, as well as by crown ether or GA activation or cross-linking.
The combined F/T and cross-linking technique increases the thermal stability of chitosan.
It seems that freezing and thawing (F/T) treatment of membranes has a superior effect on
the biopolymer crystallinity when compared with cross-linking [53,54]. In Table 8.1, the
authors have made a comparison between the activities of C. rugosa lipase immobilized on
chitosan membranes used in this work and the same information published for the same
lipase on similar supports for use as catalysts in nonaqueous media [56].
8.3.6 electrodeposition Method
Chitosan's pH-responsive properties allow it to be directed to assemble (i.e., to electrode-
posit) in response to locally applied electrical stimuli. Chitosan can be electrodeposited
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