Enzyme Immobilization on Chitosan-Based Supports - Chitosan Based Hydrogels: Functions and Applications - page 365

composite membranes and their application as carriers for Ur immobilization. The chitosan
layer was deposited on the surface as well as on the pore walls of the base membrane. It was
found that the average size of the pore under a selective layer base PANMV membrane is
7 μm, whereas the membrane coated with 0.25% chitosan shows a reduced pore size, less
than or equal to 5 μm, and that with 0.35% chitosan,about 4 μm. This resulted in a reduction
of the pore size of the membrane and in an increase of their hydrophilicity. Ur was cova-
lently immobilized onto all kinds of PANMV-chitosan composite membranes using GA.
The increase of thermal stability is mainly due to MPA of Ur on the surface of the support
by covalent linkage [85].
They also compared dual-layer matrices PANMV membranes coated with the physi-
cally bound chitosan PAVMVCHI-A and chemically bound chitosan PAVMVCHI-B (low-
molecular-weight chitosan: 10 kDa) and PAVMVCHI-C (high-molecular-weight chitosan:
400 kDa) for immobilization of acetylcholinesterase (AChE). The chemical-modified
PANMV membrane (PANMV-NaOH + ethylenediamine (EDA)) was used as a base for
the prepared dual-layer membranes. For the chemical chitosan-bound membrane, chito-
san was tethered onto the membrane surface to form a dual-layer biomimetic membrane
in the presence of GA. The relative activities and V max of the covalently immobilized
enzyme on PANMVCHI-B and PANMVCHI-C membranes were higher than that on
PANMVCHI-A membrane and chemical-modified membrane with NaOH + EDA. The
bound enzymes on PANMVCHI-B and PANMVCHI-C have higher thermal and storage
stability in comparison with AChE on PANMVCHI-A membrane and free enzyme [86].
8.5.2.2 Chitosan-Tethered Polysulfone Membrane
Edwards et al. used bench-scale, single-capillary membrane bioreactors (MRBs) to deter-
mine the influence of the chitosan coating on product removal after substrate conversion
by immobilized polyphenol oxidase (PPO) during the treatment of industrial phenolic
effluents. The viscous chitosan solution was circulated over the shell side of the membrane
to coat the entire outer surface, and the solution was neutralized with 8% NaOH, forming
the gel coating. PPO was immobilized by cross-flow circulation in pH 6.8 buffer on the
shell (outer) side of the membranes. It was shown that one advantage of forming a gel-like
layer of chitosan on the capillary membranes is that greater protein loading capacities can
be achieved as compared with noncoated membranes. Two functions are therefore served
using chitosan-coated capillary membranes and immobilized PPO: an initial highly
efficient process for the removal of phenolic pollutants from water and the effective in
situ color removal from the resultant permeate. In addition, the presence of chitosan
contributes considerably to decreasing the product inhibition, which is characteristic of
PPO [87].
8.5.2.3 Chitosan-Tethered Alumina Membrane
Porous membranes may exhibit pores with radii from micrometer to nanometer that deter-
mine their use in different filtration technologies. Commercial anodic alumina membranes
are microfiltration membranes restricted to a very limited number of pore diameters. In
general, these membranes have been employed as a template for the preparation of nano-
particles, nanotubes, nanofibrils, and nanowires of different materials including polymers,
metal oxides, metals, and other nanostructured solids.
Darder prepared a set of home-made nanoporous alumina membranes of different
dimensions by electrochemical oxidation of aluminum in an acidic solution, controlling