Biomedical Engineering Reference
In-Depth Information
higher than that of free lipase. Therefore, the immobilization process slightly decreased
the affinity of lipase to the substrate. On the other hand, the activity of immobilized lipase
decreased slowly with time as compared with that of free lipase, and could retain 75.5%
residual activity after six consecutive cycles. This immobilization remarkably improved
temperature and operational stability, which made it more attractive in the application
aspects [73].
8.4.2 Chemical-grafted Chitosan Copolymer
8.4.2.1 Chitosan-Poly(Glycidyl Methacrylate) Copolymer
Chellapandian and Krishnan reported that urease (Ur) was covalently attached onto
chitosan-poly(glycidyl methacrylate) by the introduction of epoxy groups to the support.
The immobilized Ur retained 82% of its specific activity. The pH optimum of the free and
immobilized Ur remained unchanged, but the optimum temperature of the immobilized
Ur was higher than that of the free enzyme. Immobilization improved the thermal, pH,
and storage stability of the enzyme [74].
8.4.2.2 Chitosan-Grafted Poly(Butyl Acrylate) by the Photochemical Technique
Compared with pure chitosan films, the chitosan-grafted poly(butyl acrylate) films have
enhanced hydrophobic and impact strengths. Similar work has also been reported for
grafting poly(hydroxyethyl methacrylate) (pHEMA) with chitosan in the presence of
UV light.
p
-Benzoquinone has the dual functions of activating the copolymer for the
immobilization of enzymes and acting as a mediator for electron shuttling in the system.
That sulfite oxidase enzyme can retain its bioactivity when it is covalently bonded to the
chitosan-pHEMA matrix shows that fabrication of a chitosan-pHEMA enzyme-based
electrochemical biosensor can be achieved using the techniques described in [75].
8.4.2.3 Itaconic Acid-Grafted Chitosan for Reversible Enzyme Immobilization
Many protocols for enzyme immobilization involve irreversible binding between an
enzyme and a functionalized support. In the reversible enzyme immobilization, the sup-
ports could be regenerated using a suitable desorption agent, and they could be recharged
again with a fresh enzyme. On the other hand, when the covalently immobilized enzyme
becomes inactivated upon use, both the enzyme and the support should be eliminated as
wastes. In the reversible enzyme immobilization, the expensive support can be repeatedly
used and the only waste produced is a solution of inactivated enzyme. For reversible
enzyme immobilization, ion exchangers, hydrophobic gels, and metal-chelated supports
have been used. Metal ions-chelated supports have been used extensively for separation
and purification of biological macromolecules (mainly for enzyme purification) from fer-
mentation broth or biological fluids. The low cost of metal ions and the reuse of support
materials for reversible immobilization enzymes for several times without any detectable
loss of metal-chelating properties can be the attractive features of metal affinity interac-
tions with the proteins.
Among the methods of modification of polymers, grafting is one of the promising
methods. For example, grafting of a functional pendant group carrying vinyl monomers
such as itaconic acid onto the chitosan backbone could introduce novel oxygen-rich
ligands for chelating hard Lewis metal ions. These novel comb-type polymer-grafted and
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