Biomedical Engineering Reference
In-Depth Information
8.5.4.1.4 Combined Ionization Gelation Method with In Situ Polymerization
The order of the above preparation process, adsorption and subsequently cross-linking by
TPP, can be reversed. It is well known that the NH
2
group on chitosan molecules may
interact with Fe
2+
in aqueous solution. In this study, the chitosan nanoparticles were first
prepared by cross-linking with TPP in HCl solution, the chitosan nanoparticles were in
the form of a gel and porous, and then Fe
2+
was added to the solution and adsorbed by the
chitosan nanoparticles. NaOH was used to adjust the pH and precipitate Fe(OH)
2
, and a
small amount of O
2
was used to oxidize the Fe(OH)
2
into Fe
3
O
4
. As the Fe
3
O
4
nanoparticles
were present in the pores of the chitosan gel, the monodispersion was good. The whole
procedure was completed in an aqueous solution, so the method is simple and effective,
and can be used for industrial production. The saturated magnetization of composite
nanoparticles reached 35.54 emu/g and the nanoparticles showed the characteristics of
superparamagnetism. The immobilization of lipase onto the particles showed good load-
ing ability and little loss of enzyme activity, and the stability of the catalyst was very good;
it only lost 12% of enzyme activity after five batches [108].
8.5.4.1.5 Magnetic Particles/Nanowires by LBL Self-Assembly
Lee and coworkers reported that a magnetic enzyme carrier (MEC) was prepared by
immobilizing the quorum quenching enzyme (acylase) on magnetic particles to overcome
the technical limitations of free enzyme. The MEC will be retained within the bioreactor
because of its larger size as compared to the membrane pores and can be easily recovered
and reused via magnetic capture. MIEX (ORICA, Australia), a magnetic ion-exchange
resin, was adopted as a magnetic core for the follow-up enzyme immobilization. MIEX,
which is made of divinyl benzene and glycidal methacrylate, has a net positive surface
charge. Maghemite (γ-Fe
2
O
3
) makes the resin magnetic. The functionalization of MIEX was
performed by LBL deposition of an anionic polyelectrolyte (polystyrene sulfonate (PSS))
and a cationic polyelectrolyte (chitosan). Porcine kidney acylase I was adsorbed physically
on the MIEX-PSS-chitosan to prepare “adsorbed enzyme” or was covalently attached to
the MIEX-PSS-chitosan using GA as a cross-linking agent to prepare “MEC.” The MEC
showed no activity decrease under both continuous shaking for 14 days and 29 iterative
cycles of reuse. Furthermore, the comparison of the MEC with free enzyme in a batch-type
MBR showed that the MEC efficiently alleviated the membrane biofouling and showed a
great advantage over free enzyme in terms of recycled use and stability in mixed liquor.
When the MEC was applied to the laboratory scale MRB in a continuous operation, it also
enhanced the membrane permeability to a large extent compared with a conventional
MBR with no enzyme [109].
Lei et al. reported that pectinase was immobilized on GA-activated Fe
3
O
4
/SiO
2
/P S S/
chitosan microspheres by covalent attachment. In order to build more stable assembly, the
polyelectrolyte brush PSS was grafted onto the surface of Fe
3
O
4
/SiO
2
composite particles
by surface-initiated atom transfer radical polymerization using modified magnetic silica
as the initiator. Subsequently, introducing an LBL self-assembly method, deposition occurs
by electrostatic interactions between the adsorbed PSS and the chitosan layer with oppo-
site charges. Biochemical studies showed an improved storage stability of the immobilized
pectinase as well as enhanced performance at higher temperatures and over a wider pH
range [110].
Magnin et al. have reported a facile method for the preparation of biocompatible and
bioactive magnetic nanowires. The method consists of the direct deposition of polysac-
charides by LBL assembly onto a brush of metallic nanowires obtained by electrodeposi-
tion of the metal within the nanopores of an alumina template supported on a silicon
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