Biomedical Engineering Reference
In-Depth Information
The siloxane with an epoxide ring and trimethoxy anchor groups, GPTMS, could be
used to form a dense chitosan membrane in aqueous media by the one-pot process. Because
of possessing epoxy group and trimethoxy anchor groups, GPTMS acted as both an inor-
ganic resource and a bifunctional cross-linker. On the one hand, polysiloxane network for
the organic-inorganic hybrid formed resulting from self-hydrolysis and self-condensation
of GPTMS. On the other hand, the reactivity between amine groups and epoxy groups
offered a simple and convenient methodology for covalent incorporation of chitosan and
enzyme into the inorganic framework. With GPTMS as the silylating agent, Li et al. devel-
oped a novel H 2 O 2 biosensor based on in situ covalent immobilization of HRP into chitosan.
The resultant hybrid membranes are effective in the dehydration of prevaporized iso-
propanol-water mixtures with satisfactory permeation selectivity, permeation flux, and
long-term endurance (140 days) [131].
8.5.4.4.2 Macroporous Chitosan Layer Coated on Silica Gel
Xi and Wu prepared a new metal affinity chromatography (IMAC) adsorbent by coating
chitosan-PEG solution on nonporous silica gel, followed by the steps of chitosan deposi-
tion, PEG removal, cross-linking (ECO as the cross-linking agent), and copper ion loading.
The nonporous silica gel not only acted as a rigid support but also had little nonspecific
interaction between its residue exposed gel surface and protein. In order to maintain the
surface porous structure that was needed in affinity binding for the target protein, a
macroporous structure of the coated chitosan layer was obtained by the PEG molecular
imprinting and removing method. A suitable pore size could be designed in order to
achieve the maximum adsorption for a given protein through changing the molecular
mass and content of PEG in the coating solution. In the preparation procedure, the dried
chitosan-soaked silica gel was dispersed in DMSO solution, and chitosan was deposited
on the silica gel surface through the phase inversion method, which could prevent diffu-
sion of chitosan into liquid phase. This method might acquire a relatively thick chitosan
layer compared with other methods. The results proved that these kinds of ligand-free
matrices had the advantage of low nonspecific interaction, ease of preparation, high
adsorption capacity for metal-binding protein, and high stability. More importantly, poten-
tial selective adsorption of metal-binding protein could be achieved by designing the sur-
face pore size using the molecular imprinting method, as well as by utilizing the difference
in metal chelating ability [132].
In order to prove the latter ideas, the authors prepared the IMAC by chelating Cu 2+ , Zn 2+ ,
and Ni 2+ ions, respectively, on chitosan-SiO 2 . Trypsin could be adsorbed on the IMAC
adsorbent through metal-protein interaction forces. The metal ion species had significant
effects on the adsorptive capacity and the activity retention of trypsin. Zn-chitosan-SiO 2
was the best adsorbent among three kinds of M-chitosan-SiO 2 beads for trypsin immobi-
lization since it has high enzyme loading, high stability, and activity retention [133]. In
addition, the surface layer of chitosan has a porous structure and could provide a sufficient
amount of amino groups, which could be easily activated with the functional group of
epoxy, diazo, and aldehyde, respectively. The best results were obtained when trypsin was
immobilized via direct epoxy activation, which might be ascribed to the MPA between
enzyme and the support [134].
8.5.4.4.3 Chitosan Coated on Silica Gel by LBL Self-Assembly
Lei and Bi proposed a strategy for the fabrication of the silica-coated chitosan support
from LBL self-assembly. The monodisperse silica particles in the range of 150 nm were
prepared by a reported method [135]. The silica particles were first absorbed by dodecyl
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