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Abstract: The mild preparation of multifunctional nanocom-
posite hydrogels is of great importance for practical applica-
tions. We report that bioinorganic nanocomposite hydrogels,
with calcium niobate nanosheets as cross-linkers, can be pre-
pared by dual-enzyme-triggered polymerization and exfolia-
tion of the layered composite. The layered HRP/calcium nio-
bate composites (HRP=horseradish peroxidase) are formed
by the assembly of the calcium niobate nanosheets with
HRP. The dual-enzyme-triggered polymerization can induce
the subsequent exfoliation of the layered composite and
final gelation through the interaction between polymer
chains and inorganic nanosheets. The self-immobilized HRP-
GOx enzymes (GOx=glucose oxidase) within the nanocom-
posite hydrogel retain most of enzymatic activity. Evidently,
their thermal stability and reusability can be improved. Nota-
bly, our strategy could be easily extended to other inorganic
layered materials for the fabrication of other functional
nanocomposite hydrogels.
Introduction
the glucose oxidase (GOx)/glucose (Glu) system has been fur-
[
10]
ther developed to replace the exogeneous H O . The gradu-
2
2
Hydrogels are a kind of soft material that have been widely ap-
plied in industry and biomedical areas due to their porous
ally generated H O can quickly react with HRP, avoiding the
2 2
detrimental effect of excess H O .
2
2
[1]
structure and water-rich microenvironment. However, tradi-
tional hydrogels, either polymers or supramolecular compo-
nents, always exhibit weak mechanical strength and are limited
In this work, a mild method to prepare bioinorganic nano-
composite hydrogels was designed and studied. First, nega-
À
tively charged calcium niobate (Ca Nb O , CNO) nanosheets
2
3
10
[
2]
[11]
in real applications. Haraguchi and co-workers first reported
the preparation of tough nanocomposite hydrogels by using
were generated by exfoliating layered HCa Nb O . The CNO
2 3 10
nanosheets were then reassembled with positively charged
HRP to form sandwich-structured composites. Upon addition
of glucose oxidase, glucose, and acetylacetone (ACAC) to an
aqueous solution of these sandwich composites, a HRP–GOx-
cascade-catalyzed system is generated and ACAC radicals are
produced. These ACAC radicals consequently initiate the poly-
merization of monomers. The polymerization occurs in the in-
terlayer of the composite and leads to facile exfoliation of lay-
ered composite and ultimately to the formation of a nanocom-
posite hydrogel.
[3]
clay nanosheets as inorganic cross-linkers. The ability for
these inorganic nanosheets to disperse well in water is neces-
sary to facilitate interactions between the nanosheets and
[
4]
polymer chains. However, there are few synthetic methods to
achieve effective dispersion in nanocomposite systems. One
successful method used to prepare tough nylon–clay nano-
[5]
composites is the melting–intercalated method. A similar
soft-chemistry exfoliation of an intercalated composite in
water should be an effective approach for the in-situ prepara-
[6]
tion of nanocomposite hydrogels. With this method, the dis-
persion difficulties experienced during preparation and purifi-
cation of the inorganic nanosheets can be avoided. The inter-
calated composites provide enough inorganic components
and have a suitable interlayer space to accommodate mono-
mers for facile exfoliation through polymerization and further
Results and Discussions
A typical nanocomposite hydrogel consists of four compo-
nents: water, poly (ethylene glycol) methacrylate (PEGMA),
CNO nanosheets, and the bio-sourced initiator (Figure 1a). The
prepared CNO nanosheets with an ideal single-layer structure
(see Figure S1 in the Supporting Information) were used as
cross-linkers. The dual enzymes HRP and GOx were employed
to generate ACAC radicals for initiating the polymerization of
PEGMA. The detailed preparation of the bioinorganic nano-
composite gel is as follows. First, negatively charged CNO
nanosheets self-assembled with positively charged HRP mole-
cules by means of electrostatic interactions form the sandwich-
structured HRP–CNO nanocomposite (Figure 1b). The compo-
[7]
gelation by means of three-dimensional crosslinking. The ex-
ploration of a mild polymerization method is another impor-
tant issue for the in situ preparation of nanocomposite hydro-
gels. Traditional free-radical polymerizations that occur under
[8]
thermal conditions, photo or high-energy radiation, are harm-
ful for the potential biomedical applications, due to the harsh
conditions required. This is one reason why enzyme-mediated
polymerizations for the preparation of nanocomposite hydro-
[9]
gels have recently become an attractive alternative. In these
studies, horseradish peroxidase (HRP) and hydrogen peroxide
form the initiation system that triggers the polymerization of
phenol and acrylamide derivatives. Since the excess H O may
site was added to a solution of the PEGMA monomer, GO , and
x
ACAC in PBS buffer (20 mm pH 6.0) to form a turbid precursor
solution (Figures 1c and 2a). Upon vigorous stirring, the
monomers diffused into the interlayer of the HRP–CNO nano-
composite. After adding glucose to the buffer, the dual en-
zymes generated radicals that initiated the polymerization of
the monomers. The polymer chains grew from the interlayer of
HRP–CNO nanocomposite and gradually exfoliated the struc-
ture (Figure 1d). Lastly, supramolecular interactions between
the exfoliated nanosheets and polymer chains lead to the for-
mation of a transparent hydrogel (Figures 1e and 2b). The
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2
inhibit the biomolecules’ functions, H O generated in-situ in
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[
a] C.-A. Liao, Q. Wu, Q.-C. Wei, Prof. Dr. Q.-G. Wang
Department of Chemistry, Tongji University
Shanghai 200092 (P. R. China)
E-mail: wangqg66@tongji.edu.cn
[
**] HRP=horseradish peroxidase; GOx=glucose oxidase.
Chem. Eur. J. 2015, 21, 12620 – 12626
12621
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim