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. 2016 Nov 18;8(11):404.
doi: 10.3390/polym8110404.

Thixotropic Supramolecular Pectin-Poly(Ethylene Glycol) Methacrylate (PEGMA) Hydrogels

Siew Yin Chan  1   2 , Wee Sim Choo  3 , David James Young  4   5   6 , Xian Jun Loh  7   8   9
Affiliations

Thixotropic Supramolecular Pectin-Poly(Ethylene Glycol) Methacrylate (PEGMA) Hydrogels

Siew Yin Chan et al. Polymers (Basel). .

Abstract

Pectin is an anionic, water-soluble polymer predominantly consisting of covalently 1,4-linked α-d-galacturonic acid units. This naturally occurring, renewable and biodegradable polymer is underutilized in polymer science due to its insolubility in organic solvents, which renders conventional polymerization methods impractical. To circumvent this problem, cerium-initiated radical polymerization was utilized to graft methoxy-poly(ethylene glycol) methacrylate (mPEGMA) onto pectin in water. The copolymers were characterized by ¹H nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA), and used in the formation of supramolecular hydrogels through the addition of α-cyclodextrin (α-CD) to induce crosslinking. These hydrogels possessed thixotropic properties; shear-thinning to liquid upon agitation but settling into gels at rest. In contrast to most of the other hydrogels produced through the use of poly(ethylene glycol) (PEG)-grafted polymers, the pectin-PEGMA/α-CD hydrogels were unaffected by temperature changes.

Keywords: cerium; pectin; poly(ethylene glycol) methacrylate; supramolecular hydrogel; α-cyclodextrin.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Mechanism of cerium-initiated radical polymerization.
Figure 2
Figure 2
The preparation of pectin-PEGMA/α-CD gels.
Figure 3
Figure 3
FTIR spectra of the precursors (pectin and 10KPEGMA) and of copolymer P-10K.
Figure 4
Figure 4
TGA curves of the precursors (pectin and 10KPEGMA) and copolymer P-10K.
Figure 5
Figure 5
Sol-gel transition graph for different compositions of P-10K/α-CD.
Figure 6
Figure 6
Amplitude sweeps performed from 0.01% to 100% of oscillation strain at 25 and 37 °C on hydrogels prepared with 10% P-10K and 10% α-CD.
Figure 7
Figure 7
Frequency sweeps performed from 0.01 to 50 Hz of oscillation strain at 25 and 37 °C on hydrogels prepared with 10% P-10K and 10% α-CD.
Figure 8
Figure 8
Amplitude sweeps at 0.05% and 25% strains performed instantaneously for three cycles at 25 and 37 °C on hydrogels prepared with 10% P-10K and 10% α-CD.
Figure 9
Figure 9
Temperature sweep performed from 10 to 40 °C on hydrogel prepared with 10% P-10K and 10% α-CD.
Figure 10
Figure 10
Threading of α-CD onto PEG chains to form columns of stacked inclusion complexes.
Figure 11
Figure 11
Polypseudorotaxanes inter- or intra-crosslink with each other via hydrogen bonding.
Figure 12
Figure 12
Pectin-PEGMA solution turned white after the addition of α-CD: (a) original 10% P-10K solution; and (b) 10% P-10K solution after the addition of α-CD (10%).
Figure 13
Figure 13
Thixotropic behavior of pectin-PEGMA/α-CD hydrogels.
See this image and copyright information in PMC

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