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. 2022 Jun 9;8(6):366.
doi: 10.3390/gels8060366.

Synthesis and Hydrogelation of Star-Shaped Graft Copolypetides with Asymmetric Topology

Thi Ha My Phan  1 , Yu-Hsun Yang  1 , Yi-Jen Tsai  1 , Fang-Yu Chung  1 , Tooru Ooya  2   3 , Shiho Kawasaki  2 , Jeng-Shiung Jan  1   4
Affiliations

Synthesis and Hydrogelation of Star-Shaped Graft Copolypetides with Asymmetric Topology

Thi Ha My Phan et al. Gels. .

Abstract

To study the self-assembly and hydrogel formation of the star-shaped graft copolypeptides with asymmetric topology, star-shaped poly(L-lysine) with various arm numbers were synthesized by using asymmetric polyglycerol dendrimers (PGDs) as the initiators and 1,1,3,3-tetramethylguanidine (TMG) as an activator for OH groups, followed by deprotection and grafting with indole or phenyl group on the side chain. The packing of the grafting moiety via non-covalent interactions not only facilitated the polypeptide segments to adopt more ordered conformations but also triggered the spontaneous hydrogelation. The hydrogelation ability was found to be correlated with polypeptide composition and topology. The star-shaped polypeptides with asymmetric topology exhibited poorer hydrogelation ability than those with symmetric topology due to the less efficient packing of the grafted moiety. The star-shaped polypeptides grafted with indole group on the side chain exhibited better hydrogelation ability than those grafted with phenyl group with the same arm number. This report demonstrated that the grafted moiety and polypeptide topology possessed the potential ability to modulate the polypeptide hydrogelation and hydrogel characteristics.

Keywords: hydrogel; polypeptide; star-shaped polymer; topology.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study, in the collection, analyses, or interpretation of data, in the writing of the manuscript, or in the decision to publish the results.

Figures

Scheme 1
Scheme 1
(a) The representative procedure of synthesis of 6-armed poly(L-lysine)-graft-indole (6s-PLL-g-Indo) using polyglycerol dendrimer of generation 1 (PGD G1) as the 6-armed initiator. (b) The structures of PGDs of generations 2 and 3 (G2 and G3) as 12-armed and 24-armed initiators, respectively. Abbreviations: Z-L-lysine N-carboxyanhydride (ZLL NCA), 1,1,3,3-tetramethylguanidine (TMG), 6-armed poly(Z-L-lysine) (6s-PZLL), hydrogen bromide (HBr), 6-armed poly(L-lysine) (6s-PLL), 1-ethyl-3-(-3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS).
Figure 1
Figure 1
1H NMR spectra of (a’) 12-armed poly(Z-L-lysine)12 (12s-PZLL12) in TFA-d1, (b’) 12-armed poly(L-lysine)12 (12s-PLL12) in D2O, (c’) 12-armed poly(L-lysine)12-graft-indole0.10 (12s-PLL12-g-Indo0.10) in D2O, and (d’) 12-armed poly(L-lysine)12-graft-phenyl0.08 (12s-PLL12-g-Phenyl0.08) in D2O. The symbols were used to represent the different protons.
Figure 2
Figure 2
FE-SEM images of lyophilized (a)12s-PLL12-g-Indo0.10, (b) 12s-PLL12-g-Phenyl0.08, (c) 24s-PLL12-g-Indo0.11 and (d) 24s-PLL12-g-Phenyl0.13 samples. The polypeptide concentrations of 12-armed and 24-armed polypeptides were 8.0 wt% and 5.0 wt%, respectively.
Figure 3
Figure 3
XRD patterns of 12-armed and 24-armed graft polypeptides. All the samples were lyophilized before analyzing. The concentration of 12-armed and 24-armed polypeptide hydrogels were 8.0 wt% and 5.0 wt%, respectively.
Figure 4
Figure 4
SAXS spectra of 12-armed and 24-armed polypeptide hydrogel samples with the polypeptide concentration of 8.0 wt%.
Figure 5
Figure 5
Storage modulus (G’: closed symbol) and loss modulus (G”: open symbol) of (a) 12-armed and 24-armed graft polypeptide hydrogels under different angular frequencies at fixed strain (0.1%) and (b) various strains at an angular frequency of 1.0 rad/s. The polypeptide concentration of all samples was 8.0 wt%.
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