Injectable Thixotropic β-Cyclodextrin-Functionalized Hydrogels Based on Guanosine Quartet Assembly

Abstract

Facile method for the preparation of β-cyclodextrin-functionalized hydrogels based on guanosine quartet assembly was described. A series of seven hydrogels were prepared by linking β-cyclodextrin molecules with guanosine moieties in different ratios through benzene-1,4-diboronic acid linker in the presence of potassium hydroxide. The potassium ions acted as a reticulation agent by forming guanosine quartets, leading to the formation of self-sustained transparent hydrogels. The ratios of the β-cyclodextrin and guanosine components have a significant effect on the internal structuration of the components and, correspondingly, on the mechanical properties of the final gels, offering a tunablity of the system by varying the components ratio. The insights into the hydrogels' structuration were achieved by circular dichroism, scanning electron microscopy, atomic force microscopy, and X-ray diffraction. Rheological measurements revealed self-healing and thixotropic properties of all the investigated samples, which, in combination with available cyclodextrin cavities for active components loading, make them remarkable candidates for specific applications in biomedical and pharmaceutical fields. Moreover, all the prepared samples displayed selective antimicrobial properties against S. aureus in planktonic and biofilm phase, the activity also depending on the guanosine and cyclodextrin ratio within the hydrogel structure.

Keywords: antimicrobial activity; guanosine quartet; injectable hydrogel; supramolecular hydrogel; β–cyclodextrin.

Scheme 1

Schematic representation of the G4–CD structural unit synthesis: reaction of the β–CD 1,2 vicinal diols with corresponding equivalents of benzene–1,4–diboronic acid in the presence of KOH, followed by the subsequent interaction of the second boronic acid moiety with the 1,2 diols of the guanosine molecule.

Figure 1

Example of the G4–CD hydrogels network formation (a), each guanosine moiety linked to the β–CD molecule through the benzene–1,4–diboronic acid linker participate in the formation of G4 in the presence of potassium ion; possible stacking of β–CD molecules (b), driven by the multiple G4 formations; (c) picture of self–standing G4–CD_1–7 hydrogels with varied concentration of β–CD.

Figure 2

CD spectra of G4–CD_1 hydrogel in the 220–340 nm range recorded every five minutes from 60 to 25 °C.

Figure 3

Representative SEM images of freeze–dried G4–CD_1 (a) and G4–CD_7 (b) hydrogels reflecting differences in pore size and wall thickness.

Figure 4

Powder X–ray diffraction patterns of freeze–dried G4–CD_1–7.

Figure 5

AFM images of G4–CD_3: (a) scale bar–4 µm; (b) scale bar–1 µm; and (c) Z–profiles along the lines marked on the image (b).

Figure 6

Variation of (a) the viscoelastic moduli and (b) G’ as a function of strain, γ, at 25 °C and 10 rad s⁻¹. The inset figure illustrates the evolution of tan δ at 1 Pa and 10 rad s⁻¹ for all samples.

Figure 7

(a) Apparent viscosity, η, versus shear rate, $\dot{\gamma }$. The inset represents the variation of τ as a function of $\dot{\gamma }$ for investigated samples; (b) hysteresis loops for G4–CD_1 and G4–CD_7 samples; (c) viscosity recovery at an increase of up to 400 s⁻¹ and a decrease to 0 from $\dot{\gamma }$; (d) structure recovery ability determined by the continuous step strain measurements (1%–300%–1%) of G4–CD_1 and G4–CD_7 samples at ω = 10 rad s⁻¹.

Figure 8

Inversion tube test for G4–CD_7: immediately after mechanical shacking (a) and after 100 s left at room temperature (b).

Figure 9

Relative cell viability of S. aureus in planktonic and biofilm phase after incubation with G4–CD_1–7 hydrogels.