Hydrogel Cross-Linking via Thiol-Reactive Pyridazinediones

Abstract

Thiol-reactive Michael acceptors are commonly used for the formation of chemically cross-linked hydrogels. In this paper, we address the drawbacks of many Michael acceptors by introducing pyridazinediones as new cross-linking agents. Through the use of pyridazinediones and their mono- or dibrominated analogues, we show that the mechanical strength, swelling ratio, and rate of gelation can all be controlled in a pH-sensitive manner. Moreover, we demonstrate that the degradation of pyridazinedione-gels can be induced by the addition of thiols, thus providing a route to responsive or dynamic gels, and that monobromo-pyridazinedione gels are able to support the proliferation of human cells. We anticipate that our results will provide a valuable and complementary addition to the existing toolkit of cross-linking agents, allowing researchers to tune and rationally design the properties of biomedical hydrogels.

Figure 1

(a) Schematic overview of hydrogel formation between an 8-arm star PEG-thiol macromer (blue) and a bis-pyridazinedione (PD, red) cross-linker; (b) chemical structures of the cross-linkers and macromer used in this work.

Figure 2

(a) Kinetic plot showing reaction of PD 1 with thiol 2 under second order conditions. k₁ was determined from a plot of 1/[1] as described in the Supporting Information.

Scheme 1. Synthesis of Bis-PD Crosslinkers 5

Figure 3

Inverted vials demonstrating either gel (green) or liquid (red) state following mixing of 8-arm PEG-SH, 6, and PD cross-linkers 5 at different pHs and time points.

Figure 4

Plot of the storage modulus, G′, for gels formed from cross-linkers 5 at different pHs. One-way ANOVA with Benjamini–Kreuger–Yekutieli correction was used to calculate significance, **P ≤ 0.005, ***P ≤ 0.0005.

Figure 5

Plot of the storage modulus, G′, over time following mixing of 8-arm PEG-SH and PD cross-linkers 5.

Figure 6

Inverted vials demonstrating either the gel (green) or liquid (red) state following incubation of gels formed from 5DiH with different equivalents of cysteamine.

Figure 7

Plot of percentage live cells over time after seeding THP-1 cells on 5-cross-linked hydrogels, or a tissue culture plastic control. Two-way ANOVA with Benjamini–Kreuger–Yekutieli correction was used to calculate the significance, ****P ≤ 0.00005.