Abstract

In this study we mixed low concentrations of graphene oxide (GO) with microgel (MG) particles and formed composite doubly cross-linked microgels (DX MG/GO) gels. The MG particles comprised poly(ethyl acrylate-co-methacrylic acid-co-1,4-butanediol diacrylate) with pendant glycidyl methacrylate units. The MG/GO mixed dispersions formed physical gels of singly cross-linked MGs (termed SX MG/GO), which were subsequently heated to produce DX MG/GO gels by free-radical reaction. The influence of the GO concentration on the mechanical properties of the SX MG/GO and DX MG/GO gels was investigated using dynamic rheology and static compression measurements. The SX MG/GO physical gels were injectable and moldable. The moduli for the DX MG/GO gels increased by a factor of 4-6 when only ca. 1.0 wt % of GO was included. The isostrain model was used to describe the variation of modulus with DX MG/GO composition. Inclusion of GO dramatically altered the stress dissipation and yielding mechanisms for the gels. GO acted as a high surface area, high modulus filler and played an increasing role in load distribution as the GO concentration increased. It is proposed that MG domains were dispersed within a percolated GO network. Comparison of the modulus data with those published for GO-free DX MGs showed that inclusion of GO provided an unprecedented rate of modulus increase with network volume fraction for this family of colloid gels. Furthermore, the DX MG/GO gels were biocompatible and the results imply that there may be future applications of these new systems as injectable load supporting gels for soft tissue repair.

Highlights

  • The properties of hydrogels continue to evolve along with their structural complexity.[1]

  • The modulus values (G′ and E) for doubly cross-linked microgels (DX MGs)/graphene oxide (GO) were found to be proportional to CGO

  • The ductility of the SX MG/GO and DX MG/GO gels was lower than that for the respective GO-free gels. This was explained in terms of the morphology changes caused by GO, and we propose that the morphologies depicted in Scheme 1 generally apply

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Summary

Introduction

The properties of hydrogels continue to evolve along with their structural complexity.[1]. While the majority of gels investigated have been constructed from small molecules, a new type of gel has recently emerged that is constructed solely from interlinked microgel (MG) particles.[1,6] MGs are cross-linked polymer particles that swell in a good solvent[7,8] or when the pH appaprtrioclaecsh.8e−s10thLeiupeKt aalo.6f the polyacid chains comprising the showed that concentrated dispersions of pH-responsive MG particles containing pendant vinyl groups could be interlinked to form hydrogels, which are termed doubly cross-linked microgels (DX MGs) These hydrogels were constructed using sub-micrometer sized MG particles as the building blocks.

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