A Study of Physical and Covalent Hydrogels Containing pH-Responsive Microgel Particles and Graphene Oxide

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.

A study of conductive hydrogel composites of pH-responsive microgels and carbon nanotubes

“…43 Because CNTs are hydrophobic we postulated that MGs could also be used to disperse CNTs and enable preparation of DX MG/CNT gel composites. In contrast to the DX MG/GO composites 42 we show in the present study that attractive MG-to-CNT interaction are essential for hydrogel composite preparation. Whilst the previously studied DX MG/GO modulus values increased linearly with GO concentration the ductility was constant.…”

“…This observation confirmed that strong, attractive, MG-CNT interactions were present (which is a new result for MG research) and contrasts to our earlier work involving mixed MG/GO dispersions where the two components were repulsive. 42 We established that by increasing the pH to 6.8, where partial MG1 particle swelling occurred (Fig. 1e), the CNTs could be dispersed within viscous mixed MG1/CNT dispersions (Fig.…”

“…Whilst the previously studied DX MG/GO modulus values increased linearly with GO concentration the ductility was constant. 42 At variance with the latter data the ductility of the DX MG/CNT composites studied will be shown to increase with CNT concentration.…”

“…Recently, we investigated DX MG/graphene oxide (DX MG/GO) gel composites 42 which were prepared using blended dispersions of MGs and GO. The MGs and GO were both negatively charged, electrostatically repulsive and did not associate in mixed dispersions.…”

Doubly crosslinked microgel-colloidosomes: a versatile method for pH-responsive capsule assembly using microgels as macro-crosslinkers

“…Moreover, we have shown that our novel approach using vinyl-functionalised microgels as building blocks and macro-crosslinkers is general by using more than one microgel type to prepare DX MG-colloidosomes. The DX MG colloidosomes were prepared using environmentally benign conditions (pH = 6.8) and DX MGs that are biocompatible 21,22 which indicates suitability for incorporation of biological agents in future work. The DX MG-colloidosomes were strongly pH-responsive and exhibited a major pH-triggered swelling response in the physiological pH region which further supports the view that they have good potential for biomaterial applications, which will be explored in future studies.…”