title: 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.
authors.affiliation: School of Materials, The University of Manchester , Grosvenor Street, Manchester, M1 7HS, United Kingdom.
authors.forename: Zhengxing
authors.initials: Z
authors.lastname: Cui
authors.forename: Amir H
authors.initials: AH
authors.lastname: Milani
authors.forename: Paula J
authors.initials: PJ
authors.lastname: Greensmith
authors.forename: Junfeng
authors.initials: J
authors.lastname: Yan
authors.forename: Daman J
authors.initials: DJ
authors.lastname: Adlam
authors.forename: Judith A
authors.initials: JA
authors.lastname: Hoyland
authors.forename: Ian A
authors.initials: IA
authors.lastname: Kinloch
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Freemont
authors.forename: Brian R
authors.initials: BR
authors.lastname: Saunders
mesh_terms: D002627:Chemistry, Physical; D003432:Cross-Linking Reagents / Q000138:chemical synthesis / Q000737:chemistry*; D005782:Gels / Q000737:chemistry*; D006108:Graphite / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D010087:Oxides / Q000737:chemistry*; D010316:Particle Size; D013499:Surface Properties
chemical_list: D003432:Cross-Linking Reagents; D005782:Gels; D010087:Oxides; D006108:Graphite