title: Bioactivity in silica/poly(γ-glutamic acid) sol-gel hybrids through calcium chelation.
abstract: Bioactive glasses and inorganic/organic hybrids have great potential as biomedical implant materials. Sol-gel hybrids with interpenetrating networks of silica and biodegradable polymers can combine the bioactive properties of a glass with the toughness of a polymer. However, traditional calcium sources such as calcium nitrate and calcium chloride are unsuitable for hybrids. In this study calcium was incorporated by chelation to the polymer component. The calcium salt form of poly(γ-glutamic acid) (γCaPGA) was synthesized for use as both a calcium source and as the biodegradable toughening component of the hybrids. Hybrids of 40wt.% γCaPGA were successfully formed and had fine scale integration of Ca and Si ions, according to secondary ion mass spectrometry imaging, indicating a homogeneous distribution of organic and inorganic components. (29)Si magic angle spinning nuclear magnetic resonance data demonstrated that the network connectivity was unaltered with changing polymer molecular weight, as there was no perturbation to the overall Si speciation and silica network formation. Upon immersion in simulated body fluid a hydroxycarbonate apatite surface layer formed on the hybrids within 1week. The polymer molecular weight (Mw 30-120kDa) affected the mechanical properties of the resulting hybrids, but all hybrids had large strains to failure, >26%, and compressive strengths, in excess of 300MPa. The large strain to failure values showed that γCaPGA hybrids exhibited non-brittle behaviour whilst also incorporating calcium. Thus calcium incorporation by chelation to the polymer component is justified as a novel approach in hybrids for biomedical materials.
authors: Department of Materials, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.
authors: Esther M
authors: EM
authors: Valliant
authors: Frederik
authors: F
authors: Romer
authors: Daming
authors: D
authors: Wang
authors: David S
authors: DS
authors: McPhail
authors: Mark E
authors: ME
authors: Smith
authors: John V
authors: JV
authors: Hanna
authors: Julian R
authors: JR
authors: Jones
mesh_terms: D001031:Apatites / Q000138:chemical synthesis*; D001672:Biocompatible Materials / Q000138:chemical synthesis*; D001826:Body Fluids / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry*; D002254:Carbonates / Q000138:chemical synthesis*; D002614:Chelating Agents / Q000737:chemistry; D008422:Materials Testing; D044367:Phase Transition; D011099:Polyglutamic Acid / Q000031:analogs & derivatives* / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry*
chemical_list: D001031:Apatites; D001672:Biocompatible Materials; D002254:Carbonates; D002614:Chelating Agents; C413465:hydroxycarbonate apatite; C511775:poly(gamma-glutamic acid); D011099:Polyglutamic Acid; D012822:Silicon Dioxide; D002118:Calcium