title: Injectable in situ cross-linkable nanocomposites of biodegradable polymers and carbon nanostructures for bone tissue engineering.
abstract: This study investigates the effects of nanostructure size and surface area on the rheological properties of un-cross-linked poly(propylene fumarate) (PPF) nanocomposites and the mechanical properties of cross-linked nanocomposites as a function of the nanostructure loading. Three model carbon nanostructures were examined, C(60) fullerenes, ultra-short single-walled carbon nanotubes (US-tubes) and single-walled carbon nanotubes (SWNTs). Rheological measurements showed that C60 and US-tube un-cross-linked nanocomposites exhibited viscous-like characteristics with the complex viscosity independent of frequency for nanostructure concentrations up to 1 wt%. Compressive and flexural mechanical testing demonstrated significant mechanical reinforcement of US-tube and SWNT nanocomposites as compared to cross-linked polymer alone, with an up to twofold increase in the mechanical properties. Scanning electron microscopy examination of the fracture surface of cross-linked US-tube nanocomposite revealed lack of aggregation of US-tubes. Although sol fraction studies did not provide any evidence of additional cross-linking, due to the presence of US-tubes in the nanocomposites, transmission electron microscopy studies suggested the crystallization of PPF on the surface of US-tubes which can contribute to the mechanical reinforcement of the US-tube nanocomposites. These results demonstrate that the rheological properties of un-cross-linked nanocomposites depend mainly on the carbon nanostructure size, whereas the mechanical properties of the cross-linked nanocomposites are dependent on the carbon nanostructure surface area. The data also suggest that US-tube nanocomposites are suitable for further consideration as injectable scaffolds for bone tissue engineering applications.
authors.affiliation: Department of Bioengineering, Rice University, P.O. Box 1892, MS-142, Houston, TX 77251-1892, USA.
authors.forename: Balaji
authors.initials: B
authors.lastname: Sitharaman
authors.forename: Xinfeng
authors.initials: X
authors.lastname: Shi
authors.forename: Lesa A
authors.initials: LA
authors.lastname: Tran
authors.forename: Patrick P
authors.initials: PP
authors.lastname: Spicer
authors.forename: Irene
authors.initials: I
authors.lastname: Rusakova
authors.forename: Lon J
authors.initials: LJ
authors.lastname: Wilson
authors.forename: Antonios G
authors.initials: AG
authors.lastname: Mikos
mesh_terms: D001672:Biocompatible Materials / Q000008:administration & dosage / Q000737:chemistry; D001842:Bone and Bones / Q000737:chemistry / Q000378:metabolism; D002244:Carbon / Q000737:chemistry*; D019245:Compressive Strength; D003432:Cross-Linking Reagents / Q000737:chemistry; D008422:Materials Testing; D008956:Models, Chemical; D053761:Nanocomposites / Q000737:chemistry* / Q000648:ultrastructure; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure; D036103:Nanotechnology / Q000379:methods; D011108:Polymers / Q000737:chemistry*; D012212:Rheology; D023822:Tissue Engineering / Q000379:methods*; D014783:Viscosity
chemical_list: D001672:Biocompatible Materials; D003432:Cross-Linking Reagents; D011108:Polymers; D002244:Carbon