| The widely-used artificial joint implants are made of the combination of metal, polymer and bio-inert ceramics now. However, several problems exist in clinical applications, such as release of the sensitized metal ions, loosening of the implants resulting from wear particles, and weakening of the surrounding bone due to high modulus. Biphasic calcium phosphate (BCP) ceramic possesses the characteristics of β-tricalcium phosphate (β-TCP) as well as hydroxyapatite (HA). It is better than single calcium phosphate ceramic in osteogenesis performance, so it has a wide range of applications in the fields of bone defects, repairing and filling. However, the poor mechanical properties limit it as substitute of load-bearing bone. Graphene and carbon nanotubes (CNTs), discovered, focused and investigated in recent years, are confirmed to have excellent mechanical properties in both theory and experiment, which can be as the composite fillers with the performances in strengthening and toughening, anti-friction and anti-wear.An artificial joint replacement material was fabricated via incorporation of graphene nanoplatelets (GNPs), Graphene and CNTs into BCP in this dissertation. The mechanical, tribological and biological properties were investigated, and the mechanisms for the modifications were proposed further. The main contents are as follows:The GNPs/BCP composite was fabricated by hot pressing (HP), and sonication, ball milling and CTAB as dispersant were adopted to disperse GNPs in the process. The experimental results indicated that BCP particles could coat the surfaces of GNPs homogeneously to make them disperse well because of the attraction of positive and negative charges on the surfaces. Due to external pressure and flow of powders, a preferred orientation of GNPs occurred during sintering, i.e. GNPs preferred to distribute perpendicular to the HP direction, leading to anisotropic mechanical properties. Parallel to the HP direction, the composite containing1.5wt%GNPs exhibited the maximum bending strength and fracture toughness of151.82MPa and 1.74MPa·m1/2, about55%and76%higher than those of monolithic BCP, respectively. Compared to the pure BCP along the direction perpendicular to HP, the1.5wt%GNPs/BCP composite displayed higher fracture toughness and a little lower bending strength. The microhardness and relative density decreased as increase of GNPs amount. However, phase composition and grain size were not influenced by the addition of GNPs. The interface between GNPs and BCP was bonded well, with no obvious transition layer.The Graphene/BCP composite was fabricated by HP, with CTAB as dispersant accompanying with sonication and ball milling to disperse GNPs. The experimental results indicated that the distribution of Graphene perpendicular the direction of HP, preferred during sintering, resulted to anisotropic mechanical properties. The addition of Graphene contributed to increase of mechanical properties in both directions, especially the direction parallel to HP, giving rise to outstanding strengthening and toughening effect. The composite containing0.2wt%Graphene possessed the maximum bending strength and fracture toughness of156.03MPa and1.95MPa·m1/2, about59%and97%higher compared with monolithic BCP along the direction parallel to HP. Graphene did not have an effect on phase composition and relative density, however, more addition of Graphene resulted to less grain size. The interfacial bonding between Graphene and BCP was well, and no obvious transition layer could be observed. The addition of Graphene also caused anti-friction and anti-wear effect obviously and improved the tribological properties of BCP in both directions, especially the direction perpendicular to HP. The friction coefficient and wear volume of composite incorporated with Graphene reduced greatly,50%for friction coefficient and one to two orders of magnitude for wear volume slower than those of pure BCP ceramic, respectively.The Graphene/CNTs/BCP composite powders were gained with dispersive techniques of CTAB dispersant, sonication and ball milling. Then corresponding composite was fabricated by HP. The results indicated that incorporation of Graphene and CNTs together led to anisotropic mechanical properties and increase of mechanical properties at both directions at the same time, displaying obvious strengthening and toughening effect. The composite exhibited higher mechanical properties parallel to HP direction. When0.2wt%Graphene and0.5wt%CNTs were added to matrix together, bending strength and fracture toughness reached165.64MPa and2.13MPa·ml/2,69%and115%increase compared to the monolith. As increase of Graphene and CNTs in the matrix, microhardness, relative density and grain size all had the tendency to decrease. The interfacial bonding between Graphene, CNTs and BCP was well, without obvious transition layer. The composite with addition of Graphene and CNTs revealed very low friction coefficient and wear volume. In contrast with the pure, the friction coefficient of the composite decreased up70%, and the wear volume decreased up two to three orders of magnitude. The tribological properties were improved dramatically more in the direction perpendicular to HP.The incorporation of GNPs, Graphene and CNTs into BCP ceramic generates significant strengthening and toughening effect. The reinforcement mechanisms mainly include crack deflection, crack branching, bridging, pullout, grain refinement and residual stress. Meanwhile, the addition of Graphene and CNTs into BCP caused outstanding anti-friction and anti-wear effect. The carbon layers were peeled off by friction force, which formed lubricant on the surface of composite. Graphene is better than CNTs in strengthening and toughening and anti-friction and anti-wear on BCP ceramic.Cytotoxicity and bioactivity of pure BCP ceramic, GNPs/BCP, Graphene/BCP, CNTs/BCP and Graphene/CNTs/BCP composites were investigated via MTT and soaking in simulated body fluid, respectively. The experimental results showed that cytotoxicity of these five types of composites was0-1grade, i.e. no cytotoxicity. Osteoblasts near and on the surface of the composites, whose morphology was normal and adherent growth was well, could adhere, spread and proliferate on the surface. The composites all could induce the formation of bone-like apatite on their surface in simulated body fluid, displaying good bioactivity.This work was financially supported by National Natural Science Foundation of China (No.30870610and81171463). |
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