Microstructure, mechanical properties, and in vitro biocompatibility of spark plasma sintered hydroxyapatite–aluminum oxide–carbon nanotube composite

In the present work, HA reinforced with Al2O3 and multiwalled carbon nanotubes (CNTs) is processed using spark plasma sintering (SPS). Vickers micro indentation and nanoindentation of the samples revealed contrary mechanical properties (hardness of 4.0, 6.1, and 4.4 GPa of HA, HA–Al2O3 and HA–Al2O3–CNT samples at bulk scale, while that of 8.0, 9.0, and 7.0 GPa respectively at nanoscale), owing to the difference in the interaction of the indenter with the material at two different length scales. The addition of Al2O3 reinforcement has been shown to enhance the indentation fracture toughness of HA matrix from 1.18 MPa m1/2 to 2.07 MPa m1/2. Further CNT reinforcement has increased the fracture toughness to 2.3 times (2.72 MPa m1/2). In vitro biocompatibility of CNT reinforced HA–Al2O3 composite has been evaluated using MTT assay on mouse fibroblast L929 cell line. Cell adhesion and proliferation have been characterized using scanning electron microscopy (SEM), and have been quantified using UV spectrophotometer. The combination of cell viability data as well as microscopic observations of cultured surfaces suggests that SPS sintered HA–Al2O3–CNT composites exhibit the ability to promote cell adhesion and proliferation on their surface and prove to be promising new biocompatible materials.