ABSTRACT

Typical load-depth plots of the MIPS-HAp coating were obtained from the nanoindentation experiments conducted before and after SBF immersion, and these are shown in Figure 36.1a. The final depth of penetration increased only slightly with increase in immersion time from 1 to 14 days. As a result, there was only a very slight drop in the nanohardness (H) (Figure  36.1b), Young’s modulus (E) (Figure  36.1c), and the coefficient of friction (μ) (Figure 36.1d). Similar results were reported by others [10] and explained in terms of enhanced porosity. A similar logic held up in the present study as well [7]. Further, a slight initial decrease followed by increase in the nanomechanical properties had occurred, as the apatite layer deposition process

was dominant over the dissolution process during the subsequent 4 to 7 days of immersion in the SBF solution. This has been proved elsewhere [10] by ICP-AES (inductively coupled plasma atomic emission spectroscopy) study and scanning electron micrography. However, after 14 days of immersion, the nanohardness decreased very slightly in comparison to those measured at 4 and 7 days of immersion in the SBF solution (Figure 36.1a). The large number of dissolution sites observed from SEM study [7] ultimately formed a porous microstructure that possibly had slightly degraded the nanohardness of the MIPS-HAp coatings after 7 days of immersion in the SBF solution.