**2.4 Bio-compatibility test of the coating**

A direct contact method was used to perform cytotoxicity test with test samples. Samples of Pure SS-316L, CoCrMo, and Ti6Al4V, 5 wt% coatings, and 10 wt% coatings as per ISO 10993-5 are prepared. The test was done on 6 well plates. A fresh medium is used to replace the culture medium from the 3T3-L1 monolayer. On the cells test samples, negative & positive controls in triplicate were placed. After incubation at 38°C for 2, 15, and 30 days, the cell monolayer was examined

**Figure 7.** *Radial cracks on HA-CNT coating caused by microindentation.*

microscopically for the response around the test samples. The reactivity was based on the zone of lysis, vacuolization, detachment, and membrane disintegration as per norms. Hemocytometer was used for viable cell count as shown in with cell suspension >90% viability for each experiment. MTT experiments revealed that graphene-doped hydroxyapatite composite had a substantial influence on 293T cell growth and excellent biomimetic mineralization, as demonstrated by in vitro bioactivity studies.
