(a) Water contact angle values of pure PEEK, PEEK/MWNT nanocomposites and PEEK/nHA-MWNT hybrids. (b) WST-1 assay results showing cell viability of murine MC3T3-E1 pre-osteoblasts cultured on PEEK, PEEK/MWNT nanocomposites and PEEK/nHA-MWNT hybrids for 1, 3 and 7 days. * represents p < 0.05. (c) ALP activity normalized to protein content of MC3T3-E1 cells cultured on PEEK, PEEK/MWNT nanocomposites and PEEK/nHA-MWNT hybrids for different time points. (d) Photographs showing calcium mineralization (before staining) on PEEK/1.5 wt%MWNT, PEEK/30 wt%nHA-1.5 wt%MWNT and PEEK/30 wt%nHA-3.0 wt%MWNT specimens cultivated with MC3T3-E1 cells for 28 days (top panel); Calcified nodules on these specimens exhibit dark red appearance after staining with Alizarin red-S (bottom panel). Reproduced from [63] with permission of MDPI under the terms and conditions of the Creative Commons Attribution license.