**3. Results**

### *3.1. SEM Analysis of Time Deposition Study*

SEM analysis, as highlighted in Figure 1, was undertaken to examine the topographical nature of the pure PEEK substrates and the CaP thin film when the deposition time was varied. The SEM image for the pure PEEK substrate, highlighted in Figure 1a, illustrated a fairly flat surface with some scratches visible due to the abrasion of the surfaces. In comparison, the SEM images of HA modified PEEK (Figure 1b–h) indicated that there were marked di fferences between the topographies of each sample set (time deposition time points, 10–600 min, respectively). It is clear there were no voids in any of the thin films, and there was no evidence of cracking, delamination, and that the features shown below appear to be uniform. The initial interaction, as shown in Figure 1b (10 min deposition) and Figure 1c (30 min deposition), of the sputter deposited thin films and the PEEK material indicated that a physical change occurred on the surface of the PEEK material in the manner of 'pitting'. As the deposition time continued the SEM analysis indicated the development of a 'lattice-like' microstructure (Figure 1d–h). The average pore area (Figure 2a) and Feret's diameter (Figure 2b) for the pores was seen to generally increase with deposition time, until 450 min when they decreased. This was further corroborated with a calculation of the average number of pores per FOV as shown in Figure 2c. The number of pores declined with the increase in deposition time, which indicated that, with this coating process, there were fewer overall pores and that the pore area and diameter decreased, which indicated in-filling of the porous "lattice-like structure" as deposition time increased. The statistical comparison of the Feret's diameter, average pore area and number of pores is presented in Table 2, Table 3, and Table 4, respectively.

**Figure 1.** *Cont.*

**Figure 1.** SEM images of, (**a**) PEEK substrate and the deposition of CaP onto PEEK for the samples (**b**) HA10, (**c**) HA30, (**d**) HA60, (**e**) HA150, (**f**) HA300, (**g**) HA450, and (**h**) HA600.

**Figure 2.** *Cont.*

**Figure 2.** Results of the analysis of the SEM images showing (**a**). The average pore area of each modified PEEK sample; (**b**). The average Ferret's diameter of each modified PEEK sample; (**c**). The average number of pores for each modified PEEK samples.

**Table 2.** Statistical analysis of the average pore area of each across a variety of modified PEEK surfaces. *p* > 0.05: *p* < 0.05: \*, *p* < 0.01: \*\*, *p* < 0.001: \*\*\*.


**Table 3.** Statistical analysis of the average Feret's diameter of the pores across a variety of surfaces. *p* > 0.05: *p* < 0.05: \*, *p* < 0.01: \*\*, *p* < 0.001: \*\*\*.


**Table 4.** Statistical analysis of the number of pores across a variety of surfaces. *p* > 0.05: *p* < 0.05: \*, *p* < 0.01: \*\*, *p* < 0.001: \*\*\*.

