*3.2. Mechanical Testing*

Mechanical tests were used to evaluate the quality of the implants' osseointegration. It is important to note that no implant showed surface alteration or disruption.

In Figures 6 and 7 are represented the characteristic values of the load to failure (detachment force, *F*max) of implants under tensile pull-out testing, inferred for control and functionalized 3D metallic implants, at 4 and 9 weeks after surgery, respectively.

**Figure 6.** Detachment force, *Fmax*, of implants (*n* = 10) under tensile pull-out testing, inferred in the case of control 3D Ti implants (marked in blue color) and of those functionalized with (**a**) Li-C (marked in green color) and (**b**) Li-P (marked in orange color) coatings, at 4 weeks after surgery. \*\*\*\* Represents highly significant differences (*p* ≤ 0.0001). \*\* Represents significant differences (*p* ≤ 0.01).

**Figure 7.** Detachment force, *Fmax*, of implants (*n* = 3) under tensile pull-out testing, inferred in the case of control 3D Ti implants (marked in blue color) and of those functionalized with (**a**) Li-C (marked in green color) and (**b**) Li-P (marked in orange color) coatings, at 9 weeks after surgery. \*\*\*\*\* Represents highly significant differences (*p* ≤ 0.00001).

In the case of the extraction tests performed at 4 weeks (Figure 6a,b), the obtained mean detachment force values demonstrated (i) a highly significant difference between 18.6 N (±3.5), for the first control Ti group (*n* = 10), and 26.2 N (±2.9), for the Li-C test group (*n* = 10) (*p* = 0.00006) (Figure 6a), and (ii) a significant difference between 18.8 N (±3.5), for the second control Ti group (*n* = 10), and 25.4 N (±5.6), for the Li-P test group (*n* = 10) (*p* = 0.007) (Figure 6b).

When referring to the extractions performed at longer time periods, i.e., 9 weeks from surgery (Figure 7a,b), the inferred mean detachment force values indicated highly significant differences for both investigated cases: between 53.5 N (±2.2), for the first control Ti group (*n* = 3), and 106.6 N (±2.9), for the Li-C test group (*n* = 3) (*p* = 0.00003) (Figure 7a), and between 52.1 N (±2.5), for the second control Ti group (*n* = 3), and 83.7 N (±2.1), for the Li-P test group (*n* = 3) (*p* = 0.00009) (Figure 7b).

One can observe that, the failure loads of 3D Ti implants functionalized with both Li-C and Li-P coatings measured at 9 weeks were (3.4–5) and (2.3–4.8) times higher than those inferred at 4 weeks after surgery, respectively (Figures 6 and 7). It should be stressed here that, a similar trend was also observed by Yan et al., in the case of strontium-containing HA coatings [45]. Moreover, at 4 weeks after surgery, the 3D Ti implants functionalized with Li-C and Li-P coatings showed a bone attachment strength of about (1.1–1.8) and (1.1–2.1) times stronger than that corresponding to the control 3D Ti implants, respectively. After 9 weeks of implantation, the inferred values of the attachment force were about (1.9–2.1) and (1.5–1.7) times higher than controls, in the case of Li-C and Li-P samples, respectively. Therefore, one could indicate that both the PLD surface functionalization of 3D Ti implants and a longer implantation time period could positively influence the overall bone bonding strength characteristics of the investigated medical devices. With this result, the aim of this study was attained.
