**5. Effects of frequency**

**Figure 9** displays the substrates immersed in SBF for 7 days.

366 368High Energy and Short Pulse Lasers

**Figure 9.** SBF‐soaked substrates (A) 300 μm/ms, (B) 700 μm/ms.

**Figure 10** displays the results.

**Figure 10.** EDX analysis (A) 300 μm/ms, (B) 700 μm/ms.

As stated, a lower scanning speed delivers a larger number of pulses and therefore affects the surface topographic properties of the titanium more significantly. Additionally, with a larger number of pulses, the average surface temperature of the substrate increases, and therefore, a more ideal condition for the creation of titanium oxide is generated [25, 43]. **Figure 9** dis‐ plays these effects clearly. Considering **Figure 9(A)**, more apatite deposition is observed across

The apatite‐inducing ability of these titanium substrates is further analyzed using EDX.

the surface as opposed to **Figure 9(B)**, which agrees with the expectations.

Lastly, the effects of frequency on surface of titanium substrates are examined.

A range of frequencies (25, 50, and 100 kHz) is used in surface treatment, while the average laser power and pulse width are held constant to 11 W and in the range of 15–35 nm, respec‐ tively, to ensure consistency of final results (**Table 4** introduces the parameters used in more detail).


**Table 4.** Laser parameters used in surface treating of Ti substrates.

**Figure 11** shows the untreated titanium substrates using laser frequencies of 25, 50, and 100 kHz.

**Figure 11.** Non‐SBF Ti substrates at laser frequency of (A) 25 kHz, (B) 50 kHz, (C) 100 kHz.

As evident in this figure, with a higherfrequency, surface irregularities increase on the surface of the substrates. This enhances the surface topographic properties of the treated substrates and therefore increases the biocompatibility of the titanium [25, 41–43].

Furthermore, with a higher frequency, a larger amount of energy is delivered to the surface of the substrates, and the temperature increase causes more titanium oxide to form across the surface. This is similar to the results observed from the other parameters. Therefore, the substrates treated with a frequency of 100 kHz are expected to show the highest apatite‐ inducing ability across their surface.

#### **5.1. Biocompatibility assessment**

**Figure 12** displays the EDX analysis of substrates immersed in SBF for 3 days.

**Figure 12.** Ti substrates soaked in SBF for 3 days (A) 25 kHz, (B) 50 kHz, (C) 100 kHz.

As evident in **Figure 12**, oxygen concentration slightly increases with an increase in frequen‐ cy, showing an increase in the concentration of titanium oxide. The higher oxidation level of titanium results in increased negative charge across the surface. Thus, positively charged CO2, Ca2+, NOx, and H2O atoms/ions are attracted to and absorbed by the negatively charged surface of the titanium (OH<sup>−</sup> ), and create an environment with excellent affinity to biomaterials, such as proteins. The attraction forces between the apatite and the negatively charged titanium oxides are increased through the laser treatment, which, in return, increases the biocompati‐ bility of titanium [25, 42, 43].

This can be further observed by looking at the SEM photography of substrates immersed in SBF.

**Figure 13** displays the result.

In this figure, the apatite deposition layer is evident across the irradiated area. As observed from the EDX analysis, the apatite‐inducing ability of this substrate is high, which denotes the biocompatibility enhancement of the treated titanium.

**Figure 13.** Substrate soaked in SBF for 3 days at 100 kHz.
