## 4 Discussion  
To regenerate large sections of bone, the GBR membrane needs to be malleable enough to easily conform to bone morphology, and have adequate mechanical strength to maintain its form until the new bone has formed. There is a correlation between mechanical strength and thickness--thicker membranes have higher strength [23]. However, thick membranes are less flexible and formable, creating sharp edges when cutting, trimming, and bending them along the defect site. Thick membranes show less tissue adhesion, which permits penetration of soft tissue from the gap, preventing new bone formation. Thin membranes follow the bone morphology and do not create air pockets, which is advantageous for bone formation. However, with decreased mechanical strength, membranes can collapse into the defect cavity, decreasing the bone formation space and consequently the volume of new bone formed. There are reports that membranes of 100 to 200 \(\upmu\)m thickness are suitable for healing large-scale bone defects [24]. However, the lack of flexibility of membranes of this thickness gives them poor operability. An advantage of titanium membranes is that they maintain their mechanical strength even when thin. A thickness of 20 \(\upmu\)m is most suitable for GBR treatment, and accordingly, commercially available and clinically applied titanium membranes are 20 \(\upmu\)m thick. Our experiments were conducted with membranes of this thickness as well. As mentioned above in \begin{table}
\begin{tabular}{c c} \hline \hline
**Surface Treatment** & **Maximum Tensile Strength (N) (SD)** \\ \hline control (non-treated) & 309.5 \(\pm\) 29.3 \\ acid & 158.4 \(\pm\) 20.2 * \\ alkali & 295.0 \(\pm\) 48.3 \\ \hline \hline \end{tabular} SD: standard deviation; * \(p\) < 0.001 vs. other groups.  
\end{table} 
Table 2: Tensile strength of samples. Figure 4: The shapes of the water drops applied to each sample. (**a**) Control; (**b**) Acid; (**c**) Alkali group. the methods section, titanium membranes were manufactured through the extension of a titanium metal mass by applying pressure through the gap between two rollers. Consequently, the surface topography of non-treated membranes had a roughened structure. In the study, we used acid and alkali treatments for surface modification. Titanium exerts corrosion resistance by forming an oxide layer on the surface; however, it is corroded by non-oxidizing acid solutions such as H\({}_{2}\)SO\({}_{4}\) and HCl [25]. [PERSON] et al. [26] reported that corrosion is mainly due to dissolution of the membrane material--especially in acid solutions with a pH! 3. This corrosion is considered to change the surface structure and thickness of the titanium membrane. The surface of the acid treatment showed a regularly rough surface with micro scale pore structures. Although a rough surface was created on the titanium surface, the irregular rough surface and grooves which were observed in the non-treated sample were not detected. This is attributed to the fact that corrosion by strong acid slightly changed and smoothed the topography rather than providing the irregularly roughed non-treatment membrane. The effect of acid treatment was also reflected in membrane thickness. Thickness and mechanical tensile strength of acid treatment were significantly decreased compared with non-treated membrane and alkali membrane. Also, the SEM image appeared different surface topography, according to the results of thickness and tensile strength measurements. Several studies have reported that acid treatment modifies the wettability of titanium surfaces [12; 22]. In wettability test, the contact angle of acid treatment was significantly higher than non-treated and alkali treatment. Currently, we have no clear explanation for this discrepancy. However, these past studies were performed using finely polished, smoothly surfaced titanium disks as control samples. In our study, the control membrane had an irregular rough surface caused by the manufacturing process.