## 3 Results and Discussion
### In Vitro Studies  
Figure 4 illustrates the cell-material interaction for the two types of membrane. SEM images show that a very small number of cells were found on the surface of the PCL-AC membrane. Regarding the morphology, the cells were not able to spread but shrank to nearly round shapes. In contrast, the PCL-7 AA/3 AC membrane displayed a higher significant number of L929 cells adhering on the surface, which were fully stretched and, hence, larger in size. As shown by the proliferation assay (Figure 4B), the proliferation rate calculated from the fluorescent signal every 2 days was approximately equal for the two types of membrane. This indicates that the influence of the two types of membrane on biocompatibility and cell proliferation rate was not significantly different. However, the number of cells found on the PCL-7 AA/3 AC membrane was always higher than the number of cells found on the PCL-AC membrane at all time points. This could be due to the clear difference in the number of cells initially adherent to the surface, which was supported by SEM images. These results indicate that the PCL-7 AA/3 AC membrane was more supportive of cell attachment than the PCL-AC membrane. This agrees with other studies that showed that the smaller pore size of the PCL-7 AA/3 AC membranes increases the surface area, increasing the surface for initial cell attachment [22]. Although the larger fiber diameters in the PCL-AC membrane also increased the surface area for cell adhesion, this effect might have been restricted by the hydrophobicity of the fibers [23] and outweighed by the large mean pore size [24]. Moreover, compared to the size of L929 cell pellets shortly post-seeding (8-10 \(\upmu\)m) [25], the PCL-AC pores were larger, while the PCL-7 AA/3 AC membrane acted as a barrier, retaining the cells on the surface. This indicates that the seeded cell pellets might infiltrate directly through the large pores of the PCL-AC sample [26] and helps explain the equal proliferative rates of the two membranes, which needs to be examined further in subsequent studies. Figure 3: (**A**) Water contact angle, (**B**) FT-IR spectra, and (**C**) Tensile curves of PCL-AC and PCL-7 AA/3 AC membranes. First and foremost, the use of relatively safe solvents like AC and AA is beneficial and sustainable, in line with the search for green solutions in all fields, including electrospinninging research, to eliminate the harmful effects of toxic organic solvents on human health and the living environment. The presented results indicate that the applications of the two fabricated membranes can be diverse. The clinical study of [PERSON] et al. reported that although sample extracts showed no sign of toxicity in vivo, chitosan films prepared from AA caused skin irritation in patients due to the acetate anions remaining on the films [27]. As demonstrated in Figure 3B, the solvent was completely removed from the PCL-7 AA/3 AC membrane during the electrospinninging process, which implies a possible use of the 7 AA/3 AC mixed solvent in co-electrospinning of PCL and other natural polymers like chitosan, gelatin, and collagen for clinical applications such as wound dressings, without causing allergy. In addition, the small pore size of the PCL-7 AA/3 AC membrane suggests its potential clinical and surgical use as a barrier membrane, for example in guided bone regeneration for atrophic jaw reconstruction [28]. For this purpose, PCL-7 AA/AC was effective not only in retaining the cells on the surface but also in supporting cell adhesion and proliferation, an important and necessary factor determining the success of a barrier membrane in guided bone regeneration [29]. Meanwhile, the high tensile strength and hydrophobic properties of the PCL-AC membrane suggest its applications in the textile industry, for example, for waterproof clothing.