# Enhancement of Mechanical Properties of PCL/PLA/DMSO2 Composites for Bone Tissue Engineering
## 3 Results
### Fractography Analysis  
The surface and cross-sections of the specimens were analyzed before and after the three-point bending test to investigate the interface adhesion challenges using SEM. The SEM images are shown in Figures 5 and 6. Figure 5 shows the surface of the composites before the bending test. The surface of the PLA/PCL composites (Figure 5c) transitioned to a rough surface as PCL fillers were added into the PLA matrix. Pure PLA (Figure 5a) and pure PCL (Figure 5b) surfaces exhibited clear surfaces without any defects and agglomeration challenges [19]. However, the surface of the PLA/PCL composites (Figure 5c) became rough due to interface adhesion issues [19; 31; 62]. The surface of the PLA/PCL/DMSO\({}_{2}\) composites (Figure 5d-f) transitioned to a smooth surface as the DMSO\({}_{2}\) content increased compared to the surface of PLA/PCL composites (Figure 5c). This is the reason why PLA, PCL, and DMSO\({}_{2}\) composites were formed through a bonding reaction, whereas PLA and PCL composites were connected by a mechanical anchoring effect [36; 63; 64]. Figure 6 shows the cross-sectioned surfaces of the composites after the bending test. The cross-sectioned surface of the composites transitioned to a brittle-ductile combination state, characterized by a debonded PCL filler, as PCL was added into the PLA matrix. As shown in Figure 6a, the pure PLA matrix exhibited brittle characteristics, consistent with the references [32; 65], and pure PLA demonstrated the highest yield strength and modulus [32; 56]. On the other hand, as shown in Figure 6b and the stress-strain curve (Figure 4), the cross-sectioned surface exhibited ductile characteristics, with the matrix being elongated. Figure 6c shows the surface with a brittle-ductile combination characteristic. The PLA/PCL composites showed that the yield strength and modulus exhibited an increase compared to pure PCL, and the composites demonstrated greater ductility than pure PLA, as depicted in the stress-strain curve (S-S curve) and scanning electron microscopy (SEM) image. In addition, a debonded PCL particle was observed on the PLA matrix, consistent with previous studies by various researchers [19; 29; 31; 32]. In this study, the debonding of the PCL filler on the PLA matrix was confirmed. The cross-sectioned surface transitioned to a ductile state with an increase in DMSO\({}_{2}\) content. Figure 6d depicts a surface with both brittle and ductile characteristics. The brittle characteristics are attributed to PLA/PCL composites, while the addition of DMSO\({}_{2}\) induces ductile characteristics. As shown in Figure 6e,f, it is evident that the PLA matrix exhibits significant elongation compared to other composites, excluding pure PCL. The composite surface reveals numerous dimples and regions displaying plastic deformation, indicative of ductile fracture. Moreover, with an increase in DMSO\({}_{2}\) concentration, the ductility of the surface also increased. This outcome aligns directly with the enhancement in ductility (elongation) observed during bending tests. The presence of some porosities is attributed to the extraction of PCL particles [57]. Figure 7 shows the FTIR spectra of pure PLA, pure PCL, PLA/PCL composites, and PLA/PCL/DMSO\({}_{2}\) composites. As shown in Figure 7a-c, the presence of CH\({}_{2}\), C=O, CH\({}_{3}\), and C-O peaks are indicated. CH\({}_{2}\) stretching bands were observed at 2995-2915 cm\({}^{-1}\), a C=O stretching band appeared at 1760-1670 cm\({}^{-1}\), a CH\({}_{3}\) bending band was found at 1480-1346 cm\({}^{-1}\), and a C-O stretching band was noticed at 1210-1000 cm\({}^{-1}\). As shown in Figure 7d-f, the FTIR spectra were based on the spectrum of PLA/PCL composites, and -COOH bands and -COH bands, based on hydrogen at 1320-1210 cm\({}^{-1}\) and 1127-1042 cm\({}^{-1}\), respectively, were observed for PLA/PCL/DMSO\({}_{2}\) composites. The FTIR spectra of PLA/PCL composites indicated the absence of any chemical bonding reactions. [PERSON] et al.