## 3 Results and Discussion
### Morphology Study  
Nanoparticles, due to their size, may exhibit some unique features strictly correlated with their size and morphology. Thus, both inorganic and organic NPs (periclase/PDA) were investigated over a TEM microscope. As it can be observed in Figure 7a MgO nanoparticles are predominantly rectangular in shape, exhibiting well-defined edges and corners. This geometric form is indicative of their crystalline structure. The size of the nanoparticles varies from 20 to 100 nm in length. On the contrary, polymeric NPs prepared from dopamine chloride are characterized by a more regular, oval morphology. Moreover, periclase NPs appear darker compared to the surrounding media in the TEM microphotograph, which indicates higher electron density due to their heavy metal composition. This contrast allows for easy identification against other materials in the sample. As shown in Figure 7b, PDA NPs are generally smaller than the MgO nanoparticles and may exhibit a more irregular or spherical shape. These particles are typically distributed in the vicinity of the MgO nanoparticles, appearing a little bit clustered or aggregated. The surface of the poly(dopamine) nanoparticles shows a rougher texture compared to the smooth, crystalline surface of the MgO particles. This roughness can be attributed to the polymeric nature of poly(dopamine), which is composed of various functional groups that enhance its interaction with other materials. Poly(dopamine) nanoparticles appear less dense than the MgO nanoparticles, resulting in lighter shades in the TEM images. To further investigate newly prepared biomaterials and confirm their fibrous nature, SEM microscope imaging has been carried out. As shown in Figure 8, all prepared samples are characterized with nanofibrous structure. The PLA nanofibers are characterized by uniform, elongated shapes with diameters in the micro- and nanometer range. The fibers may appear as continuous strands, forming a web-like structure that is highly porous and provides a large surface area, which is beneficial for applications in tissue engineering and guided bone regeneration process. Moreover, such morphology prevents biofilm formation and bacteria adhesion. Importantly, the presence of MgO nanoparticles on the surface of the PLA nanofibers is visible in the SEM images. These nanoparticles appear as discrete particles scattered inside the fiber matrix. The crystalline MgO in the form of periclase nanoparticle contributes to the mechanical strength and may enhance the bioactivity of the fibers due to prolonged Mg\({}^{2+}\) ions release, which take part in the osteogenesis process. The poly(dopamine) nanoparticles can be observed as a secondary layer on the MgO-coated PLA nanofibers. The poly(dopamine) appears as darker, irreg  
Figure 7: TEM microphotographs (a)—periclase (b)—poly(dopamine). which may vary in size. This coating can improve the adhesion of biological molecules and cells due to the presence of functional groups introduced by poly(dopamine), enhancing the overall bioactivity of the scaffold. As shown in Figure 8, the combination of MgO and poly(dopamine) nanoadditives may introduce additional surface roughness to the nanofibers. The SEM images reveal a textured surface, promoting cell adhesion and proliferation, which is essential for tissue engineering applications. What is important, the addition of PDA and periclase NPs did not negatively affect the morphology and spatial micro-architecture of the biomaterials. The porosity allows for nutrient and waste exchange, making the scaffolds suitable for cell culture environments. Thus, performed PLA-based nanofibers preparation by means of electrospinning resulted in the formation of a complex and bioactive surface that is beneficial for various biomedical applications. The SEM images show a well-distributed layer of nanoparticles on the fibers without significant aggregation, which is crucial for maintaining the functional properties of the nanofibers.