## 3 Results and Discussion
### Cellular Responses to the Investigated Samples  
Figure 9 depicts the SEM micrographs of MG-63 cells on the polished Ti, Ar plasma-modified Ti (100 W, 12 min, and 190 mTorr), and allylamine plasma-modified Ti (80 W, 22 min, and 150 mTorr) samples after culturing for one day. As shown in Figure 9a, the MG-63 cells exhibited an island-like shape and adhered flat to the polished Ti sample. A similar cell adhesion response could also be seen on the Ar plasma-modified Ti (100 W, 12 min, and 190 mTorr) sample (Figure 9b). When increasing the incubation time, it was found that the MG-63 cells almost completely adhered to the polished Ti and Ar plasma-modified Ti surfaces. However, it was clearly seen that the MG-63 cells presented a superior adhesion response with numerous filopodia (as indicated by arrows) on the surface of the allylamine plasma-modified Ti (80 W, 22 min, and 150 mTorr) sample after culturing for one day (Figure 9c). Compared with the polished Ti and Ar plasma-modified Ti surfaces, the filopodia of cells not only adhered flat, but also tightly grabbed the amino-groups deposited surface. This cell response feature could also be observed on the allylamine plasma-modified Ti sample with a longer incubation time. Accordingly, the biocompatibility results prove that the allylamine plasma-modified Ti sample with an optimal modification parameter (80 W, 22 min, and 150 mTorr) has great potential to promote cell adhesion ability.  
Surface modification of the implant materials played a crucial factor in controlling bone cells. Osteoblast alignment is vital for the realization of anisotropic bone tissue microstructure. Some of the latest studies have focused on nanogrooved topography fabricated by a laser irradiation approach to control osteoblast alignment [31; 32]. The results demonstrated the abnormal arrangement of bone matrix orthogonal to osteoblast arrangement through the nanogrooved surface. Moreover, [PERSON] et al. [33] also indicated that anisotropic dendrogenesis of osteocytes could be controlled with selective patterning of extracellular proteins. These findings provide new strategies to realize the ideal microstructure of bone tissue as well as provide molecular mechanisms for texture formation in biological systems. Furthermore, it is well known that biomaterials with amino-group coatings can enhance surface biocompatibility through cross-linking with bioactive materials such as proteins and growth factors, etc. [16; 17]. Our research team has also demonstrated that the amino-groups can be uniformly deposited on a Ti surface to bind with albumin using the promising low-temperature plasma polymerization with allylamine approach [34]. It was found that the presence of reactive functional groups on the Ti surface significantly affects the reaction between the cell and bone tissue [35; 36]. The formation of this feature can be attributed to the rapid absorption of biomolecules, mainly after the Ti implant surface is exposed to blood. Immobilized biomolecules can attract cells of host tissues to produce their own extracellular matrix and actively reshape the micronucle. Moreover, bone cells on the Ti implant surfaces will secrete non-collagen proteins, forming organic minerals to form biomineralization. Through this interaction process, absorbed bioactive materials (such as growth factors or proteins) are induced on the Ti implant surface to facilitate bone healing and  
Figure 9: SEM micrographs of the MG-63 cells on the investigated samples after culturing for one day: (**a**) Polished Ti, (**b**) Ar plasma-modified Ti (100 W, 12 min, and 190 mTorr), and (**c**) allylamine plasma-modified Ti (80 W, 22 min, and 150 mTorr).  
osseointegration [36; 37]. Therefore, the plasma polymerization with allylamine approach can be potentially used to fabricate a functional surface layer on Ti implants to cross-link with bioactive biomolecules for improving biocompatibility properties.