## 4 Discussion  
The use of natural biopolymers and nanofiller for biomedical coating applications has increased interest among researchers because of their biocompatibility and antimicrobial properties. In this study, PLA bionanocomposites containing plasticizer, hydrolyzed collagen and silver nanoparticles were obtained using melt mixing technology. The topography of PLA bionanocomposites was evaluated by AFM. The results revealed the increased roughness in the case of PLA bionanocomposites due to the presence of collagen hydrolysate. The highest value of roughness surface was also observed in the case of reactive blending of PLA reinforced with thermoplastic cassava starch (TPCS) and commercial graphene (GRH) nanoplatelets [33]. The authors attributed the increase in roughness to irregular shapes of starch granules, while the presence of GRH nanoplatelets did not have a significant contribution. FT-IR analysis revealed the presence of C-O, C-H, and O-H stretching of the -CH (CH\({}_{3}\))-OH end group of PLA [34]. The absorption peaks assigned to C=O stretch (1041-1180 m\({}^{-1}\)) and -CH\({}_{2}\) asymmetrical stretch (2853-2923 cm\({}^{-1}\)) demonstrated the existence of collagen into bionanocomposites [34]. The addition of silver nanoparticles into PLA bionanocomposites up to 1 wt.% led to increase in the intensity of main absorption bands for PLA/AgNPs 0.5 and PLA/AgNPs 1 bionanocomposites. The same effect was observed in the case of polylactide (PLA)/nano-TiO\({}_{2}\) and PLA/nano-TiO\({}_{2}\)/nano-Ag blends films obtained by solvent casting [35]. This behavior can be explained by the presence of van der Waals interactions between the HO groups of PLA and the net atomic charge on the surface of the AgNPs [23] due to the asymmetric partition of electrons. The sample containing 1.5% AgNPs did not show any increase in the intensity of absorption bands, maybe due to the agglomeration of inorganic nanoparticles during melt processing. DSC showed that the introduction of ATBC plasticizer into PLA led to the reduction in both T\({}_{\rm g}\) and T\({}_{\rm m}\), as a result of the increase of chain macromolecular mobility. This behavior was also reported in another paper [8]. Our results revealed an increase of the T\({}_{\rm g}\) and the degree of crystallinity of PLA with loading of AgNPs indicated that a small amount of AgNPs acts as a nucleating agent for increase the crystallinity of the plasticized PLA [36]. Another paper stipulated that the introduction of AgNPs had no significant effect on the T\({}_{\rm g}\) of PLA samples [30; 35], while an increase in T\({}_{\rm g}\) value was observed in the case of PLA/cassava/GRH nanoplatelets [33]. The increase in the X\({}_{\rm c}\) was also reported in the case of PLA/chitosan foam [14]. The contribution of AgNPs to the durability of PLA bionanocomposites was investigated by chemiluminescence (CL). The stability of polylactic acid is related to the \(\beta\)-scissions occurred in the molecular backbones [37]. Study by chemiluminescence revealed that two types of oxidation precursors are implicated in the thermal degradation of PLA [38]. Accordingly, the addition of AgNPs will change the rate of degradation because they interact with free radicals. The contribution of AgNPs is connected to the electronic shell structure that is incomplete. The two contradictory processes, oxidation and stabilization, have an overall effect. It is observed that the silver nanoparticles block the oxidation of free radicals and the stability is improved. The same effect was observed in the case of introduction the natural phenolic antioxidants like powdered rosmenary ethanolic extract into the PLA matrix [39]. The literature shows the evaluation of antioxidant efficacy of synthesized AgNPs using 1,1-diphenyl-2-picryl hydrazyl radical (DPPH) [40], H\({}_{2}\)O\({}_{2}\)[41], ABTS radical cation scavenging, and FRAP assays [42]. It was reported that the DPPH and ABTS cation radical scavenging activity of AgNPs increased with the increase in the concentration of AgNPs [40; 42].