## 3 Biomedical Applications of Yttrium Oxides Nanoparticles
### Antibacterial Activity  
Y\({}_{2}\)O\({}_{3}\) has been shown to reportedly contain the ability of bacterial growth suppressor against both gram-positive and gram-negative harmful pathogens. The actions of Y\({}_{2}\)O\({}_{3}\) can be divided into two types. Firstly, Y\({}_{2}\)O\({}_{3}\) gets directly into the bacterial cell wall and activates intracellular reactive oxygen species (ROS). [PERSON] and [PERSON] et al. [17] have reported that plant leaf extract of _Acalypha indica_ used NPs were found to be effective against _E. coli_, _P. aeruginosa_, _S. marcens_, and _S. aureus_, and minimum concentration was recorded as (11, 10, 13, and 13) \(\upmu\)g m\({}^{-1}\), respectively. The optimum concentration of Y\({}_{2}\)O\({}_{3}\) NPs required was reported to be (8-10) \(\upmu\)gm\({}^{-1}\). The mechanism involved is still not precise. It was understood that Y\({}_{2}\)O\({}_{3}\) nanoparticles, after invading the bacteria, act on their enzymes to inactivate them. They subsequently enhance hydrogen peroxide production that leads to bacterial cell death. It has been noted that the outcomes of their experiments indicated Y\({}_{2}\)O\({}_{3}\) NPs enable the cellular metabolism of the organism to be suppressed, causing the fatality of bacteria, and Y\({}_{2}\)O\({}_{3}\) could be used as an effective growth inhibitor of several pathogens and offers scope as an antimicrobial regulating system. Another study demonstrated by [PERSON] et al. [40] has described a water-based synthesis of yttrium fluoride NPs using the sonochemical irradiation process. In their studies, _E. coli_ and _Staphylococcus aureus_ were used as bacterial pathogens with \(\upmu\)g/ML range. They suggested that antimicrobial activity was dependent on the size of the NP and highlighted that yttrium-based NPs have been used to develop antimicrobial and active biofilm production, which was attributable to their low solubility conferring external protection on the cell organelles.  
The application of NPs as antimicrobials could contribute to an innovative model of targeting cellular organelles with existing antibiotics [84; 89; 90]. Recently, [PERSON] et al. evaluated the metal ion of yttrium, molybdenum, and thallium efficacy against bacteria _K. pneumoniae_ and _Acinetobacter baumannii_[91]. They found that higher concentration was needed to inhibit the growth of biofilms, compared to planktonic control. Minimal inhibitory concentration (MIC) of metal ions in planktonic cells does not affect biofilm. Yttrium ions and rhenium ions were possible for biofilm production. [PERSON] et al. [92] used yttrium, Zn, and TiO\({}_{2}\) synergistically as antibacterial materials, and formed doping Zn and yttrium nanoparticles. They were reported to contribute great effectiveness to the antibacterial activity of TiO\({}_{2}\). Several research reports provided that yttrium fluoride nanoparticles were added to the conventional orthodontic composite resin (Transbond XT) at different concentrations of prepared and showed significant antibacterial activity against _Streptococcus mutans_ with adhesion strength comparable to a conventional resin that is responsible for enamel demineralization, causing white spot lesions [93; 94].