2.2.6. Titanium Dioxide

Titanium is widely used in many surgical applications (e.g., prostheses and implants) because of its excellent biocompatibility, good mechanical properties, and lower mass density than steel [327]. The low density and high specific strength of titanium results in lightweight implants with good mechanical properties [238,239]. Furthermore, the smooth surface of Ti mesh prevents bacterial contamination instead of adsorbate materials. Therefore, titanium mesh provides an excellent solution to guide bone regeneration [243].

Nanostructured TiO2 materials of various morphologies such as nanoparticles, nanorods, nanowires, nanotubes, and other hierarchical nanostructures can be produced using different techniques such as, for example, microwaves [328,329], hydrothermal/solvothermal processes [330,331], sol–gel [332,333], anode oxidation [334,335], chemical vapor deposition [336,337], sonochemical processes [338,339], and green synthesis [340–342].

As can be seen from Figure 18, nanostructured TiO2 is a multifunctional material for a wide range of applications in engineering and biomedical areas. Interestingly, TiO2 nanoparticles represent a miniature of electrochemical cells capable of light-induced redox chemistry. This quality can be used for manipulating biomolecules and cell metabolic processes. TiO2 nanoparticles prove to have a higher affinity for binding proteins and other cellular components when used within cellular environment [343,344]. TiO2 nanoparticles can also be used to enhance photodynamic therapy (PDT) and sonodynamic therapy (SDT) [345].

**Figure 18.** Schematic representation of the many fields of applications of nanostructuredTiO2.

Titanium nanotubes (TNTs) possess excellent biocompatibility and drug-releasing performance. Furthermore, they can be generated on the surface of the existing medical implants [346,347]. The physical adsorption of the drugs promotes the anti-inflammatory properties of the TNTs, and with improved osteoblast adhesion, the drug-eluting technique is extended [348].

TiO2 based scaffolds are biocompatible, have good osteoconductive performance and antibacterial properties [349], and show high porosity, excellent interconnectivity, and sufficient mechanical strength [350,351]. Nanostructured TiO2 can be combined with several polymers including polylactic acid (PLA) [352]; poly(ether-ether ketone) (PEEK) [353]; poly(lactic-co-glycolic acid) (PLGA) [354]; and inorganic materials such as SiO2 [355], Al2O3 [356], bioglass [357], hydroxyapatite [358], graphene [359], and calcium phosphate [360].

Nano-TiO2 surface coated implants can limit autoimmune reactions between the underlying bone tissue surfaces and the implant [361]. However, material deterioration or generation of chronic inflammation in the implanted tissues may reduce success rate [361,362]. Various TiO2 nanostructures were used for loading and eluting cefuroxime as an antibiotic on orthopedic implants [363].
