In recent years, a strong interest has emerged in hybrid composites and their potential uses, especially in chitosan-titanium dioxide (CS-TiO 2 ) composites, which have interesting technological properties and applications. This review describes the reported advantages and limitations of the functionalization of chitosan by adding TiO 2 nanoparticles. Their effects on structural, textural, thermal, optical, mechanical, and vapor barrier properties and their biodegradability are also discussed. Evidence shows that the incorporation of TiO 2 onto the CS matrix improves all the above properties in a dose-dependent manner. Nonetheless, the CS-TiO 2 composite exhibits great potential applications including antimicrobial activity against bacteria and fungi; UV-barrier properties when it is used for packaging and textile purposes; environmental applications for removal of heavy metal ions and degradation of diverse water pollutants; biomedical applications as a wound-healing material, drug delivery system, or by the development of biosensors. Furthermore, no cytotoxic effects of CS-TiO 2 have been reported on different cell lines, which supports their use for food and biomedical applications. Moreover, CS-TiO 2 has also been used as an anti-corrosive material. However, the development of suitable protocols for CS-TiO 2 composite preparation is mandatory for industrial-scale implementation.Materials 2020, 13, 811 2 of 27 they are synthesized by different methods (intercalation of the polymer, sol-gel, hydrothermal, electro-deposition, chemical and physical vapor deposition, suspension and liquid phase deposition). These methods are effective to enhance the technological and mechanical properties of each individual component and also reveal new functionalities [1,3]. Currently, there is a special interest in combining natural polymers such as chitosan (CS) with inorganic materials like titanium dioxide (TiO 2 ) to obtain hybrid composites (CS-TiO 2 ) with beneficial properties [3][4][5][6].Chitosan (CS) is a natural biopolymer (linear polysaccharide comprising 1-4 linked 2-amino-deoxy-β-D-glucan) generally obtained by deacetylation of chitin, the main structural component of crustacean exoskeletons. CS exhibits a poly-cationic character and is non-toxic and biodegradable [7]. CS is considered a biological functional compound with multiple interesting properties. It can form films for food and pharmaceutical applications, including edible coatings, packaging material, or as drug-eluting carrier [5,7]. Its adsorbent capacity can have environmental applications during photocatalytic processes of waste-water treatment [8], and it also has inherent antibacterial and antifungal properties [9]. It is biocompatible with several organic and inorganic compounds by the presence of free amino and hydroxyl functional groups in its structure, which can react with other functional groups by electrostatic forces, hydrogen bonds, or by compound-soak up into the polymeric matrix, thus improving its mechanical and biological properties [10]...
