**3. Chitin and chitosan overview**

In recent years, the use of biopolymers has increased due to their broader application in cosmetics, pharmaceuticals, food industry, biomedical, agriculture, and environmental products. Chitin was discovered in 1811 by Braconnot and chitosan, in 1859, by Rouget [17]. Chitin is made of N-acetyl-D-glucosamine monomer units linked with β(1,4) glycosidic linkage, whereas chitosan is the deacetylated form of chitin [18]. In addition, chitosan presents a rigid crystalline structure due to interand intramolecular hydrogen bonds as a result of the amine and hydroxyl groups [18].

Chitosan is a long chain of hydrophilic polysaccharide with a chemical formula of β(1–4) 2-asetamide-2-deoxy-D-glucopyranose. Chitosan is also known to be a natural polymer with similar molecular structure as cellulose; however it varies in the C-2 chain where the hydroxyl group in cellulose is replaced by amine (NH2). Chitosan is used to inhibit biofouling, being nontoxic and biocompatible, and also possesses inherent antimicrobial properties [19].

Chitin can be extracted from the exoskeletons of crustaceans and fungi by a two-step chemical processing: demineralization and deproteinization [20]. A wide variety of chemical processes allow preparing chitosan: solution casting, dipping and spray coating, compression molding, blending, layer-by-layer, and 3D printing [21].

Chitin along with chitosan is considered the most abundant natural polysaccharides after cellulose. Due to the abundance of waste of shrimps, crabs, and other

**77**

*Biodegradable Chitosan Matrix Composite Reinforced with Titanium Dioxide for Biocidal…*

crustacean exoskeletons, chitin and chitosan are both a cost-effective and abundance product. As polymers, they can be shaped as membranes, films, nanofibers, capsules, tablets, microspheres, pastes, gels, powders, filaments, granules, sponges, and hydrogels. Biomedical uses of chitosan and chitin include drug delivery systems, tissue engineering, and wound healing, as a result of their extensive biocompatibility and biodegradability. For instance, chitosan can be degraded in vertebrates mainly by lysozyme and certain bacterial enzymes in the colon [22]. Moreover, chitosan presents a high in vivo biocompatibility and biodegradability with minimal inflammation and body reaction when applied as tissue [23]. Moreover, the film adhesion on tissue can induce the proliferation of fibroblasts, indicating high biocompatibility [23]. Despite the great biological properties, such as biocompatibility, nonimmunogenicity, antibacterial, and anti-tumorigenicity, there is a lack of sufficient knowledge on the regenerative mechanism of this biopolymer [24]. Another advantage is their functionalization, especially in the hydrophilic group, hydrophobic group, cationic group, targeting ligand, thiol group, and amino acid. This can lead to various gene therapy applications by improving their solubility, toxicity, buffering capacity, escapes in endosome, cellular uptake, genetic material release, transfection efficiency, and silencing efficiency [17]. Chitosan is also known for its anti-inflammatory effects on in vivo tissue applications, which can be applied to inhibit growths of Gram-positive and Gram-negative bacteria. Acting alone, chitosan has shown much promise in wastewater treatment, as it can be used in the removal of dyes, odor, organic pollutants, and inorganic heavy metal ions from industrial wastewater [21]. It can also be applied as an antifouling material used on boat paint because of its prevention on bacteria formation [25]. A problem is that parameters such as molecular weight of chitosan, acetic acid concentration, sterilization process, thickness of the matrix, pH of the medium, and cell parameters (i.e., age, concentration, and bacteria

*DOI: http://dx.doi.org/10.5772/intechopen.84397*

type) led to important differences on microbial growth [18].

Titanium dioxide has many commercially available applications in the food industry as a food additive, in the cosmetic industry as a makeup additive and sunscreen, and in the health industry as a drug delivery system [26]. It has also been used as a treatment of wastewater to remove pollutants [27]. Pure titanium dioxide when exposed to ultraviolet light (wavelength less than 400 nm) becomes a photocatalytic material [28]. This is largely dependent on particle size, shape, surface characteristics, and the dioxide crystal structure [29]. Different TiO2 crystal structures (viz., anatase, rutile, and brookite) have different photocatalytic properties [29]. Sayes et al. demonstrated that the anatase polymorph is more reactive under ultraviolet light (UV) [30], which renders it more cytotoxic. Furthermore, Blinova et al. stated that pure anatase induces apoptosis but does not generate ROS, while rutile does initiate cell death through the formation of ROS [31]. Davis et al. proposed that anatase particles under 100 nm have a strong UV absorption [32]. Nevertheless, TiO2 is a proven photocatalytic material under UV light. When this energy is greater than the band gap, i.e., 3.06 eV for rutile and 3.23 eV for anatase [33], the electrons in the valence band (VB) are excited to the conductive band (CB), producing a corresponding hole in the valence band and highly reactive

) on the TiO2 surface, as shown in **Figure 3**. The electrons and holes react with water and air to form the highly chemical active ROS. There are four main and common ROS: superoxide radical (O2<sup>−</sup>), hydroxyl radical (OH<sup>−</sup>), hydrogen peroxide (H2O2), and singlet oxygen (O<sup>−</sup>) [34]. They range from less acute (O2− and H2O2) to more acute (O2<sup>−</sup> and O<sup>−</sup>) [34]. Not all

**4. Titanium dioxide**

reactants (e<sup>−</sup> and h+

*Biodegradable Chitosan Matrix Composite Reinforced with Titanium Dioxide for Biocidal… DOI: http://dx.doi.org/10.5772/intechopen.84397*

crustacean exoskeletons, chitin and chitosan are both a cost-effective and abundance product. As polymers, they can be shaped as membranes, films, nanofibers, capsules, tablets, microspheres, pastes, gels, powders, filaments, granules, sponges, and hydrogels. Biomedical uses of chitosan and chitin include drug delivery systems, tissue engineering, and wound healing, as a result of their extensive biocompatibility and biodegradability. For instance, chitosan can be degraded in vertebrates mainly by lysozyme and certain bacterial enzymes in the colon [22]. Moreover, chitosan presents a high in vivo biocompatibility and biodegradability with minimal inflammation and body reaction when applied as tissue [23]. Moreover, the film adhesion on tissue can induce the proliferation of fibroblasts, indicating high biocompatibility [23]. Despite the great biological properties, such as biocompatibility, nonimmunogenicity, antibacterial, and anti-tumorigenicity, there is a lack of sufficient knowledge on the regenerative mechanism of this biopolymer [24]. Another advantage is their functionalization, especially in the hydrophilic group, hydrophobic group, cationic group, targeting ligand, thiol group, and amino acid. This can lead to various gene therapy applications by improving their solubility, toxicity, buffering capacity, escapes in endosome, cellular uptake, genetic material release, transfection efficiency, and silencing efficiency [17]. Chitosan is also known for its anti-inflammatory effects on in vivo tissue applications, which can be applied to inhibit growths of Gram-positive and Gram-negative bacteria. Acting alone, chitosan has shown much promise in wastewater treatment, as it can be used in the removal of dyes, odor, organic pollutants, and inorganic heavy metal ions from industrial wastewater [21]. It can also be applied as an antifouling material used on boat paint because of its prevention on bacteria formation [25]. A problem is that parameters such as molecular weight of chitosan, acetic acid concentration, sterilization process, thickness of the matrix, pH of the medium, and cell parameters (i.e., age, concentration, and bacteria type) led to important differences on microbial growth [18].
