**4. Preparation of hydrogel using modified xylan**

Hydrogels are physical or chemical cross-linked three-dimensional polymer networks which swell upon by absorbing water without dissolving in it. The shape and the volume of hydrogels can be reversibly changed by various external stimuli such as pH, temperature, light, and electric and magnetic fields. Xylan is a renewable natural polymer bearing the advantages over other polymers in terms of non-toxicity, biocompatibility, biodegradability, and natural abundance. The ease of functionalization or chemical cross-linking of the hydroxyl moieties present in the backbone of xylan make it an attractive precursor for hydrogel preparation. Recently, xylan-based hydrogels have gained attention because of the multi-responsive behavior toward pH, organic solvents, and ions.

#### **4.1 Preparation of hydrogel using carboxymethyl xylan as a precursor**

Hydrogel using CMX, a modified xylan is prepared by dissolving it in distilled water and stirring it at 60°C in a water bath followed by addition of ammonium persulfate (APS) solution, acrylic acid, and methylene-bis-acrylamide (MBA). A series of chemical reaction takes place in the mixture which is continued for about 4 hours and results as hydrogels which is taken out and washed with water properly and cut into small pieces [17]. The chemical reactions for the preparation of hydrogel are presented in **Figure 7**.

#### **4.2 Preparation of hydrogel using dialdehyde xylan as a precursor**

In this method, prepared dialdehyde xylan (DAX) as shown in **Figure 5**, a biocompatible gel material employed as a biopolymer-based crosslinker to enable the formation of 3D gel network. The transparent, clean, and non-toxic DAX-crosslinked hydrogel could be obtained from the Schiff base reaction between aldehyde groups of DAX and amino groups of gelatin (G) [16, 18]. The demonstrated xylan-based hydrogel through a simple approach opened a new door for skin care products from natural and renewable biomass (**Figure 8**).

#### **4.3 Preparation of hydrogel using carboxymethyl cellulose (CMC) as a precursor**

Carboxymethyl cellulose (CMC) is used as a precursor for preparation of stimuliresponsive hydrogels. The carboxymethyl group adds a negative charge to the pyranose backbone of xylan, and it significantly increases the cross-linking points and reactive sites. Thus, thermal radical reactions are often employed with the crosslinker to prepare CMC-based homopolymer and copolymer hydrogels. Overall, the CMC-based hydrogels are used as carriers for drugs and biological macromolecules.

CMC-based hydrogel is prepared by dissolving the carboxymethyl cellulose to distilled water followed by the addition of potassium persulfate (KPS) at 70°C for

**Figure 8.** *Reaction involved in the preparation of hydrogel from DAX.*

half an hour. The neutralized acrylic acid (AA) is added into the reaction mixture and subsequently the continuing stirred for about 2 hours. Thereafter, the pH of the reaction mixture is raised upto 8 by the addition of NaOH solution. The resulting outcome is precipitated by the addition of acetone. The precipitates of CMC-g-PNaA are dried in a vacuum oven for 24 hours at 60°C.

The CMC-g-PNaA (2% w/v) is further dissolved in distilled water by using a mechanical stirrer at 300 rpm for 6 hours. Then, 50 mL of CMC-g-PNaA solution is added dropwise in the 100 mL aqueous solution of FeCl3 (0.02 mol). The mixture converts into spherical hydrogel beads which are filtered, washed with distilled water, *Xylan-Based Hydrogels: A Polymeric Carrier for Sustained and Targeted Delivery of Drugs DOI: http://dx.doi.org/10.5772/intechopen.109201*

**Figure 9.**

*Chemical reactions of CMC react with radical-anion to form CMC-free radicals.*

**Figure 10.** *Chemical reactions of CMC-free radicals with AA and finally with ferric ions.*

and dried in a vacuum oven for 24 hours [19]. The chemical reactions involved in preparation of hydrogel from CMC are shown in **Figures 9** and **10**.
