*2.1.1 Synthesis of oxidized chitosan (OCS)*

*Chitin and Chitosan - Physicochemical Properties and Industrial Applications*

for preparing magnetic nanoparticles, such as co-precipitation [46], sol–gel [47], solvothermal [48], sonochemical and chemical vapor deposition phase (CVD) [49]. Among these methods, co-precipitation is considered as the simplest, most effi-

*Schematic representation of magnetic drug delivery system under the influence of external magnetic field.*

Ferrogels characterized by the presence of magnetic particles incorporated in polymer gels, are the subject of extensive research due to those magnetic particles and magnetic fields which have an extended application and clinical acceptance [50, 51]. Recent studies have shown controlled release of many drugs from ferrogels subject to magnetic fields [52, 53]. Ferrogels (FG) have made also injectable and biodegradable. However, typical drug delivery ferrogels have a disadvantage due to the cross-linking

There are only a few reports in the literature on the synthesis of Fe3O4 by coprecipitation method. In this paper, a macroporous ferrogel which is sensitive to magnetic field was studied. Furthermore, we are probably the first scientific team that reports the preparation of novel hydrogels and ferrogels based on chitosan and oxidized chitosan as cross-linking agent embedded Fe3O4/drug (5-FU, caffeine and ascorbic acid). **Figure 2** shows the magnetic drug delivery system under the influence of external magnetic field. The kinetics and in-vitro drug release profile of the

Chitosan (in powder form was prepared in our laboratory from exoskeletons of shrimp waste and purified, with degree of deacetylation >90% was determined by conductimetric titration), iron (II) sulfate heptahydrate (FeSO4.7H2O, sigma-Aldrich), iron (III) chloride (FeCl3.6H2O, Sigma-Aldrich), Caffeine (sigma-Aldrich), 5-Fluorouracil (sigma-Aldrich), Ascorbic acid (Fluka), Sodium metaperiodate (NaIO4, sigma-Aldrich), Hydrochloric acid (sigma-Aldrich), Ethylene glycol (sigma-Aldrich), Acetic acid (sigma-Aldrich), Sodium bicarbonate (Panreac),

agent toxicity, which limits the macroporous biomaterials synthesis [37].

drugs were studied in PBS pH (7.4) buffered solution at 37°C.

cient, and most economic method.

**Figure 2.**

**2. Materials and methods**

Sodium hydroxide (Sigma-Aldrich).

**2.1 Materials**

**6**

Oxidized chitosan (**Figure 3**) was prepared according to a previously reported method [54, 55]. The purified chitosan (1 g) ([GlcN] = 5.34 mM) was dispersed in 50 ml Hydrochloric acid solution HCl (10−3 M) at pH ranging from 4 to 5, and kept under magnetic stirring at 4°C for 30 min. Then 1 ml aqueous solution of sodium periodate 0.534 mM, P0 = 0.1 (P0 = moles of NaIO4 x moles of GlcN) was added to the mixture. The reaction system was covered with aluminum foil to prevent photo induced decomposition of periodate ion. The reaction lasted for 30 min at 4°C and it was interrupted by the addition of 1 ml ethylene glycol to inactivate any unreacted periodate in a molar ratio of 1:1. The oxidized derivative was washed by distilled water for 5 h and the dry product was obtained by freeze-drying.
