Extraction of chitosan from Aspergillus niger mycelium and synthesis of hydrogels for controlled release of betahistine Gustavo Muñoz a , Carlos Valencia b , Nora Valderruten c , Eduardo Ruiz-Durántez c , Fabio Zuluaga a,⇑ a Departamento de Química, Universidad del Valle, AA. 25360 Cali, Colombia b Escuela de Ciencias Básicas-Salud, Universidad del Valle, AA. 25360 Cali, Colombia c Facultad de Ciencias Naturales, Universidad Icesi, AA. 25608 Cali, Colombia article info Article history: Received 20 September 2014 Received in revised form 24 March 2015 Accepted 30 March 2015 Available online 3 April 2015 Keywords: Aspergillus niger Chitosan Hydrogel Drug delivery In vivo biocompatibility study abstract Chitosan was extracted from the fungus Aspergillus niger, an alternative source of chitin that is widely available as a byproduct of the industrial production of citric acid. Chitosan with deacetylation degree (DD) of 73.6% was characterized by elemental analysis, capillary viscometry (molecular weight of 1.9  10 5 g/mol), Fourier transform infrared (FTIR), nuclear magnetic resonance ( 1 H NMR, 13 C NMR and 15 N NMR) spectroscopies, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Fungal chitosan was crosslinked with glutaraldehyde and glutaric acid to obtain hydrogels. Chitosan hydrogels were characterized by FTIR and by scanning electron microscopy (SEM), which showed that these materials have irregular, polydisperse, and interconnected pores. Kinetic studies of the release of betahistine from the swollen hydrogels showed a Fickian diffusion mechanism. Finally, hydrolytic degradation of chitosan hydrogels under simulated physiological conditions (pH 7.4 and 37 °C) was investigated as well as in vivo biocompatibility tests using New Zealand white rabbits as animal models. Ó 2015 Elsevier B.V. All rights reserved. 1. Introduction Local industrial production of citric acid by aerobic fer- mentation of sugars with the fungus Aspergillus niger produces 13,500 tons/year of wet mycelium as byproduct (Ing. Gonzalo Gnecco, Sucromiles S.A. industries, private communication) which could be a profitable source of chitin and chitosan [1–3]. Mycelial cell walls consist of polysaccharides such as chitin, a linear biopolymer formed by N-acetyl-D-glucosamine units linked by gly- cosidic b(1,4) bonds [4]. Chitin is the second most abundant polysaccharide in nature after cellulose, and can be found also in the exoskeletons of crustaceans and mollusks and in insect cuticles [5]. Chitin can be converted to chitosan by deacetylation process [3,6]. Chitosan is soluble in aqueous acidic solutions and its solubil- ity depends of the deacetylation degree (DD) and molecular weight, a high DD and low molecular weight increase the solubility [7,8]. Due to its biocompatibility, biodegradability and abundance in nature [9], both chitin and chitosan have attracted much research interest, and they have found applications in the pharmaceutical, textile, paper and food industries, as well as in agriculture and medicine [10–14]. Chitosan has often been obtained from the exoskeletons of crus- taceans by a process involving several steps: demineralization with hydrochloric acid, deproteinization, deacetylation of chitin, extrac- tion of chitosan in acidic medium and precipitation in alkaline medium [15,16]. However, this process is restricted due to the problems of seasonal and limited supply in some countries. On the other hand, extraction of chitosan from fungi does not require demineralization step and the starting material is available year- round at very low cost. The mycelia of various fungi including Absidia coerulea, Absidia glauca, A. niger, Gongronella butleri, Mucor rouxii and Rhizopus oryzae have been suggested as alternative chi- tosan sources [17–20]. In this work the mycelium of the fungus A. niger from a local citric acid production plant was used as non ani- mal source of chitosan. The cross-linking of the chitosan chains produces three-dimen- sional networks. Due to the presence of several hydroxyl groups in chitosan, the resulting networks, behave as hydrogels, which are able to swell rapidly, retain large volumes of water, and maintaining their original shape [21]. Swelling or phase transition of hydrogels can change according to environmental conditions, such as temperature, pH or ionic strength. Hydrogels are also used as controlled release systems, both as epidermal and http://dx.doi.org/10.1016/j.reactfunctpolym.2015.03.008 1381-5148/Ó 2015 Elsevier B.V. All rights reserved. ⇑ Corresponding author at: Departamento de Química, Facultad de Ciencias Naturales y Exactas, Universidad del Valle, AA. 25360 Cali, Colombia. Tel.: +57 2 3212100. E-mail address: hector.zuluaga@correounivalle.edu.co (F. Zuluaga). Reactive & Functional Polymers 91-92 (2015) 1–10 Contents lists available at ScienceDirect Reactive & Functional Polymers journal homepage: www.elsevier.com/locate/react