International Journal of Biological Macromolecules 37 (2005) 99–104 Low viscosity hydrogel of guar gum: Preparation and physicochemical characterization Pablyana L.R. Cunha a , Rondinelle R. Castro b , Francisco A.C. Rocha c , Regina C.M. de Paula a , Judith P.A. Feitosa a,∗ a Departamento de Qu´ ımica Orgˆ anica e Inorgˆ anica, Universidade Federal do Cear´ a, C. Postal 12.200, 60.455-760 Fortaleza, CE, Brazil b Departamento de Farmacologia e Fisiologia, Universidade Federal do Cear´ a, Fortaleza, CE, Brazil c Departamento de Medicina Cl´ ınica, Universidade Federal do Cear´ a, Fortaleza, CE, Brazil Received 17 August 2005; received in revised form 31 August 2005; accepted 6 September 2005 Available online 10 October 2005 Abstract Guar gum was cross-linked with glutaraldehyde and characterized by GPC, rheology, WADX, SEM and TGA. This guar gum is a galactomannan polysaccharide, that contains small amount of arabinose, glucose and uronic acid, besides galactose and mannose. The polymer has high molar mass, with M w , M n and M v values of 2.0 × 10 6 , 1.2 × 10 6 and 1.9 × 10 6 g/mol, respectively. The reticulation follows a slow process and lead to a viscosity increase of 40 times compared with the original gum solution. The final viscosity was similar to that of Hylan G-F 20, a hyaluronate derivative, commercially used in viscosupplementation treatment. The gel contains 95.6% of water and the amount of residual glutaraldehyde is much lower than the LD-50. Porous structure was detected by SEM and thermal stability was improved by the cross-linking. The low viscosity, the small amount of remained glutaraldehyde, and the thermal stability indicates that the guar hydrogel has potential to be applied as biomaterial with specific rheological requirements. © 2005 Elsevier B.V. All rights reserved. Keywords: Guar gum; Hydrogel; Viscosity; Thermal stability; Glutaraldehyde; Hylan 1. Introduction Hydrogels are three dimensional networks composed of a polymer backbone, water and a cross-linking agent to produce a complex structure of high molecular weight. They have gained much importance in a wide variety of applications in the medical pharmaceutical industry and related fields [1]. Research involv- ing highly hydrophilic, biocompatible hydrogels receives ample attention, for example, in drug delivery formulations [2,3], in the production of contact lenses, humor-vitreous substitutes [3] and as viscosupplementation agent in knee osteoarthritis [4–7]. Guar gum (GG) is a polysaccharide originating from the seed endosperm of the plant Cyamopsis tetragonolobus. It is a galac- tomannan, which consists of a (1→4) linked -mannopyranosyl backbone partially substituted at O-6 with -d-galactopyranosyl ∗ Corresponding author. Tel.: +55 85 40089973; fax: +55 85 40089978. E-mail address: judith@dqoi.ufc.br (J.P.A. Feitosa). side groups, with the ratio of mannose to galactose ∼1.6–1.8:1 [8]. It has been extensively used in a range of applications because of its unique ability to alter rheological properties [9]. In biological application, GG and modified GG were used as a carrier for colon targeted [10] and transdermal drug delivery system [11]. Chemical cross-linking is a highly versatile method to cre- ate hydrogels with good mechanical stability. Gliko-Kabir et al. [12,13] have reported some hydrogels of GG cross-linked with glutaraldehyde (GA) and phosphate. Burruano et al. [14] have proposed a guar gum-based formulation that is cross-linked with borate for the development of synthetic cervical mucus. Glutaraldehyde is an important reagent in the biomedical field. It has been used as a cross-linking agent for the preparation of dextran hydrogels [15] and for several drug delivery sys- tems, such as polyampholyte hydrogels based on carboxymethyl chitosans [12], fibroin blends films [16] and gelatin hydrogel incorporating cisplatin [17]. It has been utilized for preparation of bioprosthesis, such as heart valves and elastic cartilages [18]. 0141-8130/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.ijbiomac.2005.09.001