Hidrogéis de goma guar oxidada e carboximetilquitosana com potencial aplicação como sistemas injetáveis

Abstract

Injectable hydrogels are a class of polymeric materials that can be prepared in situ by extruding their components directly into the desired location in a minimally invasive manner. They can be formulated from chemical or physical crosslinking. The Schiff base formation is a chemical crosslinking method has been highlighted because of the mild conditions of reaction. Injectable hydrogels crosslinked by Schiff base reaction prepared from natural polymers have gained special attention, since these have properties such as biodegradability and biocompatibility. Thus, the proposal of this work was to synthesize hydrogels based on oxidized guar gum and carboxymethylchitosan from the Schiff base reaction crosslinking, aiming at the application as injectable systems. Guar gum (GG) was modified by sodium periodate oxidation at different degrees of oxidation (20, 50 and 80%). The oxidized derivatives (OXGG) were characterized by Infrared absorption spectroscopy (FTIR) and Gel Permeation Chromatography (GPC). The chemical modification was confirmed by the appearance of a low intensity band at 1723 cm-1, attributed to stretching of C=O aldehyde, in the FTIR spectrum of OXGG. The oxidation caused a reduction in the molar mass of GG, as revealed by the GPC chromatograms of the oxidized derivatives. Chitosan (CTS) was chemically modified by carboxymethylation reaction with chloroacetic acid in order to obtain a water-soluble derivative. The obtained derivative (CMCTS) was characterized by FTIR and 1H Nuclear Magnetic Resonance (1H NMR). This data corroborated with the 1H NMR spectrum and, in addition, indicated an additional substitution in C3 hydroxyls. The hydrogels were prepared by mixing their precursors (OXGG and CMCTS), previously dissolved in phosphate buffer pH 7.4 (PBS), at different volume / volume (v / v) ratios of GGOX/CMCTS (1: 1, 1: 2 and 2: 1). The hydrogels presented relatively low values of gel time (tgel), being the ratio 1:2 with the highest tgel among the others. The rheological analysis of the gelation process of the hydrogels indicated that the tgel is temperature dependent. The FTIR spectra of the hydrogels showed that the crosslinking reaction did not fully consume the aldehyde groups. Scanning electron microscopy (SEM) images of the cross-section of the hydrogels revealed that that their polymeric networks are equipped with pores of different sizes and varied shapes, being influenced by the degree of oxidation of GG. The short time of gelation makes these hydrogels possible candidates for application as injectable systems in tissue engineering such space filling agent and/or controlled release of drugs.