Preparação e caracterização de potenciais suportes porosos (scaffolds) a base de géis de gelatina/goma do cajueiro (Anacardium occidentale) oxidada

Abstract

Every single year, many patients suffer a loss or a failure in an organ or a tissue, due to a result of a certain disease or an injury. Many studies have been developing ways to repair organs or tissues, using the knowledge of Tissue Engineering. This particular methodology makes the usage of porous supports (scaffolds) as an environmental structure for the growth in cells and tissues, thus, the Gelatin scaffolds duly produced, are for the regeneration of cartilage and bone tissues. The Gelatin hydrogels obtained without a crosslinker would dissolve the temperature rapidly in the human body and this will greatly limit its applications. The difficulty is the fact that the crosslinkers are toxic. The oxidized polysaccharides duly investigated are crosslinkers and less toxic. The Oxidation of the polysaccharides with sodium periodates is a simple technique, which introduces multiple functional groups, such as the aldehyde making the polysaccharides capable of acting as a crosslinker for the macromolecular polymers containing amino groups, as the gelatin. The cashew gum (CG) is extracted from trees in the northeastern Brazil and it was characterized as a heteropolysaccharide containing the β-D-galactose (72-73%), α-D-glucose (11-14%), arabinose (4.6 -5%), rhamnose (3.2 to 4%) and the glucuronic acid (4.7 to 6.3%) by a mass percentage. This study aims the CG oxidation through a sodium periodate, in order to produce a polyaldehyde (CGO) that will interact with the gelatin to produce a hydrogel CGO/GE and be lyophilized for obtaining a porous structure, which is used to release the BSA, therefore, oxidations in percentages of 17, 46 and 71%, named CGO2, CGO5 and CGO8 were implemented. The IR spectra from the following oxidized derivates, CGO5 and CGO8, were observed and a different aspect in a new band with reference to the CG and CGO2 at 1735 cm-1 ascribed to the stretching vibration of the C=O bond in the aldehydes, which showed the oxidation. This study also shows the nuclear magnetic resonance spectra appearances of the signals  5.6 and  5.7, corresponding to a residual intra-hemiacetal formed between an aldehyde group and a neighboring hydroxyl group, as well as a decrease in the signal strength of the CH3 inside the rhamnose ( 1.3) and the offshoot from this particular signal, suggesting that an oxidation has occurred. The GPC chromatograms of the CG and the oxidized derivates, show that the molecular weight peak (Mpk) decreases with the increasing degrees in oxidation of the CG. Through the rheological tests, we observed that the increasing reaction in the temperature, decreases the time in the crossover, thus, indicating that the gel was formed rapidly at higher temperatures. Likewise, comparing different degrees of oxidation, the greater the degree of oxidation is, the faster the G' crosses G''. Porous gels from the CGO/GE were duly obtained through the freezing method and drying by lyophilization (freeze-drying). The micrographs on the surface were obtained from the porous average and the medium pore diameter decreases with the increase observed in the degree of the oxidation for the CGO, therefore, the CGO2/GE with the highest average of 201 ± 66 mM is followed by the CGO5/GE 150 ± 49 mM and the CGO8/GE 94 ± 22 microns. Hence, based in the agreement with the pore diameter obtained by the SEM, the gels of the CGO2/GE showed the highest average porosity, 53.00 ± 0.19% CGO5/GE followed by 39.02 ± 0.39% and the CGO8/GE 21.24 ± 2.38%. The swelling for the CGO/GE was CGO2/GE> CGO5/GE> CGO8/GE. We noticed that during the days of the swollen gels, a higher amount of the BSA released from the said gels. The CGO2/GE released 35.7% and then dissolved. The CGO8/GE released 82% of the BSA until the 13th day.