Synthesis of low and medium molecular weight chitosan based hydrojels, characterization and investigation of biodegradability properties

Chitosan which has the biggest advantage of being a renewable resource and an environmentally friendly natural biopolymer has attracted a lot of attention with its numerous unique properties such as biocompatible, biodegradable, antimicrobial, antitumor effect, good absorption capacity and nontoxicity in recent years. And it has become a preferred biomaterial from food to cosmetics, from agriculture to many medical applications. Nowadays, environmental concerns and the need for environmentally friendly renewable resources have increased. For this reason, it is of great importance to produce high value-added products by recycling these wastes caused by the seafood industry, which has a large market share in our country. In this thesis, it is aimed to prepare chitosan hydrogels cross-linked with glutaraldehyde by taking of all these advantages and characteristics. The effects of the molecular weight and the different cross-link concentration of chitosan which are the most basic parameters characterizing chitosan, on the mechanical and physical properties of the synthesized gels were investigated in detail by experimental studies. Several suitable properties of successfully synthesized chitosan hydrogels are presented that will allow them to be used in wound dressings, drug release applications, agricultural and tissue engineering applications, etc. The analyzes of chitosan hydrogels cross-linked with %1, %3, %5, %7 ve %10 glutaraldehyde (GA) were evaluated comparatively for low and medium molecular weight. FTIR spectra of all hydrogels was examined, it was observed that imine bonds (C=N) were formed confirming the Schiff reaction of chitosan and GA. In absorption studies, the highest swelling values were observed in the pH 2.0 medium and gels containing 1% GA due to the protonation of amino groups of chitosan. These results were supported by SEM and optical microscope images. As a result of the DSC-TGA analysis, it was found that the thermal degradation of chitosan took place in three stages and the decomposition temperatures decreased slightly with increasing amount of the GA in the gel matrix. It was observed that the compressive modulus values of hydrogels increased with increasing molecular weight and cross-linking ratio, besides the this situation decreased the degradation rate of chitosan hydrogels which became more stable and preserved their structural integrity. This situation is considered to be advantageous in the release studies where slow and controlled degradation is desired. The present results showed that the determination of the properties, function and areas of use of the synthesized chitosan hydrogens did not depend on a single variable, but it was revealed that besides the molecular weight and crosslinker concentration, the parameters such as ambient pH, sol content, distribution of acetamide groups in the chitosan molecule, preparation form, etc. were also directly effective. Therefore, it is very important to provide optimum values for the development of a chitosan hydrogel with desired properties.