Reagent-free covalent crosslinking of chitosan-gelatin films for medical applications
Zakharyuta, Anastasia (2010) Reagent-free covalent crosslinking of chitosan-gelatin films for medical applications. [Thesis]
Official URL: http://192.168.1.20/record=b1301591 (Table of Contents)
A reagent-free, inter-molecular covalent crosslinking technique was developed in order to incorporate desirable traits such as flexibility, mechanical robustness and high interconnective porosity into composite chitosan-gelatin base films. Since any form of contact between biomaterials and reactive chemicals typically raises safety concerns, the principle goal in developing a reagent-free method was to bypass all adverse physiological effects that might otherwise be induced by some reactive chemical step in the processing history of the biomaterial. Intrinsically antimicrobial and biodegradable chitosan-gelatin compositions were targeted. To being, chitosan-gelatin films were prepared in lyophilisate format and heat-treated under dehydrative vacuum conditions, yielding crosslinked porous materials. The mechanical properties, morphology, porosity and pore interconnectivity of this material were fine-tuned by varying the starting composition and experimental conditions, eventually yielding a product amenable to cell proliferation tests. Structural changes of the material were spectroscopically probed after heat application, revealing subtle but general alterations in the hydrogen-bonding of amide groups. While new covalent bonds were not established by direct observation, minor inter-molecular crosslinking could be concluded from the observable swelling of the material in PBS buffer and its inability to re-dissolve under the most stringent of non-destructive reducing conditions. In fact, dehydrothermal processing was found to have dramatically improved the long-term stability of the film in aqueous media, even under proteolytic conditions. Processed films also retained the antimicrobial traits of chitosan, as evidenced by the lack of visible growth within the film and surrounding media. Mechanical tests implied that the dehydrothermally-crosslinked films, once rehydrated, possessed the necessary flexibility and tensile strength to potentially assume many of the minor-load applications expected of chemically crosslinked soft biomaterials. Typical in vitro cell culture studies showed good adhesion of cells along the surface and within the pores of the film, with sub-surface proliferation apparently being aided by the concomitant and gradual biodegradation of the film structure. Finally, hemoglobin was dehydrothermally immobilized to these crosslinked chitosangelatin films, yielding a catalytically active oxygen-loading film and further attesting to the benign nature of this crosslinking technique. Based on these positive outcomes, it follows to reason that reagent-free covalent crosslinking may conveniently yield suitable and safer alternatives to many soft biomaterials commonly used in medical applications.
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