Date of Degree
PhD (Doctor of Philosophy)
In this work, aldehyde-functionalized chitosan was produced by the reaction of chitosan in the solid state with nitrogen oxide gases, generated in situ from a HNO3/H3PO4 - NaNO2 mixture. This reaction is more advantageous than the existing methods to produce aldehyde-functionalized chitosan, since the depolymerization was slower and the purification process of the products was easy and straightforward. The appearance of characteristic peaks in the Fourier transform infrared and carbon-13 nuclear magnetic resonance spectra (1733 cm-1 and 183.4 ppm, respectively) of the product confirms the presence of the aldehyde functionality in the modified chitosans. The pH-dependent 1H-NMR spectra also revealed the presence of aldehyde groups. However, as the pH increased from 2.0 to 6.0, the resonance due to the aldehyde gradually disappeared and a new resonance appeared at 8.05 ppm, which is attributable to the formation of Schiff's base between the aldehyde and the free amine groups. This aldehyde-derivative of chitosan formed a gel in situ by simply dissolving it in water at a concentration of 6% (w/w) without any added external crosslinker. This gel show potential use as drug carrier and as scaffold for vascular tissue engineering.
In addition, cellulose:chitosan composites were prepared with the main purpose of obtaining a compliant hollow tube for vascular bypass application. Elastic properties of membranes made of this composite with different ratios between each polymer were determined using uniaxial tests and the ratio that yielded the less stiff membrane was chosen to prepare a small diameter hollow tube. The presence of chitosan had a favorable impact on the elasticity of the membranes, where the cellulose:chitosan 5:5 ratio showed the lowest Young's modulus. Small diameter tubular constructs were fabricated using this optimal cellulose:chitosan ratio and assessed for their suitability as coronary artery bypass grafts. The compliance of the tubes was found to be 5.91 %/mmHg x 10-2, which is higher than those of Dacron, ePTFE and saphenous vein. Burst strength tests revealed that the tubes can withstand at least 300 mmHg. Finally, the tubes showed satisfactory cell attachment property when myofibroblast cells adhered and proliferated on the lumen of the samples.
Copyright 2011 Eduardo Pereira Azevedo
Azevedo, Eduardo Pereira de. "Aldehyde-functionalized chitosan and cellulose:chitosan composites: application as drug carriers and vascular bypass grafts." doctoral PhD diss., University of Iowa, 2011.