1. Thermosensitive chitosan hydrogels for biomaterial applications
Rong Zeng
Fudan University Supervisor : Dr. Chen Xin
Queen Mary, University of London Supervisor : Dr. Ray Smith
Thermo-sensitive hydrogels are part of the family of so called ‘smart hydrogels’ – those that display environmentally sensitive behaviour. In the field of biomaterials these systems are currently the focus of much research. Chitosan, an amino-polysaccharide obtained by alkaline deacetylation of chitin is a biocompatible and biodegradable material that has been extensively studied in the biomaterials field, particularly in the area of drug delivery. Chitosan readily forms hydrogel systems either through chemical or physical crosslinking. To impart thermally induced gelation to chitosan hydrogels it is necessary to combine it with other materials. A good example is the combination of chitosan with glycerphosphate(GP) which has been studied for several years. In certain combinations this mixture gels at or around body temperature (37℃). This property makes it a very interesting system for study in the field of biomaterials and more recently tissue engineering.
Three types of interactions may be involved in the gelation process:
(1) electrostatic attraction between the ammonium groups of chitosan and the phosphate group of GP;
(2) hydrogen bonding between polymer chains as a consequence of reduced electrostatic repulsion after neutralization of the chitosan solution with GP;
(3) chitosan–chitosan hydrophobic interactions.
1H-NMR,13C-NMR,31P-NMR have been used to study the gelation process . Chemical shifts have been changed at different temperatures.
H-NMR of chitosan&GP
P-NMR of chitosan&GP
P-NMR of chitosan
Results:
1H NMR data on GP/Chitosan mixture indicates that hydrogen bonds have been disrupted as a result of increasing temperature. If GP alone is heated, the observed shifts are much smaller.
31P data again indicate that in mixture of GP/ Chitosan the hydrogen bonds have been disrupted. This is shown in a difference in shift value between GP and GP/Chitosan .