Study On Preparation And Properties Of Magnetic Chitosan Composites

Due to the biocompatibility, biodegradable nature, no toxicity and the property of being environment fridendly, chitosan(CS) and its ramifications are potentially widely employed especially in biomedical applications such as in drug delivery system and artificial soft tissues and so on. In a large number of experimental studies, CS are often made into microspheres or hydrogels as drug-coated, or used directly. The microspheres used in drug delivery syetem must have small particle size(microspheres used as injection sustained-release preparation must be in accordance with pharmacopoeia, i.e. less than 10 percent of them have the size samller than 15μm, and if have the nanosize, they will have better properties and can widely applied), and narrow distribution. The hydrogels used as artificial soft tissues, especially artificial cartilarge, must have hydroscopic and mechanical properties. References have reported that in the preparation of microspheres or hydrogels, it's improve their performances which added magnetic particles in, and they are expected to used as a new type of smart material because of their magnetical property. In this thesis, Fe₃O₄ nano- and micro-particles were added to chitosan and chitosan/polyvinyl alcohol (PVA) composites to form magnetic hydrogels.1. Fe₃O₄ nanoparticles prepared by chemical co-precipitation method assisted by ultrasonic wave.Fe₃O₄ nanoparticles were prepared by the chemical co-precipitation method assisted by ultrasonic wave of FeCl₃·6H₂O, FeSO₄·7H₂O and NH₃·H₂O. The average size was 11.8nm. It was found that the best preparation conditions are: concentration of Fe²⁺ , Fe³⁺ was at 0.1 mol/L, concentration of NH₃·H₂O was at 0.15mol/L and temperature was at 50℃. The differences between by ultrasonic wave and by stirring were compared. The TEM pictures showed that Fe₃O₄ nanoparticles prepared by ultrasonic wave had smaller sizes and distrubution, most of them were spheres with no obvious agglomeration.2. The magnetic chitosan microspheres were prepared by simple coacervation.The magnetic chitosan microspheres were prepared by simple coacervation of Fe₃O₄ nanoparticles, trimeric sodium phosphate(TPP) and CS. When the concentration of CS solution is at 1.5mg/ml, an orthogonal experiment was carried out in order to optimize the preparation conditions, which were found to be: m (Fe₃O₄) /m (CS) =1: 2, m (CS) /m (TPP) =4: 1, reaction time 8h, reaction temperature 60℃,and stirring rate at 800r/min. The microspheres of prepared under the optimal conditions tokened by XRD, TEM, IR and VSM. The microspheres average size was 13.2nm, in a size distribution range from 5nm to 40nm, and most of them were spherical. The magnetic property of these microspheres was very close to superparamagnetism. Cross-linking may be introduced between Fe₃O₄ and CS. Coacervation is a simple method, and can be easily used for large volume production.3. In order to improve the mechanical property of hydrogel, PVA was added to CS, and several series of hydrogels were made.Series A was made by blending PVA and CS directly; series B was made by blending PVA and CS first, followed by adding TPP; series C was made by blending PVA and CS first, followed by adding commercial micron-sized Fe₃O₄ particles and then adding TPP at the last step; series D was made by blending PVA and magnetic chitosan microspheres.The swelling rate, reswelling rate and mechanical properties were found to be dependent on the preparation methods, freezing-thawing cycles and the content of magnetic-particle. The preparation methods, freezing-thawing cycles and the content of magnetic-particle have a consistent effect on swelling rates and reswelling ratse, but have an opposite effect on mechanical properties. All of hydrogels had a swelling rate between 2.54 and 13.7, the tensile modulus was between 0.30MPa-3.32MPa, and the elasticity modulus was between 0.56MPa 5.02MPa. Different preparation methods, freezing-thawing cycles and contents of the magnetic particles can impact the swelling rates, tensile moduli and elasticity moduli. The magnetic properties were effected by the content of magnetic particles, the type of magnetic particles and the freezing-thawing cycles. The most influenced factor was the content of magnetic particles, and the others have a little influence. All the magnetic hydrogels had a small remanence and coercive force, and they were most influenced by the content of magnetic particles and the type of magnetic particles. The bigger the content of magnetic-particle is, the bigger the remanence and coercive force will be. Magneic hydrogels made by magnetic chitosan microspheres had a nearly superparamagnetism magnetic property.