Reinforcementof 3-d Chitosan Rod Based On The Coordination Effect Of Metal Ions

Three dimensional chitosan rod with high mechanical strength and potential application as bone internal fixation nail has been successfully prepared. Compared with traditional metal-based internal fixation materials, the prepared chitosan rod has a better biocompatibility, and will not evoke the stress shielding effect and need a second operation. Since chitosan can chelate with some metal ions to form complexes with stable structures and some metal ions are beneficial to human health, especially the recovery of bone fracture, our research group has prepared several kinds of chitosan/metal ion composite rods and conducted an in-depth study on them. We hope that chitosan rod with higher mechanical strength and better bioactivity can be obtained.1) Chitosan/Fe3+ complex rod was prepared via solution mixing and in-situ precipitation method. Because there was an intense coordination interaction between Fe3+ and chitosan, Fe3+ would pre-coordinate with chitosan molecules in aqueous state at first, and then an in-situ coordination reaction would happen between Fe3+ and chitosan during the precipitation process of chitosan. In this way, Fe3+ would coordinate with two chitosan units to form a complex with crosslinking-like structure. Not only the mechanical strength of chitosan rod was improved, but also Fe3+ was introduced in the chitosan rod. We hope the chitosan/Fe3+ complex rod can facilitate the recovery of bone facture. Fe3+, the metal ion with better bioactivity, was used to modify chitosan rod too. By comparing the properties of chitosan/Fe3+ complex rod, chitosan/Fe2+ complex rod and chitosan/(Fe2+-+Fe3+) complex rod, we found that the oroperty of chitosan/Fe3+ complex rod was the best.2) Chitosan/Zn2+ complex rod was prepared via solution mixing and in-situ precipitation method. Not only the mechanical strength of chitosan rod was improved, nut also Zn2+, the metal ion wth important in-v,vo (?) ysiological functions, was introduced into the chitosan rod. Zn2+ would coordinate with two chitosan units o form a complex with crosslinking-like structure. Moreover, Zn2+ assumed a gradient distribution under the combined effect of concentration gradient and contraction of chitosan, which contributed to an improved mechanical strength.3) The effects of Cu2+ content and acetic acid concentration on the properties of chitosan/Cu2+ composite rod were investigated when copper chloride was used as the modifying agent. The results indicated that there were very strong coordination interactions between Cu2+ and the amino group and hydrogen group in chitosan molecule. So in aqueous state and in gel state, Cu2+ can form stable complex with chitosan, which greatly increased the property of chitosan rod. The compression strength of chitosan gel rod would increase to 15 times.4) Four kinds of magnesium salts were used to modify the chitosan rod. It was found that sulfate ion could enhance the modifying efficiency of Mg2+. However, the coordination interaction between Mg2+ and chitosan was weak. Mg2+ could only coordinate with the amino group in chitosan.To sum up, by coordinating chitosan with metal ions to form complexes with crosslinking-like structures, not only the mechanical strength of chitosan rod was improved, but also metal ions with good bioactivities and important physiological functions were introduced into the chitosan rod. Among them, the bending strengths of chitosan/Fe3+ complex rod and chitosan/Cu2+ complex rod were much higher than other complex rods, and were 212 MPa and 235.7 MPa, respectively. They had a potential application as bone fracture internal fixation materials.