Preparation And Properties Study On The Chitosan Hydrogel Based On Metal Ion Coordination

Chitosan is a natural macromolecule material with extensive sources.As the only basic polysaccharide in nature,chitosan has attracted more and more attention due to its excellent antibacterial,antitumor and immunological properties,promising a variety of applications in the biomedical field.Chitosan can be used as a matrix to form a gel system by adding other biocompatible and environmentally friendly components such as polyvinylpyrrolidone（PVP）and polyvinyl alcohol（PVA）.However,the preparation of these hydrogels Process through chemical crosslinking method between crosslinking agent and chitosan molecules（chemical hydrogel）,which is likely to cause damage to the biological activity of the hydrogel.Besides,the residual cross-linking agents are likely to cause toxicity.In comparison to chemical hydrogels,hydrogels with network structure,which is formed by cross-link of intermolecular low energy bonds（such as hydrogen bonds,coordination bonds,hydrophobic interactions,etc.）are known as the physical hydrogel.At present,there are two main methods to prepare physical hydrogels:the first is hydroalcoholic solution evaporation method;the second is the alkaline solution treatment.The entanglement of chitosan molecules in alkaline atmosphere is used to realize the sol-gel two-dimensional interface transition,and gradually form a physical hydrogel.However,the chitosan hydrogel formed in the ammonia atmosphere has poor mechanical properties and low biological antimicrobial activity.So its application in the field of biomaterials is limited.In this paper,the main work of chitosan physical hydrogel is as follows:Ag⁺shows activity to a variety of pathogens and has been used extensively in a variety of antimicrobial biological materials.The CTS-Ag⁺/NH₃ physical hydrogels with excellent comprehensive properties were successfully prepared by cross-linking the chitosan-silver nitrate solution in the presence of AgNO₃ in the ammonia gas atmosphere.The structures of the hydrogels were characterized by Fourier transform infrared spectroscopy（FTIR）,X-ray photoelectron spectroscopy（XPS）,scanning electron microscopy（SEM）X-ray diffraction（XRD）and solid state nuclear magnetic resonance（NMR）.Analyzing the effects of its synthesis mechanism on the properties of CTS-Ag⁺/NH₃ physical hydrogels.The rheological properties of the hydrogels were characterized by rheological method.As the results show,CTS-Ag⁺/NH₃ physical hydrogels exhibits better homogeneity and transparency than those of chitosan hydrogels reported earlier.Due to the entanglement of chitosan molecular chain and coordination bond between Ag⁺and amino in chitosan,the CTS-Ag⁺/NH₃ hydrogels obtain better mechanical properties.The morphology and swelling properties were significantly improved by the addition of Ag⁺.In addition,the hydrogel can show excellent antibacterial properties,with the concentration of AgNO₃ in the hydrogel ranged from 0.064 wt.%to 0.424 wt.%,which is much lower than that have been reported.CTS-Ag⁺/NH₃ hydrogels exhibit excellent antibacterial activity against gram-positive bacteria and gram-negative bacteria,suggesting that CTS-Ag⁺/NH₃ hydrogels have potential as wound dressing biomaterials.Furthermore,we used Cu²⁺,which is also a transition metal,as the cross-linking agent.With the presence of CuCl₂,chitosan-CuCl₂ cross-link in the ammonia atmosphere,successfully obtaining CTS-Cu²⁺/NH₃ physical crosslinked hydrogel with excellent physical and antibacterial properties.The mechanism of the gel formation was characterized by FTIR and SEM.the coordination reaction between copper ions and amino groups of chitosan was observed.The swelling kinetics and rheological dynamics were used to analyze the CTS-Cu²⁺/NH₃.The results showed that the chitosan hydrogel with copper ions had a more stable swelling kinetics.The results of mechanical experiments show that Cu（I）ions can be converted into Cu（II）in the air,which make the CTS-Cu²⁺/NH₃physical crosslinked hydrogel a material with shape memory property.In addition,the CTS-Cu²⁺/NH₃ physical hydrogel exhibited excellent antibacterial activity against pseudomonas aeruginosa,which provided a special application value for wound infection of pseudomonas aeruginosa infection,and could be used as a biomedical dressing.