Preparation And Basic Application Of Chitosan-based Hydrogels

Chitosan（CS）as the second most abundant biopolymer after cellulose has often been considered as a natural alkaline cationic polysaccharide.Chitosan has excellent physical,chemical and biological properties and it can be extracted from the waste shrimp and crab shells.Due to the good hydrophilicity,unique three-dimensional network structure and good biocompatibility,chitosan hydrogel materials have been widely used in tissue engineering,surgical scaffolds and drug delivery.However,hydrogels prepared from natural polysaccharides usually suffer poor mechanical properties and functions,which do limit their practical applications.Therefore,in this paper,chitosan and its derivatives were used as raw materials to prepare the composite hydrogels with interpenetrating structure,enhanced mechanical properties and multi-functions.Finally,the potential applications of the hydrogels in biomedical fields were also studied.The main results are as follows:（1）A chitosan/agar composite gel with interpenetrating network and highly ordered porous structure was prepared by using ice crystal template method.Experimental results have showed that the composite gel has a high porosity（>95%）and water-sensitive shape memory properties（>90%,response time<1min）.Additionally,by adjusting the solution p H,chitosan molecules can be induced to undergo the reversible self-assembly processes within agar gel networks,and which could be used to manipulate its shape memory properties.In addition,the multi-stage degradation of the composite gel can be achieved by adjusting the p H and environmental temperature of the solution,demonstrating which has great potential to be applicated for the inorganic nanomaterial assembly and controlled-drug delivery system.（2）To overcome the shortcomings of poor water solubility and weak metal ion selectivity,the carboxymethyl chitosan（CMC）materials have been prepared from carboxymethyl modification of chitosan.Upon heating the blends of Agar/CMC and then cooling to room temperature,the carboxymethyl chitosan molecules can be evenly embedded in the agar gel and which could be used to absorb multiple kinds of metal ions(e.g.Cu²⁺,Zn²⁺,Ni²⁺,Co²⁺,Fe²⁺,Cr²⁺)via the strong and dynamic coordination interactions,resulting in an enhanced mechanical properties,shape memory,self-healing and antibacterial properties etc.Experimental results show that the maximum adsorption capacity of agarose/carboxymethyl chitosan hydrogel for metal ions is 77.2 mg/g.After coordinated with metal ions,the hydrogel mechanical strength can reach 128 k Pa（4.2 times compared to the bare control,32k Pa）.Its maximum shape recovery rates under neutral（p H=7）and alkaline（p H=12）conditions achieved the values of 92.6%and 82.7%,respectively.The conductivity of the agar/carboxymethyl chitosan hydrogel coordinated with Cu²⁺can reach 6.1×10^-4S/cm,which allows the diode to light up under 1.5 V conditions.In addition,the agarose/carboxymethyl chitosan cross-linked by metal ion coordination also shows great antibacterial properties.The antibacterial activity can be improved by adjusting the types and concentrations of metal ions and their coordination interactions with carboxymethyl chitosan.（3）The silver nanoparticles were successfully prepared from the composite hydrogel and the formation processes could mediated by the interpenetrating CMC chains within Agar gel network.Among them,the thermally responsive agar（Agar）provides a three-dimensional network framework for absorption,recollection and reduction of metal ions.The coordination interactions formed between carboxymethyl chitosan（CMC）and metal ions could induce the formation of an independent supramolecular network.By chemically reducing metal ions to the nanometals in situ,the agarose/carboxymethyl chitosan/nano silver composite gel was obtained.It was characterized by SEM,TEM,EDS and other methods,and it was found that the prepared silver nanoparticles were uniformly distributed in the gel network in a regular spherical shape.The size of metallic silver nanoparticles（Ag NPs）could be regulated by gel ratio,reaction time and conditions.Finally,the good catalytic performance of the composites have been studied by using silver nanoparticles（Ag NPs）as a catalyst for the reduction reaction of p-nitrophenol.