The Synthesis And Physicochemical Properties Of Poly(Vinylalcohol)-Gellan Gum Composite Hydrogels

Due to the favorable mechanical and lubricity properties, higher water content, special three-dimensional network structure, and better biocompatibilities. polyvinyl alcohol (PVA) hydrogel has been extensively recognized as a potential material for applications in the pharmaceutical and tissue engineering, especially in artificial biomaterials for cartilage repairing. However, some physicochemistry properties, mechanical properties and biocompatibilities of pure PVA hydrogel do not seem to be sufficient to serve as a biomaterial. It is reported that, due to the higher hydrophilic nature, cells are unable to adhere to the PVA hydrogel. To overcome these limitations and improve its performance. some researchers focus on blending PVA with other natural materials, for example dextran, cellulose and chitosans. to form composite hydrogels.Gellan Gum (GG) is a linear anionic polysaccharide produced by Pseudomonas elodea. Due to good biocompatibility, high cell culture survival rate, adjustable mechanical performance, GG has get more attention in tissue engineering. Under the presence of divalent and multivalent cathion, GG can not only screen out its own electrostatic repulsion but also can form strong ionic bond, that made the hydrogel very hard but brittle. PVA and GG have their own special characteristics, which are complementary in the bio-application. In this paper, composite hydrogels of PVA and GG with different cationic modification were synthesized. By evaluating the network structure, mechanical properties, and thermal behavior, the relationship between structure and properties can be obtained. These information is valuable in biomatrials researching.This paper includes three aspects:1. PVA hydrogel, PVA-GG and PVA-GG-Ca2+ composite hydrogels were prepared by repeated freezing and thawing method. The results of water content and SEM images show that, with the increase in the amount of GG, the water content is increased and the porosity is larger. By introducing in Ca2+. the structure is well cross-linked and the porosity is compacted. The results of XRD and FT-IR show that GG and Ca2+ neither produce new chemical bonds nor form new crystalline peak. The rheological and tensile properties of the composite hydrogels show that the mechanical properties of PVA-GG-Ca2+ was obviously higher than that of PVA and PVA-GG hydrogels. The results of thermal analysis show that, with the increase of GG. the melting enthalpy and the crystallinity of composite hydrogel is reduced. Crosslinked with Ca2+. the PVA-GG-Ca2+ composite hydrogels show better thermal stability than PVA and PVA-GG. Dehydration kinetics study show that, by introducing in Ca2+ in PVA-GG hydrogel, the electrolytic and hydrogen bonding interactions have been strengthened. Study of swelling kinetics in different medium show that, with the increasing in the amount of GG. the swelling rate constant (k) and swelling equilibrium constant (We) were rose. While in the presence of Ca2+, k and We are smaller than the corresponding PVA-GG. All these information shows that PVA-GG-Ca2+ hydrogels have better structrue, mechaincal and thermal dynamic porperties.2. PVA hydrogel and PVA-GG, PVA-GG-A13+ composite hydrogels were prepared by repeated freezing and thawing method. The results of water content and SEM images show that, with the increase in the amount of GG, the water content is increased and the porosity is larger. By introducing in Al3+. the structure is well cross-linked and the porosity is compacted. The results of XRD and FT-IR show that GG and Al3+ neither produce new chemical bonds nor form new crystalline peak. The rheological and tensile properties of the composite hydrogels show that the mechanical properties of PVA-GG-Al3+ was obviously higher than that of PVA and PVA-GG hydrogels. When WGG=1.5%, PVA-GG-Al3+ is in the best mechanical properties. The results of thermal analysis show that, with the increase of GG, the melting enthalpy and the crystallinity of composite hydrogel is reduced. Crosslinked with Al3+, the PVA-GG-Al3+ composite hydrogels show better thermal stability than PVA and PVA-GG. Dehydration kinetics study show that, by introducing in Al3+ in PVA-GG hydrogel, the electrolytic and hydrogen bonding interactions have been strengthened. Study of swelling kinetics in different medium show that, with the increasing in the amount of GG, the swelling rate constant (k) and swelling equilibrium constant (We) were rose. While in the presence of Al3+,k and We are smaller than the corresponding PVA-GG. All these information shows that PVA-GG-Al3+ hydrogels have better structrue, mechaincal and thermal dynamic porperties.3. PVA hydrogel and PVA-GG, PVA-GG-Mg2+ composite hydrogels were prepared by repeated freezing and thawing method. The influence of Mg2+ on the structrue and properties of the composite PVA-GG hydrogels is similar to the influence of Ca2+ and Al3+. The ion of Mg2+ play a role as cross-link agent, it reorganize the network structure of PVA-GG hydrogel, enhance its mechanical properties, strengthen the electrolytic and hydrogen bonding interactions between water and polymer chain, and improve the thermal stability of PVA-GG-Mg2+ composite hydrogel. All these information shows that PVA-GG-Mg2+ hydrogels have better structure, mechaincal and thermal dynamic porperties.