Preparation Of Citric Acid Cross-linked Sphingan WL Gum Hydrogel Dressing

As the largest organ of the body,the skin is the first line of defense against the effects of the external environment,yet skin damage is also one of the most prevalent medical problems.Hydrogels are considered by many scholars to be the best choice for wound dressings because of their high-water absorption and physicochemical properties similar to those of human tissue.Natural polysaccharides are often used as raw materials for hydrogel dressings due to their good biocompatibility,biodegradability,and moderate viscosity.Acidic polysaccharide hydrogels not only provide a weak acidic environment conducive to wound healing,but also have pH-responsive properties of swelling behavior and drug release behavior.Sphingan WL gum(abbreviated as WL)is a novel natural polysaccharide discovered by our group,and WL contains a carboxyl group.Therefore,in this thesis,the WL hydrogel film cross-linked with citric acid(CA)was prepared for the first time from WL,and its structure,pH-responsive swelling behavior,porosity,loading and release of the antibacterial model drug Ciprofloxacin(abbreviated as CIP),antibacterial property,biocompatibility,etc.were investigated,and the preliminary evaluation of WL hydrogel in wound dressing applications(Chapter 2).The experimental results showed that CA effectively improved the mechanical properties of WL hydrogel,but it was still fragile.To solve this problem,we also improved its mechanical properties by compounding Graphene oxide(abbreviated as GO)(Chapter 3).This thesis not only broadens the application area of WL,but also provides new potential options for hydrogel dressings.The main contents and conclusions are as follows.1.High purity WL was prepared by fermentation and polysaccharide purification of Sphingomonas sp.WG,and the GPC test showed that the heavy average molecular weight of the obtained WL was about 1.6 × 106 g/mol.then WL-CA hydrogel films with different CA contents were prepared by heat curing using CA as cross-linking agent.the results of ATR-FTIR and TG proved that WL-CA hydrogels were esterified and crosslinked with CA.WL-CA films could absorb water rapidly and reached the swelling equilibrium within 2 h.The swelling increased with pH and decreased with the increase of cross-linking agent.The results of solvent replacement method showed that WL-CA5 and WL-CA10 hydrogels have high porosity(> 60 %),and WL-CA hydrogels have moderate adhesion to skin.The rheological performance tests showed that WL-CA hydrogels had G’ > G" and storage modulus G’ up to 2 k Pa.furthermore,WL-CA10 with better overall performance was used as a carrier and loaded with antibiotic CIP by physical adsorption method with a loading rate of 24.5 %.the WL-CA-CIP hydrogel films exhibited pH-responsive sustained drug release behavior and met the KorsmeyerPeppas release kinetics.Antibacterial tests using E.coli and S.aureus as models showed that WL-CA10 inhibited the growth of E.coli for 3 days and did not inhibit the growth of S.aureus,which was caused by the residual of CA,a cross-linking agent with antibacterial activity;WL-CA-CIP inhibited the growth of E.coli for up to 10 days and S.aureus for up to 7 days.Finally,the toxicity of the hydrogels was evaluated using three types of cells,NIH 3T3,HUVEC and 293 E,as models,and the results showed that WLCA0,WL-CA10 and WL-CA-CIP hydrogels exhibited excellent biocompatibility.2.The preparation of GO using Hummers method.the successful preparation of GO nanosheets with uniform thickness(1 nm)was demonstrated by XRD,UV,TEM,SEM,and AFM.Then GO was added to WL-CA10 with better comprehensive properties,and WL-CA-GO composite hydrogel films with different GO contents were prepared.The mechanical properties of the solvated WL-CA-GO hydrogels were characterized by manual tensile twist experiments and rotational rheometry,and the results showed that WL-CA-GO1 possessed certain stretchable properties and the storage modulus G’ of WLCA-GO10 could reach 7 k Pa,which increased by 5.8 k Pa compared with WL-CA10.Under the infrared light illumination of 808 nm with an optical power of 0.865 W,the The temperature variation range of ΔT = 24.6 ℃～ 50.3 ℃ for WL-CA-GO and ΔT = 2.6 ℃for WL-CA10.The above results demonstrate that the addition of GO effectively improves the mechanical properties of WL-CA hydrogel and gives it a good photothermal response behavior.