Preparation and properties of marine-derived sphingan WL gum-metal ion composite hydrogels

Sphingan WL gum produced by marine Sphingomonas sp. WG is a new kind of extracellular polysaccharide reported by our group in 2016. This work selected five metal ions, Na+, Zn2+, Ca2+, Cu2+, and Fe3+, to prepare sphingan WL gum-metal ion (WL-M) composite hydrogels by immersion-adsorption method for the first time. With the increase of immersion solution concentration, the volume of WL-M shrinks, the water content decreases, and the content of metal ions increases. WL-Na2, with the highest water content (91.81%), has the lowest metal ion content (20.76 mg/g); WL-Cu4, with the highest metal ion content (99.80 mg/g), has the lowest water content (73.07%). The results of inductively coupled plasma optical emission spectroscopy show that the adsorption capacity (mg/g) of metal ions by WL is in the order of Cu2+ > Zn2+ > Fe3+ > Ca2+ > Na+. Fourier transform infrared and X-ray photoelectron spectroscopy results suggest that carboxyl and hydroxyl groups are the main active sites of WL interacting with metal ions. The rheological test results reveal that the order of cross-linking effect is Ca2+ > Fe3+ > Cu2+ > Zn2+ > Na+. The G' of WL-Ca4 is the largest, reaching 154.9 Pa at 1 rad/s. The metal ion release behavior was found to follow the Korsmeyer-Peppas model (R-2 > 0.97, n < 0.43) and be pH responsive. WL-Ca3 shows good biocompatibility, self-healing, and injectable properties. The above results indicate that the WL-Ca hydrogels have the most promising application prospects in biomedicine and deserve further research.