Oxidized Sodium Alginate/Silk Fibroin Composite Scaffold For Skin Repair

The skin is the largest human organ and plays an important role in the body’s defense against external harmful factors.Skin tissue engineering is the main solution to solve the problem of insufficient skin supply in clinic.Skin tissue engineering has high biocompatibility requirements for materials.Natural polymeric materials are derived from nature and have incomparable advantages in biocompatibility.Silk fibroin(SF)has a wide source and good biocompatibility,while sodium alginate(SA)can provide adequate mechanical properties to tissue-engineered skin,however,SA itself has too large molecular mass and the degradation products are difficult to be discharged by filtration through human kidney and has a certain safety hazard,so it is crucial to solve the problem of SA degradation performance.First,oxidative modification of SA by sodium periodate was applied to prepare partially oxidized sodium alginate(N-POSA),and N-POSA was crosslinked with SF via Schiff base structure to prepare composite scaffolds(POSA/SF).The oxidation mechanism of SA by sodium periodate was investigated.Sodium periodate oxidizes the ortho hydroxyl groups in SA to two aldehyde groups and produces a ring opening effect that decreases the relative molecular weight.The characteristic peaks of Schiff base structure were found in the FT-IR spectra,leading to the conclusion that N-POSA was successfully crosslinked with SF,and the degradability of the material was promoted,which had no toxic effect on L929 cells.Secondly,to improve the mechanical properties of the POSA/SF composite scaffolds,partially oxidized sodium alginate(T-POSA)was prepared by oxidative modification of SA using the TEMPO system,and its and N-POSA crosslinking with SF were carried out by the EDC system,N-POSA crosslinked SF composite scaffold by EDC system(N-POSA/SF)and T-POSA crosslinked SF composite scaffold by EDC system(T-POSA/SF)were prepared by freeze-drying technique.The TEMPO system can oxidize hydroxyl groups and mainly produce carboxyl groups,while the sodium periodate mainly produce aldehyde groups,and they both can control the molecular weight of the products by means of oxidation.The crosslinking of POSA with SF benefited from the mediation of carboxyl and amino groups reaction by EDC system.A theoretical explanation is proposed for the changing trend of tensile strength with oxidation dosage in POSA/SF composite scaffolds.The degradation performance of the composite scaffolds was promoted relative to that before oxidation,and the degradation rate was controllable,which could have a certain promoting effect on the growth and proliferation of L929 cells.Finally,based on the oxidation of SA by the sodium periodate and the TEMPO system,the POSA of the two systems were further oxidized by sodium chlorite in order to improve the carboxyl content and improve the crosslinking efficiency.Totally oxidized sodium alginate by TEMPO system(T-TOSA)and totally oxidized sodium alginate by sodium periodate(N-TOSA)were prepared.N-TOSA crosslinked SF composite scaffold by EDC system(N-TOSA/SF)and T-POSA crosslinked SF composite scaffold by EDC system(T-TOSA/SF)were prepared by freeze-drying technique.After further oxidation of POSA,the aldehyde group content decreased and the carboxyl group content was promoted,which was in accordance with the theory.The molecular weight of TOSA is not much different from POSA and both can be excreted from the human body through renal filtration.The tensile strength of composite scaffolds was effectively promoted.Its degradation profile is desirable.It can promote the growth and proliferation of L929 fibroblasts and the healing of skin wounds,thus becoming a new generation of skin materials for tissue engineering and having great potential in skin repair.