Study On Preparation And Structural Properties Of ROS-Responsive Silk Fibroin Composites

Silk fibroin(SF)is a natural polymer protein with excellent biocompatibility and biodegradability,has been widely studied in the biomedical field.SF has great applications in drug-loading systems,but does not have targeted and intelligent responsiveness.It causes severe side effects or damage to normal tissues during clinical treatment,especially during tumor chemotherapy.Thioketal(TK)is a part of the reactive oxygen species(ROS)responsive polymer used in the preparation of drug delivery.It is responsive to abundant ROS and chemical bond breaks will occur,releasing the drug.In this paper,ROS-responsive TK was synthesized.SF/TK composite films,porous scaffolds and microspheres were prepared.ROS responsiveness,drug loading capacity and drug releasing were studied..The molecular weight of TK was identified by mass spectrometry(MS),and its structure was tested by nuclear magnetic resonance spectroscopy(1H-NMR).The results proved that TK was successfully prepared.The structure of SF/TK composites was investigated by Fourier transform infrared(FTIR),Raman,and X-ray diffraction(XRD).Using pure SF material as a control group,results showed that the addition of TK didn’t affect the formation of stable β-sheet structure and Silk Ⅱ crystal structure of SF materials.Results of X-ray photoelectron spectroscopy(XPS)showed that the addition of TK introduced C-S groups.Scanning with an energy spectrometer(EDS)showed that the S content increased after the introduction of TK.Observing the morphology and structure of the composite material under the scanning electron microscope(SEM),the surface of the SF/TK porous scaffold showed uniform pores and regular shapes,while the SF/TK microspheres had uniform sphere shapes and good shape.The average particle size of SF/TK microspheres was about 272 nm.The ROS responsiveness of SF/TK composites was further explored by treatment with an oxygen cleavage environment containing 50 mM KO2 at 37℃.Observation by electron microscopy revealed that compared with the control group,there were obvious pore deformation and fragmentation accumulation on the internal morphology of the SF/TK porous scaffold after ROS-cleavage.When SF:TK=100:3,a significant cleavable effect was exhibited,and at 100:5,the internal cleavable damage of the porous scaffold was more obvious.Through the compression performance test,it was found that the compressive strength of the SF/TK composite porous scaffold decreased after ROS-cleavage.Especially when SF:TK=100:3,the change of compressive strength was the most obvious,which decreased by 17.09%.At the same time,tensile mechanical experiments were performed on the SF/TK composite film before and after ROS-cleavage,and it was found that after ROS-cleavage,the tensile fracture strength also decreased most significantly when SF:TK=100:3,a decrease of 21.09%.The results of ROS-cleavage of SF/TK composite smooth membrane and porous scaffold indicate that the addition of TK gave ROS responsiveness to the composite material,and the ROS-cleavage of TK can promote the decomposition and fragmentation of the material.With the increase of the proportion of TK,the ROS responsive performance of the material gradually increased,indicating that TK successfully chemically linked SF and served as a bridge between SF molecules.According to the results of ROS responsive cleavage,SF/TK microspheres were prepared at a ratio of SF:TK=100:3 and the drug loading study was performed.The hydrophobic drug camptothecin(CPT)was selected,which can treat breast cancer,and its drug loading and release properties were explored.When initially adding 2mg CPT(2 mL 2%SF/TK solution),the drug loading and encapsulation efficiency of SF/TK drug-loaded microspheres were 2.08%and 66.26%,respectively.The average particle size was about 400 nm,and the morphology of the drug-loaded microspheres remained uniformly spherical.The drug release properties of SF/TK drug-loaded microspheres were studied in an ROS-cleavable environment.SF:TK=100:0 drug-loaded microspheres were used as a control group.The results showed that as the ROS-cleavable time increased,the particle size of SF/TK drug-loaded microspheres gradually decreased,it reduced from 426 nm to 257 nm after 16 h,while the particle size in the control group did not decrease significantly.The drug release behavior under oxygen environment showed that the drug release rate of SF/TK drug-loaded microspheres was better than that of the control group,especially in the first 12 h,the release rate of SF/TK drug-loaded microspheres was 2.5 times that of the control group after 2 h.