| Tissue engineering scaffolds provide new prospects for cartilage injury healing.The silk fibroin/type II collagen scaffold can promote the proliferation and differentiation of chondrocytes in in vivo and in vitro experiments,and there are few studies on its degradation performance.Since excessive degradation will hinder the repair process,it is important to evaluate the degradation performance and the effect of degradation on the mechanical properties.The in vivo degradation experiment is greatly affected by external factors and takes a long time,and the dynamic degradation process cannot be detected.Therefore,it is of great practical significance to realize scaffold degradation through numerical simulation.The purpose of this study was to study the degradation mechanism,mechanical properties and composition changes of scaffolds under mechanical stimulation.First,we established a flow-solid coupling model of the scaffold and simulated the stress-strain effect on the scaffold under different perfusion velocities.The results showed that the greater the perfusion velocity,the greater the stress on the scaffold and the more pronounced the strain,but the range of stresses on the scaffold was able to promote cell proliferation.Secondly,the mathematical models of random hydrolysis and stress-stimulated degradation of polymer were established and embedded in the finite element model of scaffold degradation,the degradation performance of scaffolds at different perfusion velocities and different degradation times was simulated and compared with the experimental results.The results showed that the simulation results were in good agreement with the experimental results,which showed that with the increase of degradation time,the scaffolds first degraded rapidly and then the degradation rate decreased.With the increase of perfusion velocity,the greater the force on the scaffold,the greater the degradation rate of the scaffold,that is,stress stimulation can promote the degradation of cartilage scaffold.Then,finite element simulation,theoretical prediction and experimental test were used to study the mechanical properties of the scaffolds with different degradation periods under the action of irrigation velocity.The stress relaxation results showed that the interlaminar stresses on the scaffold decreased with the increase of degradation time and strain,and the superficial and bottom layers were always more stressed;the creep results showed that the deformation variable of the scaffold increased with the degradation time,but decreased with the increase of the number of layers of the scaffold.It was found that the simulation results and the theoretical prediction results were in good agreement with the experimental results,which indicated that the finite element model and the theoretical model established could predict the mechanical properties of the scaffold during the degradation process.Finally,we used infrared spectral detection and SEM morphological observation to study the changes of microstructure and component content of the scaffold during the degradation process.With the increase of perfusion rate,the changes of component content were more obvious,both showed an increase of β-sheet andα-form structure content and a decrease of irregular curl structure content;with the increase of degradation time,the changes of component content showed a fast and then slow process;the regression curve of component content showed that β-sheet structure played a dominant role in the degradation.Morphologically,as the degradation time increases,the pores gradually collapse and join into sheets,resulting in a fast and then slow degradation process of the scaffold.In this paper,the degradation performance of the silk fibroin/type II collagen cartilage scaffold under different perfusion velocity and the effect of degradation on its mechanical properties were obtained from macroscopic to microscopic levels using three methods: finite element simulation,theoretical prediction and experimental testing. |
