Objective To explore the differences of three-dimensional porous blended silk scaffolds with different sericin ratios in terms of molecular structure, mechanical properties, and biological characteristics. Methods Fibroin/sericin blended aqueous solution [concentration 8% (W/V)] with various sericin ratios 0%, 2%, 4%, 6%, 8%, 10%, 12% and NaCl asa porogen with different particle sizes (125-200, 200-300, 300-450, 450-600, 600-900, 900-1 100 μm) were used to fabricate the three-dimensional porous blended silk scaffolds. Gross observation of the formation of three-dimensional porous blended silk scaffolds of different sericin ratios and pore sizes was performed. Scanning electron microscope (SEM) was used to detect the distribution and diameter of the pore sizes. Its porosity was calculated by l iquids replacement method. X-ray diffractometer (XRD) and fourier transform infrared (FTIR) were used to detect its internal molecular structure. Its mechanical properties, enzyme degration rate in vitro and experiment on SD rats in vivo, and histolgy observation after coculturing homogeneous scaffold (sericin ratio 0-12%, NaCl particle size 600-900 μm) with adipose tissue-derived mesenchymal stem cells (ADSCs) were detected. Results Gross observation showed that the higher of the ratio of sericin protein, the greater of the porogen sizes scope which used to form homogeneous silk scaffolds. The result of SEM showed that the pores of the three-dimensional porous blended silk scaffolds had uniform distribution and was connected with each other. Its pore sizes was in the scope of the porogen sizes, and its porosity all above 90%. The angel corresponding to the characteristic peak of the sericin/fibroin blended scaffolds were 20.6° and 24.6° (XRD), and the wavelength corresponding to the characteristic peak of the sericin/fibroin blended scaffoldswere 3 296, 2 933 and 1 629 cm-1 (FTIR) which was the same as the angel and wavelength corresponding to the characteristic peak of the natural silk. The mechanical properties of the sericin/fibroin blended scaffolds was improved with the increase of sericin ratios, and the compressional resil ience reached 100% when the ratio ≥ 6%. The different ratios of sericin and the different particle size of porogen had no significant effect on the enzyme degradation rate in vitro. The histological observation 14 days after ADSCs-scaffold co-culture indicated that the scaffolds had slow degradation rate, and sl ight inflammatory response in vivo. ADSCs were well attached to the sericin/fibroin blended scaffolds of different sericin ratios, with varied morphology, rich cytoplasm, and nuclear enrichment, the l ight staining ECM was observed surrounding the cells. Conclusion The mechanical property of the three-dimensional porous blended silk scaffolds is improved by silk sericins with ratio ≥ 6% obviously, which will lay the groudwork for further research and making of strengthen silk scaffolds.
Superficial cartilage defect is an important factor that causes osteoarthritis. Therefore, it is very important to investigate the influence of superficial cartilage defects on its surface morphology and mechanical properties. In this study, the knee joint cartilage samples of adult pig were prepared, which were treated by enzymolysis with chymotrypsin and physical removal with electric friction pen, respectively. Normal cartilage and surface treated cartilage were divided into five groups: control group (normal cartilage group), chymotrypsin immersion group, chymotrypsin wiping group, removal 10% group with electric friction pen, and removal 20% group with electric friction pen. The surface morphology and structure of five groups of samples were characterized by laser spectrum confocal microscopy and environmental field scanning electron microscopy, and the mechanical properties of each group of samples were evaluated by tensile tests. The results show that the surface arithmetic mean height and fracture strength of the control group were the smallest, and the fracture strain was the largest. The surface arithmetic mean height and fracture strength of the removal 20% group with electric friction pen were the largest, and the fracture strain was the smallest. The surface arithmetic mean height, fracture strength and fracture strain values of the other three groups were all between the above two groups, but the surface arithmetic mean height and fracture strength of the removal 10% group with electric friction pen, the chymotrypsin wiping group and the chymotrypsin soaking group decreased successively, and the fracture strain increased successively. In addition, we carried out a study on the elastic modulus of different groups, and the results showed that the elastic modulus of the control group was the smallest, and the elastic modulus of the removal 20% group with electric friction pen was the largest. The above study revealed that the defect of the superficial area of cartilage changed its surface morphology and structure, and reduced its mechanical properties. The research results are of great significance for the prevention and repair of cartilage injury.