Abstract: BACKGROUND: The annulus fibrosus is an important part of the intervertebral disc, and is the key to maintain the mechanical and physiological functions of the intervertebral disc. Therefore, the construction of a biological scaffold that mimics the structure of the natural annulus fibrosus is essential for tissue engineering to repair the intervertebral disc.
OBJECTIVE: To construct biomimetic orientated microchannel and control scaffold with silk fibroin as raw material, and to evaluate its feasibility as a tissue engineered annulus fibrosus scaffold. 
METHODS: The polycaprolactone was used as raw material to construct 60° oriented fiber pattern by melt spinning technology, and filled with 15% silk fibroin solution, quick-freeze with liquid nitrogen, freeze-drying by lyophilizer. Polycaprolactone material was eluted by chloroform. The preparation of the orientated microchannel fibrous ring scaffold was completed; at the same time, a common silk fibroin scaffold was prepared as a control. The microscopic morphology and mechanical properties of the scaffold were characterized. The third-generation rabbit annulus cells were inoculated on the two scaffolds respectively. The viability and proliferation ability of the cells on the scaffold were analyzed by Live/Dead staining and CCK-8 assay. The two scaffolds were implanted subcutaneously in rats, and the scaffolds were removed 4 weeks later for hematoxylin-eosin staining.
RESULTS AND CONCLUSION: (1) Stereoscopic microscope and scanning electron microscope showed that there were a large number of regular channels arranged on the surface of the oriented microchannel scaffold and the channels penetrated deeply into the scaffold, and there were only a few cracks on the surface of the control scaffold. The diameter of two kinds of scaffolds was (152.0±9.3) μm. The porosity was (89.0±3.3)% in the oriented microchannel  group and (73.0±2.6)% in the control group. (2) The compression elastic modulus was (2.65±0.11) MPa in oriented microchannel group and (3.05±0.13) MPa in the control group (P < 0.05). (3) The Live/Dead staining and scanning electron microscope results showed that cells grow well on both scaffolds. In the control group, the scaffold cells only attached to the scaffold surface. The cells grew into the scaffolds along the microchannels and the extracellular matrix was secreted sufficiently. CCK-8 assay showed that the oriented microchannel scaffolds could promote cell proliferation. (4) Hematoxylin-eosin staining revealed that a lot of extracellular matrix components and cells were found in the oriented microchannel scaffolds. In the control group, a lot of cells and extracellular matrix only grew on surface of scaffold. (5) It is concluded that the oriented microchannel silk fibroin scaffold can simulate natural annulus fibrosus microstructure, which have good mechanical property; and the cells can along the channel grow into the scaffold, which has good biocompatibility. It is a suitable biological scaffold for the construction of annulus fibrosus scaffold.

Key words: tissue engineering, annulus fibrosus, intervertebral disc, silk fibroin, microchannel, biocompatibility, biological scaffold material, degenerative disc disease, freeze-drying, tissue repair