The Direct Effect of Nanofiber-based Vitamin D Sheet Engineered with 3D Printing for Tendon-to-bone Healing and Muscle Regeneration after Repair in a Chronic Rotator Cuff Tear Model of Rabbit (217)

OBJECTIVES: To compare the efficacy between the direct effect of nanofiber-based vitamin D sheet engineered with 3D printing (VTD sheet) and vitamin D supplementation (VTDS) as diet on tendon-to-bone healing and muscle regeneration after repair in a chronic rotator cuff tear model of rabbit. METHODS: A total of 64 rabbits were randomly allocated into two groups (n=32), then each groups was allocated into four small groups (Group A, A’: VTDS only, Group B, B’: Normal diet + sheet without vitamin D, Group C, C’: Normal diet + VTD sheet, Group D, D’: VTDS + VTD sheet, n=8 each). The supraspinatus tendons which were detached and left for 6 weeks were repaired in a transosseous manner with the sheet only for groups B and B’, and VTD sheet for groups C, C’, D and D’ (Figure 1). Groups A, B, C, and D were extracted at 4weeks after repair, while groups A’, B’, C’, and D’ were extracted at 12 weeks after repair. Serum 25-OH vitamin D level was checked at the time of making tear, repair, and extraction. Regarding tendon-to-bone healing, the expression (relative ratio to control) of genes including type 1 collagen (COL1), type 3 collagen (COL3), bone morphogenic protein-2 (BMP-2), scleraxis (SCX), SOX9, and aggrecan (ACAN) was assessed at 4 weeks (Groups A, B, C, and D), and at 12 weeks (Groups A’, B’, C’, and D’) after repair. The histological and biomechanical evaluations of tendon-to-bone healing were done at 12 weeks after repair. Regarding muscle regeneration, rotator cuff muscle cross-sectional areas were measured at 4 and 12 weeks after repair. Enzyme-linked immunosorbent assay (ELISA) was done to calculate vitamin D level in muscle at 12 weeks after repair. RESULTS: Serum vitamin D level of group D and D’ was highest among groups at the time of repair and extraction (p < 0.001). At 4 weeks after repair, mRNA expression of COL1 in group D was highest among groups (A, B, C, D; 0.86 ± 0.25, 0.90 ± 0.27, 0.93 ± 0.19, and 1.06 ± 0.25, respectively, p = 0.046). At 12 weeks after repair, group D’ showed most dense collagen density (p = 0.037) and had highest load to failure among groups (A’, B’, C’, D’; 102.3 ± 12.6 N, 99.5 ± 8.3 N, 102.3 ± 18.5 N, and 139.6 ± 25.3, respectively, p = 0.024). Regarding muscle regeneration, the cross-sectional area of muscle fiber was largest in group D and D’ at 4 and 12 weeks after repair (p < 0.05, figure 4) with highest vitamin D level of muscle by ELISA at 12 weeks after repair (p = 0.003). CONCLUSIONS: The use of nanofiber-based vitamin D sheet engineered with 3D printing may promote tendon-to-bone healing and regenerate rotator cuff muscle after repair in a chronic rabbit rotator cuff tear model.