[Experimental study on the osteogenic effect of graphene-coated nickel-titanium memory alloy anchors on acute supraspinatus tendon injuries in rabbits with bone loss].

OBJECTIVE: (1)To reverse design a new type of nickel-titanium(NiTi) memory alloy anchors with graphene coating, and to compare their mechanical properties with those of ordinary titanium alloy anchors, as well as their effects on osteoblast proliferation and osteogenic activity in mice. (2)To evaluate the effect of graphene-coated NiTi memory alloy anchor nail on local osseointegration, bone formation and tendon-bone healing strength after rotator cuff injury with bone loss.

METHODS: (1) A novel NiTi shape memory alloy anchor was designed and fabricated, followed by surface modification with graphene coating and characterization of the modified anchor. The effects of graphene-coated NiTi alloy materials on the proliferation and viability of mouse osteoblasts were detected, and the mechanical properties of different anchors were compared. (2) A rabbit model of bone loss was established. Micro-CT was performed 3 months later to verify the successful establishment of the model. (3) A model of acute supraspinatus tendon tear in rabbits with bone loss was established, and histological evaluation, biomechanical evaluation, and Micro-CT examination were conducted.

RESULTS: (1) Graphene was successfully coated on the surface of NiTi alloy materials, which exhibited good hydrophilicity. (2) Bioactivity:Graphene-coated NiTi alloy materials showed the strongest enhancement effect on osteoblast proliferation and osteogenic activity, with statistically significant differences compared with the blank control group, titanium alloy group, and uncoated group (P<0.05). (3) Anchor mechanical testing:in the bone loss model, regardless of the pull-out angle, the maximum pull-out force of NiTi alloy anchors was higher than that of titanium alloy anchors at the same angle, with a statistically significant difference (P<0.05). (4) The local trabecular bone thickness and number in the bone loss model group were significantly lower than those in the non-model control group (P<0.05), while the trabecular bone spacing showed the opposite trend with a statistically significant difference (P<0.05), verifying the successful establishment of the model. (5) Histological results:At 6 and 12 weeks postoperatively, the experimental group showed normal bone tissue structure;compared with the other two groups, it had more bone marrow cells in the bone marrow cavity, higher trabecular bone content, thicker trabecular bones, more chondrocyte formation, and denser, more orderly arrangement of collagen fibers. (6) Biomechanics:the maximum tensile strength and stiffness of all groups showed an increasing trend over time. The maximum tensile strength and stiffness of the experimental group were superior to those of the other two groups, with statistically significant differences(P<0.05). (7) Imaging findings:the trabecular bone thickness and number in the experimental group were higher than those in the other two groups (P<0.05);on the contrary, the trabecular bone spacing was significantly reduced, with a statistically significant difference(P<0.05).

CONCLUSION: (1)G-coated NiTi memory alloy anchor nails have good hydrophilic, biocompatible, osteogenic, and mechanical properties. (2)G-coated NiTi memory alloy anchor nails can effectively promote local osteogenesis, improve the microenvironment of tendon-bone healing, increase the anchor nail pullout resistance and improve the quality of tendon-bone healing.