Introduction: When a divided flexor tendon cannot be repaired primarily because of tendon loss, tendon grafting must be performed to restore function to the digit. As the availability of donor tendons is limited, researchers are attempting to produce bioartificial tendons (BAT) by seeding an acellular scaffold with different types of cells. Although most laboratories use tenocytes, other cell types such as mesenchymal stem cells (MSC) may be better suited for this task. The goal of this study was to compare the properties of bone marrow derived MSC and fat derived MSC with sheath tenocytes and endotenon tenocytes in an effort to determine the optimal cell type for tendon engineering. Methods: New Zealand White Rabbit flexor tendons were harvested and treated to prepare cell cultures of sheath tenocytes and endotenon tenocytes. Rabbit bone marrow and fat were then harvested to prepare cell cultures of MSC. Insulin like Growth Factor 1 (IGF-1), Platelet Derived Growth Factor (PDGF), and basic Fibroblast Growth Factor (b-FGF) were added to optimize cell growth. Growth kinetics were then compared between the different cell types by use of cell proliferation, senescence, and collagen-1 production assays. Next these four cell types were seeded onto acellular collagen scaffolds and implanted as tendon grafts in rabbit flexor tendons. Five rabbits were grafted with each cell type. The specimens from each group were harvested at 4 weeks (n=3) and at 8 weeks (n=2) and compared histologically. Seeded scaffolds were also compared to acellular scaffolds (n=5) and untreated autogenous grafts (n=5) to evaluate viability and inflammatory reaction. Results: The addition of growth factors increased the rate of tenocyte (sheath and endotenon) cell growth by a factor of 4x and 6x respectively. Both fat and bone marrow MSC rates increased by factors of 1.8x and 2.6x respectively. The proliferation rate of fat derived MSC at passage 12 was only 2% less than the rate at passage 3. The proliferation rate of bone marrow derived MSC decreased by 40% from passage 3 to passage 12. Stains for β-galactosidase and for collagen 1 demonstrated that approximately 1 in 1000 fat and bone marrow derived MSC was senescent at passage 9 and that collagen-1 production was unchanged from passage 1 to 9. The BAT constructs seeded with both MSC types as well as those seeded with tenocytes were viable and had the histologic appearance of tendon grafts when harvested. The inflammation decreased from week 4 to week 8. Acellular controls did not retain their characteristic tendon architecture. The inflammatory response was similar to that seen in untreated autogenous controls. Conclusion: Bioengineered tendon grafts are a viable source of graft material for use in the reconstruction of flexor tendon defects. Although most studies to date have used tenocytes, fat derived MSC and bone marrow derived MSC are also candidates for BAT engineering. MSC proliferation rates are comparable to tenocyte proliferation rates. Both proliferation rates and staining demonstrated little senescence of the MSC, although bone marrow derived MSC had more senescence by proliferation assay compared to fat derived MSC. Cultured cells remain functional as demonstrated by continued collagen-1 production. Finally, in vivo models show that seeded BAT (either tenocytes or MSC) are viable and do not have increased inflammation compared to acellular controls. Further studies of physiologic parameters such as strength and post operative range of motion of BAT are needed.
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