Effect of Fibrin Formulation on Initial Strength of Tendon Repair and Migration of Bone Marrow Stromal Cells in Vitro

Abstract

Cell-based tissue engineering techniques have been introduced to improve tendon repair outcomes. The purpose of this study was to determine optimal concentrations of fibrinogen and thrombin for use as a scaffold to deliver stromal cells to the tendon repair site. Lacerated flexor digitorum profundus tendons from forty canine forepaws underwent simulated repair with fibrin gel interposition. The tendons were divided into five groups with different ratios of fibrinogen (mg/mL) to thrombin (NIH units/mL) used to form the gels. These ratios, which ranged from those found in normal hemostasis to those used clinically as adhesives, were 5:25 (the physiological ratio, used as a control), 40:250 (a low adhesive concentration of fibrinogen and a low adhesive concentration of thrombin [low-low group]), 80:250 (high-low group), 40:500 (low-high group), and 80:500 (high-high group). The failure load and tensile stiffness at time zero, compressive stiffness of the fibrin gel, and cell viability and migration were evaluated. The failure loads of the high-low and high-high groups were significantly higher than that of the control group. The tensile stiffness of the high-high group was significantly higher than that of the control group. The high-low and high-high groups had significantly higher compressive stiffness than the other groups. While there was no significant difference among the groups regarding cell viability, the cells in the control, low-low, and low-high gels were spindle-shaped whereas those in the high-low and high-high groups were rounded. Cells migrated across scratch gaps within twenty-four hours in the control, low-low, and low-high groups, but not in the high-low and high-high groups. Higher concentrations of fibrinogen resulted in stronger and stiffer gels, but the strength was far less than that of a tendon suture and these gels were associated with a more rounded cell morphology and reduced cell migration. Therefore, lower concentrations of fibrinogen should be used if a fibrin gel is employed to deliver cells for tendon repair. Concentrations of fibrinogen lower than those used in fibrin glue may be more appropriate if fibrin is employed to create a cell delivery matrix for tendon repair.