Effectiveness of xenogenous-based bovine-derived platelet gel embedded within a three-dimensional collagen implant on the healing and regeneration of the Achilles tendon defect in rabbits

Background and objective: Tissue engineering is an option in reconstructing large tendon defects and managing their healing and regeneration. We designed and produced a novel xenogeneic-based bovine platelet, embedded it within a tissue-engineered collagen implant (CI) and applied it in an experimentally induced large tendon defect model in rabbits to test whether bovine platelets could stimulate tendon healing and regeneration in vivo. Methods: One hundred twenty rabbits were randomly divided into two experimental and pilot groups. In all the animals, the left Achilles tendon was surgically excised and the tendon edges were aligned by Kessler suture. Each group was then divided into three groups of control (no implant), treated with CI and treated with collagen-platelet implant. The pilot groups were euthanized at 10, 15, 30 and 40 days post-injury (DPI), and their gross and histologic characteristics were evaluated to study host–graft interaction mechanism. To study the tendon healing and its outcome, the experimental animals were tested during the experiment using hematologic, ultrasonographic and various methods of clinical examinations and then euthanized at 60 DPI and their tendons were evaluated by gross pathologic, histopathologic, scanning electron microscopic, biophysical and biochemical methods. Results: Bovine platelets embedded within a CI increased inflammation at short term while it increased the rate of implant absorption and matrix replacement compared with the controls and CI alone. Treatment also significantly increased diameter, density, amount, alignment and differentiation of the collagen fibrils and fibers and approximated the water uptake and delivery behavior of the healing tendons to normal contralaterals (p < 0.05). Treatment also improved echogenicity and homogenicity of the tendons and reduced peritendinous adhesion, muscle fibrosis and atrophy, and therefore, it improved the clinical scores and physical activity related to the injured limb when compared with the controls (p < 0.05). Conclusion: The bovine platelet gel embedded within the tissue-engineered CI was effective in healing, modeling and remodeling of the Achilles tendon in rabbit. This strategy may be a valuable option in the clinical setting.