Tendon injuries are difficult to heal because they do not regenerate by restitution but by the formation of a fibrotic scar. This scar tissue has poorer mechanical properties and often leads to long-term pain, discomfort and disability in movement. The particular physiology of tendons (hypovascular, hypocellular) and their structural, mechanical properties currently make it difficult to achieve complete and permanent repair of the damaged tissue using available treatments, especially when a complete tear is present. Despite multiple efforts, treatment options for tendon injuries are limited, which has led to the development of alternative therapies, such as the administration of growth factors, the use of stem cells, or tissue engineering of matrix-associated equivalents of tendons. To date, there are no techniques of restoring the original native structure of fully injured or ruptured tendons. One of the most promising methods being developed at the moment is the procedure of tissue engineering. It involves the production of tissue equivalents from the patient's own cells in the laboratory and their subsequent transplantation for safe and complete recovery of the damaged tissue.
The challenge is to determine which cell type both differentiates into tendocyte-like cells in vitro and forms three-dimensional tendon equivalents ex vivo and how they mature. Since the main player of tendo tissue is fibrocytes, we focused on this cell type. Equine cells were targeted as the initial model for the project. Fibrocytes were isolated from equine lumbar region using skin punch (diameter 3mm) and propagated in monolayer cultures. Passage 3 cells were used for the preparation of tendon regenerates. Then, the monolayer cells were transferred to three-dimensional state. The plan was to roll several detached monolayers into each other to form the shape of a suture yarn. The implant created in this way is fixed to an elastic silicone surface by means of stainless steel pins. In this way, 3D constructs can be placed in a tense state in which the elastic subsurface is stretched. The continuously applied tension provides the newly synthesized ECM molecules of the tissue regenerate with a force vector along which they can align in the direction of the stretch, allowing the structure and morphology of tendogenic tissue to form. The fabricated tissue equivalents were studied biomechanically, histologically, and biochemically.
The initial results of the generated tendon regenerates show a promising perspective in further application as an in vitro model as well as in in vivo treatment."