Targeting tendon-bone junction regeneration: development of a gradient scaffold.

The tendon-bone (T-B) junction is the transition zone from soft to hard tissue, prone to acute and overuse injuries in both human and equine athletes. Functional integration between tendon and bone remains a major challenge after injury, as the presence of inflammation affects the healing process, resulting in the formation of scar tissue. Tissue engineering strategies should be explored to support T-B regeneration. To this end, the characteristic gradient structure of the junction, i.e. the spatial distribution with a gradual decrease in collagen fiber organization while proteoglycan and mineral content is gradually increasing, should be mimicked. To develop such a functional scaffold, tailor-made photo-crosslinkable and biodegradable polymers (i.e. urea/urethane-based norbornene-endcapped precursors and thiolated decellularized extracellular matrix) will be synthesized and characterized. Then, the developed materials will be 3D printed into a continuous scaffold exhibiting a gradient in mechanical properties. Finally, by encapsulating undifferentiated mesenchymal stem cells (MSCs) during 3D-printing along with their differentiation factors, the MSCs will gradually differentiate towards the desired phenotypes. Undifferentiated MSC will secrete anti-inflammatory factors, which is beneficial to counter the inflammation observed immediately after injury. Once the MSC are differentiating, trophic factors will be produced, which is beneficial to support T-B regeneration.