Rotator cuff tendon tears are one of the most common musculoskeletal injuries, yet the management of patients with massive rotator cuff tears remains a challenge. Surgical treatment with graft augmentation has shown improvement in strength and tendon healing with decreased gap formation compared to traditional all-suture repair. Biological grafts made of decellularized extracellular matrix are typically used to augment large to massive rotator cuff tears. While these grafts provide a natural structure and contain protein components that promote cellular growth and collagen formation during the healing period, they have inferior mechanical properties compared to native tendon tissues, which results in a high re-tear rate. Synthetic grafts made from resorbable polymers have also shown enhanced mechanical performance with minimal risk of disease transmission compared to biological grafts, but the biocompatibility of synthetic grafts remains a concern, because the synthetic foreign bodies may increase the risk of infection. Further, neither graft type mimics the gradient structures and components of the tendon-to-bone interface at the repair site, which is another factor leading to injury recurrence. Therefore, tissue engineering techniques, which use a combination of scaffolds, cells, and bioactive molecules, have been considered an alternative strategy for rotator cuff tissue regeneration, particularly due to the possibility of having a multi-phase structure with corresponding cells in different zones.

To develop a graft that is suitable for rotator cuff tissue engineering, we first compared yarns made from the natural biopolymer, collagen, with yarns made from the synthetic polymer, polylactic acid (PLA), in terms of their tensile properties and in vitro biocompatibility. PLA yarns were more resistant to enzymatic degradation, maintaining tensile properties better than collagen yarns. After coating the PLA yarns with collagen, they also had good biocompatibility and were able to support tenocyte growth and proliferation. We then fabricated the PLA yarns into narrow ribbon patches via flat braiding. The braided structure resulted in mechanical properties that mimicked natural tendon tissue, enabling them to be used as augmentation grafts for rotator cuff tendon repair. Different structures with a range of mechanical properties were fabricated by changing the braiding parameters, identifying the possibility of designing and constructing a graft with a gradient structure using braiding technology. Next, tendon-derived stem cells (TDSCs), a unique cell line with multi-differentiation potential, were successfully isolated from rat tendon tissues and seeded on a collagen-coated PLA braided scaffold. The results from in vitro cell studies showed that TDSCs were able to adhere, proliferate, and differentiate into tenocytes on a modified PLA braided scaffold, demonstrating that this scaffold is biocompatible, and when seeded with TDSCs, may provide a viable tissue engineering strategy for rotator cuff tendon repair.

This study to develop tissue engineering solutions for rotator cuff tendon regeneration had several innovations. First, our study was the first to compare collagen yarns and PLA yarns directly, providing a reference for future material selection in tissue engineering applications. Second, flat braiding was used for the first time to fabricate tendon repair scaffolds, demonstrating the possibility of fabricating a multi-phase structure that mimics the tendon-to-bone interface. Third, TDSCs were seeded on a synthetic textile-based scaffold for the first time and demonstrated multi-differentiation potential. Overall, our work presents a novel textile-based tissue engineering approach that can be used to mimic the native gradient structures of the tendon-to-bone interface and provides good performance in mechanical properties and biocompatibility, making it a promising solution for improved tendon repair.