Enhancement of Tendon-to-Bone Healing: Choose a Monophasic or Hierarchical Scaffold?

3-Dimensional Bioprinting of a Tendon Stem Cell-Derived Exosomes Loaded Scaffold to Bridge the Unrepairable Massive Rotator Cuff Tear

BACKGROUND

Unrepairable massive rotator cuff tears (UMRCTs) are challenging to surgeons owing to the severely retracted rotator cuff musculotendinous tissues and extreme defects in the rotator cuff tendinous tissues.

PURPOSE

To fabricate a tendon stem cell-derived exosomes loaded scaffold (TSC-Exos-S) and investigate its effects on cellular bioactivity in vitro and repair in a rabbit UMRCT model in vivo.

STUDY DESIGN

Controlled laboratory study.

METHODS

TSC-Exos-S was fabricated by loading TSC-Exos and type 1 collagen (COL-I) into a 3-dimensional bioprinted and polycaprolactone (PCL)-based scaffold. The proliferation, migration, and tenogenic differentiation activities of rabbit bone marrow stem cells (BMSCs) were evaluated in vitro by culturing them in saline, PCL-based scaffold (S), COL-I loaded scaffold (COL-I-S), and TSC-Exos-S. In vivo studies were conducted on a rabbit UMRCT model, where bridging was repaired with S, COL-I-S, TSC-Exos-S, and autologous fascia lata (FL). Histological and biomechanical analyses were performed at 8 and 16 weeks postoperatively.

RESULTS

TSC-Exos-S exhibited reliable mechanical strength and subcutaneous degradation, which did not occur before tissue regeneration. TSC-Exos-S significantly promoted the proliferation, migration, and tenogenic differentiation of rabbit BMSCs in vitro. In vivo studies showed that UMRCT repaired with TSC-Exos-S exhibited significant signs of tendinous tissue regeneration at the bridging site with regard to specific collagen staining. Moreover, no significant differences were observed in the histological and biomechanical properties compared with those repaired with autologous FL.

CONCLUSION

TSC-Exos-S achieved tendinous tissue regeneration in UMRCT by providing mechanical support and promoting the trend toward tenogenic differentiation.

CLINICAL RELEVANCE

The present study proposes a potential strategy for repairing UMRCT with severely retracted musculotendinous tissues and large tendinous tissue defects.

Dual-Targeted Metal Ion Network Hydrogel Scaffold for Promoting the Integrated Repair of Tendon-Bone Interfaces

The tendon-bone interface has a complex gradient structure vital for stress transmission and pressure buffering during movement. However, injury to the gradient tissue, especially the tendon and cartilage components, often hinders the complete restoration of the original structure. Here, a metal ion network hydrogel scaffold, with the capability of targeting multitissue, was constructed through the photopolymerization of the LHERHLNNN peptide-modified zeolitic imidazolate framework-8 (LZIF-8) and the WYRGRL peptide-modified magnesium metal-organic framework (WMg-MOF) within the hydrogel scaffold, which could facilitate the directional migration of metal ions to form a dynamic gradient, thereby achieving integrated regeneration of gradient tissues. LZIF-8 selectively migrated to the tendon, releasing zinc ions to enhance collagen secretion and promoting tendon repair. Simultaneously, WMg-MOF migrated to cartilage, releasing magnesium ions to induce cell differentiation and facilitating cartilage regeneration. Infrared spectroscopy confirmed successful peptide modification of nano ZIF-8 and Mg-MOF. Fluorescence imaging validated that LZIF-8/WMg-MOF had a longer retention, indirectly confirming their successful targeting of the tendon-bone interface. In summary, this dual-targeted metal ion network hydrogel scaffold has the potential to facilitate synchronized multitissue regeneration at the compromised tendon-bone interface, offering favorable prospects for its application in the integrated reconstruction characterized by the gradient structure.