Effect of kartogenin-loaded gelatin methacryloyl hydrogel scaffold with bone marrow stimulation for enthesis healing in rotator cuff repair

Background Strategies involving microfracture, biomaterials, growth factors, and chemical agents have been evaluated for improving enthesis healing. Kartogenin (KGN) promotes selective differentiation of bone marrow mesenchymal stem cells (BMSCs) into chondrocytes. Gelatin methacryloyl (GelMA) is a promising biomaterial for engineering scaffolds and drug carriers. Herein, we investigated KGN-loaded GelMA hydrogel scaffolds with a bone marrow–stimulating technique for the repair of rotator cuff tear. Methods KGN-loaded GelMA hydrogel scaffolds were obtained by ultraviolet GelMA crosslinking and vacuum freeze-drying. Fifty-four New Zealand rabbits were randomly divided into (1) repair only (control), (2) microfracture + repair (BMS), and (3) microfracture + repair augmentation with a KGN-loaded GelMA hydrogel scaffold (combined) groups. Tendons were repaired by transosseous sutures. The structure, degradation, and in vitro KGN release of the scaffolds were characterized. Animals were euthanized 4, 8, and 12 weeks after repair. Enthesis healing was evaluated by macroscopy, microcomputed tomography, histology, and biomechanical tests. Results The KGN-loaded GelMA hydrogel scaffolds are porous with a 60.4 ± 28.2-μm average pore size, and they degrade quickly in 2.5 units/mL collagenase solution. Nearly 81% of KGN was released into phosphate-buffered saline within 12 hours, whereas the remaining KGN was released in 7 days. Macroscopically, the repaired tendons were attached to the footprint. No differences were detected postoperatively in microcomputed tomography analysis among groups. Fibrous scar tissue was the main component at the tendon-to-bone interface in the control group. Disorderly arranged cartilage formation was observed at the tendon-to-bone interface in the BMS and combined groups 4 weeks after repair; the combined group exhibited relatively more cartilage. The combined group showed improved cartilage regeneration 8 and 12 weeks after repair. Similar results were found in tendon maturation scores. The ultimate load to failure and stiffness of the repaired tendon increased in all 3 groups. At 4 weeks after repair, the BMS and combined groups exhibited greater ultimate load to failure than the control group, although there was no difference in stiffness among groups. The BMS and combined groups exhibited greater ultimate load to failure and stiffness than the control group, and the combined group exhibited better values than the BMS group at 8 and 12 weeks after repair. Conclusion Compared with the bone marrow–stimulating technique, the KGN-loaded GelMA hydrogel scaffold with bone marrow stimulation improved enthesis healing by promoting fibrocartilage formation and improving the mechanical properties. Strategies involving microfracture, biomaterials, growth factors, and chemical agents have been evaluated for improving enthesis healing. Kartogenin (KGN) promotes selective differentiation of bone marrow mesenchymal stem cells (BMSCs) into chondrocytes. Gelatin methacryloyl (GelMA) is a promising biomaterial for engineering scaffolds and drug carriers. Herein, we investigated KGN-loaded GelMA hydrogel scaffolds with a bone marrow–stimulating technique for the repair of rotator cuff tear. KGN-loaded GelMA hydrogel scaffolds were obtained by ultraviolet GelMA crosslinking and vacuum freeze-drying. Fifty-four New Zealand rabbits were randomly divided into (1) repair only (control), (2) microfracture + repair (BMS), and (3) microfracture + repair augmentation with a KGN-loaded GelMA hydrogel scaffold (combined) groups. Tendons were repaired by transosseous sutures. The structure, degradation, and in vitro KGN release of the scaffolds were characterized. Animals were euthanized 4, 8, and 12 weeks after repair. Enthesis healing was evaluated by macroscopy, microcomputed tomography, histology, and biomechanical tests. The KGN-loaded GelMA hydrogel scaffolds are porous with a 60.4 ± 28.2-μm average pore size, and they degrade quickly in 2.5 units/mL collagenase solution. Nearly 81% of KGN was released into phosphate-buffered saline within 12 hours, whereas the remaining KGN was released in 7 days. Macroscopically, the repaired tendons were attached to the footprint. No differences were detected postoperatively in microcomputed tomography analysis among groups. Fibrous scar tissue was the main component at the tendon-to-bone interface in the control group. Disorderly arranged cartilage formation was observed at the tendon-to-bone interface in the BMS and combined groups 4 weeks after repair; the combined group exhibited relatively more cartilage. The combined group showed improved cartilage regeneration 8 and 12 weeks after repair. Similar results were found in tendon maturation scores. The ultimate load to failure and stiffness of the repaired tendon increased in all 3 groups. At 4 weeks after repair, the BMS and combined groups exhibited greater ultimate load to failure than the control group, although there was no difference in stiffness among groups. The BMS and combined groups exhibited greater ultimate load to failure and stiffness than the control group, and the combined group exhibited better values than the BMS group at 8 and 12 weeks after repair. Compared with the bone marrow–stimulating technique, the KGN-loaded GelMA hydrogel scaffold with bone marrow stimulation improved enthesis healing by promoting fibrocartilage formation and improving the mechanical properties.