Engineered Tissue Graft for Repair of Injured Infraspinatus Rotator Cuff Tendon

Rotator cuff tears constitute a vast majority of shoulder-related injuries, occurring in a wide population range and increasing in incidence with age. Current treatments for full thickness tears use suture to secure the ruptured tendon back to its native attachment site and often retear due to improper enthesis regeneration. To reduce the occurrence of retear, our laboratory developed an engineered tendon graft for rotator cuff repair (ETG-RC) to serve as an underlayment to traditional suture repair. We hypothesize the ETG-RC will aid in the repair of the torn rotator cuff tendon by promoting the regeneration of a functional enthesis. This devitalized graft fabricated from ovine-derived bone marrow stromal cells was evaluated for biomechanical and histomorphology properties in an ovine infraspinatus rotator cuff repair model. Compared with a current standard practice Suture-Only model, the ETG-RC repair showed comparable high strain-to-failure forces, greater fibrocartilage deposition, regeneration of zonal gradients, and Shapey's fibers formation, indicative of enthesis regeneration. Enthesis regeneration after rotator cuff repair should repair mechanical properties and alleviate the need for subsequent surgeries required due to retear. The ETG-RC could potentially be used for repairing other tendon injuries throughout the body.

Exosomes Derived From Kartogenin-Preconditioned Mesenchymal Stem Cells Promote Cartilage Formation and Collagen Maturation for Enthesis Regeneration in a Rat Model of Chronic Rotator Cuff Tear

BACKGROUND

Poor tendon-to-bone healing in chronic rotator cuff tears (RCTs) is related to unsatisfactory outcomes. Exosomes derived from mesenchymal stem cells reportedly enhance rotator cuff healing. However, the difficulty in producing exosomes with a stronger effect on enthesis regeneration must be resolved.

PURPOSE

To study the effect of exosomes derived from kartogenin (KGN)-preconditioned human bone marrow mesenchymal stem cells (KGN-Exos) on tendon-to-bone healing in a rat model of chronic RCT.

STUDY DESIGN

Controlled laboratory study.

METHODS

Exosome-loaded sodium alginate hydrogel (SAH) was prepared. Moreover, exosomes were labeled with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindotricarbocyanine iodide (DiR) or 1,1'-dioctadecyl-3,3,3'3'-tetramethylindocarbocyanine perchlorate (Dil) for in vivo tracking. Bilateral rotator cuff repair (RCR) was conducted in an established chronic RCT rat model. A total of 66 rats were randomized to control, untreated exosome (un-Exos), and KGN-Exos groups to receive local injections of pure SAH, un-Exos, or KGN-Exos SAH at the repaired site. The presence of DiR/Dil-labeled exosomes was assessed at 1 day and 1 week, and tendon-to-bone healing was evaluated histologically, immunohistochemically, and biomechanically at 4 and 8 weeks.

RESULTS

Both un-Exos and KGN-Exos exhibited sustained release from SAH for up to 96 hours. In vivo study revealed that un-Exos and KGN-Exos were localized to the repaired site at 1 week. Moreover, the KGN-Exos group showed a higher histological score and increased glycosaminoglycan and collagen II expression at 4 and 8 weeks. In addition, more mature and better-organized collagen fibers with higher ratios of collagen I to collagen III were observed at 8 weeks in the tendon-to-bone interface compared with those in the control and un-Exos groups. Biomechanically, the KGN-Exos group had the highest failure load (28.12 ± 2.40 N) and stiffness (28.57 ± 2.49 N/mm) among the 3 groups at 8 weeks.

CONCLUSION

Local injection of SAH with sustained KGN-Exos release could effectively promote cartilage formation as well as collagen maturation and organization for enthesis regeneration, contributing to enhanced biomechanical properties after RCR.

CLINICAL RELEVANCE

KGN-Exos injection may be used as a cell-free therapeutic option to accelerate tendon-to-bone healing in chronic RCT.

Designing a novel vacuum aspiration system to decellularize large-size enthesis with preservation of physicochemical and biological properties

Background

Functional and rapid enthesis regeneration remains a challenge after arthroscopic rotator cuff (RC) repair. Tissue-engineering a large-size biomimetic scaffold may be an adjuvant strategy to improve this clinical dilemma. Herein, we developed an optimized protocol to decellularize large-size enthesis as scaffolds for augmenting RC tear.

Methods

A novel vacuum aspiration system (VAS) was set up, which can provide a negative pressure to suck out cellular substances from tissue blocks without using chemical detergents. Large-size enthesis tissue specimens were harvested from canine infraspinatus tendon (IT) insertion, and then decellularized with an optimized protocol [freeze-thaw processing followed by nuclease digestion and phosphate buffer saline (PBS) rinsing in the custom-designed VAS], or a conventional protocol (freeze-thaw processing followed by nuclease digestion and PBS rinsing), thus fabricating two kinds of acellular enthesis matrix (AEM), namely C-AEM and O-AEM. After that, the C-AEM and O-AEM were comparatively evaluated from the aspect of their physicochemical and biological properties.

Results

Physiochemically, the O-AEM preserved the morphologies, ingredients, and tensile properties much better than the C-AEM. Biologically, in vitro studies demonstrated that both C-AEM and O-AEM show no cytotoxicity and low immunogenicity, which could promote stem cells attachment and proliferation. Interestingly, O-AEM showed better region-specific inducibility on the interacted stem cell down osteogenic, chondrogenic and tenogenic lineages compared with C-AEM. Additionally, using a canine IT repair model, the injured enthesis patched with O-AEM showed a significant improvement compared with the injured enthesis patched with C-AEM or direct suture histologically.

Conclusions

The proposed VAS may help us fabricate large-size AEM with good physicochemical and biological properties, and this AEM may have potential clinical applications in patching large/massive RC tear.

Preparation of Decellularized Triphasic Hierarchical Bone-Fibrocartilage-Tendon Composite Extracellular Matrix for Enthesis Regeneration

Tendon to bone (enthesis) rupture, which may cause disability and persistent pain, shows high rate of re-rupture after surgical repair. Tendon or enthesis scaffolds have been widely studied, but few of these materials can recapitulate the tissue continuity. Thus, this study is conducted to prepare a triphasic decellularized bone-fibrocartilage-tendon (D-BFT) composite scaffold. The D-BFT scaffold is developed using a combination of physical, chemical, and enzymatic treatments using liquid nitrogen, Triton-X 100, sodium-dodecyl sulfate, and DNase I, which effectively removes the cell components while preserving the biological composite and microstructure. Moreover, the mechanical properties of D-BFT are highly preserved and similar to those of the human Achilles tendon. Additionally, in vitro, mesenchymal stem cells (MSCs) adhered, proliferated, and infiltrated into the D-BFT scaffold, and MSC differentiation is confirmed by up-regulation of osteogenic-related and tenogenic-related genes. The repair outcomes are explored by applying the D-BFT scaffold in the model of femur-tibia defects in vivo, which shows good repair results. Thus, the D-BFT scaffold developed in this study is a promising graft for enthesis regeneration.

Effect of Suture Absorbability on Rotator Cuff Healing in a Rabbit Rotator Cuff Repair Model

BACKGROUND

Various suture materials can be clinically used for rotator cuff repair (RCR). RCR with high-strength nonabsorbable sutures may not be ideal, because it may cause stress shielding, which may hinder enthesis regeneration and maturation in the tendon-bone interface. RCR with strength-decreasing sutures (ie, absorbable sutures) may be a better choice. However, the effects of suture absorbability on enthesis regeneration and maturation have not been investigated.

HYPOTHESIS

The use of absorbable sutures in RCR would produce a better tendon-bone connection structure, which provides histological and biomechanical advantages over the use of nonabsorbable sutures.

STUDY DESIGN

Controlled laboratory study.

METHODS

A supraspinatus tear was created on the right shoulder in 108 of 120 skeletally mature male rabbits. The animals were randomly divided into 3 groups, with 36 rabbits in each group, to undergo RCR individually with total absorbable, partial absorbable, and nonabsorbable sutures (TAS, PAS, and NAS). Twelve animals in each group were sacrificed at 4, 8, and 12 weeks after surgery, with 6 operated shoulders used for histological evaluation to detect enthesis regeneration and maturation and the other 6 for biomechanical testing. The remaining 12 animals without supraspinatus tear were used as control.

RESULTS

At 12 weeks, in the tendon-bone interface, enthesis regeneration was detected in the TAS group but not in the NAS group. A mature enthesis appeared in the TAS group but not in the NAS group. In the PAS group, enthesis regeneration was also observed; however, the fibrocartilage was not abundant and the enthesis maturity not good as compared with the TAS group. Biomechanical testing showed that the rotator cuff-greater tuberosity connection structure in the TAS and PAS groups had greater values of ultimate load to failure, stiffness, and stress than the NAS group at all time points.

CONCLUSION

In RCR in an acute rabbit rotator cuff tear model, the use of sutures with absorbability lead to enthesis regeneration, increased maturity of rotator cuff insertion, and enhanced rotator cuff-greater tuberosity connection.

CLINICAL RELEVANCE

Compared with the use of NAS, the use of TAS or PAS might be a better choice for RCR.