Engineered Cell Sheets for the Effective Delivery of Adipose-Derived Stem Cells for Tendon-to-Bone Healing

Biomimetic gradient scaffolds for the tissue engineering and regeneration of rotator cuff enthesis

Rotator cuff tear is one of the most common musculoskeletal disorders, which often results in recurrent shoulder pain and limited movement. Enthesis is a structurally complex and functionally critical interface connecting tendon and bone that plays an essential role in maintaining integrity of the shoulder joint. Despite the availability of advanced surgical procedures for rotator cuff repair, there is a high rate of failure following surgery due to suboptimal enthesis healing and regeneration. Novel strategies based on tissue engineering are gaining popularity in improving tendon-bone interface (TBI) regeneration. Through incorporating physical and biochemical cues into scaffold design which mimics the structure and composition of native enthesis is advantageous to guide specific differentiation of seeding cells and facilitate the formation of functional tissues. In this review, we summarize the current state of research in enthesis tissue engineering highlighting the development and application of biomimetic scaffolds that replicate the gradient TBI. We also discuss the latest techniques for fabricating potential translatable scaffolds such as 3D bioprinting and microfluidic device. While preclinical studies have demonstrated encouraging results of biomimetic gradient scaffolds, the translation of these findings into clinical applications necessitates a comprehensive understanding of their safety and long-term efficacy.

Dual cross-linked COL1/HAp bionic gradient scaffolds containing human amniotic mesenchymal stem cells promote rotator cuff tendon-bone interface healing

The tendon-bone interface heals through scar tissue, while the lack of a natural interface gradient structure and collagen fibre alignment leads to the occurrence of retearing. Therefore, the promotion of tendon healing has become the focus of regenerative medicine. The purpose of this study was to develop a gradient COL1/ hydroxyapatite (HAp) biomaterial loaded with human amniotic mesenchymal stem cells (hAMSCs). The performance of common cross-linking agents, Genipin, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS), and dual cross-linked materials were compared to select the best cross-linking mechanism to optimize the biological and mechanical properties of the scaffold. The optimal COL1/HAp-loaded with hAMSCs were implanted into the tendon-bone rotator cuff interfaces in rats and the effect on the tendon-bone healing was assessed by micro-CT, histological analysis, and biomechanical properties. The results showed that Genipin and EDC/NHS dual cross-linked COL1/HAp had good biological activity and mechanical properties and promoted the proliferation and differentiation of hAMSCs. Animal experiments showed that the group using a scaffold loaded with hAMSCs had excellent continuity and orientation of collagen fibers, increased fibrocartilage and bone formation, and significantly higher biomechanical functions than the control group at the interface at 12 weeks post operation. This study demonstrated that dual cross-linked gradient COL1/HAp-loaded hAMSCs could promote interface healing, thereby providing a feasible strategy for tendon-bone interface regeneration.

Cell Sheet Technology: An Emerging Approach for Tendon and Ligament Tissue Engineering

Tendon and ligament injuries account for a substantial proportion of disorders in the musculoskeletal system. While non-operative and operative treatment strategies have advanced, the restoration of native tendon and ligament structures after injury is still challenging due to its innate limited regenerative ability. Cell sheet technology is an innovative tool for tissue fabrication and cell transplantation in regenerative medicine. In this review, we first summarize different harvesting procedures and advantages of cell sheet technology, which preserves intact cell-to-cell connections and extracellular matrix. We then describe the recent progress of cell sheet technology from preclinical studies, focusing on the application of stem cell-derived sheets in treating tendon and ligament injuries, as well as highlighting its effects on mitigating inflammation and promoting tendon/graft-bone interface healing. Finally, we discuss several prerequisites for future clinical translation including the selection of appropriate cell source, optimization of preparation process, establishment of suitable animal model, and the fabrication of vascularized complex tissue. We believe this review could potentially provoke new ideas and drive the development of more functional biomimetic tissues using cell sheet technology to meet the needs of clinical patients.

Efficacy of transplantation of lipoaspired mesenchymal stem cells in the treatment of chronic rotator cuff tears. Experimental model in rats

BACKGROUND AND AIM

Rotator cuff tears emerge in approximately 30% of the population over 60 years of age. Arthroscopic surgical treatment of these lesions is the treatment of choice, however, despite the improved repair techniques, the rate of re-tears ranges between 11 and 94%. Therefore, researchers seek to improve the biological healing process through the use of different alternatives such as mesenchymal stem cells (MSCs). Our objective is to evaluate the efficacy of a Cellular Therapy Drug made from allogeneic stem cells derived from adipose tissue in a rat model of chronic rotator cuff injury.

MATERIAL AND METHODS

The supraspinatus lesion was created in 48 rats for subsequent suturing at 4 weeks. MSCs in suspension were added to 24 animals after suturing, and HypoThermosol-FRS® (HTS) to 24 animals as a control group. Histology (Åström and Rausing scale) and the maximum load, displacement and elastic constant of the supraspinatus tendon were analyzed in both groups 4 months after the repair.

RESULTS

No statistically significant differences were found in the histological score comparing the tendons treated with MSCs with respect to the tendons treated with HTS (P=.811) nor in the results of maximum load (P=.770), displacement (P=.852) or elastic constant (P=.669) of the tendon in both groups.

CONCLUSIONS

The addition of adipose-derived cells in suspension to the repair of a chronic cuff injury does not improve the histology or biomechanics of the sutured tendon.

[Translated article] Efficacy of transplantation of lipoaspired mesenchymal stem cells in the treatment of chronic rotator cuff tears. Experimental model in rats

BACKGROUND AND AIM

Rotator cuff tears emerge in approximately 30% of the population over 60 years of age. Arthroscopic surgical treatment of these lesions is the treatment of choice, however, despite the improved repair techniques, the rate of re-tears ranges between 11 and 94%. Therefore, researchers seek to improve the biological healing process through the use of different alternatives such as mesenchymal stem cells (MSCs). Our objective is to evaluate the efficacy of a cellular therapy drug made from allogeneic stem cells derived from adipose tissue in a rat model of chronic rotator cuff injury.

MATERIAL AND METHODS

The supraspinatus lesion was created in 48 rats for subsequent suturing at 4 weeks. MSCs in suspension were added to 24 animals after suturing, and HypoThermosol-FRS® (HTS) to 24 animals as a control group. Histology (Åström and Rausing scale) and the maximum load, displacement and elastic constant of the supraspinatus tendon were analysed in both groups 4 months after the repair.

RESULTS

No statistically significant differences were found in the histological score comparing the tendons treated with MSCs with respect to the tendons treated with HTS (P=0.811) nor in the results of maximum load (P=0.770), displacement (P=0.852) or elastic constant (P=0.669) of the tendon in both groups.

CONCLUSIONS

The addition of adipose-derived cells in suspension to the repair of a chronic cuff injury does not improve the histology or biomechanics of the sutured tendon.

Mussel-Derived Bioadaptive Artificial Tendon Facilitates the Cell Proliferation and Tenogenesis to Promote Tendon Functional Reconstruction

Tendon injuries range from acute-related trauma to chronic-related injuries are prevalent and bring substantial pain, functional loss, and even disability to the patients. The management of tendon injuries is tricky due to the innate limited regenerative capability of the tendon. Currently, surgical intervention of tendon injuries with artificial tendons remains the standard of care. However, most of artificial tendons are manufactured with synthetic materials, which possess relatively poor biomimetic characteristics and inadequate inherent biodegradability, hence rendering limited cell proliferation and migration for tendon healing. To address these limitations, this work develops a mussel-derived artificial tendon based on double-cross-linked chitosan modification. In this design, decellularized artificial tendon serves as a natural biomimetic scaffold to facilitate the migration and adhesion of tendon repair cells. Additionally, as the cells proliferate, the artificial tendon can be degraded to facilitate tendon regeneration. Moreover, the chitosan cross-linking further enhances the mechanical strength of artificial tendon and offers a controllable degradation. The in vitro and in vivo experimental results demonstrate that mussel-derived artificial tendon not only accelerate the tendon functional reconstruction but also enable harmless clearance at postimplantation. The finding provides a promising alternative to conventional artificial tendons and spurs a new frontier to explore nature-derived artificial tendons.

Scaffold- and graft-based biological augmentation of rotator cuff repair: an updated systematic review and meta-analysis of preclinical and clinical studies for 2010-2022

BACKGROUND

Despite advancements in the surgical techniques of rotator cuff repair (RCR), there remains a high retear rate. Biological augmentation of repairs with overlaying grafts and scaffolds may enhance healing and strengthen the repair construct. This study aimed to investigate the efficacy and safety of scaffold-based (nonstructural) and overlay graft-based (structural) biological augmentation in RCR (excluding superior capsule reconstruction and bridging techniques) in both preclinical and clinical studies.

METHODS

This systematic review was performed in adherence to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines, as well as guidelines outlined by The Cochrane Collaboration. A search of the PubMed, Embase, and Cochrane Library databases from 2010 until 2022 was conducted to identify studies reporting the clinical, functional, and/or patient-reported outcomes of ≥1 biological augmentation method in either animal models or humans. The methodologic quality of included primary studies was appraised using the Checklist to Evaluate a Report of a Non-pharmacological Trial (CLEAR-NPT) for randomized controlled trials and using the Methodological Index for Non-randomized Studies (MINORS) for nonrandomized studies.

RESULTS

A total of 62 studies (Level I-IV evidence) were included, comprising 47 studies reporting outcomes in animal models and 15 clinical studies. Of the 47 animal-model studies, 41 (87.2%) demonstrated biomechanical and histologic enhancement with improved RCR load to failure, stiffness, and strength. Of the 15 clinical studies, 10 (66.7%) illustrated improvement in postoperative clinical, functional, and patient-reported outcomes (eg, retear rate, radiographic thickness and footprint, and patient functional scores). No study reported a significant detriment to repair with augmentation, and all studies endorsed low complication rates. A meta-analysis of pooled retear rates demonstrated significantly lower odds of retear after treatment with biological augmentation of RCR compared with treatment with non-augmented RCR (odds ratio, 0.28; P < .00001), with low heterogeneity (I2 = 0.11).

CONCLUSIONS

Graft and scaffold augmentations have shown favorable results in both preclinical and clinical studies. Of the investigated clinical grafts and scaffolds, acellular human dermal allograft and bovine collagen demonstrate the most promising preliminary evidence in the graft and scaffold categories, respectively. With a low risk of bias, meta-analysis revealed that biological augmentation significantly lowered the odds of retear. Although further investigation is warranted, these findings suggest graft and scaffold biological augmentation of RCR to be safe.

Biofabrication of functional bone tissue: defining tissue-engineered scaffolds from nature

Damage to bone leads to pain and loss of movement in the musculoskeletal system. Although bone can regenerate, sometimes it is damaged beyond its innate capacity. Research interest is increasingly turning to tissue engineering (TE) processes to provide a clinical solution for bone defects. Despite the increasing biomimicry of tissue-engineered scaffolds, significant gaps remain in creating the complex bone substitutes, which include the biochemical and physical conditions required to recapitulate bone cells' natural growth, differentiation and maturation. Combining advanced biomaterials with new additive manufacturing technologies allows the development of 3D tissue, capable of forming cell aggregates and organoids based on natural and stimulated cues. Here, we provide an overview of the structure and mechanical properties of natural bone, the role of bone cells, the remodelling process, cytokines and signalling pathways, causes of bone defects and typical treatments and new TE strategies. We highlight processes of selecting biomaterials, cells and growth factors. Finally, we discuss innovative tissue-engineered models that have physiological and anatomical relevance for cancer treatments, injectable stimuli gels, and other therapeutic drug delivery systems. We also review current challenges and prospects of bone TE. Overall, this review serves as guide to understand and develop better tissue-engineered bone designs.

MicroRNA expression changes in the development of rotator cuff tendon injuries

Traumatic or degenerative rotator cuff (RC) tendon injuries are a leading cause of persistent shoulder pain and reduction of mobility with associated disability and dysfunction, which require each year more than 250,000 surgical repairs in the United States. MicroRNAs (miRNAs) are small noncoding RNAs, that in the posttranscriptional phase lead to the development and function of tissues. The aim of this review was to identify miRNA expression changes in patients with RC pathologies and to determine their relevance as a potential novel diagnostic and potentially therapeutic tool for RC disorders. Various miRNAs seemed to be key regulators in the muscle architecture, determining several modifications in muscle atrophy, skeletal muscle mechanical adaptation, lipid accumulation, and fibrosis in the presence of RC tears. The search was executed using PubMed, Medline, Scopus, and Cochrane Central. We included studies written in English that evaluated the role of miRNA in diagnosis, physiopathology, and potential therapeutic application of RC tendon injuries. We included 11 studies in this review. Many miRNAs emerged as key regulators in the pathogenesis of RC tears, inflammation, and muscle fatty degeneration. In fact, they are involved in the regulation of myogenesis, inflammatory cytokines, metalloproteases expression, muscle adaptation, adipogenesis, fibrogenic factors, and extracellular matrix synthesis. The gene expression may be altered in the pathological processes of tendon lesions. Therefore, the knowledge of all the gene mechanisms underlying RC tendinopathy should be achieved with future diagnostic and clinical studies.

Cryopreserved Adipose-Derived Stem Cell Sheets: An Off-the-Shelf Scaffold for Augmenting Tendon-to-Bone Healing in a Rabbit Model of Chronic Rotator Cuff Tear

BACKGROUND

Adipose-derived stem cell (ADSC) sheets have been shown to promote tendon-to-bone healing. However, conventional laboratory preparation methods for ADSC sheets are time-consuming and risky, which precludes their diverse clinical applications.

PURPOSE

To explore the utility of off-the-shelf cryopreserved ADSC sheets (c-ADSC sheets) for rotator cuff tendon-to-bone healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

The ADSC sheets were cryopreserved and thawed for live/dead double staining, TdT-mediated dUTP Nick-End Labeling (TUNEL) staining, scanning electron microscopy observation, and biomechanical testing. Clone formation, proliferative capacity, and multilineage differentiation of ADSCs within the c-ADSC sheets were assayed to explore the effect of cryopreservation on stem cell properties. A total of 67 rabbits were randomly divided into 4 groups: normal group (without supraspinatus tendon tears; n = 7), control group (repair alone; n = 20), fresh ADSC (f-ADSC) sheet group (repair; n = 20), and c-ADSC sheet group (repair; n = 20). Rabbit bilateral supraspinatus tendon tears were induced to establish a chronic rotator cuff tear model. Gross observation, micro-computed tomography analysis, histological or immunohistochemical tests, and biomechanical tests were conducted at 6 and 12 weeks after repair.

RESULTS

No significant impairment was seen in the cell viability, morphology, and mechanical properties of c-ADSC sheets when compared with f-ADSC sheets. The stem cell properties of ADSC sheets also were preserved by cryopreservation. At 6 and 12 weeks after the repair, the f-ADSC and c-ADSC sheet groups showed superior bone regeneration, higher histological scores, larger fibrocartilage areas, more mature collagen, and better biomechanical results compared with the control group. No obvious difference was seen between the f-ADSC and c-ADSC sheet groups in terms of bone regeneration, histological score, fibrocartilage formation, and biomechanical tests.

CONCLUSION

c-ADSC sheets, an off-the-shelf scaffold with a high potential for clinical translational application, can effectively promote rotator cuff tendon-to-bone healing.

CLINICAL RELEVANCE

Programmed cryopreservation of ADSC sheets is an efficient off-the-shelf scaffold for rotator cuff tendon-to-bone healing.

An Update on Adipose-Derived Stem Cells for Regenerative Medicine: Where Challenge Meets Opportunity

Over the last decade, adipose-derived stem cells (ADSCs) have attracted increasing attention in the field of regenerative medicine. ADSCs appear to be the most advantageous cell type for regenerative therapies owing to their easy accessibility, multipotency, and active paracrine activity. This review highlights current challenges in translating ADSC-based therapies into clinical settings and discusses novel strategies to overcome the limitations of ADSCs. To further establish ADSC-based therapies as an emerging platform for regenerative medicine, this review also provides an update on the advancements in this field, including fat grafting, wound healing, bone regeneration, skeletal muscle repair, tendon reconstruction, cartilage regeneration, cardiac repair, and nerve regeneration. ADSC-based therapies are expected to be more tissue-specific and increasingly important in regenerative medicine.

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.

Quantitative Magnetic Resonance Imaging-Based Tendon Healing of Different Regions of the Shoulder: Comparison Between the Suture-Bridge and Single-Row Techniques

Background

Rotator cuff retears occur more often at the proximal region with the suture-bridge (SB) technique than at the typical footprint region with the single-row (SR) technique. Few longitudinal clinical trials have focused on the postoperative tendon quality of the repaired rotator cuff at different regions between the 2 techniques.

Purpose

To compare tendon healing of the proximal and distal regions between the SB and SR techniques.

Study Design

Cohort study; Level of evidence, 3.

Methods

Included were consecutive patients who underwent arthroscopic rotator cuff repair and undertook clinical and magnetic resonance imaging (MRI) examinations at 3, 6, and 12 months postoperatively between 2016 and 2017. These patients were divided into the SB and SR groups according to the technique used. The repaired tendon was segmented into distal and proximal regions on ultrashort echo time-T2* mapping images. Clinical outcomes (Constant score, American Shoulder and Elbow Surgeons score, Fudan University Shoulder Score, and visual analog scale for pain) and MRI-based tendon healing (T2* values) of different regions were compared between the 2 groups. The differences in T2* values and clinical scores were determined by 1-way analysis of variance for repeated measurements.

Results

A total of 31 patients (17 in SB group and 14 in SR group) were included. At 12-month follow-up, significant improvements from preoperatively were achieved for all patients in all clinical scores (P < .001 for all). No significant between-group differences were found in T2* values of the distal region at any time point; however, the mean T2* value of the proximal region at 3 months was significantly higher in the SB group compared with the SR group (P = .03). This difference became nonsignificant at subsequent follow-up time points.

Conclusion

Significant clinical improvements over time can be expected in the first year after arthroscopic rotator cuff repair. In the early postoperative period, higher T2* values in the proximal region of the repaired tendon (representing inferior tendon quality) were seen with the SB technique compared with the SR technique; however, this phenomenon was resolved over time.

Combination of autologous osteochondral and periosteum transplantation effectively promotes fibrocartilage regeneration at the tendon-bone junction of the rotator cuff in rabbits

PURPOSE

Rotator cuff tendon-bone healing often leads to scarring and low biomechanical strength, resulting in a tendency to re-tear. This study examined whether combining autologous osteochondral transplantation and periosteum transplantation increases fibrocartilage transition zone regeneration and improves biomechanical fixation.

METHODS

A total of 48 New Zealand white rabbits were divided into the periosteum, autologous osteochondral, combination of autologous osteochondral and periosteum, and control groups. The supraspinatus tendon was cut from the greater tuberosity and repaired by different transplants. A total of 12 rabbits were used for histological examination (haematoxylin and eosin staining, Masson's staining and Safranin-O staining) at 4, 8 and 12 weeks after the repair, and 36 rabbits were used for biomechanical tests (maximal failure load and stiffness).

RESULTS

At 4 weeks following the operation, each group had a large tendon-bone gap with a small number of disordered collagen fibres. At 8 weeks, the tendon-bone gap was smaller than that before the operation, and the tendon-bone gap in each experimental group was smaller with neater and denser collagen fibres and chondrocytes than in the control group, with the osteochondral combined periosteum group having the best results. At 12 weeks, the typical tendon-bone transitional structure was observed in the osteochondral combined periosteum group, and more collagen fibres and chondrocytes were generated in each group. The osteochondral combined periosteum group had the largest staining area and the largest amount of cartilage. The maximum tensile strength and stiffness of each group increased over time. There was no significant difference in each group's maximum tensile strength and stiffness at 4 weeks after the operation. However, the maximum tensile strength and stiffness of the osteochondral combined periosteum group at 8 and 12 weeks after operation were significantly higher than those of other groups (P < 0.05).

CONCLUSION

Histological and biomechanical results show that autologous osteochondral transplantation combined with periosteum transplantation can effectively promote the regeneration of fibrous cartilage in the tendon-bone junction of the rotator cuff. It is concluded that this technique is a new treatment method to promote tendon-bone healing in the rotator cuff.

Bioprinted living tissue constructs with layer-specific, growth factor-loaded microspheres for improved enthesis healing of a rotator cuff

Substantial challenges remain in constructing the native tendon-to-bone interface for rotator cuff healing owing to the enthesis tissues' highly organized structural and compositional gradients. Herein, we propose to bioprint living tissue constructs with layer-specific growth factors (GFs) to promote enthesis regeneration by guiding the zonal differentiation of the loaded stem cells in situ. The sustained release of tenogenic, chondrogenic, and osteogenic GFs was achieved via microsphere-based delivery carriers embedded in the bioprinted constructs. Compared to the basal construct without GFs, the layer-specific tissue analogs realized region-specific differentiation of stem cells in vitro. More importantly, bioprinted living tissue constructs with layer-specific GFs rapidly enhanced the enthesis regeneration in a rabbit rotator cuff tear model in terms of biomechanical restoration, collagen deposition, and alignment, showing gradient interface of fibrocartilage structures with aligned collagen fibrils and an ultimate load failure of 154.3 ± 9.5 N resembling those of native enthesis tissues in 12 weeks. This exploration provides a feasible strategy to engineer living tissue constructions with region-specific differentiation potentials for the functional repair of gradient enthesis tissues. STATEMENT OF SIGNIFICANCE: Previous studies that employed acellular layer-specific scaffolds or stem cells for the reconstruction of the rotator cuff faced challenges due to their insufficient capability to rebuild the anisotropic compositional and structural gradients of native enthesis tissues. This manuscript proposed a living tissue construct with layer-specific, GFs-loaded µS, which can direct in situ and region-specific differentiation of the embedded stem cells to tenogenic, chondrogenic, and osteogenic lineages for functional regeneration of the enthesis tissues. This bioprinted living tissue construct with the unique capability to reduce fibrovascular scar tissue formation and simultaneously facilitate enthesis tissue remodeling might provide a promising strategy to repair complex and gradient tissues in the future.

Decellularized Bovine Pericardial Patch Loaded With Mesenchymal Stromal Cells Enhance the Mechanical Strength and Biological Healing of Large-to-Massive Rotator Cuff Tear in a Rat Model

PURPOSE

The purpose of this study was to determine whether the addition of decellularized bovine pericardial patch loaded with mesenchymal stromal cells enhanced bone-to-tendon healing and improved the biomechanical strength of large-to-massive rotator cuff tears in a small animal model.

METHODS

Adipose-derived mesenchymal stromal cells (MSCs) from rat inguinal fat were isolated, cultured, and loaded onto decellularized bovine pericardium patches. To simulate large-to-massive tears, rats were managed with free cage activity for 6 weeks after tear creation. A total of 18 rats were randomly allocated to repair-only (control), repair with pericardial patch augmentation (patch), or repair with MSC loaded pericardial patch augmentation (patch-MSC). Each group had 6 rats (one shoulder of each rat was used for histological evaluation and another for biomechanical evaluation). MSCs seeded on the pericardial patches were traced on four shoulders from 2 other rats at 4 weeks after surgery. Histological evaluation for bone-to-tendon healing and biomechanical testing was carried out at 8 weeks after repair.

RESULTS

MSCs tagged with a green fluorescent protein were observed in the repair site 4 weeks after the repair. One shoulder each in the control and patch groups showed complete discontinuity between the bone and tendon. One shoulder in the control group showed attenuation with only a tenuous connection. Fibrocartilage and tidemark formation at the bone-to-tendon interface (P = .002) and collagen fiber density (P = .040) and orientation (P = .003) were better in the patch-MSC group than in the control or patch group. Load-to-failure in the patch-MSC and patch groups was higher than that in the control group (P = .001 and .009, respectively).

CONCLUSION

Decellularized bovine pericardial patches loaded with adipose-derived and cultured mesenchymal stromal cells enhanced healing in terms of both histology and mechanical strength at 8 weeks following rotator cuff repair in a rat model.

CLINICAL RELEVANCE

Large-to-massive rotator tears need a strategy to prevent retear and enhance healing. The addition of decellularized bovine pericardial patch loaded with MSCs can enhance bone-to-tendon healing and improve biomechanical healing of large-to-massive rotator cuff tears following repair.

Advances toward transformative therapies for tendon diseases

Approved therapies for tendon diseases have not yet changed the clinical practice of symptomatic pain treatment and physiotherapy. This review article summarizes advances in the development of novel drugs, biologic products, and biomaterial therapies for tendon diseases with perspectives for translation of integrated therapies. Shifting from targeting symptom relief toward disease modification and prevention of disease progression may open new avenues for therapies. Deep evidence-based clinical, cellular, and molecular characterization of the underlying pathology of tendon diseases, as well as therapeutic delivery optimization and establishment of multidiscipline interorganizational collaboration platforms, may accelerate the discovery and translation of transformative therapies for tendon diseases.

Irisin promotes the proliferation and tenogenic differentiation of rat tendon-derived stem/progenitor cells via activating YAP/TAZ

Tendinopathy is a common tendon disorder characterized by pain, swelling, and dysfunction. Current evidence has demonstrated that the depletion of stem cell pool and non-tenogenic differentiation of tendon-derived stem/progenitor cells (TSPCs) might account for the pathogenesis of tendinopathy. FNDC5/Irisin, as a novel exercise-induced myokine, is proved to be involved in the exercise-induced protective effects on musculoskeletal disorders. However, whether irisin can affect TSPCs fate is still unknown. To ascertain the roles of irisin on the proliferation and tenogenic differentiation of TSPCs, rat TSPCs were isolated and incubated with irisin. Cell viability, phenotypic changes, and related signaling pathways were evaluated by CCK-8 assay, colony formation assay, real-time PCR, Western blot, immunofluorescence, and proteasome activity assay. We found that irisin treatment increased the proliferative and colony-forming abilities, and promoted the tenogenic differentiation of TSPCs by upregulating the expression of YAP/TAZ. In conclusion, our work showed for the first time that irisin promotes the proliferation and tenogenic differentiation of rat TSPCs in vitro by activating YAP/TAZ, and the process was associated with a ubiquitin-proteasome proteolytic pathway. In conclusion, irisin and agents targeting YAP/TAZ may be promising therapeutic options for tendinopathy.

Extracellular Vesicles Delivered by Injectable Collagen Promote Bone-Tendon Interface Healing and Prevent Fatty Degeneration of Rotator Cuff Muscle

PURPOSE

This study aimed (1) to confirm the maintenance of the extracellular vesicles (EVs) delivered via injectable collagen at the application site, and (2) to evaluate the effect of EVs derived from the human umbilical cord-derived mesenchymal stem cells and loaded in an injectable collagen gel after rotator cuff repair (RCR).

METHODS

Rabbits (n = 20) were assigned to normal (N), repair-only (R), and those administered with injectable collagen after repair (RC), and EV-laden injectable collagen after repair (RCE) groups. The EVs isolated by ultra-centrifugation from the human umbilical cord-derived mesenchymal stem cells spent medium were mixed with collagen and administered accordingly. After 12 weeks, the rabbits were sacrificed to evaluate the healing of the bone-to-tendon junction and the fatty degeneration of muscle. Histomorphometric scoring for bone-tendon interface, fatty infiltration (%), and biomechanical tests were performed. Separately, groups of 3 rabbits were assigned to 3 different time points to evaluate maintenance of green fluorescence-labeled EVs with injectable collagen via tracking on the bursal side of the rotator cuff (3 groups: 3 days, 2, and 4 weeks).

RESULTS

The EVs delivered by injectable collagen remained until 4 weeks at the bursal side of the cuff tissue. The RCE group showed a significantly greater histomorphometric total score (P < .001, and P = .013, respectively) and significantly lower fatty degeneration than the RC and R groups (P = .001, and P = .013, respectively). The biomechanical tests revealed significant growing trends in load-to-failure and stiffness (P = .002, and P = .013, respectively), in the R, RC, RCE, and N groups.

CONCLUSIONS

EVs mounted in injectable collagen remained at the repair site for at least 4 weeks after application. Furthermore, they effectively promote bone-to-tendon healing via collagen maturation in bone-tendon interface and preventing fatty degeneration of rotator muscle after RCR as compared with collagen-only or repair-only groups.

CLINICAL RELEVANCE

The combination of collagen with EVs significantly promotes rotator cuff healing demonstrating potential clinical application during partial rotator cuff tear or after RCR.

The Plug-Type Patch Results in Immediate and Postoperative Advantages in Graft-to-Bone Integration for Bridging Massive Rotator Cuff Tears in a Chronic Rabbit Model

BACKGROUND

Various patches have been used to bridge massive rotator cuff tears (MRCTs) by reconnecting the cuff tendons to the humeral head, but the outcomes continue to be suboptimal. Notably, the graft-bone junction is a vulnerable site for failure, which requires optimization in patch design and techniques to enhance initial and postoperative fixation strength at the graft-bone interface.

HYPOTHESIS

The plug-type patch (Plug-Pat) through intratunnel fixation would optimize mechanical characteristics in initial graft-to-bone fixation and subsequently improve postoperative biomechanical and histological properties in graft-to-bone healing when compared with the routine rectangular patch (Rect-Pat).

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 60 mature male New Zealand White rabbits underwent acute rotator cuff defects to create chronic models with MRCTs. The fascia lata autograft was then harvested to prepare a Plug-Pat, which was distally rooted in the bone tunnel and proximally sutured to native tendons in a horizontal mattress fashion to reconnect the humeral head and cuff tendons. The control group was repaired with a routine Rect-Pat that was secured onto the bone surface for graft-bone fixation. After surgery, the cuff-graft-bone complexes of rabbits in both groups were harvested immediately (0 weeks) for time-zero initial fixation strength and refreshed contact area assessment, and at 6 or 12 weeks for postoperative biomechanical and histological evaluation.

RESULTS

The Plug-Pat significantly enhanced initial fixation strength in comparison with the Rect-Pat (mean ± SD; failure load, 36.79 ± 4.53 N vs 24.15 ± 2.76 N; P < .001) and decreased failure at the graft-bone interface of the construct at 0 weeks, with a significantly increased refreshed bone bed contact area (52.63 ± 2.97 mm² vs 18.28 ± 1.60 mm²; P < .001) between the graft and bone. At 6 and 12 weeks postoperatively, the Plug-Pat similarly resulted in greater failure load (43.15 ± 4.53 N vs 33.74 ± 2.58 N at 6 weeks; P = .001; 76.65 ± 5.04 N vs 58.17 ± 5.06 N at 12 weeks; P < .001) and stiffness (10.77 ± 2.67 N/mm vs 8.43 ± 0.86 N/mm at 6 weeks; P = .066; 16.98 ± 2.47 N/mm vs 13.21 ± 1.66 N/mm at 12 weeks; P = .011), with less specimen failure at the graft-bone interface than the Rect-Pat. In histological analyses, the Plug-Pat had a higher postoperative graft-bone integration score than the Rect-Pat, showing a more mature intratunnel healing interface with fibrocartilage tidemark formation, improved collagen properties, and more oriented cells when compared with those at the surface healing interface in the Rect-Pat.

CONCLUSION

The Plug-Pat enhanced initial fixation strength and enlarged the refreshed contact area for graft-bone connection at time zero and subsequently improved postoperative biomechanical properties and graft-bone integration at the graft-bone healing interface when compared with the Rect-Pat.

CLINICAL RELEVANCE

The Plug-Pat using intratunnel fixation may be a promising strategy for patch design to optimize its initial and postoperative graft-bone connection for bridging reconstruction of MRCTs.

Advances in Stem Cell Therapies for Rotator Cuff Injuries

Rotator cuff injury is a common upper extremity musculoskeletal disease that may lead to persistent pain and functional impairment. Despite the clinical outcomes of the surgical procedures being satisfactory, the repair of the rotator cuff remains problematic, such as through failure of healing, adhesion formation, and fatty infiltration. Stem cells have high proliferation, strong paracrine action, and multiple differentiation potential, which promote tendon remodeling and fibrocartilage formation and increase biomechanical strength. Additionally, stem cell-derived extracellular vesicles (EVs) can increase collagen synthesis and inhibit inflammation and adhesion formation by carrying regulatory proteins and microRNAs. Therefore, stem cell-based therapy is a promising therapeutic strategy that has great potential for rotator cuff healing. In this review, we summarize the advances of stem cells and stem cell-derived EVs in rotator cuff repair and highlight the underlying mechanism of stem cells and stem cell-derived EVs and biomaterial delivery systems. Future studies need to explore stem cell therapy in combination with cellular factors, gene therapy, and novel biomaterial delivery systems.

Enhanced Repaired Enthesis Using Tenogenically Differentiated Adipose-Derived Stem Cells in a Murine Rotator Cuff Injury Model

Rotator cuff tear (RCT) is among the most common shoulder injuries and is prone to rerupture after surgery. Selecting suitable subpopulations of stem cells as a new specific cell type of mesenchymal stem cells has been increasingly used as a potential therapeutic tool in regenerative medicine. In this study, murine adipose-derived SSEA-4+CD90+PDGFRA+ subpopulation cells were successfully sorted, extracted, and identified. These cells showed good proliferation and differentiation potential, especially in the direction of tendon differentiation, as evidenced by qRT-PCR and immunofluorescence. Subsequently, we established a murine rotator cuff injury model and repaired it with subpopulation cells. Our results showed that the subpopulation cells embedded in a fibrin sealant significantly improved the histological score, as well as the biomechanical strength of the repaired tendon enthesis at four weeks after surgery, compared with the other groups. Hence, these findings indicated that the subpopulation of cells could augment the repaired enthesis and lead to better outcomes, thereby reducing the retear rate after rotator cuff repair. Our study provides a potential therapeutic strategy for rotator cuff healing in the future.

Abaloparatide Improves Rotator Cuff Healing via Anabolic Effects on Bone Remodeling in a Chronic Rotator Cuff Tear Model of Rat With Osteoporosis: A Comparison With Denosumab

BACKGROUND

Because of poor clinical outcomes, rotator cuff healing in patients with osteoporosis has recently gained attention. Antiresorptive therapy for osteoporosis has been reported to improve healing after repair. However, the comparative effectiveness of anabolic and antiresorptive agents has not been investigated.

HYPOTHESIS

Anabolic therapy with abaloparatide (ABL) would outperform antiresorptive therapy with denosumab (Dmab) to improve rotator cuff healing in the osteoporotic status.

STUDY DESIGN

Controlled laboratory study.

METHODS

A chronic rotator cuff tear model was established in ovariectomy-induced postmenopausal osteoporotic rats. Then, bilateral rotator cuff repairs were conducted in all experimental rats, which were randomly divided into control (CON), Dmab, and ABL groups to receive the corresponding subcutaneous injections. The rats sacrificed at 2 weeks (the early healing period) were used to detect osteoblast and osteoclast activities, related gene expression (osteoclastogenesis, osteogenesis, and chondrogenesis), new bone formation, and mineralization. In the rats sacrificed at 4 and 8 weeks, the bone mineral density and bone architecture at the repaired site were assessed by micro-computed tomography, and rotator cuff healing was evaluated using histological and biomechanical analyses.

RESULTS

At 8 weeks, significantly higher failure load and stiffness were observed in the ABL (25.13 ± 3.54 N, P < .001; 21.65 ± 3.08 N/mm, P < .001; respectively), and Dmab (21.21 ± 2.55 N, P < .001; 16.15 ± 2.07 N/mm, P = .008; respectively) groups than in the CON group (13.36 ± 1.70 N; 11.20 ± 2.59 N/mm; respectively), whereas the ABL treatment provided better failure load and stiffness than Dmab (P = .019; P = .003). Although tendon-to-bone healing was improved by Dmab, the most mature tendon insertion at the interface was observed in the ABL group, including a more organized collagen and fibrocartilage and higher bone quality. ABL significantly promoted bone remodeling via coupling between osteoclasts and osteoblasts (osteoblast to osteoclast ratio: 4.80 ± 0.39; P = .022), thereby stimulating more new bone formation and mineralization at the tendon-to-bone healing interface than Dmab (osteoblast to osteoclast ratio: 3.21 ± 0.75) at 2 weeks. Moreover, ABL had significant effects on gene expression [Runt-realted transcription factor 2 (Runx2, collagen type I-alpha 1 (Col1A1]), and sclerostin for osteogenesis; aggrecan and collagen type II (Col2) for chondrogenesis] in mineralized tissues, indicative of enhanced bone and fibrocartilage formation when compared with the CON and Dmab groups.

CONCLUSION

ABL promoted rotator cuff healing in osteoporotic rats by significantly increasing the mineralized tissue quality and collagen maturity at the reattachment site, leading to improved biomechanical properties, and was superior to Dmab in both biomechanical and histological analyses.

CLINICAL RELEVANCE

Anabolic therapy with ABL may outperform antiresorptive therapy with Dmab in improving outcomes after rotator cuff repair in osteoporotic patients.

The effects of orthobiologics in the treatment of tendon pathologies: a systematic review of preclinical evidence

Purpose

The aim of this systematic review is to explore the current available knowledge about tendon disorders and orthobiologics derived by preclinical experiments to evaluate their role and efficacy in the different stages and conditions related to the tendon healing processes.

Methods

The systematic review was performed according to the PRISMA guidelines. Different electronic databases (MEDLINE, Web of Science, EMBASE) were searched for studies investigating orthobiologics (PRP and cell-based products from adipose tissue or bone marrow) in animal models or veterinary clinical trials for tendon pathologies (complete/partial tendon ruptures, rotator cuff tears, tendinopathy, enthesis-related injuries). Data regarding the specific product used, the treatment site/pathology, the host and the model were collected. The results were classified into the following categories: histological, biomechanical, molecular and imaging.

Results

A large pool of preclinical studies on tendon disorders have been found on platelet-rich plasma (PRP), while data about stromal vascular fraction (SVF) and bone marrow concentrate (BMAC) are still limited and frequently focused on expanded cells, rather than orthobiologics prepared at the point of care.

The effect of PRP is related to an acceleration of the healing process, without improvements in the final structure and properties of repaired tendon. Cell-based products have been reported to produce more durable results, but the level of evidence is currently insufficient to draw clear indications.

Conclusions

The preclinical results about orthobiologics applications to tendon pathologies would support the rationale of their clinical use and encourage the performance of clinical trials aimed to confirm these data in human subjects.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40634-022-00468-w.

Evaluation of patches for rotator cuff repair: A systematic review and meta-analysis based on animal studies

Based on the published animal studies, we systematically evaluated the outcomes of various materials for rotator cuff repair in animal models and the potentials of their clinical translation. 74 animal studies were finally included, of which naturally derived biomaterials were applied the most widely (50.0%), rats were the most commonly used animal model (47.0%), and autologous tissue demonstrated the best outcomes in all animal models. The biomechanical properties of naturally derived biomaterials (maximum failure load: WMD 18.68 [95%CI 7.71-29.66]; P = 0.001, and stiffness: WMD 1.30 [95%CI 0.01-2.60]; P = 0.048) was statistically significant in the rabbit model. The rabbit model showed better outcomes even though the injury was severer compared with the rat model.

Stem cell sheet interpositioned between the tendon and bone would be better for healing than stem cell sheet overlaid above the tendon-to-bone junction in rotator cuff repair of rats

BACKGROUND

Although stem cells might enhance natural enthesis healing in surgical rotator cuff repair, not much attention has been given to the delivery and location of delivering stem cells. The purpose of this study to know where to locate those stem cells during repair.

METHODS

Animal model of chronic rotator cuff tear was created in 24 rats. Adipose-derived stem cells were engineered as a sheet and transplanted 1) between a torn tendon and humerus (interposition group) or 2) over a repaired tendon-to-bone junction (overlay group) at the time of surgical repair. Tracking of stem cells with overexpression of green fluorescent protein (GFP) were carried out at the time of sacrifice in additional 4 shoulders in each group. Histological and Biomechanical evaluation was performed to compare the differences in tendon-to-bone healing.

RESULTS

Histology showed increased fibrocartilage, a clear boundary at the mineralized fibrocartilage, abundant collagen type III, and higher total scores, especially in the interposition group. GFP-overexpression was observed at the transplanted site at 2 weeks after repair. Although two groups where stem cell sheets applied showed higher load to failure than the repair-only group, the load to failure was not different between the interposition and overlay group.

CONCLUSION

In the chronic rotator cuff repair model, stem cell sheets enhanced regeneration of the tendon-to-bone junction. This regeneration was effective when the stem cell sheet was interpositioned at the tendon-to-bone interface.

LEVEL OF EVIDENCE

Basic Science Study; In Vivo Animal Model; Histology and Biomechanics.

[Research progress of interfacial tissue engineering in rotator cuff repair]

Objective

To summarize the research progress of interfacial tissue engineering in rotator cuff repair.

Methods

The recent literature at home and abroad concerning interfacial tissue engineering in rotator cuff repair was analysed and summarized.

Results

Interfacial tissue engineering is to reconstruct complex and hierarchical interfacial tissues through a variety of methods to repair or regenerate damaged joints of different tissues. Interfacial tissue engineering in rotator cuff repair mainly includes seed cells, growth factors, biomaterials, oxygen concentration, and mechanical stimulation.

Conclusion

The best strategy for rotator cuff healing and regeneration requires not only the use of biomaterials with gradient changes, but also the combination of seed cells, growth factors, and specific culture conditions (such as oxygen concentration and mechanical stimulation). However, the clinical transformation of the relevant treatment is still a very slow process.

Long noncoding RNA H19 accelerates tenogenic differentiation by modulating miR-140-5p/VEGFA signaling

Rotator cuff tear (RCT) is a common tendon injury, but the mechanisms of tendon healing remain incompletely understood. Elucidating the molecular mechanisms of tenogenic differentiation is essential to develop novel therapeutic strategies in clinical treatment of RCT. The long noncoding RNA H19 plays a regulatory role in tenogenic differentiation and tendon healing, but its detailed mechanism of action remains unknown. To elucidate the role of H19 in tenogenic differentiation and tendon healing, tendon-derived stem cells were harvested from the Achilles tendons of Sprague Dawley rats and a rat model of cuff tear was established for the exploration of the function of H19 in promoting tenogenic differentiation. The results showed that H19 overexpression promoted, while H19 silencing suppressed, tenogenic differentiation of tendon-derived stem cells (TDSCs). Furthermore, bioinformatic analyses and a luciferase reporter gene assay showed that H19 directly targeted and inhibited miR-140-5p to promote tenogenic differentiation. Further, inhibiting miR-140-5p directly increased VEGFA expression, revealing a novel regulatory axis between H19, miR-140-5p, and VEGFA in modulating tenogenic differentiation. In rats with RTC, implantation of H19-overexpressing TDSCs at the lesion promoted tendon healing and functional recovery. In general, the data suggest that H19 promotes tenogenic differentiation and tendon-bone healing by targeting miR-140-5p and increasing VEGFA levels. Modulation of the H19/miR-140-5p/VEGFA axis in TDSCs is a new potential strategy for clinical treatment of tendon injury.

Stem cell therapies in tendon-bone healing

Tendon-bone insertion injuries such as rotator cuff and anterior cruciate ligament injuries are currently highly common and severe. The key method of treating this kind of injury is the reconstruction operation. The success of this reconstructive process depends on the ability of the graft to incorporate into the bone. Recently, there has been substantial discussion about how to enhance the integration of tendon and bone through biological methods. Stem cells like bone marrow mesenchymal stem cells (MSCs), tendon stem/progenitor cells, synovium-derived MSCs, adipose-derived stem cells, or periosteum-derived periosteal stem cells can self-regenerate and potentially differentiate into different cell types, which have been widely used in tissue repair and regeneration. Thus, we concentrate in this review on the current circumstances of tendon-bone healing using stem cell therapy.